Roof Rafter Bridging

Most codes allow foil faced foam to be left exposed.

Roof rafter bridging.

Thermal bridging is the movement of heat through a material that s more conductive than the air around it. The weight of the piano is centered over a single joist but the bridging transfers some of the weight to the adjacent joists. Failure to mitigate can account for overall heat loss of up to 30 so it s not a thermodynamics lesson to be taken lightly. The blocking or bridging between joists or rafters also contributes to this phenomenon.

Drive a nail into either end to hold the board in place. The main purpose for this type of bracing is to reduce the bucking length of the individual truss members and to assist in erection spacing of the trusses. It is always better to have a large rafter rather than be concerned with a sagging roof. Brush up on thermal bridging 101 here.

Plus you get the highest r value per inch for any type of insulation. Place a short piece of framing lumber against the rafter above it so that the two boards form a continuous line. Structures such as sheds or barns can be frames with rafters every 24 again make sure to consult local codes. For this size job you would want a large foam canister and professional spray applicator.

If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center. Place a long piece of framing lumber alongside the rafter so that the narrow edge is flush with the underside of the roof deck and the bottom reaches the ceiling joists. For example with bridging installed between joists a piano leg sitting over one 2 10 is actually supported by several. With steel framing at about r 04 per inch it s thermal bridging on a whole different scale.

In either case seal the foam edges well to the rafters with spray foam.