More french drain questions

[Kevin_in_VA]

I need to construct a french drain to alleviate the flooding we get in our basement whenever we get a really significant downpour (which has been quite frequent lately). The house is on a grade and the basement floor area in question is about 4 feet below grade (see the shaded area in the attachment) and goes to a walkout on the other end.

The soil composition is about a foot of topsoil on top of a clay base. Makes me wish I had bought a backhoe to go with the tractor.

The house construction is cinder block and brick all the way down to the slab, and there are old concrete and earth filled stoops on the front and back of the house (the house was built in 1968). There is also a 14x22 foot deck over the back stoop that is not shown in the attachment. I want to construct a french drain in the shaded areas to divert the water away from the house.

My questions are:

1) Do I have to put the french drain all the way at or below the slab level in order for it to be effective, or can I just put it a couple feet down?

2) Seeing as I am going to excavate along the wall, do I also need temporary bracing across the excavation to support the wall in lieu of the soil that has been removed?

Kevin

 

[Kevin_in_VA]

The other question I forgot to ask is typically what would it cost to have a contractor do this, and would the cost be high enough to justify my purchase of a Backhoe for my TC30, in lieu of hiring one? /forums/images/graemlins/grin.gif

 

[Darren]

I'd try to figure out where the water is coming from first. Make sure the surface water coming from the roof is being carried away from the house. Best case is you can solve the problem by simply adding subsurface drains to get the water coming off the roof far enough away that it doesn't percolate into your basement. Check the slope of the land around your house. Does it permit water to drain toward the house or away?

If the water entering your basement is due to fluctuations in the water table you'll have to install (ideally) the french drain slightly below the basement slab.

Before doing all that you might explore coating the inside basement walls with a waterproofing product like Thoroseal. Thoroseal is a commercial type product that can stop many water problems.

If you do decide to put in a drain, the block walls will not have to be supported. By installing the drain you'll actually reduce the pressure on the wall. It would be a good idea once you've excavated to also clean and coat the below grade exterior sections of the basement wall with a water proofing product.

As for the cost, it depends on your area. If you were in a metropolitan area I'd say buy ythe backhoe. It's been about ten years since I've was in Chesterfield. It seemed somewhat rural then. If it's still the same you might find that the cost of hiring a contractor is less than the backhoe. I could be wrong but my experience is that work of that type is cheaper in rural areas as compared to urban areas.

Call a few contractors and get an estimate.

 

[Kevin_in_VA]

Thanks Darren,

It appears that the seepage/flooding is not due to water table fluctuations, as we have a bored (shallow) well about 75 feet down-grade from the house and I can clearly see that the water level is below the level of the slab. The flooding usually occurs during really heavy downpours like we had with Isabel last year, and Floyd a few years before that. The ground slopes away from the house, but not as much as I'd like.

The problem is also associated with prolonged periods of rain, like we had last year before Isabel. There is moderate seepage (the floor is damp around the edges) right now, but we have had about two feet of rain since June 1.

I believe it is also compounded by the stoops (see the original attachment), as the water may be trapped in the area between them and the corner of the house in the shaded area of my drawing. There is very little if any slope between the corner of the house and the stoops. My wife wants a larger front porch, so I plan on demolishing the front stoop and replacing it with a covered porch that is open beneath. But that is not going to happen this year.

I have already made up my mind to coat the inside walls, but since it is a finished basement, will have to demo the interior before that happens. That is going to be my Fall/Winter project.

If I can get by with subsurface drains, I won't need the contractor, but If I'm going to have to go to slab level, It will definitely be an option.

Chesterfield has indeed changed in the last 10 years. It is now one of the fastest, if not the fastest growing counties in the country. It is the premier bedroom community for the Richmond area. Nevertheless a great deal of the county is still rural. Our 7.5 acres is zoned agricultural, as is just about all of the land in a half mile radius, but there is a large industrial / office park just a mile or two down the road.

Kevin