DIY Network

How to Seal an Attic Duct

Securing existing ductwork in the attic will help with eliminating dust in a house. Learn how to repair a leaking duct and seal it for good with these step-by-step instructions.

More in Remodeling

  • Time

    2 hours

  • Price Range

    $1 - $50

  • Difficulty



Step 1: Secure the Duct and Flange

Snip off the old nylon ties that are holding the duct down over the existing flange.

Slide the inner duct down over the flange. To secure it in place use heavy duty aluminum tape. Use a plastic squeegee to strengthen the seal.

Wrap new nylon ties to hold the duct in place and tighten with a tension tool to ensure a snug fit. Snip off any excess.

Step 2: Make a Permanent Seal

Roll the insulation back down, followed by the outer cover.

Add a second nylon duct strap to hold these top layers in place.

To make the seal permanent, spread a mastic sealant over the entire connection joint. Apply liberally to ensure a good seal. Leave mastic to set and dry.