Insulation Under The Roof

Water is insulation s enemy.

Insulation under the roof. The material is compressible and is thus easy to fit and is less likely to cause cracks. The insulation boards are best fitted under the roof structure whilst the mineral wool can be inserted between the beams of the roof. You can also add rigid foam insulation under the rafters which adds r value and eliminates thermal bridging through wood rafters. Look for water stains on the roof sheathing or damp or moldy spots on attic joists and existing insulation as a clue to where leaks might be.

Senior engineer manager at icynene john broniek makes the case for the unvented attic assembly and why insulating the underside of the roof makes sense. It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow. A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel. An efficient room in a roof in a new build property where over rafter insulation is not desirable.

Arguably the most popular pitched roof solution installing insulation between and under the rafters uses the depth of the structural timbers to best effect. Consider using high density r 30 batts which are as thick as r 25 batts but fit into 2x10 framing.