Finishing an Attic

Insulate your finished attic properly

Are you finishing your attic? First you'll need to insulate the ceiling. Here's how to do the job properly.

By the DIY experts of The Family Handyman Magazine

Choose your insulation

If you're finishing your attic, insulating it to the proper R-value can cause a dramatic loss of headroom if you limit yourself to fiberglass batts. To meet all three goals—insulating your finished attic, ventilating the roof and maximizing headroom—use a combination of dense batt insulation, rigid foam sheeting and air chutes.

Most codes require a specified minimum amount of headroom, and it's 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 space won't 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 in. of combined fiberglass and foam insulation.

Install air chutes before installing insulation

To effectively ventilate your roof, create a 1-in. airspace from the soffit to the ridge by installing a continuous air chute in each rafter bay. To install the air chutes, staple them directly to the roof decking.

Air chutes, when combined with soffit vents and a ridge vent, will help prevent problems with condensation and ice dams. They come in 4-ft. lengths and 14-1/2 and 22-1/2 in. widths. They're readily available at home centers and they're cheap.

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.

Video: Working With Mineral Wool Insulation

Additional Information

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Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • Fiberglass batt insulation
  • Plastic air chutes
  • Rigid foam sheet insulation

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