Frost on top of foundation

I have frost on the top of my foundation wall in the basement. I have read some things about using a spray foam to get rid of this, which is what I probably will do. I just can't figure out what causes it. It only comes in my storage room which has been dry-walled and insulated but no ceiling. (south east corner next to driveway) Mechanical room with furnace is the same idea (insulation/drywall no ceiling) but I get no frost there. Plus since I have a drop ceiling I checked at a few places around the rest of the basement and no moisture or frost. All the pockets between joists are stuffed with fibreglass insulation and cover with vapour barrier. it is the same though out the whole basement.

Generally when its not quite so cold I will just get condensation not frost in the same location but only in the same room/location. It is significant amount that I will actually get a puddle of water (very small, just enough to notice) at times coming from under the wall which is how I came to realise the frost problem.

What would cause do I get frost in this storage room? I have also checked with humidity with hygrometer, around 45% same as the rest of the house

Thanks for any feedback in advance
Cheers

RedBaron said:

What would cause do I get frost in this storage room?
I will just get condensation
I have also checked with humidity with hygrometer, around 45% same as the rest of the house

Click to expand...

Frost or "dew", the temperature of that surface is cold enough to condense moisture from the air. It seems the local humidity is higher in that area or the surface is colder.

Posting photos or drawings might provide clues as to, Why this spot?

According to this
http://www.engineeringtoolbox.com/density-air-d_680.html
moist air rises.
Perhaps a fan will circulate the air enough to stop the problem, and it's easy to try.
If the fan has no effect, that info may also be valuable.

Insulated and drywalled but no ceiling. Any insulation in the area of the rim joist above the wall?

There is fibreglass insulation (Roxul) stuffed in all the joist spaces vapour barrier carriers up from behind the drywall and covers the insulation. It is exactly the same through out the entire basement, but this room is the only one to get condensation and frost.

the area effected is behind a vapour barrier so I can't see a fan having any effect

OK you lost me; The drywall continues up from the wall and covers the insulatiion in the rim joist area, as it should. But you have exposed frost on top of the foundation? So you some exposed uninsulated concrete? If yes water will wick thru concrete from cold to warm. When it gets really cold and maybe not so much heat in that room it can't stay ahead of the cold coming thru the concrete. The furnace room will be a warmer room. When it is not freezing the water is still a problem, you may have landscaping on the outside higher on the foundation than the waterproofing.

RedBaron said:

the area effected is behind a vapour barrier so I can't see a fan having any effect

Click to expand...

If you don't know what causes it how can you decide what won't work?
The answer is in here
http://en.wikipedia.org/wiki/List_of_fallacies
somewhere.

Perhaps the sill sealer is missing under the sill plate in that location; http://www.greenbuildingadvisor.com...ressure-treated-sill-plates-and-building-code

Or the vapor barrier is leaking a little; a good read, if nothing else; read the bottom (last) paragraph about fiberglass/poly; http://www.buildingfoundation.umn.edu/RimJoist/rimjoistphenom.htm

From BSC;http://www.buildingscience.com/documents/information-sheets/critical-seal-spray-foam-at-rim-joist

Gary

By looking and feeling around I can't seem to find any evidence of sill sealer, house was built in the 1974 don't know what they used back then or if they even did that back then.

The driveway is right against the house in the area of the problem so I doubt it being a landscaping issue

Sill gasket shoiuld be between the plate and the concrete, back in the 70s they may have used roofing paper or something just to stop the wood from touching the concrete. Either way the concrete is seldem level enough to assure a tight seal the insulation and vapour barrier should have continued up to the floor between the joists.
How much foundation is showing above the driveway slab?

You might also use a candle flame to check for infiltration.

Not generally a good idea to poke a flame into tight spots. Use a punk, stick incense or even a cigar - if that's the way you roll.