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hip roof venting suggestions

3038 Views 4 Replies 3 Participants Last post by  Windows on Wash
I purchased a house in Feb '12. During the inspection, the inspector noticed a lot of mold on the roof deck. He suggested it was inadequate ventilation. We had the sellers bring in a mold remediation company and install soffit baffles. Upon reinspection the mold was gone and 7 soffit baffles had been installed. Recently I returned to the attic during an energy audit to find the mold coming back and the energy auditor mentioning it still seemed like inadequate ventilation.

So I installed soffit baffles between all rafters, 30-some in total. The insulation was completely blocking the airflow in every single location. As I installed, I made sure I could see light coming from the soffits which I'm hoping means the soffits themselves aren't clogged with insulation. I also had an insulation company come out to give a quote on adding insulation and he mentioned that there do seem to be enough soffits (see picture for what soffits look like).

The two bathroom vents on the second floor of the house used to T together and run out a single roof vent. In addition, one of the connects to the T was loose. I added another roof vent and now run each bathroom vent to its own roof vent. In addition, I taped up all connections as well as around the vent in the bathroom.

Unfortunately, I still have excess moisture in the attic. As I write, the attic is at 48F with 70% relative humidity (rh) (39 dew point) while outside it is 37F with 64% rh (26 dp). I also have a second attic, which does not have a mold problem, and it is currently 42F with 59% rh (29 dp). Our house is currently at 67F, 41% rh (42 dp) and we are not running a humidifier. The attic in question sits over two-stories of the house while the second attic is over one room and the garage.

My main question is how to properly vent the attic. The attic is 845 sq ft with 5/12 slope. There is no vapor barrier. I believe I should have around 325 sq in of venting in the ridge and 490 sq in in the soffit. There is a ridge vent, but the ridge is only 6 ft. In addition, the plywood only leaves a 3/4 in gap so at best it seems the ridge gap provides 54 sq in. But of the 6 ft, some has roof felt on the inside and the shingles overhang the vent on the outside (see pic which is taken at one end of the ridge vent). There is no other exhaust venting. At this point, I suspect the main problem is not enough exhaust venting.

What are your suggestions for how to exhaust vent a hip roof with only a 6' ridge? In addition, do you have other suggestions for how to deal with the humidity in the attic? (I will be sealing other areas that are letting air escape from the house and the energy auditor mentioned the insulation is variable depth but between R-24 and R-42 and should be brought up to R-49).


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Additional pictures

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So your baffles are ok, and your soffit is allowing enough air in. You need more insulation and more exhaust vents.

So put more insulation in and add some exhaust vents. You can go with a turbine type vent, or the old roof vents which I bet that house originally had. In addition to this, you could have some mechanical (electric) vent.

One thing I always like to say is that you never hear someone complaining that their garage is too big or that their attic is too well ventilated. Now that I think about it, I never heard someone say that the grade around their house didn't let enough water into the basement.
Air seal and insulate your attic floor.

Make sure bath fans are through the roof.

Make sure all the baffles/vent chutes are intact and properly aligned.

Add exhaust to the roof (roof louvers) and I recommend staying passive.
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