Foundation wall below-grade exterior waterproofing: builder questions wisdom
For my new home build I’m spec’ing waterproofing of below-grade foundation walls with something like Tremco Tuff-N-Dri. That’s based on reading as much as I could find about this topic, including the following: https://www.greenbuildingadvisor.com/article/dampproofing-and-waterproofing-foundation-walls https://www.jlconline.com/how-to/foundations/foundation-waterproofing-that-works_o Based on my understanding from those and other sources, waterproofing (rather than merely dampproofing with asphaltic goo) is important in order to span inevitable cracks and resist hydrostatic pressure. However, the builder says that waterproofing the exterior will drive water from the curing concrete to the interior for up to one year, and therefore asphaltic goo is a wiser choice. I’ve also seen this idea expressed elsewhere. For example, the “Solutions Guide” available as a PDF from the Form-A-Drain webpage at https://www.formadrainsolutions.com/product/platon says: “Spray-on and peel & stick methods can drive hundreds of gallons of water from concrete as it’s curing to the inside of your basement where you don’t want it—this curing/evaporation process can last up to 3 years.” While I think I understand and can explain to the builder the advantages of waterproofing, what do I tell him about why those advantages outweigh the “driving water inside” argument? Thanks in advance!
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UPDATE, JULY 7:
*** I’m posting here as an update to my oriiginal question, because I have not been able to get the “post” function to work for several days, so I have been unable to “reply” ***
Thank you for all the input and information.
sommerbros and DCContrarian, thanks for pointing out that the builder’s objection objection to waterproofing is implicitly built on the assumption that without waterproofing there would be outward drying — and that this assumption is likely to be false.
user-5946022 — thanks — right, the footing drain is definitely spec’d for (Form-A-Drain, which has both inner and outer pipes, with burrito on the outside), and we do have the detail drawings. Not sure yet whether radon extraction will be tied into the inner Form-A-Drain pipe, or separate or maybe tied in with sump pit.
Michael Maines — thanks for the advice and detailed ideas. Yes, definitely not going with corrugated footing drains. We are planning on belt-and-suspender (singular) — Tremco + drainage board rather than dimple mat (to keep costs down from dimple mat). Need to think more about the radon integration with interior footing drain vs sump pit (or both).
Peter Engel — thanks for clarifying that moisture being driven to the inside is not necessarily problematic if appropriate care (and time) is taken with drying out the interior.
And as a number of people mentioned — definitely planning on ERV and dehumidifier.
Thanks again to everyone!
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Is the basement going to be finished?
BTW - this is exactly what I did when I built my house (Tuff-n-Dri)
Ah, I forgot to mention that, sorry.
Basement slab will be *completely* unfinished (no sealing, no subfloor, nothing). There will be framing and drywall of only one bathroom, and of a couple of walls as dividers. All bottom plates are speced to have sill sealer (preferably two layers) underneath. Also, there will be rigid polyiso (Thermax White NH) on the interior right up against the foundation wall interior. All framing will stop at the polyiso and will not contact the foundation wall.
otinkyad,
As I understand it, damp proofing (ie, the black tar / "asphaltic goo" you see used all the time) is meant to stop the concrete foundation walls below grade from wicking water from damp soil, potentially allowing it to migrate through the wall to the interior. Waterproofing stops liquid water, bridges gaps or cracks, and can hold up against hydrostatic pressure.
At any slab on grade-type conditions where the foundation wall is up against dirt on the exterior and dirt/gravel/fill on the interior, dampproofing should be fine. Example, a stemwall with slab on grade on the interior, with the top of slab at the same level as top of stemwall. If any moisture migrates through the stemwall, it doesn't enter the conditioned building.
Where you have foundation walls in grade at the exterior and with living / crawl / basement space on the interior, you want to waterproof those walls. I wuold also push for drainage board, outside the waterproofing membrane, to help move liquid water away.
How long is your house going to take to be built? Chances are you'll have a fair amount of time where that concrete can be as wet as it wants on the interior while the house is framed, dried in, etc. After a year, I'm pretty sure any amount of moisture entering the home from the concrete should be minimal (unless the walls aren't waterproofed). Presumably, your house will be around much longer than a year; it seems like the builder / that Form-A-Drain site are advocating a long-term solution for a short-term problem.
@paulmagnuscalabro -- thank you!
Right, there is a basement on the interior, although it will remain largely unfinished (which I should have explained, but belatedly clarified in my reply to @begreener above). That's why I wanted the waterproofing rather than black goo. And yes, we are specing for drainage board in addition to waterproofing (budget willing).
The build should take 6-9 months, hopefully not longer than 12 months, so there should be at least three months when nothing is being done inside the basement. That gives me something to point out to the builder -- thank you!
It’s hard to imagine that damproofing promotes outward drying to any significant degree. Once the foundation is backfilled with soil that carries a high moisture content it would seem to me that outward drying is limited at best. I would begin running a heavy duty LGR dehumidifier as soon as your enclosure is airtight and keep it running until your HVAC System has been commissioned. Adding whole home dehu to your system would help to maintain and manage moisture going forward.
Even if there is outward drying, is it going to be preferential to inward drying? The only way I could see that moisture not going to the inside anyway is if there's a vapor barrier to the interior. In which case the moisture just stays in the concrete, which is fine.
Your builder is correct, and there is nothing at all wrong with that. You want long-term resistance to water infiltration. Use dehumidifiers, open windows, use an ERV and don't finish the basement until you are sure the concrete has dried.
@Michael Maines — Thank you for the guidance. If you could clarify a couple of things that would be greatly appreciated. Should I understand from what you said (a) that asphaltic goo is quite sufficient for the foundation wall, and (b) that asphaltic goo provides long-term resistance to water infiltration? I ask because this runs counter to what I have read elsewhere, including here on GBA. Thanks in advance!
It depends on your soil and drainage options. If your soil is anything but bone-dry 95% of the time, I don't trust asphalt emulsion (the typical "goo") alone to be adequate. I specify asphalt emulsion with a dimple membrane (Delta MS) leading to rigid plastic footing drains in a bed of crushed stone with a separate filter fabric, leading to open air. (Typical corrugated, flexible footing drains often crush over time.) Or, if necessary, leading to a sump and pumped at least 10' from the foundation. If using asphalt emulsion, it's important to seal the tie holes first--asphalt alone is not always enough over time.
An upgrade from that is a rubberized, waterproof elastomeric membrane, such as the Tremco product, which can be enough if you have relatively dry soil and freely-draining backfill.
For a belt-and-suspenders approach, I like a rubberized membrane with a dimple membrane to protect the rubber and allow easy drainage, though my projects are usually on tight budgets so that gets nixed.
I also always have interior footing drains, connected to the exterior drains, and doubling as radon mitigation pipes. To be most effective they need to connect at the sump in a specific way, with a backflow valve.
If the soil is questionable, I like to run a second exterior footing drain above the first, in case the first were to get clogged.
At the risk of stepping on Michael's toes, I think he meant to say that the builder is correct about the waterproofing driving the moisture to the inside. That absolutely does happen and it's not a bad thing. As others have mentioned, this is primarily a short-term issue and with your construction schedule and lack of interior basement finishes, the walls will eventually dry out. You may want to install the Thermax as late in the build as possible to give the walls some time to dry. And, as others have recommended, run a dehumidifier. The dehumidifier should be a part of your permanent plan as well.
Yes, use waterproofing + drainage board. I even added exterior insulation to mine.
The goal here is to prevent moisture from migrating into the basement. One other very important thing to do is PROPERLY install a perimeter foundation drain - proper install puts the bottom of the drainage pipe level with the BOTTOM of the footing. Too many builders want to stick the drainage pipe on top of the footing, and that is wrong. Put fabric down, put some stone down, put your drainage pipe with holes DOWN in there, then put alot more stone in then wrap it like a burrito. There are plenty of details on this site to show how it is to be done. Giving the water a path of least resistance through the foundation drain will help a great deal in keeping the basement dry.
While we are at it - I wish I had also put a foundation drain to double as a radon extraction pipe around the INSIDE of mine...