Ventilation Low Slope Roof

I have a 1975, 1550 sq ft house with a low slope roof located in Saskatchewan Canada. I have an single vehicle attached garage on the north side of the house; therefore, the roof is fairly long.

The issue I have is, ever since I moved into the house 6 years ago, every spring when it warms up I get a leak down along the main support beam in the house. (the beam is located about 4 feet from the north wall which is common to to the house and garage). If I look up in the attic I can see some frost build up along the north sides roof and a bit on the insulation. Because of the low slope it is impossible to get close to investigate further.

The problem seems to have gotten worse this year and may have something to do with me adding another R20 of blowin insullation last year. When I look up in the attic I can see a fair amount of light along the south side (soffit) but because of the attached garage there isn’t much light on the north side. I should also mention that I have 2 - 12 inch wind turbines on the roof. I dont believe I have anything venting into the attic (dehumidifiers, bath fans etc…).

The roof is shingled with asphalt shingles (look in good shape).

Any ideas on what causes this problem. I suspect it is a lack of intake ventilation (no soffit on the north side). How do I eliminate this problem? What products are available to be installed on this type of roof etc…


Not sure what your problem is from your description but the intake vent I would recommend in a snowy area is Ever-Flo eave vent. The air flow is brought in from behind and underneath the gutter system on the roof edge which leaves no way for snow infiltration.

I agree with Tar Monkey on the soffit vent.
But, in looking over my Ventilation Guide (distributed by Air Vent,Inc.), the number of 12" turbines needed for your roof area is seven (7); you may want to review and verify this with a roofer in your area.
Please check the bath fan vent just to be sure.
I know Canadian code requires outside venting of the bath fan (thank you Mr. Holmes)

i dont care were you live,
or what the scenerio.
low slope and shingles dont mix.
tear it off put on a flat roof material,
somthin ,that snow cant melt back through.
that way you know your roofs not the problem.
then take it from there.


What do you mean by “low-slope.” If the pitch is less than 2/12 shingles will not work. If it is between 2/12 and 4/12, manufacturers call for some special installation practices. Personally, I don’t like to shingle anything less than 4/12 and I certainly don’t use dimensional shingles on a pitch less than 4/12 (I find that they leak easier than 3-tabs on low-slope applications. Water tends to back up under the laminated portions).