Basement door ruminations
August 6, 2013 9:04 PM   Subscribe

We have a short (maybe 2/3, 3/4 standard height) door leading to the basement, and are contemplating making it a full-height door to have a separate entrance for a home office. Extending the door downwards seems to be the easiest option, but that will place it only a few inches above the basement floor, and I'm concerned about flooding. Is there a way to make this happen that will not increase the risk of flooding?

Some more details:
- There are structural beams right above the door, so growing the door upward is not very feasible.
- Currently, there are concrete steps leading down from ground level towards the short door, with some kind of drain at the bottom that goes to places unknown. During severe rain, water can accumulate at the bottom of the steps and takes a while to drain, but so far it's never risen high enough to penetrate through the existing door.
- We've talked to a couple contractors. One said that blowing away the existing concrete steps and making new ones, with a new drain, will be sufficient. Another said a sump pump should be installed to make sure water does not rise... something something, water table. I didn't have high confidence in the first solution, and I'd rather not rely on a pump due to power outages, etc.

Is there some kind of proper passive drainage system that will make this project reasonably flood-proof? Or at least as flood-proof as the existing situation?
posted by Behemoth to Home & Garden (5 answers total)
- This is an exterior door? The stairs are on the exterior and go down to an exterior flat area outside of the door?
-There's basically a big curb separating the exterior from the interior at the door?
- Is the ground level inside the door the same as on the outside?
posted by LionIndex at 10:29 PM on August 6, 2013

Sump pumps come with battery backup for not much more than the no-backup pump, if that changes your calculus.

How much landscaping can you do to direct water to drain elsewhere? Where I live basements necessarily have dewatering systems and sump pumps due to ground water pressure, but landscaping for drainage can help a lot, especially in heavy rain situations where the runoff (not the soak-in) is the problem.
posted by Eyebrows McGee at 11:02 PM on August 6, 2013 [1 favorite]

I'd be concerned about what your code authority would say about this more than anything else at this point. Do you meet the existing code for residential occupied basements? For a home office with a public entrance, though, you may have to meet commercial code (and then there's the question of whether you're zoned for that business activity).

Structural beams can, of course, be dealt with, but you would want an engineer to sign off on any solution. I'm not recommending this, as it is drastic, but also more expensive. There's also relocating the door to another wall entirely.

The drain probably goes to the same place as any other basement floor drains. It will have its own trap and drainway pipe, and with exterior exposure coudl easily have become clogged with debris. Try getting in there with a drain snake, if you have one, or call a Roto-Rooter type of service.

Modern basement doors are available that seal very well, so that's certainly another level of assurance to include.
posted by dhartung at 12:07 AM on August 7, 2013

Response by poster: Yes, this is an exterior door, the stairs are on the exterior, and there's a curb-type thing at the bottom separating the interior from the exterior. Inside, there are a couple more steps from the door threshold down to the basement floor.

In other words, from the outside to inside we have: ground level --> concrete steps ~3 feet down to a small area with drain --> up a few inches to door threshold --> down from door threshold to basement floor about a foot and a half.

Landscaping solutions are probably not an option, or are outside our budget for this -- I don't see an easy way to redirect water, as it's a fairly level lot and this basement entrance is pretty much the lowest point.
posted by Behemoth at 7:41 AM on August 7, 2013

Best answer: OK. If the drain outside the door is already actually draining to somewhere (we'll assume the storm drain or sewer), that somewhere is almost certainly lower than the drain, so it's already a passive drain system there. The trick will be whether that's still true after lowering that area as the first contractor suggests. If the area ends up below the drain outlet into the sewer, or too low to provide adequate fall across the run of the line to the sewer, you may not be able to passively drain the area. So, you'll probably want to have somebody figure that out first - your city should have records of the sewer/storm drain depth in the street. You may need to verify where your drain goes to. In any case, you'll probably end up digging up the entire drain line and replacing it.

The only caveat I can see is that since it already takes a while for the area to drain, you might be close to not having enough fall already; although the line could also be clogged. But then, if your basement is already lower than the exterior part, there's probably some kind of drain to relieve hydrostatic pressure from the basement walls or water that's gotten into the basement.

You will need to pay attention to what dhartung mentions. In my area, a home office is called a "home occupation" in planning speak, and you'll need to make sure it's an allowable use in your area.
posted by LionIndex at 10:30 AM on August 7, 2013

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