By Paul Bianchina
There are many styles of homes that employ vaulted ceilings - ceilings that angle up from below with no accessible attic above them - in order to increase the feeling of openness and interior space. It's a beautiful look, but no attic space above to insulate and incorrect construction can result in utility bills that soar as high as the vaulted ceiling itself.
Many of today's energy codes require that a vaulted ceiling be insulated to R-30, although that number can vary up or down depending on where you live. Many older style vaulted ceilings were constructed by first installing exposed wood beams, then placing wood decking on top of the beams and the roofing material on top of the decking. Often, little or no insulation was factored into the construction of the roof structure, and the result is an extreme amount of wasted heat - and wasted money.
Adding Insulation From AboveTo retrofit an older style open beam vaulted ceiling and still retain the desirable character of the open beams and exposed wood decking from inside, the solution is to install rigid foam insulation from above, between the top of the wood decking and the underside of the roofing. Rigid foam has a very high r-value per inch, allowing you to achieve the necessary level of insulation with the minimum amount of buildup on the roof.
Since retrofitting insulation from above requires the removal of the existing roofing, the best time to consider undertaking this project is when you're ready to reroof the house. First, the old roofing has to be removed and the top of the roof deck exposed and cleaned. Remove all of the old nails, and resecure any deck boards that may be loose.
The next step is to install furring strips running perpendicular to the direction of the decking boards. The furring strips are installed on 24" centers, and have two purposes -- they create a cavity for the new insulation, and they provide the necessary structural support for the new sheathing that will be installed later.
The height of the furring strips depends on the amount of insulation you're planning to install. Many foam insulation products have an r-value in excess of R-7 per inch, so four inches of foam would be required to achieve R-30. To create the necessary four-inch deep cavity, install 2x4 lumber on edge -- the wood is secured by toenailing it to the roof decking -- then top that with a 1 ˝" wide strip of ˝" plywood nailed on top of the 2x4.
Once the furring is installed, you're ready for the insulation. Foam insulation comes in 4x8 foot sheets, so you'll need to rip the sheets to the proper width to fit between the furring strips -- you can use a razor knife to cut and snap the sheets, or make quick work of the process using a table saw. Utilizing two inch thick foam, you'll need to stack two pieces in the cavity to make up the necessary four inches of total thickness. The foam is just placed into the cavities, and does not need to be secured in any way. Following installation of the foam, new sheathing -- typically either 1/2" plywood or 7/16" waferboard -- is installed over the top of the furring strips.
Prior to installation of the new roofing, you will need to install a trim board around the perimeter of the roof in order to conceal the exposed edge of all the furring strips. This is typically done using either 1x6 or 1x8 lumber, but other sizes of wood can also be used -- either alone or in combination with different types of moldings -- depending on the style of the home and the final look you want to achieve.
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