Product for Protecting Exterior Rigid Foam on Foundation Walls
kristik44
| Posted in Energy Efficiency and Durability on
I am moving towards putting 2″ or 3″ of rigid foam on the exterior of basement foundation walls. What product are people using to protect the foam from the grade to the sill? Details often call out “Protective board”? I have seen people use stucco but in my area, the stucco does not seem to hold up. Suggestions?
Thank you in advance!
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Hi Kristi,
In this post, Martin Holladay names a few products you might want to check out: How to Finish Exterior Foundation Insulation. I also have an inquiry in to my coworkers at Fine Homebuilding because I have a vague memory of them discussing this. I will let you know what they have seen used.
Hi Kiley! I listen to you every week on the FHB podcast! I did see this article but it is from 2010!~ I was hoping there might be some new products or solutions out there. None of the contractors I work with are thrilled with the "stucco" or cement option nor exposed plywood.
OK, here's what Matt Millham shared:
It really depends on the look you're going after. Tuff II from Styro Industries is an option - basically a tough coating that goes on like paint. There are also foams that come with a hard skin on them - basically made for the application. WallGuard is one, but I'm sure there are others.
Metal flashing tends to oilcan, so if you want to go metal, you have to go pretty thick to make it work.
Josh (Cooperstown guy) just uses Durock (tile backer board) and covers it with a bonding cement. It's not rated for outdoor use, though, so I'd have a hard time recommending that in a cold climate.
https://www.finehomebuilding.com/2020/01/02/cover-for-exposed-foundation-insulation
https://www.finehomebuilding.com/2021/01/15/high-performance-raft-slab
I have seen various coverings applied and then crack and release sooner than one would expect. So, I sought a more robust solution. I used ¾” Southern Yellow Pine plywood, treated to “Foundation Grade” rating. I screwed the plywood through the foam and into the concrete with Tapcon screws, and butted the joints tightly together. The exposed part is green preservative treatment, and can be left as is or stained with a durable penetrating stain. I think that would last indefinitely, with no deterioration, except for the stain which would need re-staining every 10-20 years. I will use this method on all projects going forward.
This is not a bad solution... I bet it works better than stucco. Thank you!
Similar to stucco, is the Tuff II product: https://styro.net/TuffIIFoamAndICFCoating.html
https://youtu.be/7SGKqb8VSHE
Another option, which we used, is metal coil stock, which I discuss here:
https://kimchiandkraut.net/2019/07/11/passive-house-continuous-insulation/
Yet another option would be PVC panels:
https://youtu.be/opmk9NoN9xE
Delta MS Dimple Mat Secured to the foam / concrete will provide protection during back fill as well as a water proofing layer that is far superior to tar. Most are still installing the polyiso on the inside of the basement though.
I use painted coil stock like that used in forming seamless gutters. Comes in many colors and is easy to work with.
https://www.edcoportal.com/Catalog/Products/soffitfasciaandtrimcoil/trimcoil?page=3&pageSize=8&sort=1
I did the same, using aluminum flashing with a baked enamel finish.
I'm interesting in this as well. My foundation walls are above grade on 2 sides. I wonder if this product works. It says they have a special adhesive. It comes in 1, 1.5, and 2 inch. Any opinion on this, it would be super easy to just basically glue it to exterior wall contains rigid foam with stucco face. Sounds to good to be true though.
https://www.homedepot.com/p/STYRO-Industries-FP-Ultra-Lite-1-5-in-x-2-ft-x-4-ft-Stucco-Grey-Foundation-Panel-SFL-200-1103/203929080
The challenge with all the solutions that cover the exterior foam, is that they also obscure visual inspection of termites, carpenter ants or other wood eating insects that may attack the house through the foam...
One solution is to put a (preferably copper) termite barrier sealed to the top of the foundation wall, extending horizontally to the exterior air. (Unfortunately typically a thermal bridge.) Copper can interfere with termite digestion, killing them. But anything they can't get through would work. So the termites could infest and hide tunnels in the foam below, but would be prevented from getting to the wall above the termite barrier. Some termite barriers are not metal, so wouldn't be as conductive a thermal bridge.
Alternatively, the termite barrier could be sealed to the top of the foundation, then out horizontally to air, then down to the ground, covering the foam from exposure. (Assuming its aesthetics are okay with you. Like painted coil stock/aluminum flashing with a baked enamel finish in the color of your choice.)
I only have one wall that has soil, the other foam would be sitting on concrete does that make a difference? Is there any fool proof system that combines everything in one. Would be easy if they made a termite resistant system for this application. They make panels but they are not designed to protect against termites.
So what your saying is exterior foam could cause an insect infestation? Foundation walls usually are concrete so it would be eating foam and traveling up the wall?
In answer to the original poster, why does stucco not last in your area. I have had stucco on my foundation walls for decades. I bought a family home so I have seen it over the years. It's also very hard to drill anything to the wall. My neighbor did mention they had some company way back when that did stucco throughout the entire neighborhood at the time and it was hard as rock.
Yes, insects in the ground get to foam through gaps or cracks in the stucco or plywood or other covering, and travel up the insulation unimpeded until they get to the framing and if they are termites or carpenter ants, they then eat the framing.
Generally in regions in which termites are a problem, you want anything on or through which a termite will tunnel exposed. So you expose the edge of the slab so you can see termite tunnels and address it before they get into your sill plate. And you just live with the energy penalty as a fate not as bad as having your house eaten by termites.
I’m in northeast, suburbs of nyc. Should I be concerned with termites? 2 of the sides of the house are next to patio and not dirt so not sure if that makes a difference. Do I leave a gap on top of stucco panels for termite inspection. So like gap after wood siding a few inches, then a z flashing then foam?
I recently used Tuff II. Can't comment on it's longevity, but it seems quite tough (flexible). It's acrylic so doesn't have the same feel as cementitious coatings. It applied fairly easy (used a pool trowel). Make sure its warm enough and doesn't get rained on.
Tyler what did you use for insulation? Did you have to do anything to prevent infect infestation?
For the plywood covering I have used, I extended that at least a couple feet into the ground, which consisted of good fill sand. Then when I backfilled against the plywood, I compacted the fill sand which is ideal for compacting. But for being buried in the ground, the plywood has to be treated to what is specified as FOUNDATION GRADE. This is the type of treated lumber that must be used on wood foundations. Not only will this plywood never rot, but it also will never delaminate. I am not sure how much it might develop small splits in the outer veneer from repeated wetting and drying and also from sunlight. But I suspect these effects would hardly affect this plywood in say 20 years. But when I installed it, I stained it with a solid color black oil based stain. Although those stain products have been changing lately.
A potential problem with bonding materials to the foam is not the strength of the bond. Bond strength can be more than adequate. But the potential problem is the tensile strength of the foam. The bond can hold, but a layer of foam can pull off as a mode of failure. The bond may be adequate for some covering methods, but maybe marginal for others.
I am in the northern climate, so termites are not in this area. Ants, however, will burrow into foam board such as XPS. I don't know how deep into the ground ants go, but by extending the plywood a couple feet into the ground, I think that may deter them. Compacting the backfill also forces the plywood against the foam very tightly, so insects would not be able to merely walk into gaps between the plywood and the foam.
Just saw this new product....
FoundationProTM: If you build in a cold climate, you know that energy code requires foundation insulation. You can place foam in the foundation wall’s interior face or, better yet, put it to the exterior, where it really belongs. The problem with the exterior arrangement comes with how to protect and finish the delicate foam. Progressive Foam introduced a surface, foundation grade insulating system with a polymeric finish. You can use it as is in either the white, gray, or beige factory finishes, or you can paint it if you want to. The installation seems simple; at the top, a PVC flange tucks under the mudsill, at the bottom, a channel holds the system in place and protects the edge, and the finished foam lays snug to the foundation wall in between. FoundationPRO is available with R-10 and R7.5 Neopor insulation. It comes in lengths of 12-feet and (for now) custom widths while the manufacturer gauges market demand. The company is still developing this product, so it’s not on their website, but you can contact Salvatore Vaccarino at [email protected].
Insulation Options: Progressive Foam’s FoundationPRO offers insulation values that include R10, R7.5, and R5. . Panels come 12-feet long and in custom widths.
Thanks! I will check this out, I'm assuming this has termite protection
Following Robert's comments above (thanks, Robert!) I ran across this:
https://buildwithhalo.com/halo-subterra/
I'm researching insulation for a floating, fully insulated slab-on-grade build and this product looks to have a lot of promise.
I'm actually considering crafting my own insulated form for a slab-on-grade. I could see that the Halo product might be able to create rounded edges on the outer slab (as some insulated slab kit/products utilize). This newer graphite EPS might be the "better mousetrap."
Just thinking this over, wouldn’t you avoid the whole problem by making a 4 foot skirt on bottom of wall with comfort board or eps covered with protective layer. Above grade walls would be easy to insulate anything underground you dig to footing. The bottom would be concrete and the top you could see if anything is crawling up. You could easily put some kind of copper lip on top for extra protection. You would lose insulation but if you insulate rim joist from inside you have that and 4 foot skirt. You would basically just be losing heat in half the wall better than worrying about termites.