Venting a garage attic

[rlz]

I recently drywalled an attached two-car garage (walls and ceiling). This left the attic area unvented. I installed two 4"x12" soffitt vents on both the front and back of the garage (total of 4). These will provide air input into the attic. I also have two 12" square vent boxes for the top of the roof. I haven't installed them yet as the shingles on the garage and house are in need to be replaced, which I'm planning on doing in the fall. I'm apprehensive about installing the roof vent due to water leakage until the new roof is installed.

I understand that venting a roof prolongs the life of the shingles, but since they are at the end of their life, would it really hurt to wait until the fall. Would the new soffitt vents allow for enough cross ventilation? BTW, when I installed the drywall and new attic insulation, I left the cavities clear of insulation where the new vents are installed to allow for the air circulation.

Robin

[willshak]

rlz wrote the following:

Can you get a ridge vent on the garage, or is it a slant roof?

[rlz]

I could have gone with a ridge vent, but since the house has four box vents, I decided to match them for the garage. The garage roof is A-frame with a 12-4 pitch (basically 19'x22')

Robin

[rlz]

I might also add that I'm in Denver where we may get snow in May and again in October. High outside temps in the summer rarely go above

1. The attic was insulated with R-19 batting.

[John Grabowski]

*Install gable vents. Warm air rises and will be replaced by the air coming in from the soffit vents. In addition to the roofing material getting too hot the underlayment will also become overheated.

[JimT]

"rlz" wrote in message news: [e-mail]... On Apr 2, 4:28 pm, willshak

[mm]

We had no vents at all in our garage attic and it lasted fine for the

7 years we were there. The garage ceiling was sheet-rocked except for a 4x8 hole for access. As with a lot of diets and medical problems, good advice is often not critical advice.

[bud--]

I doubt you will get much ventilation with just soffit vents. A roofer could tell you if your soffit vents and proposed roof vents are adequate. Your argument on shingles sounds reasonable. You could also ask a roofer if heat will damage underlaiment (in time until you replace shingles). I don't think it would.

I assume, since you insulated, you heat the garage. A major reason for ventilating an attic in snow country is to keep the attic and roof at outside temperatures. If the attic temperature is raised, the roof temperature is also raised. Snow may melt and run down the roof until it hits the roof above the soffits where it freezes. That creates ice dams.

[willshak]

If you have electricity in the garage, I would suggest a powered fan in one of the vents. You could get one with a thermostat that will only come on when the heat gets to the point that the thermostat is set for, or a manually powered fan that you turn on and off when you are doing something in the garage. Otherwise, you can do what I did on one of my sheds. I built a working cupola on the roof. I later put ridge vents on either side of the cupola.

[Phisherman]

You may want to add additional vents. 2% of the ceiling area should be equal or less than the total vent area. Ridge vents are very good. You can add a house fan to the ceiling if your garage gets too hot.