Odd basement drainage feature?

September 30, 2012 11:00 AM

We're thinking about making an offer on a house. However, it has an odd feature in the basement that may be related to drainage. Can anyone tell us what this might do or what could be behind the wall? Picture here - it's the 4" bumpout in the back left corner.

There are small round vents at the bottom of the wall. The vents looked like soffit vents to me. We asked the current owner about it, and they said that the previous owner had some "moisture" after a storm and they installed this feature to fix it. (6+ years ago). The current owners say the basement has been dry the entire time they've owned the house.

There is no sump pump. The basement is fully buried on the left and back walls in the picture - the house is on a steep hill, so there's also an exterior door on the wall behind the camera.

We're in Oregon. It rains all winter here. Basements aren't common, but we have seen them in a few other houses.

posted by WowLookStars to home & garden (11 answers total)

Is that drywall and the rest is cinder block? I've seen plumbing concealed that way when people finish their basements. Whats upstairs?
posted by Mr. Yuck at 11:08 AM on September 30, 2012

Have you had an independent home inspection done?
posted by dhartung at 11:29 AM on September 30, 2012

Yes, the walls are drywall. Not sure what the exterior walls are. The kitchen is above it, so it could easily be plumbing. Thanks for that possibility!

We have not had an inspection yet - having a hard time deciding if we really want to buy a house or not. :) A through inspection is on our must-do list if we proceed, for sure.
posted by WowLookStars at 11:35 AM on September 30, 2012

Could it be connected to HVAC?
posted by thirteenkiller at 11:43 AM on September 30, 2012

It's pretty impossible to say from your picture what is going on. A person with construction knowledge could likely inspect those vents, maybe remove one with a screwdriver, and suss out what is behind there. If you're worried about flooding, look for other signs of water damage and moisture. Also pay attention to the grading around the exterior of the house - the ground should slope away from the house.

On preview: those vents are really small for HVAC. Those bumpouts do look like chases for plumbing though.

If you do contract a home inspection, ask the inspector to specifically look at this issue and address it in their written report.
posted by werkzeuger at 11:48 AM on September 30, 2012

One story that I can create from the suggested facts are that the concrete or concrete and cinderblock wall becomes moist from the slope above that section of wall. There might be no frank water on the concrete, but if you have a moist concrete wall, any drywall its vicinity needs to be vented to prevent mold.

How is that drywall attached? Is it attached directly to the concrete (bad), attached to plywood that is attached to the wall, or attached to furring strips or studs (best)? You can tell by knocking on the drywall. If it sounds hollow, that's good. If it sounds solid, that means that it is attached with no airgap to the concrete walls, which would explain why they decided to fur out the corner and ventilate the stud spaces behind it.

Pull one of the vents, and take a look in there, with an inspection mirror and a flashlight. Look for signs of mold on the back of the drywall. Look for efflorescence (white stains that run with gravity) on the concrete walls, expecially around the mortar (if it is cinderblock) or around cracks or features in the wall (if it is concrete). Efflorescence or mold is a sign of a moisture problem.

If you see studs in there, or furring, then you will be able to deduce the understructure of the drywall that is *not* in the bumpout.

Or, as other people have already said, house inspector.
posted by the Real Dan at 11:48 AM on September 30, 2012 [1 favorite]

I think the Real Dan's answer is very likely. Basement corners are often the worst places for water infiltration because downspouts often drain into the ground around the building corners. Does this house have gutters and downspouts?
posted by werkzeuger at 11:54 AM on September 30, 2012

Where I live now, the water line that comes into the house from the well is so cold that the condensation causes water to collect on the floor. Does the water come into the house there?
posted by Mr. Yuck at 12:16 PM on September 30, 2012

Radon venting?
posted by FauxScot at 1:18 PM on September 30, 2012

Perhaps a type of passive convection airflow?
posted by Thorzdad at 6:43 PM on September 30, 2012

Thank you all for the suggestions / possibilities. It's nice to have some plausible explanations to put our minds at ease, and we'll definitely bring it up with the home inspector (if we end up moving forward on this house). We'll update the thread if we find out what it is!
posted by WowLookStars at 7:00 PM on September 30, 2012