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Baffling and blocking

Norman Bunn | Posted in Energy Efficiency and Durability on

The trusses are up, so now I have a better idea of what I am dealing with in my attic. First off, all attic spaces will be ventilated and there will be no HVAC up there and few penetrations (no can lights!).

For the “regular” attic, I plan for R-40 or so with blown cellulose (could be more, but that’s my minimum goal). At the exterior wall top plate, I have 20-24″ of heel, so a lot of space. However, I want to prevent the insulation from getting into the soffits and stopping any windwashing. So, with 24″ on center trusses, what is my best (easiest, cheapest, longest lasting, most energy efficient) way of sealing this area, while letting it ventilate?

I am thinking of using SmartBaffle in the vaulted sections (will address that in a later question), and I see it can be bent to accomplish this windwashing function, but don;t know if that is the “best”. If so, I would install this so it is on the outside of the top plate, thus allowing the top plate to be insulated.

CZ 3A – Greenville, SC



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  1. T Carlson | | #1

    Normally your exterior sheathing would run right up to the underside of the top chord, so if you have 20" of heel and only 12" of cellulose you wont get any wind washing. If your trusses have an overhang return block you can notch the sheathing or if its above the soffit line I have often cap nailed housewrap as a barrier since its easier, faster, cheaper to serve as a barrier,

  2. GBA Editor
    Martin Holladay | | #2

    There are several commercial ventilation baffles on the market, and it's also possible to build your own baffles. The choice is yours. Here is a link to an article that explains the options: Site-Built Ventilation Baffles for Roofs.

  3. Expert Member
    Malcolm Taylor | | #3


    As T said, running the sheathing up to the top chord is a good idea. Not only does it restrain the insulation, but because with raised-heals that high, the truss are a lot less stable than regular ones, even with the prescribed bracing and roof sheathing.

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