DEAR TIM:
I bought some fiberglass insulation (faced) to install in the PEAK of my garage 24" on center between the roof trusses. Now I've been told that if I put this insulation in the peak I will have serious condensation problems and the insulation will be destroyed very rapidly. Any truth to these concerns?
I live in east central Minnesota. The Garage is unheated but will be heated several times thru the winter to work on vehicles etc.
Terry S.
Minneapolis, MN
Terry,
It is fine to insulate the garage ceiling but you must always maintain a 1.5 to 2 inch air space between the fiberglass and the underside of the wood roof sheathing. Then you must have continuous ridge and soffit ventilation to exhaust the water vapor that will collect between the insulation and the underside of the roof.
The fiberglass is virtually indestructible. Water will not harm hit in either liquid or vapor form. But I am slightly concerned about you using faced insulation. If it is kraft paper, it represents an exposed fire hazard.
You can have condensation problems if the garage floor was poured without a high-performance vapor retarder. The heat source in the garage can also cause condensation. If it is a vent-free fuel-burning appliance that runs on natural gas, propane, kerosene, etc., all of these fuels produce water vapor as they burn. That water vapor will condense on cold surfaces such as the roof sheathing. If enough water condenses long enough, you bet it can rot out both the roof sheathing and trusses.
Tim Carter
Ask the Builder
http://www.askthebuilder.com
W3ATB clear on your final