New Roof Question

[kpeluso]

I faced a similar dilemma when redoing my roof. I ended up adding a ridge vent because it seemed like a good way to boost attic ventilation, especially with the heat we get here. It helped with energy bills and keeping the attic cooler. If you’re on the fence, just make sure your current vents are doing their job well. It’s a small extra cost for peace of mind, but if you’re confident in your existing setup, you might be fine without it.

[Snipe Hunter]

The #1 place I find mold doing home inspections is in the attic. Usually no vents or just gable vents. A lot has to happen for gable vents to work and it's probably pretty rare when they do work. They only really passively vent the area around the vent. I see mold closer to the middle of the attic on the sheathing, rafters and in the insulation. I also see it in the corners of the attic that get no air movement at all.

Heat rising creates the draw from the soffit vents and exhausts out the ridge vent. You get some of that effect with gable vents and a ridge vent as the air is drawn from the gable vents and out the ridge but it doesn't do much of anything below the gable vents, in the center of the attic or in the corners of the attic.

Heat is only part of the problem. Moist air trapped in the attic is the bigger issue.

You get moist air in the attic and at night the roof cools and all that trapped moisture condenses on the rafters/trusses and sheathing. Bam, mold and rotted wood.

With a ridge and soffit system, air is always moving. Even in the winter, warm air still rises so it keeps working.

Winter also has it's own issues, especially if you have bathroom exhaust vents terminating in the attic as opposed to the exterior. Dumping all that wet air in the attic and then it freezes on the sheathing and roof structure. It can't dry out, it just keeps soaking into the wood every time it thaws.

If you do the ridge vent (highly recommended) and you install soffit vents, try to get a vent between each set of rafters/trusses and make sure the insulation is cleared away from the vent so air can flow. Install baffles if you can get in there. I would double up the soffit vents in the corners of the attic.

If you don't have a soffit, roofers can install vents under the shingles at the lower courses of shingles. Called "shingle over vents".

If you don't want to do any of this: Installing a powered vent near the ridge in the middle of the attic will draw air from the gable vents and at least provide some active ventilation. Connect it to a Humidistat AND a Thermostat switch so it turns on when it's hot and when it's humid. You still aren't venting below the gable vents or in the eves but at least you are protecting the upper structure of the framing and sheathing.

One other thing we haven't really talked about is how much good ventilation keeps the shingles cooler and they last a lot longer. The oils in the shingles get cooked over an unvented attic. The shingles shrink and dry out and the longevity of the shingles are reduced. Soffit vents and ridge vents are cheaper than shingles.

[joe1086]

Good info Neil. 

Say a house has existing soffit and gable vents, and a roofer adds a ridge vent. Shouldn't the gable vents be boarded up for better airflow? It's an ongoing discussion in our neighborhood.

[Snipe Hunter]

Good info Neil. 

Say a house has existing soffit and gable vents, and a roofer adds a ridge vent. Shouldn't the gable vents be boarded up for better airflow? It's an ongoing discussion in our neighborhood.

probably a good idea as long as there are sufficient soffit vents

[MKepke]

Cub - how did the roof replacement go?

Did you end up installing ridge vents?

-Mark

[Cub_Cadet_GT]

Cub - how did the roof replacement go?

Did you end up installing ridge vents?

-Mark

Replacement went, well roofer did a great job. I did not install the ridge vent at the recommendation of my roofer. Took them 3 days, I had some rotten sheathing at the leading edge of the front of the house that needed to be replaced. Old roof did not have ice and water shield and previous owner never cleaned the gutters.