Developing a basement waterproofing/drainage strategy
I’m having trouble landing on a strategy for waterproofing (or maybe dampproofing) and drainage that is affordable while not cheaping out.
Relevant info:
– New construction, cast-in-place concrete walls with good mat of vert and horiz bars to minimize cracks, full finished basement ~7ft below grade. The slab will have 2″ rigid below and vapor barrier (over crushed stone).
– Sandy well draining soils
– Most of the neighboring homes are older with field stone basement walls and no water problems. I went in the neighbors basement and he’s got it packed with furniture and misc storage right on his slab. Stone walls. I asked him and he said he’s never had a drop of water.
– Building inspector told me to not even put in footing drains, he said there’s no need based on his observations in the area
– No town stormwater system and site is not steep enough to daylight. Footing drains will need to come into the house/sump and then I pump to the rear of my lot (yuck – but I dont’ see any other option)
——我的混凝土承包商推荐rubberized spray on membrane and footing drains. He wouldn’t be doing the work so that’s not his incentive. He lives in the area and has also never had water but said “what if you do ever get water, then you’ll kick yourself”. Fair enough but there is a price tag.
– Several have told me that asphalt based dampproofing is worthless and if that’s my plan to not even bother.
– A local engineer told me that if it was him he’d put in a perimeter footing drain, run it into the house to a pit and then monitor it for a few years to see if it’s actually getting anything – if it is then I could run the remainder out to a drywell at the rear of lot (although the cost to do that later is probably 2x-3x doing it during construction).
Questions:
1. How to decide on dampproofing vs waterproofing?
2. Is asphalt based dampproofing effective and durable? Any recommendations for products, application tips etc? If I do this myself and apply multi-coat with a good product is that a good solution or are they not durable?
3. If waterproofing is preferred are there decent DIY products out there? I’m getting quotes of about $3.5k to spray on w/proofing. Add in the drains, sump, etc and i’m North of 5k to waterproof a building in a dry area on a very budget project – I’m willing to do a lot of dirty work to save that.
4. If I did do waterproofing could I then safely omit the footing drain? What if I install interior drains and sump (doubling as passive radon)?
5. What about dampproofing and a drainage board? Intuitively drainage board feels like a good solution – it keeps wet soil off the face of the wall, doesn’t require perfect execution (vs waterproofing), and can be diy’d.
6. I’m not a fan of taking outside water into the house. Given the site conditions though I don’t see an alternate. Given the site conditions and neighbors lack of water issues noted would anyone risk simply omitting an exterior drain system?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
You may be able to find a local geologist or geotechnical engineer who can answer your question for real - Where is the local season high water table? A relatively inexpensive soil test can verify that the soil under your foundation is freely draining. If so, waterproofing is not necessary. Dampproofing is always necessary, unless you have waterproofing. I disagree that ashpalt-based dampproofing is worthless. It's been used successfully for decades. it doesn't stop water and it's not supposed to. It stops dampness from wicking through the foundations.
If you're really going to attempt DIY, you can lay the footing drains yourself, and even sling the gravel. it's a lot of wheelbarrow work, but possible. If you go with dampproofing, you can use a dimpled drainage mat like Delta-drain. I particularly like their mat because they sell it as a system with fasteners, edge termination and other useful accessories. The extra drainage space would significantly upgrade a dampproofing layer. If you want to try DIY'ing a waterproofing system, take a look at fully adhered membranes - something like Bituthene, made by GCP (formerly Grace). It comes in manageable rolls that can be installed by one or two people.
If you are not in a very cold climate, you could put in an outside sump pit to connect to your drains. You just need a long piece of culvert with a cap at the top and a sump pump at the bottom. This would eliminate the need for interior sumps and your concern over bringing outside water inside. I agree with the suggestion to install the drains and the sump pit and monitor it for water for a couple of years.
Thanks, Peter.
In looking into the drainage board option it works out to a decent number. It looks like it turns out to be roughly a financial wash between 1) footing drain w/internal sump + dampproofing + drainage board vs. 2) spray applied rub-r-wall (with no footing drain). Cheapest option would be diy 2 coats of good dampproofing and diy footing drains.
Rub-r-wall seems to be a pretty robust system based on my reading. Does it seem reasonable if using rub-r-wall to omit footing drains?
Back to the comments I've had on dampproofing - I've had several contractors tell me that whenever they have to dig next to an existing wall it's usually gone even if the wall isn't terribly old. Not sure if that's just poor application, poor product?
One more question. I see many details showing a ~1ft wide zone of crushed stone in landscape fabric backfill against the wall. This seems great but I don't see how you build this in practical manner. Unless i'm driving the excavator and time is free this seems to be pretty fussy to build. Am I missing something? It seems to me you'd have to have someone keep backfilling gravel and fill in small lifts while someone else works the landscape fabric up so it doesn't get buried.
I'm in a cold climate so no outdoor sump option.