Wet crawlspace fix

Ed T Duck · 08-06-2013, 10:08 AM

Hi all,
So I'm trying to stop water welling up into a crawl space (raised foundation) after heavy rain (fortunately not too often in my climate). I'm hiring contractors and the solution they proposed involves digging a trench around the house and ~1-2 feet below the foundation wall, then filling with concrete, to basically provide an additional barrier to stop subsurface water intrusion. See attached photos for an idea.

Does anyone have experience with that type of fix? Does it work? Any concern about damage to the foundation?

Thanks in advance!

**Gunnar Alquist** · 08-06-2013, 10:49 AM

Originally Posted by Ed T Duck

Hi all,
So I'm trying to stop water welling up into a crawl space (raised foundation) after heavy rain (fortunately not too often in my climate). I'm hiring contractors and the solution they proposed involves digging a trench around the house and ~1-2 feet below the foundation wall, then filling with concrete, to basically provide an additional barrier to stop subsurface water intrusion. See attached photos for an idea. Does anyone have experience with that type of fix? Does it work? Any concern about damage to the foundation? Thanks in advance!

Ed,

Where are you located? CA has a lot of different climates. Knowing approximate location would be helpful.

That's a new one on me. Do they have references? Anything you can look at?

What is your lot type? Sloped/flat? What is your soil type?

Seems to me ground water will still come up from underneath. Drainage (curtain/french) is the typical fix. Is there some reason they aren't installing drainage?

Ed T Duck · 08-06-2013, 12:25 PM

East of downtown LA, so quite dry for most of the year. Soil is Clay loam. The home is on a slight slope (roughly 1-2 degree) from back to front. However, at the rear of the house the garden is very steep (elevates to about 15 feet in as many feet) and has been terraced into three levels, with a retaining wall at the base. The retaining wall is about 6 feet from the part of the house with the crawlspace problem.

They come highly rated on Angieslist and are licenced contractors. I raised my concern about damage to the foundation, but they said it would be safe and they've done this procedure countless times. I still have my doubts though, and some expert opinions would be great! They said they "don't do french drains" ...

**John Kogel** · 08-06-2013, 01:39 PM

It might work in some situations, but not for everybody everywhere. Since you are getting a trench dug, why not install the tried and true perimeter drain which is proven to work in all climates?

Ed T Duck · 08-06-2013, 01:50 PM

Unlike the photos, the surface will be concrete+tile, not dirt. My understanding was that perimeter drains are not recommended under concrete.

**Raymond Wand** · 08-06-2013, 02:03 PM

Filling the trench with concrete? How is that going to aid drainage? Where will the water drain to?

Something is amiss.

Ed T Duck · 08-06-2013, 02:25 PM

Well, according to them, it's supposed to stop sub-surface water intrusion. The surface water will be drained with appropriate grading of the hardscape leading around and out the front of the house.

**John Kogel** · 08-06-2013, 08:45 PM

In my rainy climate, perimeter drain pipes go around the foundation, without exception. It makes no difference if they pour concrete walkways on the surface, because the builder provides a cleanout for the drain system, just a vertical pipe with a cap, and they use a good quality PVC pipe that won't collapse. So go ahead and por slabs on top of that. Make sure the walkways have a positive slope away from the walls.

The pipe costs $1.40 a foot, so cheap builders will use the corrugated black poly pipe we cal Big O. That stuff can collapse or buckle.

For new builds another set of pipes is laid near the surface. That system is solid PVC pipe and carries the water from the downspouts out to a drain at the street, storm drain system or an open ditch.

Ed T Duck · 08-07-2013, 10:48 AM

Thanks John- that is very useful. I will look into a perimeter drain.

**William Cline** · 08-17-2013, 10:09 PM

Glad you are looking at a perimeter drainage. If the ground water wells up past your existing foundation, what would keep it from welling up around a deeper porous concrete pour? We all realize that concrete alone does not stop water it is porous. Perimeter drainage and then crawl space ground coverage is the solution used in our area of California, Santa Cruz county.

**Robert** · 08-18-2013, 03:33 PM

Originally Posted by Ed T Duck

Hi all,
So I'm trying to stop water welling up into a crawl space (raised foundation) after heavy rain (fortunately not too often in my climate). I'm hiring contractors and the solution they proposed involves digging a trench around the house and ~1-2 feet below the foundation wall, then filling with concrete, to basically provide an additional barrier to stop subsurface water intrusion. See attached photos for an idea.

Does anyone have experience with that type of fix? Does it work? Any concern about damage to the foundation?

Thanks in advance!

As I see it, the main problem you have is the presence of water. I see little benefit in pouring concrete around your existing foundation. Unprotected concrete is porous and absorbs water.

Around my area, the normal practice is to cover the foundation with a coat of sealant and a platon membrane that sheets subsurface water down to a drain that runs at the level of the footing. This removes the water so it doesn't rise up under the floor or put pressure on the wall to enter.

A much more commonly accepted fix would be to ensure that the grade funnels water away from the house and install a drain to handle the subsurface water. I'm afraid you are going to see the same problem the next time you get much rain.

Greg Madden · 08-20-2013, 09:09 AM

If the structure does not have gutters you'll want to add them and pipe the water away from the house so it can't contribute to the problem.

Ted Menelly · 08-20-2013, 06:56 PM

OK so, porous concrete? Well, yes, a little bit of water comes through it. But if you are talking on the surface with a slope away from the home and under that you put a French drain in around to a lower point in the property? That would or should do the trick.

As far as porous concrete , It is not like water flows through it. If it slopes water runs down it and maybe a little gets through but then you have that French drain to hopefuly move the water that is in the ground around and away from you crawl.