Cathedral Roof Insulation Details

Cathedral ceilings built using 2 x 12 roof rafters allow enough space for the fiberglass batt insulation and a 1 5 gap for ventilation.

Cathedral roof insulation details.

Once this happens the water drips into your insulation or soaks into the roof sheathing. I guess the key is to make it unvented and add in other air impermeable layers. Pa302 2 ceilings without attic spaces n1102 2 2 r402 2 2. Once it gets into the attic space or the space between the roof and the ceiling of a cathedral ceiling the air cools rapidly and the water held in the air condenses on to a near by cold surface usually the underside of the roof or the roofing nails.

Johns manville aptm foil faced insulation sheathing board is an excellent choice for insulating attics and cathedral vaulted ceilings. Reduce under roof insulation level to 3 fiberglass r 11 under the cathedral ceiling not good energy savings not recommended but functional just poor insulation value. Attics and cathedral vaulted ceilings. Press the kraft faced insulation batts between the joists.

At insulation location for cathedral ceilings we describe a high labor method that combines providing an air barrier above fiberglass insulation in a cathedral ceiling to avoid heat loss by air movement in the roof combined with the addition of solid foam insulation to provide a much higher r value for the completed cathedral ceiling structure. This type of construction is also structurally sound and. This not a code requirement but ought to be only 1 inch is typically specified. This type of roof assembly is designed so the air can flow up the soffit vent through an insulation baffle pass through the 1 5 gap between the insulation and roof sheathing then exit through a ridge vent.

This will ensure adequate airing. When applied to the. The side exposing the kraft paper must face downward. Vented ceiling across rafters.

Cathedral ceilings on the other hand traditionally feature straight sides that slope upward at the same angle as the exterior roof line. There must be at least 1 inch 2 54 cm of space beneath the roof s plywood sheathing. Where the design of the roof ceiling assembly does not allow sufficient space for the required insulation such as cathedral ceilings the minimum required insulation for such roof ceiling assemblies shall be r 30. In vented cathedral ceiling assemblies a minimum 2 inch clear airspace is recommended between the underside of the roof deck and the top of the cavity insulation.

Polyiso provides one of the highest r values per inch of any rigid insulation r 6 at 1 inch.