Potential attic ventalation issues with attic fan suggest solution
Hello,
I have a roof that needs to be replaced soon and got quotes. 3 roofers said that the attic ventilation is not great and it is making the attic too hot (HVAC and ductwork is in attic). None found widespread mold, rotting wood, or warped wood in the attic. They all recommended an attic fan (powered or solar).
1 roofer said that the ventilation is fine and suggested just to replace the shingles (They were to most expensive by $2k, but come Master certified with GAF and have a 25 year GAF workmanship warranty and well reviewed).
The three roofers who said that there is an issue commented that there is a double beam at the top of the roof that makes the installed ridge vent ineffective. They say that I should be seeing daylight coming from the top of the roof for the ridge vent, but they do not. One also says that the insulation is all the way against the soffits and thus isn’t letting air through them. When I went to look I do see insulation against the roof where the soffits may be, but I also see about 4-5 baffles in different parts of the attic. My understanding is that those let in air through the roof. Each of these roofers have recommended an attic fan as a solution.
As I do my research I noticed that attic fans seem to have a bad rap. I am hesitant for an attic fan because of this and fairly sure that my attic is not air sealed (ductwork, wires, and see metal housings in ceiling in attic), we have a gas range, and my crawlspace isn’t the best for moisture.
I’m looking for suggestions on what I should do? Just go with the one roofer who believes nothing is wrong (most expensive by several thousand dollars), go back to one of the roofers suggested an attic fan, but was potentially willing to try something else and see what they suggest about fixing the issue with the ridge vent?
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Replies
pfrankel,
The problem with powered attic exhaust fans is that the replacement air has to come from somewhere, and that somewhere is often air drawn form the conditioned house below.
The way to fix the roof is to ventilate properly. If there are soffit vents that are blocked by the insulation, solving that problem is as easy as adding baffles at the eaves. Rather than a ridge vent, you can use spot vents near the peak.
Whether it's a good idea to have mechanical equipment in the attic is a separate question.
How much attic ventilation do you currently have in terms of square feet of vent at the ridge and at the soffit and how mant square feet of roof do you have?
100% of the moisture got into your attic on the back of leaking into your attic thru your ceiling. I would first concentrate my efforts at stopping this flow of warm moist air. The most likely thing to look for is 2 dozen recessed light fixtures that you will need to remove.
Have you had a blower door test?
What building climate zone?
Walta
"3 roofers said that the attic ventilation is not great and it is making the attic too hot."
It's a real common misconception that the purpose of attic ventilation is to cool the attic. It's not. It's to prevent moisture from building up. As both Malcolm and Walta have pointed out, the moisture in the attic comes from humidity in the living space leaking through the ceiling.
Roofer #4 has a strong case that the existing ventilation is fine, there's no sign of moisture damage.
You want the air flowing into the attic to be cool dry air coming from outside, at the eaves. Hot air rises, and water vapor is less dense than air, so you want air flowing out at the top of the roof to take that moisture away. A vent fan in the attic tends to pull warm, moist air through leaks in the ceiling and makes any moisture problem worse.
You don't have to be able to see light through the ridge vent, it just needs to be able to let air out. The vent doesn't have to be huge. The minimum is one square foot of ridge vent per 600 square feet of attic, with the same amount at the soffits. If your attic is 24 feet wide that's about a quarter inch on each side of the ridge.
Depending on the layout a gable vent may help as well.
It's also a common misconception that it's OK to put HVAC equipment in a ventilated attic. It's not, but more ventilation doesn't fix that.