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Start at the bottom of the roof and place the first piece of rigid foam insulation against the metal flashing, starting at the center line. Nail it around the edges with roofing nails. Concrete & Clay Roof Tiles; Slate Roof Tiles; Metal Roofing; Composite Shingles; Low Slope Roofing. Single Ply Roofing; Built-Up Roofing; Built-Up Roofing Asphalt; Modified Bitumen Roofing; Structured Metal Panels; Roofing Insulation; Roofing Accessories. Roofing Felt; Metal Roofing Accessories; Roofing Fasteners; Roof Cements & Coatings; Roof.
The greater your home’s thermal resistance factor, or R-value, the more energy efficient it is. With rising heating and cooling costs and the desire to minimize our environmental footprint, many homeowners are opting to add insulation to their attics to reduce heat transfer. Rigid foam insulation is available in two main types; polystyrene foam and foil-faced polyisocyanurate foam. Both install in the same manner but the foil-faced product offers slightly more R-value for the same foam board thickness.
1
Measure the length and width between two rafters in your attic and transfer the measurements to a 4-ft-by-8-ft of rigid foam insulation board.
2
Snap a chalk line between the length measurements for use as a cutting guide.
3
Cut the foam board, on the outside edge of the chalk line. Cutting on the outside edge of the line ensures that the board fits snugly between the rafters. A table saw is optimal for cutting rigid foam, but you can use a utility knife if no saw is available.
4
Position the foam board between the rafters and push it upward until it fits snugly against the underside of the roof deck. The snugness of the foam itself, should be sufficient to hold the strips in place, but if a strip seems a bit loose, you can drive the tip of an 8d nail on the inside of the rafter to act as a brace.
5
Measure, cut and insert additional strips of rigid foam board until the insulation fills all the rafter spaces. This insulating method is only acceptable when the attic will not be finished.
1
Select rigid foam insulation boards that are at least 1/2 inch less in thickness than the rafter space is deep if you plan to finish the attic as living space.
2
Measure and cut the foam boards as instructed above, but instead of pushing them all the way to the back of the rafter space, push them only until the surface is flush with the rafters. This allows a 1/2-inch gap at the back of the rafter space, which is necessary for ventilation.
3
Cut and fit all the rafter spaces with foam board in the same manner. When you’re using foil-faced foam board insulation, apply foil tape along the rafters to form an airtight seal.
Things You Will Need
- Measuring tape
- Chalk line
- Table saw (or utility knife)
- Foil tape (optional)
- Hammer (optional)
- 8d nails (optional)
Tips
- When installing rigid insulation in an attic to be finished as a living space, you must provide a route by which hot air can escape. This requires the use of soffit vents and a roof ridge vent to allow circulation, since sidewall vents are terminated during the remodeling process.
- In addition to installing the foam board on the underside of the roof deck, you can attach it to the bottom edges of the rafters in the same manner you would hang drywall. You can then install drywall right over the sheets by using drywall screws that are 1 inch longer than the combined thickness of the insulation and the drywall panels.
- When installing a foil-faced foam board insulation, the foil side should face you.
Warning
- Do not nail through the foam board insulation into the roof deck, which can cause roof leaks.
References (1)
About the Author
Glenda Taylor is a contractor and a full-time writer specializing in construction writing. She also enjoys writing business and finance, food and drink and pet-related articles. Her education includes marketing and a bachelor's degree in journalism from the University of Kansas.
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- Jupiterimages/Photos.com/Getty Images
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Taylor, Glenda. 'How to Attach Rigid Insulation on the Underside of the Roof Deck?' Home Guides | SF Gate, http://homeguides.sfgate.com/attach-rigid-insulation-underside-roof-deck-36798.html. Accessed 25 June 2019.
Taylor, Glenda. (n.d.). How to Attach Rigid Insulation on the Underside of the Roof Deck? Home Guides | SF Gate. Retrieved from http://homeguides.sfgate.com/attach-rigid-insulation-underside-roof-deck-36798.html
Taylor, Glenda. 'How to Attach Rigid Insulation on the Underside of the Roof Deck?' accessed June 25, 2019. http://homeguides.sfgate.com/attach-rigid-insulation-underside-roof-deck-36798.html
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