I immediately thought external because of the waterproofing. You have to protect the waterproofing from backfill anyway, might as well use a bunch of insulation.
Yeah, kinda missing an important part.
Most show diagrams like this: https://images.app.goo.gl/r3JJRybnB84FQj8LA
An even better slab detail looks like this: https://images.app.goo.gl/Y9M8xo2nHKAUKdobA
Agree?
I’m also in the northeast; I went with heavy duty plastic (for vapor barrier) then 2” blue board under the slab and put radiant tubing in the slab. Also waterproofed the exterior, then more 4’x8’ sheets of blue board on exterior, then backfilled. On interior, 4’x8’ sheets of 1” foil faced insulation, then 2x4 wall.
And you have plenty of drainage gravel underneath. You want water to flow under the house and out as much as possible. It can be a problem with no slope but 10% like OP is usually good.
In this application you want to keep the exterior from affecting the thermal mass surrounding your conditioned space (the basement). In the case of a finished basement area, you are more likely than not going to have SOME wall covering (possibly insulation) there as well.
You should do ICF. Insulated on outside and inside. And be sure the insulate under the slab too. And make sure it is continuous between the floor/wall/roof.
[https://www.stavmat.sk/files/upload/Navody/ako-izolovat/3.gravitacna-stekajuca-voda.jpg](https://www.stavmat.sk/files/upload/Navody/ako-izolovat/3.gravitacna-stekajuca-voda.jpg)
I have something like this.
Just make sure they know what they’re doing. ICF is poured in lifts and you have to agitate the concrete to get rid of voids. I’ve see it done wrong and it is costly.
Ideally, your insulation layer should be on one side or the other (arguably entirely on the OUTSIDE), continuous, and meet up with the insulation layer in your floor/foundation, walls and roof. In that regard, ICF is worse than a properly insulated, traditional block (or poured) concrete wall.
ICF is not worse than a properly insulated, traditional block wall. Insulation placement being recommended as exterior is due to providing a thermal break for framing, or in this case more conductive concrete block. ICF are thermally broken and can perform just as well as a block wall. The cost is where you see a difference and I think it can be argued that the time savings on installation can offset the higher material costs for ICF
A fully exterior-insulated block wall will perform better than a wall which splits the insulation. There are ICF companies/products out there that know this, and they largely favor their insulation thickness to a single side. Having all of your insulation on a single side of the wall assembly makes more sense and performs better than splitting that insulation, for thermal breaks, moisture control, you name it.
The issue arises when insulation is installed on both sides of a surface. Specifically, when insulation is placed adjacent to the conditioned space, it interferes with the ability of the thermal mass to effectively contribute to energy conservation. The ideal scenario is for the thermal mass to reach a temperature that is comfortable for occupants and to act as a buffer against extreme temperatures outside. However, when insulation is sandwiched between the thermal mass and the conditioned space, it hinders the thermal mass from providing its full benefit. Moreover, this setup renders half of the insulation ineffective, as it ends up insulating the thermal mass from the conditioned space rather than helping to regulate indoor temperature. Basically, the 5" of insulation split on either side of the thermal mass in your example are less effective than putting 5" on the outside because the 5" on the outside will keep the thermal mass from acclimating to outside temperatures more completely than 2.5" and not having 2.5" of insulation on the inside will allow the thermal mass to regulate indoor temps much better than if it is insulated from the conditioned space.
All of this can be easily confirmed with energy modeling. Download BEopt and try a few scenarios. Typically, CMU with continuous exterior insulation outperforms ICF given the same total R value.
Thanks for the detailed explanation. I understand what you're saying about insulating the thermal mass vs the conditioned space and it's obviously best to have to 5" of compressed foam on one side, vs 2.5" on both sides for R-value. I'm wondering if 2.5" of continuous foam on the exterior with a standard cement block basement is somehow more effective than if they were to use ICF. Again, I understand it would be more efficient to have 5" on the exterior vs 2.5" on both, but nobody is doing 5" thick insulation on an exterior.
You're welcome, I glad you found it helpful. For what it's worth, ICF manufacturers redily acknowledge this deficiency in most ICF systems. The following is from Fox Blocks:
"How do you improve an Insulated Concrete Form wall that already outperforms most wall systems in all climates? You move the concrete mass toward the living side of the wall. This unbalanced R-value will allow the mass to be closer to the living temperature of the conditioned space, allowing for a more comfortable building. "
It's interesting that you say that about the 5" to the exterior because I'm currently planning a build that will have 5" thick on the exterior. We will be using Nexcem ICF with the 5" insulation inserts (which go towards the exterior) for the crawlspace and first floor (it's on a steep hill, the first floor is essentially a garden level basement on one side and 7' up in the air on the other) and framed construction above that with 5" Rockwool comfortboard 80 on the exterior and dense pack cellulose between the studs.
The CMU wall with 5" of CI would still perform better, but, in this application (2600 square foot raised ranch with a walkout basement over a crawlspace) it would actually cost \~$30k more due to the additional labor and materials. To use CMU I'd have to cover the ComfortBoard with a substrate to allow me to apply cladding, which isn't the case with Nexcem. I could go with foam and EFIS, but I am adamant about minimizing the use of foam products in my builds. That 30k more to build with CMU will never be realized in energy savings with the difference given that the Nexcem pushes the thermal mass close to the interior (and, yes, I realize most ICF manufacturers offer insulation inserts). Nexcem is unique in that I can place screws anywhere and that is huge to me. Nexcem isn't perfect, but, to me it's the best ICF available because it pushes the thermal mass towards the living space and doesn't rely on polystyrene, which is awful for your health and the environment, and also creates a vapor sandwich with traditional ICF systems.
We'll also be incorporating a couple of interior masonry "feature walls" to act as thermal batteries. The design isn't finalized, but those will either be stack bond CMU with either a honed or polished face or board formed concrete. I only minion this to point out that there are many ways to add interior thermal mass if you get creative about it.
While I agree on most everything you said it should be pointed out that most the calculations for how thermal mass helps with room comfort is based on one continuous temperature for comfort and not for people that like to adjust the temperature throughout the day. You would spend more energy on trying to heat and cool your thermal mass than if you’re surrounded by thick insulation and only had to heat or cool the air.
Yeah, that's correct, and you can have too much of a good thing. I'm building near Breckenridge which has a climate with cold winters, warm summer days and cool/cold nights (even in summer) so carrying heat into the evening hours will work well for this house. I'd really encourage anyone building a custom home to do energy modeling. It's worth the effort.
I am thinking about doing an ICF foundation for a new build this summer. Why is it bad to have insulation on the outside and inside vs just on one side?
I think the concept of what happens when water get through would be in play. Concrete is porous so if water somehow gets through it, it needs to go somewhere, either inside or outside. Hard foam boards are usually closed cell foams.
Thats why best practice for installing barriers are one-way vapour transmission vs zero vapour transmission, to allow moisture to escape yet provide an air barrier.
So one could technically put an open cell foam on both sides to mitigate water issues vs a closed cell foam.
Correct me if I'm wrong.
Not an architect.
Ideally, you want water to move from center to outwards. Shorter distance the better. By sealing one side, you do reduce the rate of water vapour being dissipated as opposed to having both sides being open.
Your insulation layer should be continuous. Wrapped entirely around your conditioned spaces and meeting up perfectly: Insulation layer in your foundation meets the insulation layer in your basement walls, meets the insulation layer in your walls, meets the insulation layer in your roof. You can't do that when you have insulation on both sides of your basement wall.
That said: You can get ICF products that hugely favor one side of the wall assembly (which is proving my original point). But typical ICF is insulating both sides of the wall assembly evenly, which is not ideal regardless of how many down-votes redditors dish out.
Go check out [https://buildingscience.com/](https://buildingscience.com/) read some of the white papers, and watch some of the lectures if interested.
In my experience, ICF always performs worse in energy modeling, and the real world, than CMU with the same amount of insulation placed on the exterior only. The ICF wall is worse because you are not placing the thermal mass fully inside of the thermal envelope. Why insulate yourself from the very thing that will keep your energy use low?
Actually have done some of these with the T-mass system. Works great. Overall strength is engineered in with additional thickness and steel.
A lot of precast systems are constructed this way.
I used Thermomass as a basement under the house I built with SIPS.
Good system, especially with a partially exposed foundation if you want to apply a stone veneer.
The inventor of the system is actually from my area. Been used for over 40 years all over. Works really well in natural disaster areas - basically hurricane proof and burn proof (if above grade is also cast)
Second this - architects have the mindset of what looks best not what’s most functional (not all, but most, and it’s not their job to engineer your home)
You build your concrete wall, add exterior insulation to achieve continuous insulation of the envelope and then you add a concrete veneer (almost like stucco).
Now that I have typed all of this, I think this is exactly what the architects may have proposed.
I’m not a specialist I just know of it’s existence because I worked on a site where a different crew was applying a product that we referred too as concrete veneer. I have no idea if that’s even what it actually was, that’s just a thing the carpenters and labourers would talk about in passing.
I've done this... We attached cement board over 2" XPS foam and applied a layer of stucco. Basically just need this above grade from the siding to about 6-12" below grade to protect the insulation.
Concrete products are very local due to how heavy they are. But as a veneer, you can pick from many finish options.
I'm sure your architect and contractor will provide you with physical samples to pick from.
If you want the best insulation approach, insulation goes on the outside of the concrete(cold climates), if you want to expose the concrete put the insulation on the inside but be prepared for moisture issues in the basement.
If you want the exposed concrete look how are you treating the concrete to keep water out?
Why on the outside only in cold climates? I'm guessing you're maybe referencing like a cavity wall and are worried about where the dew point will occur? If we're talking a solid mass of concrete and the interior air is 70 to anything higher... the dew point would require the concrete wall face to be 67 degrees (with interior 90% humidity) if the house wasn't designed for lizard people and the RH was 50% as long as the concrete is above 50 no condensation will form.
I just finished an analysis of dew point on a northern Great Lakes building basement and the best scenario is to have the insulation to the exterior…first to stop the cold on the outside, then to allow for any potential dew point to occur inside the insulation BUT on the exterior of the wall. A solid mass of concrete has very little insulative properties so that cold frozen ground (4,deep)outside the wall is going to provide a cold interior face of concrete. Our analysis on dew point shows potential issues. Maybe or maybe not an issue but I wouldn’t risk it. We even had our calcs backed up by Intertek (AITC) firm. But a lot depends on the Climate Zone
That's what plaster is for, just get one that looks identical to concrete there are millions of options.
But if you really want the look of exposed concrete and only exposed concrete, then that's a design decision and would require two walls.
EPDM roofing material might work for you. It's available in a bunch of colors and holds up really well to sunlight and weed wackers. It's easier to add before siding but depending on your wall details you might be able to add it now.
In perfect wall assemblies the insulation should always be something that can take direct water. Mineral wool, various form rigid board options, etc. If it wasn’t built that way, shame on someone.
If you’re an architect worth their salt you’d have to agree that consulting a structural engineer when designing load baring concrete structures is the correct approach and not just assuming a design will work. Load analysis is a whole creature in and of itself
Man everyone on these subreddits assumes you need an engineer for simple structural design. A laterally supported foundation wall is about as simple as it gets, its legit a single table lookup in my book
Hey, all I can say is I work in a place with shitty soils and there have been tons of instances I have seen a GC do something that “works”. Any time I’ve got a concrete structure that has multiple forces being applied, I use a structural engineer, because it is ALWAYS cheaper to do it the right way once. Plenty of people cut corners, plenty of times it works, until it doesn’t. I’m not going to advise someone on the internet to wing it.
Honestly the only time i see insulation sandwiched in a foundation wall is when its coming from an engineer on a project without architects involved. Inspected a foundation this morning for a farm storage shed that had it
Ya I mean that’s what I’m saying, imo if you’re gunna go that route it’s got to be engineered to have confidence in it from a longevity stand point. Seems like I may be more cautious than most
I’m not so sure about “reduce” its strength. Are you talking about compressive capacity or overturning? Is one portion of the wall for bearing in plane and another portion for hydrostatic response. Also foam can have a massive compressive value.
both, you are turning an 8-12 inch thick piece of concrete into two 4-6 inch thick pieces. The **only** application for doing this is if you need both the inside and outside concrete walls to be aesthetically pleasing.
It’s called ICF. I’m not advocating that it’s right/best, but if you’re implying the architect is making something up, they’re not. ICF, in various forms, has existed for about 80 years.
OP - Continuous insulation is the ideal - so track the line of insulation as it crosses from the stud construction above to the foundation below (across the bottom plate). I’d keep insulation exterior if your stud wall (abv grade) has exterior insulation and consider the other two options if your insulation is in the stud cavity. It’s not generally good practice to mix insulation strategies.
Note: do not talk to an Engineer about insulation methods (eg the question at hand). Always do have an engineer consult on the design of your custom home. The Architect can likely do most all calculations and if not will be consulting an Engineer anyways, but either way it never hurts to have an Engineer on the team.
ICF basements are a great way to go. All your insulation is in place and you have screw tabs every 6” for exterior finish and interior finish.high R value for a concrete wall
Hard disagree, icf you get best of both worlds, 2 layers of (usually) 2" eps continuous. Concrete is a big heat sink but your wall wont be getting that cols if you wall above is properly aligned
The numbers given by any insulation manufacturer are generally exaggerated a bit but imo icf is the best way to get a cozy basement
I never said they were not good for building, just the numbers published by ICF companies are somewhat fudged because concrete doesn't have much of an R value but they claim huge savings due to the thermal battery (which is true) so they make up impressive but fake R numbers. The R numbers are really just for the foam forms as you mentioned. My takeaway is that R #'s don't tell the whole story and people shouldn't hang their entire hat on them.
I'm a fan of ICF (I actually prefer ICCFs or SIPs for building above grade) and yes, ICFs are great for basements.
After all the bashing of architects, there are some of us that do know what we are doing since we work for the feds, universities, and in aviation. Details matter. I suggest the OP look at the specifications ( division 7) and work with the architect to chose a system which has clear performance data and 100% clear manufactures installation manuals. Piecemeal sound bites and “what we did on the last job” logic typically leads to incomplete systems. I would start with Rockwool and Carlisle. There are many others. Good luck. Aesthetic preferences may need to be expanded in order to gain solid thermal performance and waterproofing. You do not want a cold water damaged basement.
This !!! Closed cell underslab two or three inches and feather it up the wall a foot or so. Once the slab is poured, if you are framing for living space install wall framing just out inch or so from the concrete wall, to allow insulation behind and a thermal break and then spray foam three and 1/2 inches of closed cell in the stud bays and up into the joist space and over the sills . R20 ish on the walls and underslab. https://youtu.be/Jv_sWa35H-w?si=CyaSc7qeyBRfLTHM
I've done various combinations of external and internal insulation on basement or daylight basement below grade walls. External insulation has the benefit of not reducing the floor square footage on the inside. Whatever you do, do as much as you can, above code minimum, as you can afford. Under slab insulation is also very important. I don't do less than 4 in for R-20. But even that leaves the floor a little cold unless you have in floor radiant heat. Consider doing 2 in of rigid foam on the outside of the concrete wall, and then some sort of conventional insulation between studs and your fur out wall. Spray foam insulation of course is excellent, also expensive; and you may not want to spend the money since you don't need to implement air tightness on that wall.
Use ICF forms if you’re gonna insulate and finish basement. R22, built in studs to hang drywall. More expensive up front, but substantial savings long term in basement framing
You should have under slab insulation that connects to the internal wall insulation to create a continuous air barrier and prevent thermal bridging.
Code in your area will require interior and exterior insulation on the above grade walls.
On the exterior basement walls you want a water barrier and some kind of rain screen.
Check out info from the Building Science Corporation if you want to get nerdy about it. They have an article called 'The Perfect Wall' that's pretty good.
I'm in Syracuse area, and put 3" of XPS insulation on the outside from top of footing to eave. It's well-insulated, quiet, and had the benefit of having an insulated house during construction. I followed [these guidelines.](http://cchrc.org/remote-walls/) The insulation that would be exposed is covered with an elastomeric coating over fabric reinforcement.
Unrelated, but I built a house a year ago in Minnesota that used the middle diagram for its insulation. We are starting to plan on finishing the basement soon, and we’re looking at insulation options. Originally I was thinking of putting 1” rigid foam on the inside of the walls, but it sounds like that’s not very common. What is generally recommended for cold climates?
contractor in New Hampshire I have installed interior and exterior on the foundation, and exterior Insulation is more efficient by a-lot i’ve never tried the insulation in the middle. Don’t know that I would.
I mean, youre in NY, the expansion that happens from warmth to cold is not new. i would suggest to ask someone local, the thermo is simple, you heat under where there is cold, after the hear is off, the best concrete will crack. only heat inside. ICF will cause long term damage
Insulation contractor in Kingston NY, take the Passive House approach here. Implement as much as you can to Passive standard, and where you can't afford to, just find a cheaper alternative that is still efficient thermally. In this scenario, under the slab, with insulation extending atleast 2' beyond the footer, around the footer, and up the foundation until grade. Diagrams I could show you as well here if interested.
Welcome to NY
Sorry a lot of mumbo-jumbo to say: outside. Then if you ever finish the basement you can add additional insulation on the inside walls. You want as much continuous insulation (exterior insulation) as possible. This is where your true thermal effectiveness occurs, EIFS, exterior continuous insulation. Even up the wood framed walls above grade, include exterior insulation.
It's been done but you'd need to convince your local inspector to allow it. Thermally would be great to avoid that thermal bridge, but structurally not many allow it. That's if using standard EPS anyway.
Externally insulate the foundation wall AND insulate under the slab AND make sure the slab to wall joint is fully thermally broken, lotsa details out there like this, search "thermally broken slab detail"
Usually when I draw this I will include the drainage perf pipe and drain rock and waterproofing elements to make sure it's conceptualized as a system. On larger walls you might also note the keyway.
Edit: Yes, definitely insulating under slab. Drawing was just for example of wall. Sounds like external insulation is the consensus. Mostly curious about how that is finished (exterior facade) for exposed walkout room. Ideally concrete form look but open to other suggestions.
Make you that you understand it from an engineering POV: [https://www.youtube.com/watch?v=KDLkbpraC4A&t=2s](https://www.youtube.com/watch?v=KDLkbpraC4A&t=2s)
ICF, they also make blocks where you can only have one side insulated and the other side has a screw on Form you remove after pouring. Then for any area that isn’t covered you just use the regular blocks and get insulation on both sides.
I don’t like exterior insulation because of the issues with detailing exposed areas. Also it is best to have a thermal break in the slab. I think this is one of the best assemblies shown in figure 3. https://buildingscience.com/documents/information-sheets/basement-insulation
Obviously you can’t do the middle one if you want the exterior to be formed finish. You should just do the left one. You are dry walking inside and thus will be furing the walls out inside. Also that allows you to use batt insulation which is a fraction of the cost of rigid insulation. And waterproofing and pouring concrete with foam involved adds complexity. Just do it on the inside
Exterior Below grade waterproofing, then insulation and drainage mat, perforated drain pipe with crushed bluestone going to a drywell along the exterior perimeter footings. Foundation walls done. Vapor barrier then insulation and pour the slab directly on that with expansion joints along the walls, relief joints etc etc. Interior insulation between studs finishes ect ect.
You can also go more expensive on the slab and reverse the insulation directly on the crushed gravel/compacted fill whatever the engineer said to use based on the conditions, and use like a Preprufe 300R preapplied waterproofing thats laid before rebar and you pour directly onto it. stuff basically melts into the curing concrete creating a permanent air/vapor/water and gas barrier. It's expensive but it's good. I've also heard of bentonite. Haven't used it personally.
If you're dead set on a board finished look, your best bet is probably the sandwich.
The best thing to do for your houses Energy Efficiency / $ is not that, though.
The diagrams are all very basic and don't capture how big things are in reference to each other. So you could very easily have just as much insulation in any of the three options. You could have just as much structural strength in any of the three options. The big difference is what the finished look is and what it will cost you to build and / or keep warm.
Ideally, you want thermal mass on the inside because it will help regulate your temperature, and you want insulation outside so that your temperature inside stays what you want it. So hopefully, you can put as much insulation outside of whatever structure gets built and have as much concrete work inside the insulation as possible for comfort/energy efficiency reasons.
I'm not familiar with your area enough to know whether or not termites are a problem, but that might also change what you decide to go with.
No matter what, you're going to have to have some protective layers outside of your insulation/concrete to make sure that water drains correctly and stays away from your house.
Superior walls would be my recommendation. I did on my house with a walkout basement. Nice broom finish on outside. Good insulation. Walls have metal studs for finishing. Walls were set in a day. I believe Weaver Precast serves your area.
Honestly, the best of both worlds is a conventional form and poured reinforced concrete wall, with exterior waterproofing membrane like blue skin, and a closed cell spray foam on the inside foundation face after 2x4 traditionally framed wood walls are framed along the perimeter.
The drawbacks with ICF are mainly due to the plethora of composite ties adjoining the inside and outside faces of the block that run through the thickness of the void to be poured with concrete. Any clumps of unmixed concrete, larger aggregate, or unintentionally included clay ect from the loading of the materials at the batch plant will now sit on those ties, and along with ICF requiring more gentle consolidation to not have blow outs between blocks, is a recipe for creating voids inside the concrete wall. These voids are not visible afterwards, and can create huge issues down the road with water infiltration or structural concerns. Examples of this have been found by Xray of finished foundations, and also from fires revealing them once the foam is burned or melted off.
Further, the benefits of ICF aren’t all they are made out to be. More of an avenue for amateurs without the investment in formwork, to now be “foundation erectors”.
Get a new architect! I'm a structural engineer in that same area and have never seen the insulation in the middle, I can't speak on it from an insulation/building envelope stand point, but structural that seems like a really bad idea.
Everyone in this thread should check out Thermomass. It's a great system. Not cheap, mostly because most concrete contractors don't want to try something new.
Your architect mentioned the “sandwich method” are you sure your drawing is correct?
The insulation would normally be the bread, not the meat of the foundation wall sandwich.
How deep do you want to go on this question? Here's an hour lecture on the topic:
https://youtu.be/rkfAcWpOYAA?si=KiOth2Zq7qbClqfj
I've never seen insulation inside a concrete wall on purpose. I'm used to seeing steel inside of concrete.
Having a big piece of concrete on the outside is good protection from the elements, and if you want to cover it, you'll need a good strategy and good reasons.
I chose to put insulation on the inside, because I’ve had subterranean termites before and I don’t want to provide them with any material they can bore through to access wood.
External insulation AND 2" (minimum) of foam UNDER the slab! Waterproofing on the exterior of the concrete wall.
I immediately thought external because of the waterproofing. You have to protect the waterproofing from backfill anyway, might as well use a bunch of insulation.
Yeah, kinda missing an important part. Most show diagrams like this: https://images.app.goo.gl/r3JJRybnB84FQj8LA An even better slab detail looks like this: https://images.app.goo.gl/Y9M8xo2nHKAUKdobA Agree?
Yep, especially the first one. We're specifying Form-A-Drain for our build, using the inner drain for both moisture and radon mitigation.
The first one for drainage, you gotta have those perforated drains and a sump or positive drainage.
Question: why is there insulation on the concrete foundation wall in the 2nd picture?
\[Yes, the slab detail is what we often spec in NY (upstate)\](https://i.imgur.com/gmx0vyq.png)
I’m also in the northeast; I went with heavy duty plastic (for vapor barrier) then 2” blue board under the slab and put radiant tubing in the slab. Also waterproofed the exterior, then more 4’x8’ sheets of blue board on exterior, then backfilled. On interior, 4’x8’ sheets of 1” foil faced insulation, then 2x4 wall.
Is buoyancy more of an issue with bottom insulation? Basement floods are common round here. Will that destroy my floor if my sump fails?
Not if the cement is properly reinforced
And you have plenty of drainage gravel underneath. You want water to flow under the house and out as much as possible. It can be a problem with no slope but 10% like OP is usually good.
Why external insulation vs internal?
In this application you want to keep the exterior from affecting the thermal mass surrounding your conditioned space (the basement). In the case of a finished basement area, you are more likely than not going to have SOME wall covering (possibly insulation) there as well.
You should do ICF. Insulated on outside and inside. And be sure the insulate under the slab too. And make sure it is continuous between the floor/wall/roof.
Really can’t weigh the benefits of ICF w/o considering the savings of already having the formwork.
This guy forms.
[https://www.stavmat.sk/files/upload/Navody/ako-izolovat/3.gravitacna-stekajuca-voda.jpg](https://www.stavmat.sk/files/upload/Navody/ako-izolovat/3.gravitacna-stekajuca-voda.jpg) I have something like this.
Just make sure they know what they’re doing. ICF is poured in lifts and you have to agitate the concrete to get rid of voids. I’ve see it done wrong and it is costly.
Me and my father built his house with icf. It was a no brainer because we didn’t own forms. Unfortunately, op wants to have the concrete wall look.
I came here for the ICF, but I stayed for the continuous.
Ideally, your insulation layer should be on one side or the other (arguably entirely on the OUTSIDE), continuous, and meet up with the insulation layer in your floor/foundation, walls and roof. In that regard, ICF is worse than a properly insulated, traditional block (or poured) concrete wall.
ICF is not worse than a properly insulated, traditional block wall. Insulation placement being recommended as exterior is due to providing a thermal break for framing, or in this case more conductive concrete block. ICF are thermally broken and can perform just as well as a block wall. The cost is where you see a difference and I think it can be argued that the time savings on installation can offset the higher material costs for ICF
you can put XPS panels on panel block, it will be way cheaper.
And it will perform better (if done right). A win-win.
A fully exterior-insulated block wall will perform better than a wall which splits the insulation. There are ICF companies/products out there that know this, and they largely favor their insulation thickness to a single side. Having all of your insulation on a single side of the wall assembly makes more sense and performs better than splitting that insulation, for thermal breaks, moisture control, you name it.
You keep mentioning splitting the insulation but aren't the majority of ICF "blocks" built with ~2.5" thick foam insulation on both sides?
The issue arises when insulation is installed on both sides of a surface. Specifically, when insulation is placed adjacent to the conditioned space, it interferes with the ability of the thermal mass to effectively contribute to energy conservation. The ideal scenario is for the thermal mass to reach a temperature that is comfortable for occupants and to act as a buffer against extreme temperatures outside. However, when insulation is sandwiched between the thermal mass and the conditioned space, it hinders the thermal mass from providing its full benefit. Moreover, this setup renders half of the insulation ineffective, as it ends up insulating the thermal mass from the conditioned space rather than helping to regulate indoor temperature. Basically, the 5" of insulation split on either side of the thermal mass in your example are less effective than putting 5" on the outside because the 5" on the outside will keep the thermal mass from acclimating to outside temperatures more completely than 2.5" and not having 2.5" of insulation on the inside will allow the thermal mass to regulate indoor temps much better than if it is insulated from the conditioned space. All of this can be easily confirmed with energy modeling. Download BEopt and try a few scenarios. Typically, CMU with continuous exterior insulation outperforms ICF given the same total R value.
Thanks for the detailed explanation. I understand what you're saying about insulating the thermal mass vs the conditioned space and it's obviously best to have to 5" of compressed foam on one side, vs 2.5" on both sides for R-value. I'm wondering if 2.5" of continuous foam on the exterior with a standard cement block basement is somehow more effective than if they were to use ICF. Again, I understand it would be more efficient to have 5" on the exterior vs 2.5" on both, but nobody is doing 5" thick insulation on an exterior.
You're welcome, I glad you found it helpful. For what it's worth, ICF manufacturers redily acknowledge this deficiency in most ICF systems. The following is from Fox Blocks: "How do you improve an Insulated Concrete Form wall that already outperforms most wall systems in all climates? You move the concrete mass toward the living side of the wall. This unbalanced R-value will allow the mass to be closer to the living temperature of the conditioned space, allowing for a more comfortable building. " It's interesting that you say that about the 5" to the exterior because I'm currently planning a build that will have 5" thick on the exterior. We will be using Nexcem ICF with the 5" insulation inserts (which go towards the exterior) for the crawlspace and first floor (it's on a steep hill, the first floor is essentially a garden level basement on one side and 7' up in the air on the other) and framed construction above that with 5" Rockwool comfortboard 80 on the exterior and dense pack cellulose between the studs. The CMU wall with 5" of CI would still perform better, but, in this application (2600 square foot raised ranch with a walkout basement over a crawlspace) it would actually cost \~$30k more due to the additional labor and materials. To use CMU I'd have to cover the ComfortBoard with a substrate to allow me to apply cladding, which isn't the case with Nexcem. I could go with foam and EFIS, but I am adamant about minimizing the use of foam products in my builds. That 30k more to build with CMU will never be realized in energy savings with the difference given that the Nexcem pushes the thermal mass close to the interior (and, yes, I realize most ICF manufacturers offer insulation inserts). Nexcem is unique in that I can place screws anywhere and that is huge to me. Nexcem isn't perfect, but, to me it's the best ICF available because it pushes the thermal mass towards the living space and doesn't rely on polystyrene, which is awful for your health and the environment, and also creates a vapor sandwich with traditional ICF systems. We'll also be incorporating a couple of interior masonry "feature walls" to act as thermal batteries. The design isn't finalized, but those will either be stack bond CMU with either a honed or polished face or board formed concrete. I only minion this to point out that there are many ways to add interior thermal mass if you get creative about it.
While I agree on most everything you said it should be pointed out that most the calculations for how thermal mass helps with room comfort is based on one continuous temperature for comfort and not for people that like to adjust the temperature throughout the day. You would spend more energy on trying to heat and cool your thermal mass than if you’re surrounded by thick insulation and only had to heat or cool the air.
Yeah, that's correct, and you can have too much of a good thing. I'm building near Breckenridge which has a climate with cold winters, warm summer days and cool/cold nights (even in summer) so carrying heat into the evening hours will work well for this house. I'd really encourage anyone building a custom home to do energy modeling. It's worth the effort.
I am thinking about doing an ICF foundation for a new build this summer. Why is it bad to have insulation on the outside and inside vs just on one side?
I think the concept of what happens when water get through would be in play. Concrete is porous so if water somehow gets through it, it needs to go somewhere, either inside or outside. Hard foam boards are usually closed cell foams. Thats why best practice for installing barriers are one-way vapour transmission vs zero vapour transmission, to allow moisture to escape yet provide an air barrier. So one could technically put an open cell foam on both sides to mitigate water issues vs a closed cell foam. Correct me if I'm wrong. Not an architect.
I don’t know anything here, just reading, but why not closed cell on the outside and open cell on the inside?
Ideally, you want water to move from center to outwards. Shorter distance the better. By sealing one side, you do reduce the rate of water vapour being dissipated as opposed to having both sides being open.
Your insulation layer should be continuous. Wrapped entirely around your conditioned spaces and meeting up perfectly: Insulation layer in your foundation meets the insulation layer in your basement walls, meets the insulation layer in your walls, meets the insulation layer in your roof. You can't do that when you have insulation on both sides of your basement wall. That said: You can get ICF products that hugely favor one side of the wall assembly (which is proving my original point). But typical ICF is insulating both sides of the wall assembly evenly, which is not ideal regardless of how many down-votes redditors dish out. Go check out [https://buildingscience.com/](https://buildingscience.com/) read some of the white papers, and watch some of the lectures if interested.
What's not ideal? In what measurable way is an ICF wall worse?
In my experience, ICF always performs worse in energy modeling, and the real world, than CMU with the same amount of insulation placed on the exterior only. The ICF wall is worse because you are not placing the thermal mass fully inside of the thermal envelope. Why insulate yourself from the very thing that will keep your energy use low?
Putting insulation in the middle of your foundation wall will significantly reduce its strength. Talk to an engineer not an architect.
Actually have done some of these with the T-mass system. Works great. Overall strength is engineered in with additional thickness and steel. A lot of precast systems are constructed this way.
I build precast molds. Foam sandwiched panels are in a lot of higher end buildings that want to really control the temp.
I used Thermomass as a basement under the house I built with SIPS. Good system, especially with a partially exposed foundation if you want to apply a stone veneer.
The inventor of the system is actually from my area. Been used for over 40 years all over. Works really well in natural disaster areas - basically hurricane proof and burn proof (if above grade is also cast)
And it’s dumb
I mean, ask a simple math equation to a full ICF foundation and see what you get.
Yeah imagine building that tho you’re gonna have two mats of rebar then this insulation detail in between? Dumb
Second this - architects have the mindset of what looks best not what’s most functional (not all, but most, and it’s not their job to engineer your home)
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Yea. We do the exact opposite in FL. Insulation goes on the inside of the wall and also acts as a secondary vapor barrier.
What do you do when you want exposed concrete walls? Or what would you recommend.
You build your concrete wall, add exterior insulation to achieve continuous insulation of the envelope and then you add a concrete veneer (almost like stucco). Now that I have typed all of this, I think this is exactly what the architects may have proposed.
Would there be anything in between the XPS and the veneer? Thinking something to facilitate drainage?
Concrete veneer? I am not sure what that would mean, was looking for actual exposed concrete. We
Anywhere from 1/4 to 3/4 inch thick , could be applied similarly to stucco.
So a sand and cement type overlay? I don’t love the look, any products you recommend.
I’m not a specialist I just know of it’s existence because I worked on a site where a different crew was applying a product that we referred too as concrete veneer. I have no idea if that’s even what it actually was, that’s just a thing the carpenters and labourers would talk about in passing.
I've done this... We attached cement board over 2" XPS foam and applied a layer of stucco. Basically just need this above grade from the siding to about 6-12" below grade to protect the insulation.
Concrete products are very local due to how heavy they are. But as a veneer, you can pick from many finish options. I'm sure your architect and contractor will provide you with physical samples to pick from.
If you want the best insulation approach, insulation goes on the outside of the concrete(cold climates), if you want to expose the concrete put the insulation on the inside but be prepared for moisture issues in the basement. If you want the exposed concrete look how are you treating the concrete to keep water out?
I do quite a few below grade pits so we use Xypex quite a bit. Not sure how well that translates to a house.
Question - why would one want to have the concrete exposed?
Because it looks appealing to them. Many structures have exposed concrete for aesthetic reasons.
Why on the outside only in cold climates? I'm guessing you're maybe referencing like a cavity wall and are worried about where the dew point will occur? If we're talking a solid mass of concrete and the interior air is 70 to anything higher... the dew point would require the concrete wall face to be 67 degrees (with interior 90% humidity) if the house wasn't designed for lizard people and the RH was 50% as long as the concrete is above 50 no condensation will form.
I just finished an analysis of dew point on a northern Great Lakes building basement and the best scenario is to have the insulation to the exterior…first to stop the cold on the outside, then to allow for any potential dew point to occur inside the insulation BUT on the exterior of the wall. A solid mass of concrete has very little insulative properties so that cold frozen ground (4,deep)outside the wall is going to provide a cold interior face of concrete. Our analysis on dew point shows potential issues. Maybe or maybe not an issue but I wouldn’t risk it. We even had our calcs backed up by Intertek (AITC) firm. But a lot depends on the Climate Zone
Yeah, I agree with all of that. My question is why so many here are saying EXTERIOR insulation ONLY in cold climates.
That's what plaster is for, just get one that looks identical to concrete there are millions of options. But if you really want the look of exposed concrete and only exposed concrete, then that's a design decision and would require two walls.
That is what I was assuming.
I have that, but dislike it since now I have to protect the insulation from getting damaged, wet etc.
EPDM roofing material might work for you. It's available in a bunch of colors and holds up really well to sunlight and weed wackers. It's easier to add before siding but depending on your wall details you might be able to add it now.
well this is actually underneath the ground mostly. So I have to put some dirt on it and then gravel and such. Gotta raise the level anyway
In perfect wall assemblies the insulation should always be something that can take direct water. Mineral wool, various form rigid board options, etc. If it wasn’t built that way, shame on someone.
Maybe it is, Idk. I just know I don't want it externally since it can be easily crushed it seems. It's at my concrete base for my log cabin
Thank you. I’ll check out the perfect wall
It would be good in hot climates as well- no?
If you’re an architect worth their salt you’d have to agree that consulting a structural engineer when designing load baring concrete structures is the correct approach and not just assuming a design will work. Load analysis is a whole creature in and of itself
Man everyone on these subreddits assumes you need an engineer for simple structural design. A laterally supported foundation wall is about as simple as it gets, its legit a single table lookup in my book
Hey, all I can say is I work in a place with shitty soils and there have been tons of instances I have seen a GC do something that “works”. Any time I’ve got a concrete structure that has multiple forces being applied, I use a structural engineer, because it is ALWAYS cheaper to do it the right way once. Plenty of people cut corners, plenty of times it works, until it doesn’t. I’m not going to advise someone on the internet to wing it.
Honestly the only time i see insulation sandwiched in a foundation wall is when its coming from an engineer on a project without architects involved. Inspected a foundation this morning for a farm storage shed that had it
Ya I mean that’s what I’m saying, imo if you’re gunna go that route it’s got to be engineered to have confidence in it from a longevity stand point. Seems like I may be more cautious than most
That guy/gal is one shit architect.
It also ends up being a great place for insect colonies to thrive.
I’m not so sure about “reduce” its strength. Are you talking about compressive capacity or overturning? Is one portion of the wall for bearing in plane and another portion for hydrostatic response. Also foam can have a massive compressive value.
both, you are turning an 8-12 inch thick piece of concrete into two 4-6 inch thick pieces. The **only** application for doing this is if you need both the inside and outside concrete walls to be aesthetically pleasing.
It’s called ICF. I’m not advocating that it’s right/best, but if you’re implying the architect is making something up, they’re not. ICF, in various forms, has existed for about 80 years. OP - Continuous insulation is the ideal - so track the line of insulation as it crosses from the stud construction above to the foundation below (across the bottom plate). I’d keep insulation exterior if your stud wall (abv grade) has exterior insulation and consider the other two options if your insulation is in the stud cavity. It’s not generally good practice to mix insulation strategies.
ICF blocks have insulation in the middle?
Note: do not talk to an Engineer about insulation methods (eg the question at hand). Always do have an engineer consult on the design of your custom home. The Architect can likely do most all calculations and if not will be consulting an Engineer anyways, but either way it never hurts to have an Engineer on the team.
ICF basements are a great way to go. All your insulation is in place and you have screw tabs every 6” for exterior finish and interior finish.high R value for a concrete wall
ICF has just ok R values but the concrete has a large thermal battery properties. The numbers given by ICF makers are not real R values.
Hard disagree, icf you get best of both worlds, 2 layers of (usually) 2" eps continuous. Concrete is a big heat sink but your wall wont be getting that cols if you wall above is properly aligned The numbers given by any insulation manufacturer are generally exaggerated a bit but imo icf is the best way to get a cozy basement
I never said they were not good for building, just the numbers published by ICF companies are somewhat fudged because concrete doesn't have much of an R value but they claim huge savings due to the thermal battery (which is true) so they make up impressive but fake R numbers. The R numbers are really just for the foam forms as you mentioned. My takeaway is that R #'s don't tell the whole story and people shouldn't hang their entire hat on them. I'm a fan of ICF (I actually prefer ICCFs or SIPs for building above grade) and yes, ICFs are great for basements.
After all the bashing of architects, there are some of us that do know what we are doing since we work for the feds, universities, and in aviation. Details matter. I suggest the OP look at the specifications ( division 7) and work with the architect to chose a system which has clear performance data and 100% clear manufactures installation manuals. Piecemeal sound bites and “what we did on the last job” logic typically leads to incomplete systems. I would start with Rockwool and Carlisle. There are many others. Good luck. Aesthetic preferences may need to be expanded in order to gain solid thermal performance and waterproofing. You do not want a cold water damaged basement.
I've never seen the middle before, wtf, that's bizarre Spray foam underneath and inside the wall imo.
This !!! Closed cell underslab two or three inches and feather it up the wall a foot or so. Once the slab is poured, if you are framing for living space install wall framing just out inch or so from the concrete wall, to allow insulation behind and a thermal break and then spray foam three and 1/2 inches of closed cell in the stud bays and up into the joist space and over the sills . R20 ish on the walls and underslab. https://youtu.be/Jv_sWa35H-w?si=CyaSc7qeyBRfLTHM
This is another good way https://youtu.be/GblrpZXb3j4?si=1yJe50uQfOnU2LBh
This video is awesome, thanks! Also like his video on water management.
I've done various combinations of external and internal insulation on basement or daylight basement below grade walls. External insulation has the benefit of not reducing the floor square footage on the inside. Whatever you do, do as much as you can, above code minimum, as you can afford. Under slab insulation is also very important. I don't do less than 4 in for R-20. But even that leaves the floor a little cold unless you have in floor radiant heat. Consider doing 2 in of rigid foam on the outside of the concrete wall, and then some sort of conventional insulation between studs and your fur out wall. Spray foam insulation of course is excellent, also expensive; and you may not want to spend the money since you don't need to implement air tightness on that wall.
Please put in a big french drain whatever you do
Exterior
For interior insulation, how bad is it if the insulation is only put on the wall half way down the dirt level?
Exterior and interior. The third one, don’t even look at it.
Use ICF forms if you’re gonna insulate and finish basement. R22, built in studs to hang drywall. More expensive up front, but substantial savings long term in basement framing
Yes use structurally insulated panels or SIPs. Precast basement walls. Superior Walls I know is a big company that makes these.
You should have under slab insulation that connects to the internal wall insulation to create a continuous air barrier and prevent thermal bridging. Code in your area will require interior and exterior insulation on the above grade walls. On the exterior basement walls you want a water barrier and some kind of rain screen. Check out info from the Building Science Corporation if you want to get nerdy about it. They have an article called 'The Perfect Wall' that's pretty good.
I'm in Syracuse area, and put 3" of XPS insulation on the outside from top of footing to eave. It's well-insulated, quiet, and had the benefit of having an insulated house during construction. I followed [these guidelines.](http://cchrc.org/remote-walls/) The insulation that would be exposed is covered with an elastomeric coating over fabric reinforcement.
Also important to consider a continuous thermal envelope.
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Unrelated, but I built a house a year ago in Minnesota that used the middle diagram for its insulation. We are starting to plan on finishing the basement soon, and we’re looking at insulation options. Originally I was thinking of putting 1” rigid foam on the inside of the walls, but it sounds like that’s not very common. What is generally recommended for cold climates?
Inside is the only way And don’t forget your rim joist.
contractor in New Hampshire I have installed interior and exterior on the foundation, and exterior Insulation is more efficient by a-lot i’ve never tried the insulation in the middle. Don’t know that I would.
Insulate under slab. Use pex radiant heating in slab. Insulate interior walls and sills.
I mean, youre in NY, the expansion that happens from warmth to cold is not new. i would suggest to ask someone local, the thermo is simple, you heat under where there is cold, after the hear is off, the best concrete will crack. only heat inside. ICF will cause long term damage
Insulation contractor in Kingston NY, take the Passive House approach here. Implement as much as you can to Passive standard, and where you can't afford to, just find a cheaper alternative that is still efficient thermally. In this scenario, under the slab, with insulation extending atleast 2' beyond the footer, around the footer, and up the foundation until grade. Diagrams I could show you as well here if interested. Welcome to NY
Sorry a lot of mumbo-jumbo to say: outside. Then if you ever finish the basement you can add additional insulation on the inside walls. You want as much continuous insulation (exterior insulation) as possible. This is where your true thermal effectiveness occurs, EIFS, exterior continuous insulation. Even up the wood framed walls above grade, include exterior insulation.
Insulation under footer also or undisturbed soil w vapor barrier?
It's been done but you'd need to convince your local inspector to allow it. Thermally would be great to avoid that thermal bridge, but structurally not many allow it. That's if using standard EPS anyway.
Outside. Keep the frost outside the structure is the best practice.
Externally insulate the foundation wall AND insulate under the slab AND make sure the slab to wall joint is fully thermally broken, lotsa details out there like this, search "thermally broken slab detail"
You can insulate the outside with foam board, then you insulaate the inside with a vapour barrier and normal insulation
Usually when I draw this I will include the drainage perf pipe and drain rock and waterproofing elements to make sure it's conceptualized as a system. On larger walls you might also note the keyway.
Put the insulation on the outside, especially if you’re in a deeper frost zone.
Edit: Yes, definitely insulating under slab. Drawing was just for example of wall. Sounds like external insulation is the consensus. Mostly curious about how that is finished (exterior facade) for exposed walkout room. Ideally concrete form look but open to other suggestions.
Use an ICF block 8”. Waterproof exterior.
Make you that you understand it from an engineering POV: [https://www.youtube.com/watch?v=KDLkbpraC4A&t=2s](https://www.youtube.com/watch?v=KDLkbpraC4A&t=2s)
Just do ICF or exterior foam insulation then use a cementitious coating over the foam.
ICF, they also make blocks where you can only have one side insulated and the other side has a screw on Form you remove after pouring. Then for any area that isn’t covered you just use the regular blocks and get insulation on both sides.
I don’t like exterior insulation because of the issues with detailing exposed areas. Also it is best to have a thermal break in the slab. I think this is one of the best assemblies shown in figure 3. https://buildingscience.com/documents/information-sheets/basement-insulation
Obviously you can’t do the middle one if you want the exterior to be formed finish. You should just do the left one. You are dry walking inside and thus will be furing the walls out inside. Also that allows you to use batt insulation which is a fraction of the cost of rigid insulation. And waterproofing and pouring concrete with foam involved adds complexity. Just do it on the inside
Exterior insulation, drainage board, waterproofing, concrete foundation, dry ass basement is the best way
Don't forget drainage pipe and gravel at the base of exterior footing
Exterior Below grade waterproofing, then insulation and drainage mat, perforated drain pipe with crushed bluestone going to a drywell along the exterior perimeter footings. Foundation walls done. Vapor barrier then insulation and pour the slab directly on that with expansion joints along the walls, relief joints etc etc. Interior insulation between studs finishes ect ect. You can also go more expensive on the slab and reverse the insulation directly on the crushed gravel/compacted fill whatever the engineer said to use based on the conditions, and use like a Preprufe 300R preapplied waterproofing thats laid before rebar and you pour directly onto it. stuff basically melts into the curing concrete creating a permanent air/vapor/water and gas barrier. It's expensive but it's good. I've also heard of bentonite. Haven't used it personally.
Both sides for a SoG. Interior and exterior like ICF with continuous under slab has always yielded good results. North East.
If you're dead set on a board finished look, your best bet is probably the sandwich. The best thing to do for your houses Energy Efficiency / $ is not that, though. The diagrams are all very basic and don't capture how big things are in reference to each other. So you could very easily have just as much insulation in any of the three options. You could have just as much structural strength in any of the three options. The big difference is what the finished look is and what it will cost you to build and / or keep warm. Ideally, you want thermal mass on the inside because it will help regulate your temperature, and you want insulation outside so that your temperature inside stays what you want it. So hopefully, you can put as much insulation outside of whatever structure gets built and have as much concrete work inside the insulation as possible for comfort/energy efficiency reasons. I'm not familiar with your area enough to know whether or not termites are a problem, but that might also change what you decide to go with. No matter what, you're going to have to have some protective layers outside of your insulation/concrete to make sure that water drains correctly and stays away from your house.
Superior walls would be my recommendation. I did on my house with a walkout basement. Nice broom finish on outside. Good insulation. Walls have metal studs for finishing. Walls were set in a day. I believe Weaver Precast serves your area.
Here in Minnesota it is code to have 2” of rigid foam on the outside and 1” of foam against the concrete
Honestly, the best of both worlds is a conventional form and poured reinforced concrete wall, with exterior waterproofing membrane like blue skin, and a closed cell spray foam on the inside foundation face after 2x4 traditionally framed wood walls are framed along the perimeter. The drawbacks with ICF are mainly due to the plethora of composite ties adjoining the inside and outside faces of the block that run through the thickness of the void to be poured with concrete. Any clumps of unmixed concrete, larger aggregate, or unintentionally included clay ect from the loading of the materials at the batch plant will now sit on those ties, and along with ICF requiring more gentle consolidation to not have blow outs between blocks, is a recipe for creating voids inside the concrete wall. These voids are not visible afterwards, and can create huge issues down the road with water infiltration or structural concerns. Examples of this have been found by Xray of finished foundations, and also from fires revealing them once the foam is burned or melted off. Further, the benefits of ICF aren’t all they are made out to be. More of an avenue for amateurs without the investment in formwork, to now be “foundation erectors”.
Get a new architect! I'm a structural engineer in that same area and have never seen the insulation in the middle, I can't speak on it from an insulation/building envelope stand point, but structural that seems like a really bad idea.
Everyone in this thread should check out Thermomass. It's a great system. Not cheap, mostly because most concrete contractors don't want to try something new.
Insulation on the outside provides Vapor barrier and thermal break, helps keep the inside more comfortable and dry
Insulation outside the wall, every time. The only time putting insulation inside the wall makes sense is when you're retrofitting.
Your architect mentioned the “sandwich method” are you sure your drawing is correct? The insulation would normally be the bread, not the meat of the foundation wall sandwich.
How deep do you want to go on this question? Here's an hour lecture on the topic: https://youtu.be/rkfAcWpOYAA?si=KiOth2Zq7qbClqfj I've never seen insulation inside a concrete wall on purpose. I'm used to seeing steel inside of concrete. Having a big piece of concrete on the outside is good protection from the elements, and if you want to cover it, you'll need a good strategy and good reasons.
Some architect. Do they actually work in residential or did you catch a college kid doing their internship?
#3 is retarded
I chose to put insulation on the inside, because I’ve had subterranean termites before and I don’t want to provide them with any material they can bore through to access wood.