Dampproofing Foundation Walls
hi GBA,
construction drawings specified that stem walls have exterior waterproofing layer. Builder did not put it in, however there was a vapor barrier added on the interior of the stem walls all the way up the wall and french drains line the building. Builder claimed that this is an east coast detail and not needed here. Code is murky as the section detailing it says dampproofing is required for “living space”, while this is for a conditioned crawl space so I don’t actually know if that qualifies or not. Location is zone 5b, so it’s fairly dry but there is a hill behind us. Recommendations? Putting a barrier on the exterior now would likely be significant cost and delays. Is the interior vapor barrier sufficient? Is the only concern condensation issues from the stem wall, which should be blocked by the interior vapor barrier?
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Replies
Your first question is a legal one more than a technical one - you simply didn't get what you paid for and specified. At a minimum, the builder owes you a fat rebate, but that seldom happens. Exterior waterproofing is not an East Coast or West Coast issue - water and the physics behind its movement still apply on both sides of the country, and that argument is moot anyhow because he signed a contract with waterproofing specified.
Performance-wise, it might work. Maybe not. The builder has essentially saved himself time and money and has shifted the risk of future failure to you. I somehow doubt he will be extending a no-moisture warranty to you for the life of the house. Exterior waterproofing works. Interior plastic films and French drains can also work, but they are a Band-Aid solution for exterior water problems that should be addressed on the exterior. If there was no water accumulating in the foundation trenches when they were open, and if the soils around your house are granular and well-draining, then the risk is lower.
I also have a question related to your terminology. You seem to be using the terms "waterproofing" and "dampproofing" somewhat synonymously, with "vapor barrier" throwm in as if it does the same thing. This may be your builder's fault, as they often do the same thing.
-Damp-proofing is a coating on a foundation that limits capillary transmission of moisture from the soil to the foundation. This is the same effect as a sponge soaking up water from a countertop. With proper damp-proofing, there will be little moisture wicking into and through the foundation and less need for a plastic vapor barrier in any form on the inside.
-Waterproofing is a higher level of protection. Waterproofing materials can stop the ingress of bulk water through the foundation if there is standing water on the exterior. Damp-proofing cannot do this reliably. Waterproofing also provides damp/vapor control at the same time.
-Interior vapor barriers generally take the shape of a plastic membrane of some type that may be both waterproof and vapor-proof. If detailed well, they can handle both bulk water and vapor that manage to get through the foundation. But again, a foundation that is inherently dry is just better over the long term than one that is wet.
FWIW, the risk of high-cost failures (flooding, mold, etc) are low in a dry region, and especially so for a conditioned crawl space. But even occasional water seepage would make the crawl space less attractive for storage, if that is part of the plan, and it will increase the energy cost of managing the moisture that does happen to get inside.
Carson,
There are three sources of water that can affect your crawlspace. Bulk-water intrusion through cracks and tie holes in the foundation, moisture that moves though capillary action through the concrete, and interior moisture the can condense on the cold interior face of the wall. Unlike damp-proofing, interior poly really doesn't stop any of them. The first two only get blocked once they have made their way though the concrete into the crawlspace, and the third simply condenses on the poly rather than the wall if it isn't protected by insulation.
Whether any of these will occur on your build is very site specific.
thanks Peter, I mentioned all three because 1. plans mention waterproofing, 2. code specified dampproofing (only for "living space"), and I got 3. the interior vapor barrier. This is tricky because my builder in theory is also trying to save me money here. Who would I ask locally if this is a serious threat? I asked the engineer that did our drainage system and he wasn't able to help. Should I contact the building department? I suspect they would just repeat code, and it's not clear that it applies (and they already green lighted it).
malcolm, if water made it's way through the foundation and was stopped at the poly what is the issue though? concrete likes to be wet right? there is insulation against the vapor barrier so I don't think condensation would be an issue.
Carson,
It really depends on how much water makes its way through. If you have enough that it pools on the floor that's a problem.
On a conceptual level this is a bit like open-cladding. The place to deal with possible bulk-water intrusion is at the exterior plane of the building. Measures taken further into the assemblies should be seen as back-ups.
To circle back a bit. Builders in the PNW have been damp-proofing the exterior of foundation walls for more than half a century
After talking to other builders in this area and the architect, it seems that putting water management on crawlspace walls is very rare here and the architect said they only added it to the plans because it was "boilerplate" for them in their climate. It's still a bit worrying about long term issues, and I suspect that conditioned crawlspaces here are also very rare, but the architect recommended following local advice. I'm east of the cascades in zone 5b, so the climate here is far different than the coastal area.
As Malcom said, whether this could actually be a problem is soooo site specific. What did they backfill your foundation with? Gravel? Parent material? Was that material made of clay or sand and gravel?
I damp proofed my foundation walls because that is standard in my area, but what is also standard is for the excavation company to backfill with drain-rock around the entire foundation. I'm no physicist but I cannot foresee any water pressure building up along the walls with gravel as backfill.
So I believe the details of the install matter to answer the question, aside from the legal aspect of course.
Hi Joe,
Thank you for the reply. The soil here is rocky ash, climate is high desert. Parent material is backfilling with existing soil? Builder dug out the subs soil because he said they used too much soil from the lot vs trucking in gravel and seems to be surrounding the building with coarse gravel. That doesn’t sound like someone trying to cut corners, just trying to make sure I shouldn’t insist on adding thousands to the build. It’s increasingly sounding like it may not be a necessary detail.