Condensation on Storm Shelter Ceiling

5 years ago

We're having an issue with moisture in our basement storm shelter. The way the people had the house built, they built the foundation to extend out underneath the front porch. Under the front porch, there is dirt, but when moved away there is a visible concrete slab. The slab is the roof of the storm shelter area in the basement. They simply built a 2nd cinderblock wall to separate the storm shelter from the finished basement. The issue is that inside the storm shelter is a tin ceiling. We're assuming this is what they used to allow for pouring a concrete slab over top of it. That tin is continuously damp. We've Damtited the walls to ensure those were sealed well, but the condensation is obviously coming from the temperature difference between the outside and inside through the ceiling.

We are considering using foam insulation board- maybe 2 layers to create a 2 inch barrier- and use spray foam to fill in the corners and cracks between the boards. Only concern is will mold begin to grow behind that foam insulation board... Any better suggestions? We would love to use the space as it was intended, but if we can't dry out the condensation and get rid of the mildew smell we will be forced to just block it off... really hoping to avoid that.

I've attached a rough sketch of the area. hopefully it helps.

Any advice would be much appreciated! Thank you!

Featured Answer

PRO

BobH

5 years ago

Condensation is caused by humid air hitting a cold surface. You can work on reducing the moisture in the air with a dehumidifier if the space is not vented to the outside. Warm the surface by installing some type of insulation.

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Comments (7)

cat_ky
5 years ago
A storm shelter should have vents to the exterior for fresh air exchange. It should also have a way to escape, if something comes down and blocks the entry, during a severe storm.
lizg516 thanked cat_ky
PRO
Patricia Colwell Consulting
5 years ago
I would not want to be in there during a storm with no fresh air of course you get condensation and I agree it needs an exit . I think right now is a really good time to rip out to the bare walls and rebuild with proper venting and materials not tomention a way to get out.
lizg516 thanked Patricia Colwell Consulting
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lizg516
Original Author
5 years ago
@Patricia Colwell Consulting @cat_ky @BobH We hadn't even thought of the ventilation factor. That is so true that it would be bad to be blocked in if the house toppled on top of us. It would perhaps be better used as a storage closet once we get the humidity under control... Would the insulation on the ceiling work in this situation, or would moisture just get trapped between the tin ceiling and insulation board and rot?
aziline
5 years ago
Cold storage under a front porch is very common where I am. Ours does have a vent on either end. My husband has a few things in cabinets that moisture would harm so he keeps dehumidifiers that he can dry and put back in just in case.
lizg516 thanked aziline
millworkman
4 years ago
"It is important to have a safe room because its purpose is to save your life if something happens."

OK, wow, thanks for that tidbit of info.
Mary Elizabeth
4 years ago
What year was your house built? What location, climate wise, are you in?

We have a similar set up. It runs the full length on the front of the house (about 45'). No tin, just a solid concrete pour, over a foot thick. (Originally for cold storage.)

My husband did just what you suggested. He installed 2 layers of foam board insulation, with spray foam to fill & seal the gaps. Totally solved the moisture issue.

He waited for the warmest part of the summer, and then ran a dehumidifier to dry it out as much as possible. I think it was late August when he did the foam. Well before any low temps at night.

We're in Minnesota, so temps range from 20 below to 100 above. Our house was built in 1965.