© 1996 - 2008 by
  Owens Corning

The rafters in cathedral ceilings are usually made of 2x12s or 2x10s, and Owens Corning makes two special high-density insulation products specifically for these rafters -- R-38C for 2x12s and R-30C for 2x10s. These products are appropriate for cathedral ceilings because the R-38C batt is 10 1/4 inches thick, which leaves over one inch of vent space for free air flow in a 2x12 joist. The R-30C batt, at 8 1/4 inches thickness, is designed to do the same thing in a 2x10 joist.

If you have trouble finding Owens Corning cathedral ceiling products at your store, just use our Dealer/Contractor Locator to look for the name of the Certified Energy Professional® (CEP) in your area. As a contractor specially trained on the full Owens Corning product line, your CEP can assist you in finding and installing any Owens Corning insulation product.

Recommended Insulation Products:

1. Before insulating begins, a ventilation baffle like Owens Corning Raft-R-Mate® attic rafter vents should be installed at the eave of every joist, to make sure the ventilation space is not blocked by insulation.

2. To install the insulation, push the material up between the rafters until it's flush with the edge of the wood. If a faced insulation product is being used, the facing goes toward the inside of the house -- the warm side in heating climates. At least one inch of ventilation space is required between the insulation and the roof deck. Some local codes require even more vent space, so find out what's called for in your area. Owens Corning R-30C and R-38C insulation are specifically designed to leave a one-inch air space when the insulation is properly installed in the joist cavity. If a standard insulation batt is being used, or if the code requires more vent space, install ventilation baffles such as Owens Corning Raft-R-Mate® attic rafter vents along the entire run of each rafter cavity in order to ensure a vented installation, but allow a 1 to 2 inch gap between each Raft-R-Mate® attic vent.

3. Insulation should be kept three inches away from recessed lighting fixtures unless the fixture is marked "I.C." (Insulated Ceiling), which is designed for direct contact with the insulation. If insulation is placed over an unrated fixture, it may cause the fixture to overheat and perhaps start a fire. Also, the insulation should always be installed at least three inches away from any metal chimneys, gas water heater flues or other heat-producing devices.

4. When installing faced R-38C or R-30C cathedral ceiling batt insulation, position the batt between rafters to make sure the vent space is maintained. If stapling is required to secure faced insulation, staple the facing flange to either the face or inside of the rafter every 8 - 12 inches. If glueing the drywall, you will have to inset staple. Many drywall installers will prefer inset stapling.