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Questions about roof ventilation - Ridge or Power Vent Fans?

Questions about roof ventilation - Ridge or Power Vent Fans?

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Old 03-30-14, 09:16 AM
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Question Questions about roof ventilation - Ridge or Power Vent Fans?

I am in the process of getting quotes for my roof which is 16sq. The house is located in Southern NH and was built in 1996 with 20 year shingles which aren’t looking that great. The roof has a ridge vent with only about 1”to 1-1/2” total gap. The attic is vented through the full length soffit vents on both the front and rear of the house. Inside the attic there is some rusting showing on nails and the gable end roof sheets of plywood have some staining (Noted by the contractor: Most likely due to wind blown rain). Also the full bathroom fan is vented into the Attic (Noted by another contractor and I am upset I never noticed it during the home inspection last april). The Master ¾ bath fan is vented to the soffit.

I personally think that with the combination of small ridge gap and the two fans being vented incorrectly that is why there is some moisture on the nails. So I obviously need to vent both bathrooms up and out the roof.

My question is this:
Do I just stick with a Ridge vent cut back 1-1/2”each side (3”total) and go with it? Or do I consider installing a Power ventilator fan with Humidity and Temp control?

Thanks
 
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Old 03-30-14, 09:22 AM
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Bright nails will rust with just exposure to the moisture in the air. Fans should be fixed ASAP. Your ridge vent and soffit vents should be enough. A power ventilator is normally used in the summer to help cool a hot attic.
 
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Old 03-30-14, 09:44 AM
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You will always have "some" frost in an attic simply because the roof is cold and your house is losing heat and humidity. Ventilation may help, but so would sealing any and all penetrations from the ceiling into the attic. Things like the 1" holes that electrical lines pass through... the space around 2" and 4" pipes for your sewer vents, any hvac penetrations, etc. These are also places where warm humid air enters the cold attic space where it can condense. Making sure your bath vent runs outside can help.

Power vents can cause as many problems as they solve. Generally they will speed the heat loss from your home in the winter by pulling out conditioned air. Same thing in the summer, although the amount they save by dropping the attic temperature a few degrees may break even with the amount of conditioned air they pull from the home. I haven't seen any studies on that.

Depending on the brand of ridge vent, and the construction method of your roof, the amount that was cut out may be correct. Too wide of a cut and you may risk inviting rain and snow in. For instance, GAF Cobra ridge vent recommends 7/8" per side, or 1 3/4" gap between the sheathing if looking up from below. That's if you have a truss roof, with no ridge board. If you have a ridge board, that same 7/8" clear gap per side applies, but since the ridge board blocks the peak of the roof, you have to add in the 3/4" of wood (x 2) so you would cut 1 5/8" from center and have a 3 1/4" gap between sheathing if looking up from below. See their instructions here.

Cutting out more ridge ventilation would be a big mistake if you don't follow the mfg's instructions, which I would assume the installer did correctly in the first place.
 
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Old 03-30-14, 10:54 AM
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Sorry for not adding that earlier - The roof is Trussed 24" on center- I am thinking if I go with a Ridge vent - It would be the Snow Country or Snow Country advanced.

I am getting the roof done in the next 2-3 weeks and then in the Fall I plan on pulling all the fiberglass insulation, Putting in Accu-Vent Baffles, air sealing all penetrations and then either blowing in or having it done - 16" of insulation.

During the energy audit/IR inspection/blower door test I had 7.48 ACH50 which the auditor stated is pretty good since new homes in Mass must be 7.00 or lower to meet code.

-Steve
 
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