Thread: turbine with static vents

I did a house today with a hip roof and a footprint of about 1000 sq ft. The house is 37 yrs old. There was soffit venting, although I didn't climb into the attic space to confirm daylight. There were 4 static roof vents and one turbine. Two vents were about 2 ft away, on either side of the turbine. The house had a north/south exposure with full sun on the south side for most of the day. The shingles on the south side of the 5 yr old roof were starting to curl and claw. The sheathing in the attic was discoloured. My thoughts were that there was too much roof venting which was depressurizing the attic. I also wondered about cross venting but I can't seem to find any info on that. Somehow, there was inadequate air flow but find it difficult to articulate the issues to my client. I ended up just writing "further investigation required by a qualified contractor". He understood what I was trying to say but I had no concrete solutions for him aside from vague mathematical equations. Any suggestions?

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RALPH

did you look in the attic at the access panel and see anything, you said you didn't walk??

cvf

Yes, that's how I know that the sheathing was discoloured. I don't risk crawling in attics. I had a guy blame me for cracks in his ceiling once in the lower level on a backsplit. I took great pleasure in explaining to him that I don't go into attics unless there's a floor and the access to the lower attic was in the bulkhead of a stair well. He said "Oh......ok." . At the end of the day, my client needs a "professional" to address the issue which was duly noted. I just wish I could've given him better solutions, although I think 50% soffit venting and 50% roof venting pretty much sums it up. I think perhaps the turbine was excessive.

Here's a pic of the sheathing. Not that dramatic, I know, but the 5yr old shingles were prematurely wearing on the southern exposure. This is a pic of the north plane. It was hard to get into the attic access too. I was crammed in a closet and was warned that the access trim was loose. Good thing I went to my chiro this morning.

Still not adequately vented. Check for sofit venting and that it is not obstructed by insulation and add additional ridge vent/other static venting.

The turbine is going to pull air from the area with the least resistance. The static vent a few feet away is much easier than the partially blocked soffits all the way down by the cieling. The attic is not getting air exchanges. Replace the turbines with more static vents and open up the soffit vents to ensure air exchange.

With multiple sources for attic ventilation you run the risk of loosing the flow of air through convection. Attics normally do not vent or exchange air with the the wind, it comes from convection. Warm air rises and the cool air sinks. The cooler air enters at the soffits, warms and rises to the top and hopefully exits thought the highest vent. One reason the ridge venting is one of the better methods of venting.

With the static vents and the turbine vent it is very likely that the convection process has been stopped. The air enters the static vent and exits the turbine or vice versa.

My theory on attic ventilation is that more is better no matter what form it may take. The idea is to keep the attic as close to the outside temperature as possible. The ideal roof would be a roof with no sides that covered the house....kinda floating above the house to keep out the rain. IMO....

Originally Posted by James Duffin

My theory on attic ventilation is that more is better no matter what form it may take. The idea is to keep the attic as close to the outside temperature as possible. The ideal roof would be a roof with no sides that covered the house....kinda floating above the house to keep out the rain. IMO....

Take a gable roof with soffit, gable and ridge vents. Where is the ridge vent going to get its air from? The gable vents. The soffit vents will not draw because the ridge vent is being satisfied by the gable vents. The air is being drawn in the gable and exhausted out the ridge vent. The center of the attic is not exchanging air. More is not always better.

Close off the gable vents and the ridge vents will draw from the soffit vents. The attic will have complete air exchanges. Adding turbines, passive vents, thermostatically controlled fans and gable vents to a soffit/ridge system will disturb the natural air flow.

If you are near the GTA, here is your qualified contractor:

Welcome to Canam

Sheathing discoloration is usually caused by air leakage into the attic. Maybe the shingles were damaged by ice damming (also caused by air leakage).

The turbine vent can make the problem worse by depressurizing the attic and pulling warm/moist air from the house into the attic.

Not sure about their retrofit cap installation instructions with the "just nail it and caulk it" approach, but I do like the retrofit/replacement caps for turbine vents. Here

Originally Posted by James Duffin

My theory on attic ventilation is that more is better no matter what form it may take. The idea is to keep the attic as close to the outside temperature as possible. The ideal roof would be a roof with no sides that covered the house....kinda floating above the house to keep out the rain. IMO....

Please provide some science to support your claim. As a homeowner I do not want someone making up there own theories. I want to see the science behind their claims