How to Insulate an Attic When Finishing
Maximize headroom when insulating an attic.
IntroductionAre you finishing your attic? Here's how to save the most headroom when installing insulation.
- Fiberglass batt insulation
- Plastic air chutes
- Rigid foam sheet insulation
Knowing how to insulate an attic while leaving adequate clearance can be tricky. That’s because insulating it to the proper R-value can cause a dramatic loss of headroom if you limit yourself to fiberglass batts. To maximize headroom, while properly insulating your attic and ventilating the roof, use a combination of dense batt insulation, rigid foam sheeting and air chutes.
Most building codes require a specified minimum amount of headroom. It’s often tough to meet this requirement when insulating a finished attic, especially since most codes require insulation equal to R-38 or more. However, most inspectors I’ve spoken with will lower the insulation requirement if it means that the finished attic will have the required headroom. To get the most R-value with the least thickness, use batt insulation with higher R-value per inch in combination with rigid foam insulation. Rigid foam sheeting has an R-value ranging from R-5 to R-10 per inch of thickness. This means you can have a combined R-value ranging from R-23 to R-31 with only 5-1/2 inches of combined fiberglass and foam insulation.
Project step-by-step (2)
Why Your Roof Needs Air Chutes
- To effectively ventilate your roof, create a 1-inch airspace from the soffit to the ridge by installing a continuous air chute in each rafter bay.
- Note: Air chutes, when combined with soffit vents and a ridge vent, will help prevent problems with condensation and ice dams.
Air Chute Installation is Easy
- Note: Air chutes come in 4-foot lengths and 14-1/2 and 22-1/2 inch widths.
- Staple them directly to the roof decking for better insulating roof rafters.
- Note: Air chutes work only when the rafter spaces run from the soffit to the ridge. This method won’t work where rafter spaces stop short, such as in a valley, or in the corner of a hip roof.