Exterior Peel and Stick Membrane on ABOVE grade ICF Walls
I’m building an all ICF home in Climate Zone 5. We’re planning to use the manufacturer recommended peel and stick waterproofing membrane before grade. For the above grade walls, we’re also planning to install a weather resistive barrier to prevent bulk water intrusion – I’m aware of the debate about whether or not this is necessary and have decided that since there’s any debate about it, I’m just going to install one for peace of mind. The ICF block manufacturer doesn’t require an above grade wrb, however, they say that if you want to use one or if it’s required by code, they recommend using tyvek or similar. We’re using horizontal strapping with vertical vinyl siding as our cladding.
I’m thinking about using a non-breathable steep roof underlayment peel and stick membrane instead and I’m just wondering if there are any durability risks to installing something non breathable like that on the above grade exterior walls. I’m not looking to get into a debate about whether this is a waste of money, the extra cost is worth it to me for ease of installation, skipping hundreds of penetrations to hold building paper up, etc. I’m just concerned about any problems with the walls not being able to breathe out dry to the exterior (we will have latex painted drywall on the interior). I asked the ICF manufacturer rep and he said “it should be fine”, but I was hoping for a little more reassurance. Obviously this would be bad for a wood framed wall, but I would think that the EPS foam and concrete shouldn’t be harmed by whatever water vapor might enter the walls from the interior – I don’t think it would be good for them to be soaked, but if they somehow got a little moisture and had to dry to the interior through the foam and drywall I wouldn’t expect any issues.
Am I missing anything? Can anybody think of any problems with waterproofing it this way (other than it possibly being unnecessary or overkill)?
Thanks in advance.
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A typical ICF form like Nudura (2 5/8 of EPS foam on each side of concrete core) has a Class II Vapor Retarder rating of 0.624 PERM-INS. This rating is WITHOUT the 6" monolithic concrete core inside, the rating is for the EPS only. Therefore, as you mentioned and are aware, no vapor barrier is required and it would serve no purpose. With that being said, if you still want to install one, you can. Just use a peel & stick membrane that is compatible with EPS foam. DO NOT use P&S membranes that use petroleum as that will eat the foam.
https://www.vancouvericf.com/dampProofing.php
If you were using stucco, then you could NOT use a P&S membrane as the stucco would need to attach directly to the EPS foam. Since you are using siding, the above P&S should work.
Concrete doesn't mind being wet for the most part. Septic tanks, dams, sidewalks, pools, docking piers, etc. all sit under water for decades without issues. Salt water can corrode the rebar inside the concrete and that can cause problems but otherwise concrete is perfectly happy & safe being wet. It's not like organic wood that needs to dry out when wet or it can rot and fail if not allowed to dry.
Even if your ICF wall was "soaked" with moisture, it can still dry out to the interior even with a P&S membrane on the outside and drywall and latex paint on the interior. Not ideal as you don't want all that moisture coming into the home but it can dry if needed. Not sure where the moisture would be introduced into the wall core but it can be brought in from the footing or the roof area if not properly detailed.
Peter,
Thank you very much for taking the time to respond. Yes, I'm aware that we don't need a vapor barrier, I'm more concerned about bulk water intrusion (rather than vapor diffusion) that could potentially get behind the foam and then through to the inside through a cold joint or a window or door opening (I know there are some options but most flashing techniques wouldn't necessarily work if there's already water behind the foam higher up the wall).
Thanks, we will certainly be sure not to use a peel and stick that's petroleum or solvent based.
I was thinking the same thing as you regarding the concrete (and foam for that matter) being fine from being wet. I'm not sure where the moisture would come from either, hopefully it wouldn't come at all, but inevitably it somehow seems to find it's way into every house I've owned. There is also the initial drying/curing of the high moisture content concrete walls that are already going to be encased in 2.625" of EPS on each side...this p&s membrane will only slow that drying process, but I don't think it's an issue, just wanted to run it by some folks who are smarter than me. Also, if other water or moisture does get into the walls, I just want to make sure that I wouldn't be making the problem worse by eliminating (or very significantly limiting) the wall's ability to dry to the exterior.
We will be monitoring indoor humidity and will have an ERV and whole house dehumidifier, so a non-recurring water intrusion event that ends up drying to the interior shouldn't be an indoor humidity problem (if there is an issue or leak somewhere hopefully we'll discover it quickly and fix it which is why I'm saying non-recurring... if it takes longer than I'm hoping to discover it I'm looking to avoid any damage from the extended wetness in the walls).
What are your thoughts on the risk of getting wet or moldy drywall if the walls can only dry inward and as a result tend to stay wet longer when water intrusion does occur? I will make sure not to use wallpaper or other impermeable finishes on my drywall, but we will of course have mirrors, cabinets and other wall coverings that are less permeable than 2 coats of latex paint.
Thanks again!
As Peter noted, it isn't required...per code...however, that doesn't mean it isn't a good idea, but it is an added expense if you weren't calculating that.
We are in the same position, albeit in zone 4...we are using Vycor env-s...spoke to Grace technical support and they confirmed it would be good to use on ICF. You probably want to consider a primer, just as you would with your below grade membrane.
One thing to note about the Vycor...it is a vapor open membrane, which is why I went with it. The reason for this being the sandwich of materials that you end up with in your ICF, it could be risky to slap a vapor closed barrier on and then be forced to dry to the inside of your house...this isn't inherently an issue, but depending on your other building details, you might find yourself trying to dry to the outside, which is then a problem depending on your added barrier.
H4X,
Thanks for your response - I'm glad to hear that I'm not the only one who thinks it's not a total waste. Thanks for the recommendation on the Vycor. We have been considering that product (and 3M makes (or at least at one time made) a similar breathable peel and stick), but it's significantly more expensive, especially if we need to use a primer, which may not be necessary if we can get it on quickly before the block gets dirty. I believe the FT synthetic (with labor) will cost me 3-4 times the cost of Tyvek/Typar with mechanical fasteners and labor. The Vycor is about 2.5-3 times the price of the FT Synthetic, so the cost is really getting up there for something that's probably belt and suspenders, but we may still end up doing it for the exact reason you mention - may not be inherently bad, but if we're not thinking of something and we end up with the wrong conditions for some reason the assembly would just be more forgiving if it could breathe and dry to the exterior.
On the other hand, half of the house is a below grade finished basement that will get the 60 mil Nudura peel and stick and that's not breathable and should be fine. The only differences I can think of for the basement are that: 1) in different seasons the basement walls and the above grade walls will be exposed to different temperature differentials on each side of the assembly, which theoretically makes them have different risks for condensation in the assembly that could potentially benefit from being able to dry in both directions, but with these ICF walls I'm really not concerned about the dew point/condensing surface, which is one of the many reasons we're using it, 2) the basement walls are below grade and are therefore probably at higher risk of bulk water intrusion from hydrostatic pressure/groundwater and leaks from anywhere above that have run down and not made it inside yet, and 3) the below grade walls would have much less opportunity for drying to the exterior anyway because they're buried in cold wet soil (with well draining gravel all around the foundation of course but still). So #2 and #3 above are probably the only "real" reasons I can think of to justify spending extra for vapor open above grade if I'm not worried about it below grade...in other words, we should want to do it below grade too but it's not an option so we just doing it above grade where we can.
Do you feel the same way? Or am I missing something that makes the ability of the basement walls to breathe to the exterior less important? Like I mentioned before, I'm not too concerned about the foam or concrete becoming damaged, just thinking more about cabinets and other things attached directly to drywall (or cabinets attached directly to plywood that is attached directly to drywall) that's installed directly over the foam where there's a non breathable peel and stick on the exterior. Just don't want to create a potential for trapped moisture/mold. Thanks again.
Hi! We are also building an ICF house in Zone 5, and I’ve had all your above questions on wrb for the exterior of our ICF blocks, to prevent bulk water intrusion, but still allow the water to dry out to the exterior and not have increased water or moisture the inside on the drywall. I’m curious what you ended up doing for your above grade ICF exterior wrb and inside for your drywall? Any insight would be so greatly appreciated!
Hi Z5Eagle,
I am the OP on this thread -can't seem to get into that other account.
We ended up using a breathable peel and stick membrane on the exterior made by Vaproshield - https://vaproshield.com/products/wall-wrb-ab/revealshield-sa
So far that's worked well. We went with that product because my builder ended up having some leftover from a commercial job.
We used regular drywall on the interior attached directly to the ICF and haven't had any moisture issues.
I hope that's helpful!