How to Vent a Cathedral Roof

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Ventilating the rafter spaces in a home attic is mandatory by most city building codes. Unventilated cathedral roofs can get too hot and water vapor from the room below can become trapped. Without properly installed ventilation, the entire roof system can collapse, and the shingles can fail. Ventilation provides air circulation in the attic so that heat and extreme cold cannot damage the rafter boards. No matter what type of roof you have, venting is required. Cathedral roofs have little space between the ceiling and the rafters, so proper insulation is also important. If you'd like a few ideas on venting your cathedral roof, read through the following steps.

Things You'll Need

  • 2-by-10 rafter boards
  • 1-by-6 roof sheathing
  • Pipe vents
  • Roof paper
  • Ice dam barrier
  • Roof shingles
  • Rigid foam board
  • Foam insulation
  • Circular saw
  • Roof vent
  • 8-penny nails
  • Staples
  • Staple gun
  • Vent screens
  • Screws
  • Frame your cathedral roof with 2-by-10 roof rafters. Make sure the roof sheathing over the rafters comes all the way up to the ridge beam on both sides.

  • Make sure all utility pipes are properly vented through the roof, and the flashing is secured in place. Place an ice and water barrier 4 feet up from the roofs eaves. Cover the remaining roof with paper.

  • Apply the roof shingles over the paper. Create a block between the top plate and the roof sheathing, at the eaves, with a rigid foam board.

  • Spray in a foam insulation, and when it dries cut back any excess. This provides proper insulation between the interior walls and the exterior roof. Insulating your cathedral roof is the first step to proper roof ventilation.

  • Keep a minimum 2 inch space between the top of the rigid insulation and the bottom of the roof plywood. This leaves room for air to get in through the soffit or eave vents, and also makes a space for airflow at the top of the roof for roof vents.

  • Before you put paper and final roofing, cut a hole in your plywood roof diaphram, set a roof vent over the hole and tag it with 8-penny nails. Place the paper over the top of the flashing, so water runs off and over the flashing, not inside it. Staple down the roof paper.

  • Prepare for the placement of your vent screens, in the soffits, under the eaves, during construction. Style depends on architectural drawings. These are non-structural and are simply applied over the holes with a few screws at the corners and sides.

Tips & Warnings

  • It is important to have intake air vents at the eaves or soffits, as well as out take vents on the top of the roof.
  • Keeping a proper amount of space, when applying the foam insulation, is mandatory for proper airflow.

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  • Photo Credit http://www.edmonds.com.au/html/products/cathedral_ceiling_ventilation_kit_250mm.htm
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