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Attic Insulation Baffles Every Other Bay

BlackFeet | Posted in Energy Efficiency and Durability on

Hello All. 

I searched the topic and came up empty handed.  Here is the issue:

I am building a single level house with 16″ raised heel trusses.  The attic is unconditioned.  There will be soffit and ridge vents.

So the insulation guy says he is going to place baffles every other bay.  I asked him what is going to hold the blown in insulation in the unbaffled bays.  He said in those bays they put bat fiberglass at the ends of each bay to keep the blown fiberglass in the attic.  

Anyone ever heard of this or seen it?  Any thoughts are welcome!

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  1. charlie_sullivan | | #1

    I've seen it. It's not best practice. What you want is a good air barrier between the side of the insulation and the outside air, and free air flow up the vent path. What you get is intermediate air flow inhibition in both directions. if your air sealing of your attic floor is impeccable, you don't need great venting so it's OK on that account. And with the raised heel trusses you'll do better than most houses despite the inferior air blocking. But if you've gone to the trouble to get 16" raised heel trusses, it seems like you are aiming for at least a pretty good performance level and it would be worth doing well-sealed baffled in every bay.

    Can you have whoever is doing your air sealing do the baffles too, instead of the insualtion contractor?

  2. Expert Member
    BILL WICHERS | | #2

    They are thinking the vents are to ventilate the air in the open space of attic, but that's only part of it. There needs to be air circulation against the underside of the roof sheathing too, so that it doesn't see condensation and not dry out. Because of this, the "every other bay" venting is a little risky.

    I would make them vent every bay, which is proper and best practice. Don't let them do the "we've always done it this way" line on you.


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