Advice for a leaky basement
Here in the Pacific Northwest, we’re dealing with an atmospheric river and my friends basement is flooding. It’s happened a few times in recent years and they are at their wit’s end. I’m trying to help them with some ideas.
Situation:
– Older house with a concrete basement.
– Cracks in the basement wall that let water in during major rainstorms.
– Drainage in the yard behind the wall that has the problem is not great but there is also no obvious fix (the neighbours lot is higher than theirs.)
– Digging down to the bottom of the foundation to install a waterproof membrane on the wall and a new drain tile is too expensive for them (they would sell the house instead.) It’s partly complicated because of specific on-site factors (e.g. would need to demolish a deck, some very mature landscaping, etc. to get machinery in and access the foundation wall from the outside.)
– The basement is finished. It’s ok if major renovations are needed but they would like to be liveable when all is said and done.
My thoughts:
– Let’s assume they need to fix this on the inside. They can start by removing the wood stud wall on the inside that holds up the drywall.
– They could then try an epoxy product (and maybe a paint on sealer after) to seal that entire wall.
– Then near the bottom of the wall, they could add weep holes to intentionally allow water in. That water could then go into a drain tile system that would be installed inside of the house along the edge of the basement floor. They might need to build a little curb wall when they re-finish to accommodate this.
– The water would flow to a sump in the basement where it would then be pumped out.
Does something like that sound reasonable? Are there are other things they should be considering? Any particular resources we should look at?
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Replies
I wouldn't depend on any interior sealer alone. I'd suggest adding a dimple mat as well, sealed to the wall. Can they at least put in a French drain to intercept and divert surface runoff? Or install an "underground roof", as described at https://www.greenbuildingadvisor.com/article/an-underground-roof?
Thanks Frank. I'm going to take a closer look to see what might be possible in the yard. Re a dimple mat - are you suggesting I could install that on the interior side of the wall?
Yes, drainage mat on the inside of the wall and running all the way down past the slab to a new interior drain, as Walta describes below. Patch the slab and rebuild the stud wall a couple inches away from the drain mat. Then spray foam the gap with closed cell foam, sealing the edges of the mat at top, sides and bottom. You don't want any radon or other soil gas entering the basement through any wall cracks or the new drainage gap at the edge of the slab. If you don't find a poly sheet below the slab, then laying poly on top and embedding the edges in the spray foam will help block moisture and radon.
But If you are in an area with radon potential, it would be a good idea to run your plans by a radon mitigation specialist first. A new interior perimeter drain could also be used as part of a radon mitigation system if designed right.
The second GBA article provided below by Freyr has a link to this page that illustrates how to do it: https://hammerandhand.com/best-practices/manual/7-basements/7-4-basement-retrofit/
The same GBA article also says that "NSW crystalline coatings should NOT be considered primary waterproofing when a permanent cover eliminates ready inspection and maintenance needed to address new crack formation."
That makes me think that covering it with a stud wall is a bad idea. But if the basement is big enough, maybe you could leave a 2' wide space behind the stud wall, complete with a door. Then the owner can check the wall regularly and apply more waterproofing as needed. In this scenario you would not cover the concrete with drain mat and spray foam.
The real question is if you collect this water where will you put it? Footing drains are the best option but they need a sloped pipe that leads to daylight lower than the basement floor on the property. If you have that then they work great.
For existing building installing footing drains are always too expensive. The lower cost option is to cut out the basement floor around the perimeter for about 12-18 inches dig a sloped trench too a sump with a pump and discharge the water farther down the slope.
Has something changed or has this house always been flood prone?
If the neighbors have changed the grade and are deviating more water onto the property, they have legal remedy.
Walta
Thanks Walta. That interior trench idea with a sump pump is what I am thinking but I'm struggling with how to then finish the basement after that is done.
canada_deck,
If it was going to flood, today was the day. That atmospheric river hit us hard. The highway is washed out in both directions, and I've never seen as much surface water everywhere. It would be election day too, so we had to rustle up generators for the polling machines when the power went out.
A couple of suggestions.
I think Frank D's belt and suspenders approach is a good one. I would use Xypex on the wall rather than epoxy, and a dimple mat inside that. I'm not at all sure weep holes are a good idea. They may relieve hydro-static pressure, or they may just be a convenient way for water that would otherwise stay outside to make its way into the building. Intentionally drilling holes isn't something I've heard of as a strategy. You want to limit the amount of water the sump has to deal with, so I'd be inclined to try and keep out as much as you can.
Thanks Malcolm. Yes, it was a wild amount of water and thanks for the suggestion. To clarify, your suggestion would be:
- Remove the current drywall and 2*4s on the interior side of the wall.
- "Paint" the interior side of the concrete foundation wall with Xypex.
- Add a dimple mat
- Rebuild the 2*4 wall with insulation and drywall
?
Should I have some type of detail at the bottom of the dimple mat in case some water does come through that would direct the water to a sump inside?
Another idea that has come to mind is for them to dig a few holes near the house on the outside and put sump pumps in those.
Instead of having to full excavate the entire wall down to the footings, they would just make a handful of holes (let's say 12" in diameter that go down 8 feet) that are pretty close to the edge of the house. They could use a pipe of some type (sewer pipe) to prevent the hole from collapsing and then put a sump pump in the bottom of each hole to bring the water up (and it would then be redirected to daylight on the low side of the house and running away from the house.) These would basically be shallow wells and the goal would be to lower the water table near the edge of the house.
Another thing I am wondering is if they should abandon the idea of having a finished 2*4/insulation/drywall wall on that side. Could they apply the Xylex and then apply a layer of stucco on the interior side of that wall for a finished surface?
canada_deck,
You still want some version of an interior perimeter drain. Ideally it's a full one with rock and pipe with the dimple board draining into it, but a small tench in the slab will do in a pinch.
The "wells" are another those things I've never heard of. I'm a bit wary of making up solutions, especially those that would need need multiple pumps, with all the complexity and expense that would come with that approach. My feeling is to commit to one side of the wall and do the best job you can afford.
The basement walls need foam board insulation. What you use as a finish on that isn't too important. I'd stick with studs and drywall.
Basements huh? They are one of the first things I'm going to ban when I become dictator.
A few resources:
https://www.greenbuildingadvisor.com/article/interior-waterproofing-of-basement-walls
https://www.greenbuildingadvisor.com/article/installing-basement-waterproofing-from-the-negative-side
The second article has a bunch of links for related resources all about basement waterproofing.
Yes you will have to replace the flooring after the concrete is replaced and any framed walls will also be in the way and get redone.
This link seems to cover it well.
https://drycretewp.com/everything-you-need-to-know-about-french-drain-basement-waterproofing/
Walta
canada-deck,
FWIW, I dealt with a cracked 50's era poured foundation that leaked during heavy rain. The client had tried hydro cement to no avail. I contracted with a local company that (easily) cleaned out the failed hydro cement and filled the cracks with a very liquid form of epoxy that was placed in lifts like concrete. I later did a gut rehab on the same house and the sealing job was still holding 6 years later.
The company did advise before beginning that in some cases the exterior soil can pull away from the foundation and all the epoxy would flood into that gap preventing the crack from filling properly. I took the risk of having to halt the sealing if the first fill showed such a condition. I would have been out the set up and prep costs. Fortunately, all went well.
Sadly, it may a similar soil shifting that has brought out the current problem.
Another thing to look for is weeping form tie locations. This particular foundation had leaks at the mid panel ties where the steel rod had rusted out to leave a pencil size hole all the way through. Luck was with me again, the epoxy took and sealed them as well.
You might want to check out polyurethane technologies if available to residential level jobs. The polyurethane sealing was used on my (embarrassingly) favorite TV show, "Oak Island Treasure" The process successfully plugged a tunnel feeding sea water into a drop shaft they were digging. No word on how much it cost.
Finally, I used a Thorocrete product to seal my personal block wall basement with success. It was at the time the recommended sealant for grain elevators and agricultural water tanks. I have also used Xypex, but as a direct additive to my current foundation. Not sure how it would do as a surface treatment. The literature says the additive will allow my foundation to self seal cracks up to 1/32". So far no need to confirm that possibility.