Rainwater flooding our garage
September 30, 2014 3:37 PM   Subscribe

How do you suggest I approach fixing this drainage issue at the side of our garage?

Whenever it rains heavily here, maybe 2-6 times a year, water runs off the roof, falls to the base of the wall on the side of our garage, and then into the garage where it covers about half the floor. I can continue squeegeeing it out when this happens but (1) I'd rather not, and (2) I'm concerned about possible structural damage that the water may be causing.

I've considered having a gutter installed but our other gutters overflow during big rains which means it may not carry all the water away. I've also thought maybe some flashing could be added that would throw the water away from the house and into the dry creek bed which seems to drain well.

Would sealing the base of the wall be a better approach? What kind of business would do something like this?

Thanks for any and all suggestions!
posted by davcoo to Home & Garden (7 answers total) 1 user marked this as a favorite
I'd get the highest capacity gutters I could find and make sure that the outlet is several feet away from the structure. It's not the most attractive extension, but protecting the foundation and structure is more important.
posted by quince at 3:46 PM on September 30, 2014

What's happening is that most of the surface area of the roof is being deposited in the comparatively small area of the drip line of your roof.

Your goal is to keep the water away from the foundation of the building. There are three practical ways I know of to do this (there may be more):
Gutters and an outlet
French drain
Serious regrading

Gutters are likely the cheapest, but will have the highest maintenance (and that tree will likely clog the gutters).
posted by plinth at 3:57 PM on September 30, 2014

I was going to suggest a French Drain, but if there is a creek bed nearby, that seems a no-brainer.
posted by jbenben at 4:01 PM on September 30, 2014

A French drain is the most common way to handle runoff from a roof, but with the runoff from a large section of roof concentrated in one spot, it might not be able to handle the volume. If the flow can be channeled downhill, gutters plus an outlet would be good. If no downhill outlet is possible, then a dry well may be the thing.

We had a wet garage problem which was fixed by a curtain drain across the entrance to the garage plus a dry well.
posted by SemiSalt at 4:08 PM on September 30, 2014

Install gutters of sufficient size and slope, and a ground-level, hidden pipe to carry the water a sufficient distance away. Your other gutters are undersized. Compute the area drained by the gutter you would install, find out the expected maximum "inches-per-hour" storm rating for your area, and work from there. Here's a decent page on it:


Regrading is not indicated, as the scene is fully landscaped.

A french drain has to be dug in such a way as to not undermine the slab (that is, dug no closer than the drain is deep), and is problematic again because of the landscaping.

Note that in that valley the water may come sluicing down like a waterfall, and overshoot the gutter entirely. You might have to install some kind of deflector in the gutter to catch it if it contributes to your garage drainage problem, but wait until you've got the basic gutter installed before addressing that problem.
posted by the Real Dan at 4:20 PM on September 30, 2014

We had a similar problem and it was solved with a French Drain that connected to conduit which funneled the water to the drainage ditch behind our house.

Money well spent.
posted by Ruthless Bunny at 4:29 PM on September 30, 2014

That "dry creek bed" in the foreground, does it drain away from the house? And i'd need to see a pic down the wall, but it seems like you might be able to build a berm with groundcloth that'll carry water away from the house.
posted by at at 7:42 AM on October 1, 2014

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