Does 1×3 strapping reduce thermal bridging?
dirkgently
| Posted in GBA Pro Help on
For those not familiar with the term strapping it is 1×3 boards.
It seems to be a New England thing to install 1×3 perpendicular to ceiling joists prior to installing drywall on the ceiling.
Does this practice significantly reduce thermal bridging of Rafter/ceiling joists in a cathedral ceiling application?
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Replies
No, this is done strictly for the dry-waller's benefit. With batt insulation, strapping between the framing and the drywalling can actually create thermal bypasses if the paper is not face stapled, or increase convective looping if the other side is exposed to the air.
It actually does provide a modest thermal break, but it's nothing to write home about. The thermal performance of the horizontal air films in the 3/4" deep trapped space is about R0.6-0.9.
That increases to about R2 with a foil facer on the top side of that cavity (still nothing to write home about.)
But if you are blowing in cellulose, wouldn't it have more benefit than with batts?
Your ceiling insulation should normally be twice the depth or more of the ceiling joists so the joists will be completely covered in 8" or so of insulation. There's your thermal break right there. I think we all wish walls were that easy.