Condensation question - Contractor Talk - Professional Construction and Remodeling Forum

Jim R · 02-04-2009, 05:22 PM

I have a question. I build in the upper midwest, where we have had a very cold January, preceeded by a lot of December snow. Last weekend, we had a couple of warm days (upper 30's), with humidity up to 80%. Got a call monday from a client who had frost on the under side of the roof deck. A little background on the house: Ranch house, about 5 years old. R-48 blown fiberglass insulation, vapor barrier, energy heels, and well ventilated (absolutely no ice damming). Condensation was forming on the north side of the house only, which was snow covered. I have never had a callback from this customer prior to now, and there is no sign of any long term moisture damage. Appears to be a one time occurence.
Question is: has anyone else dealt with this, and is it possible that with the higher humidity and warmer outside air ventilating the attic, that the condensation occured without any abnormal heat or vapor loss from the house. I know that for condensation to occur, the air has to be warmer than the surface it is contacting, (again, roof was still snow covered). Was it the "perfect storm"? If not, why no frost on the south side?

SLSTech · 02-04-2009, 05:30 PM

Hi Jim - mind posting an intro & putting your location in your profile?

There is a great feature on this site called Search - here are some threads in just the last 2 weeks - FYI, there are many more of them out there to

http://www.contractortalk.com/f15/al...d-house-52312/
http://www.contractortalk.com/f80/po...nsation-51913/
http://www.contractortalk.com/f11/dr...-wanted-51811/
http://www.contractortalk.com/f80/ic...olution-51209/
http://www.contractortalk.com/f15/me...ng-help-50734/

FoxBuilt · 02-04-2009, 08:01 PM

Jim I had the same thing happen last week on a home. Mine did not have any baffels for the air from the soffits to come in and out the roof vents, so I installed them and hoping it will solve the problem. Some more posts would help us, I didn't find any answers in the links provided.

neolitic · 02-04-2009, 08:06 PM

Quote:

Originally Posted by Jim R

I have a question. I build in the upper midwest, where we have had a very cold January, preceeded by a lot of December snow. Last weekend, we had a couple of warm days (upper 30's), with humidity up to 80%. Got a call monday from a client who had frost on the under side of the roof deck. A little background on the house: Ranch house, about 5 years old. R-48 blown fiberglass insulation, vapor barrier, energy heels, and well ventilated (absolutely no ice damming). Condensation was forming on the north side of the house only, which was snow covered. I have never had a callback from this customer prior to now, and there is no sign of any long term moisture damage. Appears to be a one time occurence.
Question is: has anyone else dealt with this, and is it possible that with the higher humidity and warmer outside air ventilating the attic, that the condensation occured without any abnormal heat or vapor loss from the house. I know that for condensation to occur, the air has to be warmer than the surface it is contacting, (again, roof was still snow covered). Was it the "perfect storm"? If not, why no frost on the south side?

I think you've got it.
Warmer outside air condensing on
the still cold north side of the roof.

RayGoerdt · 02-04-2009, 08:08 PM

wondering if there are any vents going out that side of the house, dryer, bathroom, high efficiency furnace? maybe something added after you built it?

maybe also check location and condition of stack vent.

just some thoughts, hope all works out well!

SmithBuilt · 02-04-2009, 09:21 PM

It may even have the proper ventilation and still have the occasional moisture. I'm starting to believe natural ventilation does not work very well in NC.

I have not been able to find any studies done on attic ventilation.

But this was done by a well known researcher.

http://www.oikos.com/esb/30/atticvent.html

cleveman · 02-04-2009, 10:49 PM

What is your location?

How did the homeowner find out about this? Do they check their attic every morning, or did they just get lucky?

Jim R · 02-05-2009, 07:33 AM

I am located in Madison, Wisconsin. The roof is ventilated on the north side, same as the south. I did go into the attic and check for a loose bath fan vent or some other source of moisture, original or added, and found nothing. As to how the customer dicovered it; at some point the accumaulated frost started to melt, and they noticed a drip coming through a recessed can housing on the front porch, and then looked in the attic.