Cathedral Roof Insulation Details

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.

Cathedral roof insulation details.

Vented ceiling across rafters. There must be at least 1 inch 2 54 cm of space beneath the roof s plywood sheathing. The side exposing the kraft paper must face downward. Johns manville aptm foil faced insulation sheathing board is an excellent choice for insulating attics and cathedral vaulted ceilings.

This not a code requirement but ought to be only 1 inch is typically specified. This type of construction is also structurally sound and. 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. Press the kraft faced insulation batts between the joists.

I guess the key is to make it unvented and add in other air impermeable layers. Once this happens the water drips into your insulation or soaks into the roof sheathing. 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.

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. 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. Pa302 2 ceilings without attic spaces n1102 2 2 r402 2 2. Hot humid climate all metal cathedral roof must use r 11 batts incredibly helpful 5 thread.

This will ensure adequate airing. Cathedral ceilings built using 2 x 12 roof rafters allow enough space for the fiberglass batt insulation and a 1 5 gap for ventilation. So if you must use fiberglass insulation batts and you dont have access to spray foam or closed cell boards what do you do. Here are some older home cathedral ceiling roof insulation and ventilation options that you may consider.

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.