Subterranian drain pipe level with cove joint

[CORJB]

Hi All,

I'm new to this and hoping for some advice.

An inspection of a 40-year-old house has revealed that the french drain pipe encircling the house at the foundation level (some 8 feet below the surface) is placed on (not below) the concrete footing. It was explained to me that this causes the water to remain level with (not below) the concrete slab, and that it's only a question of when (not if) the hydrostatic pressure will cause either the cove joint or the basement floor itself to leak.

The water level in the sump hole tends to be high, and the sump tends to run more often as a result. But the basement is dry - no rot or mold, no cracks in the floor or wall.

The house itself is on gently sloping land, but the south wall has flat to negative slope toward the house.

The drainage expert has quoted us a reasonable $125 or so per linear foot to retrench the entire perimeter of the foundation, dig a trench about a foot below the footing and do the french drain properly, the way it should have been done 40 years ago. We'd like to finish the basement, and he tells us that unless we redo the drain properly, we'll always have problems with the floor/walls.

My question is this: his solution obviously makes sense, but it's a 20-25K fix. The drain currently works, but it's obviously 12 inches higher than it should be to eliminate water pressure on the joint. To get the job done, I'm wondering if it's truly necessary to encircle the whole house. Instead, could I trench out a simpler gravity drain 9 or even 10 feet down and leading away from 1 or 2 corners of the house, thereby reducing the hydrostatic pressure and eliminating the risk of infiltration & foundation cracks?

What do you think?

[John Kogel]

How does he know the drain tile is laid on the footing?

Where do your downspouts drain to?

What if you elevated the basement floor? Probably no head room. But you will want a raised subfloor.

A curtain drain would be dug behind the house, down to the hardpan or clay layer because that is where the water is. Poke a probe in the ground to find the hard layer.

Put sump pits at the two corners? Then if they don't fill you know the ground is draining.

[Marc]

Pump runs a little longer...but there's yet an issue.

The expert's solution appears to be in search of a problem.

Marc

[CORJB]

Thanks for your replies.

He found the pipe sitting on the footing by digging - excavator dug down 8 feet along the exterior of the foundation wall until it reached the pipe, which was sitting on (rather than alongside or below) the concrete slab. Here's an image I found that captures the situation:

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What he concluded was that the pipe (with the perforations on top) would only drain water to the level of the footing/slab, rather than below it, causing water to accumulate not below the basement floor level, but at it. Thus the buildup of hydrostatic pressure. He said that if the floor ever cracks (or if we were to install a radon vent eventually), water would infiltrate. The problem is compounded by the sump pit being relatively shallow.

The downspouts drain away from the house- there's an extension pipe - but only on the back of the house. On the front, there are no gutters but I'm planning to install one.

There's no smell or visible evidence of mold and the basement floor is uncracked. I believe that if there were a severe hydrostatic pressure issue, the floor would have cracked after 40 yeas. But then, I want to finish the basement and don't want humidity issues to screw up the floor, walls and air.

It's a pretty moist environment- east-coast Canada with extreme highs, lows and lots of precipitation.

But I figure that if the major issue the expert is signalling (great point Marc- perhaps no issue at all) is that the drain placement & pump setup doesn't keep the water level low enough, could that not be solved by using a subterranean gravity drain not replacing the current perimeter drain, but merely drawing water away from the foundation in one or two corners of the house.

I'm sorry- I wish I had better vocabulary to describe what I'm thinking - does any of this make sense?

[Marc]

Yeah, you're coming across just fine.

A while back I was watching an episode of one of them home repair shows and they talked about a type flooring that was ideal for basements below ground level because of it's moisture permeability qualities. The moisture would evaporate rather than build up.

I forgot what it was called but I'm sure it's much less than 20, 25 grand.

Marc

[CORJB]

Thanks Marc. I think that's DRIcore. Looks pretty neat.

The drainage fix I'm considering would be like trenching the corners of a tent, only underground - starting from the corners of the foundation slab. I don't know if having only a couple of such underground drains/conduits would be sufficient to lower the waterlevel all around the foundation, or if they would only drain the water in their immediate vicinity.

[kurt]

How are you going to finish the basement?

[Jim Katen]

He found the pipe sitting on the footing by digging - excavator dug down 8 feet along the exterior of the foundation wall until it reached the pipe, which was sitting on (rather than alongside or below) the concrete slab.

That's an extremely common situation. Builders used to do it that way all the time. I agree that the drain should have been installed at the bottom of the footing and it would work better at the bottom of the footing, but it might be ok as it is. Even though the holes in the pipe are facing up, water will still enter the pipes at the joints. In general, the water will have a hard time building up to the level of the top of the slab with the pipes in that location.

What he concluded was that the pipe (with the perforations on top) would only drain water to the level of the footing/slab, rather than below it, causing water to accumulate not below the basement floor level, but at it. Thus the buildup of hydrostatic pressure. He said that if the floor ever cracks (or if we were to install a radon vent eventually), water would infiltrate. The problem is compounded by the sump pit being relatively shallow.

What he says is possible, but not likely. A concrete basement floor slab is not very waterproof. If the underground water level had ever risen above the level of the floor slab, the water would have just entered the basement. It doesn't need cracks or a radon hole - it finds its way. Do you really believe that a 40-year old concrete basement could function like a boat hull to hold out water? It just doesn't work that way. If the underground water level rises above the level of the floor, you'll see the water. It's that simple.

Also, the placement of the drain doesn't "cause" water to accumulate. It "allows" it to accumulate. There could be other reasons - reasons that have nothing to do with the manmade drainage system - that are limiting the level of the water.

But I figure that if the major issue the expert is signalling (great point Marc- perhaps no issue at all) is that the drain placement & pump setup doesn't keep the water level low enough, could that not be solved by using a subterranean gravity drain not replacing the current perimeter drain, but merely drawing water away from the foundation in one or two corners of the house.

Depends on your soil. If it's very permeable, then a single drain can exert a drainage effect over a fairly long distance. If the soil is clay, then the effect of a single drain is only exerted over a very short distance.

The fact that the basement has remained dry (supposedly) for 40 years is very encouraging. On the other hand fate has a way of slapping you upside the head when you presume to tempt it.

If I were in your place, I'd install the missing gutter, perfect the downspout drainage to get the downspout water as far from the house as I could, grade the yard away from the house, and forgo the excavation project. Then I'd finish the basement with materials that could sustain an occasional flood. If, after that, fate were to screw with me, I'd jackhammer up the perimeter of the basement floor slab and put the drain tile there - for 1/3 the cost of doing it from the outside.

[kurt]

Then I'd finish the basement with materials that could sustain an occasional flood.

That means XPS foam, no studs, and if I was going drywall, I'd take a shot with DensGlass.

If, after that, fate were to screw with me, I'd jackhammer up the perimeter of the basement floor slab and put the drain tile there - for 1/3 the cost of doing it from the outside.

Same here, and I agree with all the rest of it.

The guy isn't saying things that are wrong, but it's truth slanted toward disaster. 40 years old should be showing you lots of stuff if it's a disaster.

I have a hard time believing it's all that bad from the sounds of it.

[CORJB]

All makes good sense to me. The expert has a reputation for being straight & honest - but then, he can't go wrong selling a bulletproof solution at a fair price, even if that's not strictly necessary (or at least not yet). I'm hoping to avoid problems, but within a budget closer to 5k than to 25k.

You've just reminded me of something else he mentioned - that the life expectancy of these drains, with 4" perforated ABS pipe - is around 30-40 years. When inspecting it, there had been an obstruction that cleared when the camera went in, and water flowed into the sump pit. Does the sheer age of the setup change our wait & see approach?

The basement finishing would be to put in a rudimentary floor and giprock the walls, tidy up the ducts & wires in the ceiling for a playroom/home theatre, and hopefully a treadmill. Currently the basement is entirely unfinished, just a storage / laundry pit.

[Jim Katen]

. . . Does the sheer age of the setup change our wait & see approach?

The thing that kills these systems is silt and that depends on your soil. If you can get a camera through it after 40years, it can't have much silt in there. It'll be fine.

The basement finishing would be to put in a rudimentary floor and giprock the walls, tidy up the ducts & wires in the ceiling for a playroom/home theatre, and hopefully a treadmill. Currently the basement is entirely unfinished, just a storage / laundry pit.

If you use wall studs, use metal, and instead of regular drywall use Densarmor or Densglass like Kurt said.

For the floor, it's a bit of a pain, but I really like polishing the concrete and using throw rugs on top. It doesn't get more flood-friendly that that.

[David Meiland]

The contractor you're talking to is doing what I do. I fix lots of stuff, and if you want me to touch it, we're going all the way. Half-measures just make it likely I'll get called back later, and at that point, I'm in the wringer because I agreed to a half measure.

40 years of no big problems is definitely a good sign. What may happen at some point is that the existing tile will stop working, and you'll start getting water in the basement, of course during the rainy season when it's hard to rectify. There may be some value in re-doing it at full depth now, or before that failure occurs. Of course, it may go another 40 no problem. What you do now has a lot to do with whether you're the peace-of-mind-seeking type of homeowner.