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We have a relatively new house (built in 2002) with a cold storage room under the poured concrete porch. There is a door with full weatherstripping leading to it.

We'd really like to close it off (it has two vents to the outside) and turn it into a storage room (unheated), but not open to the outside to help control humidity levels. It's a relatively dry room (no pooling of water or anything).

What's the best way to close off the two vents that go outside? They are about 6 inches in diameter and about 8 inches deep (from memory, it may be more). Or should they not be closed off?

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What is the floor in that room made of? – bib Nov 1 '13 at 14:57
Walls and floor are poured concrete as well. – Daemonic Nov 1 '13 at 15:03
There's a lot of variables involved with moisture control. You may find it is better to have vents part of the year and be closed off the rest. Don't do anything permanent, unless it's operable. Some XPS foam plugs should suffice. – bcworkz Nov 1 '13 at 16:42

3 Answers 3

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TL;DR No, you shouldn't block off or remove the vents. They serve a specific purpose.

Since this is an unheated area, any moisture which makes its way down there would stay there and cause problems. Mold growth would be promoted, and it could also prematurely rot the structure of your home. There would also be a foul smell which would be very hard to get rid of.

This area can still be used for storage, just make sure that whatever is down there is protected. Plastic storage bins are perfect for storing small items. You can also put up some hooks and shelving for other items. One thing you would want to avoid is storing anything directly on the concrete floor. You could put old palettes or pieces of wood on the floor. You also want to make sure that rodents cannot get in through the vents. You can install a piece of wire mesh over them on the inside to prevent them from entering. Just make sure that the mesh is going to be strong enough to prevent them from chewing through it or pushing past it.

This space would also make a perfect root cellar. There are some plans online here which will give you tips on how to do it.

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If it's untreated space, it'll need to vents to breath otherwise it'll end up super damp. If you want to use it for storage, you probably need to look into sealing it and insulating and then using a vented door to allow the house to condition the space. Since it wasn't designed for that, it may still have issues with dampness though. I'm not sure if they build cold rooms to the same standards as regular basements.

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... Or you can run a dehumidifier. Though the degree of dampness does vary depending with weather and terrain. (And not always in obvious ways. I had friends at the top of a hill whose basement flooded after a major rainstorm; the farmer's fields just a bit below their property gathered enough rainwater to raise the water level temporarily...) – keshlam Oct 1 '14 at 20:37

I think it is best that you consult the experts on this one. This is because I think there might just be issues of a leakage in the future since it used to once be a cold storage room. There has to be a certain amount of moisture still available in there somewhere which might just leak without you knowing. It is always better to be safe than sorry and when there is ponding, it might just be a little too late.

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