Ceiling Insulation Question

[BillJ]

What are the user experiences/opinions about placing the insulation bats/rolls across the tops of the bottom rafter cords versus stapling them in place between the rafter cords from below?

Does one work better than another or is it just a matter of which is easier/ quicker to do? How does the choice impact attic venting options/ needs?

Thank you for your experienced opinions.

 

[p_mori7]

Space gain in the attic / use of space in between the bottom chords. The chords are normally 2x4 material, the batts should extend above (if R30+) and will sort of find their way together above the 2x4. Usually when batts are laid perpendicular to the bottom chords, it is to add insulation over top of what has been stuffed in between.

 

[rburke65]

Did mine from below....it fills the voids. Then I blew insulation from above.

 

[DC73]

In theory, you could get slightly better r-value by placing the batts across the tops of the bottom rafter cords IF you are also installing an airtight ceiling such as taped drywall. The better r-value comes by trapping a large air space between the insulation and the ceiling below.

Without an airtight ceiling, it's more likely to just be a choice between which way is easier.

Either way requires proper ventilation of the attic space. If you're using soffit ventilation it will be important to make sure you have sufficient air flow from the soffit to above the insulation layer.

DC

 

[rburke65]

See.? ....I didn't think of the trapped air space. Thx