Roof Rafter Bridging

It is always better to have a large rafter rather than be concerned with a sagging roof.

Roof rafter bridging.

In either case seal the foam edges well to the rafters with spray foam. With steel framing at about r 04 per inch it s thermal bridging on a whole different scale. Place a short piece of framing lumber against the rafter above it so that the two boards form a continuous line. Drive a nail into either end to hold the board in place.

The uninsulated roof framed with wood r value around 1 1 per inch means rafter lines covered with snow. The blocking or bridging between joists or rafters also contributes to this phenomenon. 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.

Most codes allow foil faced foam to be left exposed. It can consist of lateral members spanning in between trusses t or i bracing on individual members sheathing or metal strapping. 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. For this size job you would want a large foam canister and professional spray applicator.

Structures such as sheds or barns can be frames with rafters every 24 again make sure to consult local codes. Steel framing typically reduces the in cavity r value by as much as 50 while wood framing reduces in cavity r value by a bit less than 10. Thermal bridging is the movement of heat through a material that s more conductive than the air around it. Plus you get the highest r value per inch for any type of insulation.

Failure to mitigate can account for overall heat loss of up to 30 so it s not a thermodynamics lesson to be taken lightly.