Part VIII: Air Seal your Top Plates, Drop Soffits, and Chases to Save Money

Series: Installing Blown-in InsulationPermalink

Save money by adding blown-in insulation to your attic.

A big culprit for air leakage in a home is through holes in the floor of the attic. These are often found in the top-plate, drop soffits, and chases and the volume of conditioned air that escapes through them is equivalent to leaving a window wide open the year round.

Air sealing these holes and gaps will greatly reduce the expensive flow of conditioned air from inside your home to outside. All it takes is the right tools, materials, and the patience to find and then cover and seal the offending areas.

Supplies and Tools Permalink

You will want the following available at hand:

  • spray foam insulation
  • silicone caulk and caulk gun
  • measuring tape
  • extruded rigid foam insulation
  • utility knife to score the rigid boards of insulation

First, the Top Plate Permalink

The top plate is part of the wooden frame of your home and it’s where the drywall meets the walls. It’s of interest to us because it’s a source of significant air leakage in a house. There are often dozens of holes within it and gaps alongside of it.

You’ll find the offending areas of leakage by inspecting the entire length of any interior or exterior wall. It helps to have a good spatial sense of the layout of the rooms below the attic. You may find yourself crawling around for hours to finish this task, but it’s worth the effort.

If you have existing insulation you’ll want to temporarily remove it to expose the top plate. A tell-tale sign of an air leak is dirty insulation due to the fact that dusty air flows right through it. Gross, right?

Use silicone caulk to stop up smaller gaps and spray foam insulation to fill up larger gaps.

Other Likely Sources of Gaps and Small Holes Permalink

  • Recessed lighting fixtures, such as can lights
  • Kitchen range vents and bathroom exhaust fans
  • Where the drywall meets the top-plate
  • Holes for wiring and cables
  • Plumbing vent pipes

Cover and Seal Chases and Drop Soffits Permalink

Your home probably has several very big holes in the attic floor that are above soffits, utility chases, and dropped ceilings. These should be covered with drywall, plywood, or rigid extruded foam insulation.

My house had several drop soffits to cover: one above the front door and two in the master bathroom for the shower and lighting for the double sinks. For each location a very old piece of cardboard was ostensibly covering the hole, so the rigid insulation was a big improvement.

Again, it’s helpful to have a good spatial sense of where these gaps may be found in relation to your home’s floor layout. It’s also a good idea to do any electrical work before sealing these up. I had to remove a section of the rigid insulation when I decided to swap out the light fixture above the shower. Oops.

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