French Drain around Garage with Patio Above

derzer

Hello. I have a unique situation (I think). My house has an attached garage with a concrete roof. The roof is also the patio when I exit out of the living room. The garage gets slightly moist when it rains. My suspision is that the rain run off from the patio is what causes this. Its a 2 car garage.

My plan is to bury my downspouts (which I think is half the problem). I will use non perforated pipe until I get away from the garage. Then I will use perforated to leach out the water into the yard.

I'm considering putting a french drain around the patio to collect the run off.

Ideas? I know slope, filter fabric, holes at the bottom etc. My question is will this catch any water coming off the patio and send it away? I only want to go down a few feet so it acts more like a gutter. I dont want to go all the way to the footer. I have read different things on how a

joecaption

Sounds like a good plan.

jomama45

I think you're going to want to "daylight" the pipe servicing the downspouts. Most soils won't take the load of a heavy rain from downspouts.

As for the french drain, is there any way you can have some kind of gutter installed to divert the water to the surface, away from the garage?

AllanJ

A French drain will not protect from flooding anything below it. So to protect the garage floor from flooding you need to install the French drain below said floor level, which means down at footing level.

Instead you may want to look into a gutter that captures and channels away as much surface and patio water as possible without letting much soak into the ground near the foundation. We are not talking about gravel or sand or filter cloth or perforated; you need something solid like a molded plastic or poured concrete channel.

Next thing to figure out, where are you sending the water away to? Your system will not work if the "destination" fills up and then water backs up into said system.

In addition if the soil gets too soaked say from long and heavy rain storms, water will seep up onto your garage floor anyway. You may need a second drain system below garage floor level to capture that water, and with a destination possibly involving a sump pump.

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