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sbmfj 01-26-2012 04:46 PM

Frost on a concrete wall.

I own an older duplex that has a cold room or “cantina” in the basement. The cantina is right below my front porch (see picture below). I recently noticed through a small hole in the gyprock / sheetboard, that there was frozen condensation on the wall, essentially frost. I managed to remove the gyprock around that area (there happened to be a window there) and noticed that there wasn’t enough insulation around the window so I bought a can of spray foam, and filled it up. It helped a little, but I still notice that the frost keeps re-appearing when the temp gets fairly low outside (below -10 c or 14F). The frost isnt as apparent when its around 0 c or 32 F. Although the cantina has gyprock on all the walls, I can stick my finger in a few random spots, and I can feel frost here and there, it doesn’t seem that the window area is the only affected area, other areas as well seem to have frost too.

The cantina is not heated, and there really isn’t any insulation, its essentially cement walls. I don’t plan on heating it either (use it to store ski/snowboards and boots etc…). Sometimes I leave the door to the cantina (door access via basement) open as heat trickles in from the basement, this actually helps reduce the frost quite abit.

How do I avoid the frost from re-appearing? Should I insulate the room with either rigid foam board or pink wool insulation, and then apply a vapor barrier over that, and then re-install the gyprock board that’s there?

What would be the best type of insulation, rigid foam board, or the pink wool type of insulation?

I’m fairly confident that there are no cracks in the cement structure, as there are no water leaks in the spring.

Thanks allot, any help is appreciated.

Outside view, its below the porch...

Frost on wall

Windows on Wash 01-27-2012 07:59 AM

The cold room should be just that, cold.

Uncouple it from the living space completely as that is your source of moisture in most cases and what is the source of the frost.

Leaving the door to the cold room open (and it is probably poorly sealed as well) lets warm moist air into that space where it diffuses through or moves on bulk air transfer to the cold concrete and you see frost.

Get the cold room completely sealed off from the home and treat it as a true cold room.

If you want to heat the space, they you will need to insulate, address any moisture migration from outside, and supply heated air.

sbmfj 01-27-2012 10:49 AM

Thaks, ill try to seal it off and see what happens. That being said, its an older door, and there are quite a few gaps around it. Why wouldnt insulation on the walls prevent the frost?

Windows on Wash 01-27-2012 02:34 PM

If you insulate the walls, you need to make sure there is no moisture coming in from outside and that you use an air impermeable insulation.

You can certainly do that if you decide to go that route.

Keeping the warm air from the house from getting out there and insulating that connecting wall would accomplish the same end result.

sbmfj 01-29-2012 11:10 AM

Thank You WoW. What would be a good example of an "air impermeable insulation"? I'd rather try to tackle this myself so I'm not sure if spray foam insulation would be an option. Do you think standard pink insulation, or foam board with a plastic vapor barrier over it would be sufficient?

I appreciate your help/feedback.

Windows on Wash 01-30-2012 07:04 AM

Rigid foam board is best and cheapest in this application.

Make sure the seam detailing is spot on so you don't get air behind it and any condensation on the walls.

sbmfj 01-30-2012 08:55 AM

Thanks again WoW. Whats the best way to install the foam board to the cement wall, use screws? Is there an alternative to screws or nails? then I imagine install a plastic vapor barrier over the board, and then seam it with house wrap tape, or something similar?

I appreciate your help.

Windows on Wash 01-30-2012 09:05 AM

Glue it and most folks will apply some strapping overtop to spread out the clamping force.

No need for a vapor barrier if you seal the seams in the foam with tape/foam.

sbmfj 01-31-2012 07:50 AM

Thanks again. What do you mean by the strapping thats installed over it to spread out clamping force? Do you have a picture or link? Im kinda confused.


Windows on Wash 01-31-2012 09:24 AM

sort of like that...

sbmfj 01-31-2012 09:32 AM

ahh, does the nail or screw penetrate through the foam to the concrete, or only anchor its self in the foam?

Thanks for all of your help again Wash on Windows, I sincerely appreciate it!!

Have a good day!!


Windows on Wash 01-31-2012 11:14 AM

to the concrete

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