House Sweating Badly

warpmine

Scenario: Semi-detatched home. 1600 sq.ft. area flat roof with 1.5/12 slope. 2x8 framing. The home owner insisted that I blow insulation in the space between ceiling and plywood. We made sure that we didn't fill it up totally to allow air migration. AZpparently, it's all for not as it still sweats. Two ventilation passive fans were installed close to gable. Helped some. Should we add four more? (About 50 feet across)

Input appreciated.

Ed the Roofer

If I read you correctly, the individual rafter channels do not have 100% eave intake and I am unsure about the 2 ventilation passive fans. Do they exhaust trapped humidity/condensation from all of the rafter bays? Ridge venting does not sound justified for exhaust due to the pitch.

This sounds similar to a cathedral/vaulted ceiling scenario. Read Air Vents brochure on venting Hip Roofs. On the back page, there is an illustration where a skylight is installed crossing several rafters in a vaulted ceiling situation. Therefore, the Continuous airflow from the eave to the ridge line is being impeded. They suggest drilling 6 of 1" diameter holes in each rafter to create a sideways air flowage possibility. We also have routered or notched out the top of the rafter to achieve similar workable cross-ventilation concepts below dormers, below and above skylights, and on rafters intersecting the hips.

Is there any "attic" chamber, or does the framing structure resemble the vaulted ceiling scenario? Also, did you install insulation baffle vents to ensure that the blown in insulation did not clog up the air flow venting passages in the rafter chambers?

I hope this points you in the right direction, or just food for thought.

Ed

PS. check out some articles on roof ventilation and condensation disasters on the internet by "Ron Hungarter" as he has very thoroughly investigated many condensation problems and also inspect-ny.com/interiors/atticcond.htm or just inspect-ny.com

warpmine

We were positively sure that the soffit vent wasn't covered. There is some chmber on the bedroom/back side of the house which allows cross bay venting. However, the front side of house there isn't any. The owner had contracted someone to install vinyl pannels on eve however, 2/3 are solid despite the holes we punched through the old fiber cement soffit to aid the ventilation.

I've notched rafters previously to combat this problem at other projects prior to this one but not this one. I'll cjeck out the literature you suggest. Thanks/

Ed the Roofer

For a good site to check out the alcoa and certainteed web sites on their vented soffit panels. They will list the reported NFA for each of their products.

Remember, that the reported 6 sq into 12 sq in per square foot of the products are only valid if the hole in the old existing wooden soffit is cut out to the entire size of the vented portion of the new soffit panel. The functionability is compromised by the mesh screening, dust accumulation, and possible clogging of the area over the vented panel from loose insulation as well as homeowners painting over the vents or screens themselves.

When I get back to my office, I will look up the exact links for the sites I suggested before.

A major point you stated, is that only 2/3 of the panels were vented. This is the type of application I see all the time. More properly, 100 % of all soffit panels should be vented. How else is EVERY rafter bay going to have access to fresh air intake. I wish they would just stop making solid panels.

ED

warpmine

I agree about the solid panels but they have their uses on rakes.

Ed the Roofer

Yes, you are right. I only meant for the soffits on the eave edges.

Ed