Hello,
I’m located in S.E. WI. Have a detatched 2 story garage. 2nd floor is insulated with R19 kraft faced fiberglass w/ baffles between all ceiling joists. Ceiling and walls are basically unfinished except for OSB that is installed on the lower 4′ of the walls.Stair case to 2nd floor is open to 1st floor. Aprox. 1/2 of 1st floor is insulated and covered with OSB. Ceiling of 1st floor is not insulated. Have gambrel roof on east and west side of garage and gable roof on north and south. There are soffit vents thru out, but no roof vents at all. No mushroom vents or ridge vents, so air enters but has nowhere to go. All of this work was done by previous owner. Garage is 4 yrs. old.
Problem is I have noticed condensation on the insulation and beam when the outside temp has been considerably higher than the interior temp of the garage (i.e. after several weeks of well below average temps we had a day of 50 degree temps and that was the first time condensation was noticed). During home inspection stains were noticed along ridge beam. Inspector suspected that it was from rain during construction before roof was dried in. Suspect that the condensation has been forming since insulation was installed. Garage is ocasionally heated with electric heaters and condensation was never noticed. Would like to use the 2nd floor as a workshop
Questions:
Do I try to vent the roof? If so how can the gambrel portions or the roof be vented?
Should insulation on ceiling of 2nd floor be removed and replaced with foam or dense packed cellulose?
Should ceiling of 2nd floor be insulated and a wall be built to isolate the staircase and 2nd floor from the rest of the garage?
Should I sacrifice some ceiling height on the 2nd floor, remove some of the insulation, and create an attic space that could be vented with gable vents or???
Any and all advise would greatly appreciated.
Replies
One would guess that the moisture that appeared had condensed in the area above then melted and leaked down when it got warmer.
Probably the simplest "fix" is to install a tight vapor barrier below the insulation -- won't be perfect but probably adequate for an area that is not occupied most of the time (and hence won't have a lot of humidity generated). Otherwise you've got the standard cathedral ceiling problem of how to get enough ventillation into such a confined space above the insulation without eating up headroom.
That's a normal condition with leaky buildings
Because the inside of the garage was colder than the dew point of the air coming in, you got condensation. You can either heat the building, or reduce air infiltration, or both.
First of all ... condensation can be complex and tricky to sleuth the problem. However, if I read your post right, I tend to agree w/ Mr. Engel. 50 deg temp coming in ... cooling down will drive the RH way up ... to the point it will condense if it hits a cool surface. A psych chart will show this. Guessing that in WI, the air humidity might be somewhat high if you transitioned from cold to mild temps ... and if your garage is allowed to get cold ... as you indicate ... the warmer/moister air from outside may have big issues when it contacts a cold surface.
Attic venting by code is useually low (eaves) and high (ridge or gable end vents). Only having eave vents MAY not be problematic. Attic venting is partially driven by wind pressure ... which in theory may vent the attic through eave only vents (as only one side of the house is exposed to the wind). Other venting (e.g. hot summer) may need some low/high vents for thermal venting if there is no wind.
You could install a ridge vent (e.g. corivent) if you wanted to avoid e.g. mushroom vents and can't install gable end vents.
Food for thought.