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atw58 05-14-2009 01:52 PM

Too Much Soffit Venting?
Hi all,

I live near Toronto Canada and want to add blown cellulose to the existing R40 blown fiberglass in the attic. The house has a hip roof with qty 6 8X8 inch roof vents. The square footage of the attic is approx 1500 sq ft.

The builder blocked 80% of the soffits with fiberglass where the top plate and roof meets before filling with blown fiberglass. The remaining 20% have plywood nailed into the rafters to create air intake chute.

Now comes my question -- should I unblock the all remaining soffits and add similar plywood wind baffle venting or the plastic vent chutes. In the summer it is extremely hot in the attic so more intake venting from the soffits should cool things considerably. On the other hand, there will be less insulation between the top of the walls and the roof. Can there be too much soffit venting.


Ed the Roofer 05-14-2009 04:26 PM

The insulation that extends over the soffits are doing absolutely no good anyways, so unblock the soffit vents.

Unless you are in a Coastal High wind Region, the more Intake Ventilation you have, the better off you are.


Chemist1961 05-16-2009 08:19 AM

Hi Art,
Ed is absolutely on the money. You will find info
There is a correct ratio between rooftop and soffit venting. Too tight a soffit opening cfreates a funnel effect. I had my roof redone last year and increasd the rooftop vents.
The upper level is noticeable cooler in summer now and I am upgrading insul to R50 as well. I am also adding venting in the plywood soffits by doubling the grille dimension and adding additional ones. You can also install a liner baffle attached to the underside of the roof which channels air above the insulation up toward the roof top while retaining the insulation above your wall's top plate.
FYI if you have a home energy audit done for about $300 before you add the insul you will likely get a provincial/federal rebate which covers most of if not all of your entire cost. Then apply for the new HRTC home reno credit and you'll be money ahead:thumbsup:

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