Landscape Solution To Basement Moisture Problem

RJC

Homeowner wants to remodel the basement of a 120 year old house. The basement slab is about 4 feet below grade. It doesn't get much water, just an occasional damp spot on the slab after really heavy rain. But the stone foundation walls do show some efflorescence and some mold, especially below grade.

I know that the only surefire way to eliminate moisture in the basement is to install a french drain system around the perimeter of the house, thus preventing any ground water from getting to it. Due to cost and other factors, this is not an option. So the plan is to create an 8 - 10' band of relatively dry ground around the perimeter of the foundation. Could use some feedback on this.

Here's what I'm thinking:

Currently there are roofed porches that extend about 8' beyond the foundation off the front and back of the house. We will install a concrete driveway along one side of the house, sealed against the foundation. So three sides of the house should be dry.

A yard area is on the fourth side of the house. Here we plan to slope the grade away from the house and extend the gutter downspouts out into the yard. In addition, I'm thinking we should install an 8' to 10' wide planter area along the whole length of this side of the house, fed by a drip irrigation system and covered w/ heavy duty plastic covered w/bark and sealed against the house. This would not prevent all water from getting through. But I'm thinking it should transfer 80% or more of surface water out away from house.

I'm wondering how far this approach seems likely to go toward resolving the basement moisture problem? Any additional steps we could take (short of installing french drains) that we should consider?

Mike Finley

This is a very common issue here in Colorado because of expansive soils.

Don't make a planting area up against the foundation of the house, that's a big no-no. That's a disaster waiting to happen, somewhere down the road somebody else, maybe a new owner will plant some water hungry plants there and water the crap out of them all the time, by then the plastic will have been penetrated many, many times and water will go down to the basement.

Just slope it, plastic and then rock it. You see this all the time out here, you would think it is code you see it so much.

RJC

Are there any products other than plastic that might have more durability over the years - other than some form of hardscape? I know there's a sheet-like material that is used in crawl spaces, like tyvek but really impermeable. You can walk on it without puncturing it - can't think of what it's called offhand. But I wonder about using something like that...

Mike Finley

It's my understanding out here that the plastic doesn't contribute to keeping the water out of the basement as much as you are thinking. The sloping of the ground away from the house is the most important factor. The plastic is used mostly to keep weeds from growing through the rock. We have a lot of clay in our soils, hence the bentonite issue and expansive soil problems, so water doesn't run down through the soil as it would in a sandy environment, it tends to stay more on the surface and run down hill. Like I said the second part of it out here is never doing plantings next to the foundation. (You would also probably out here be introducing amended soil right next to the foundation which would absorb water instead of the native clay running it off) The exception to a planting bed here is you can get away with drought tolerant plants such as junipers, you see that here and there. But putting in a planting bed and then relying on the plastic to run the water away is a disaster waiting to happen in my opinion.