Part X: Avert Fiberglass Disaster with an Attic Insulation Dam

Series: Installing Blown-in InsulationPermalink

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

When adding blown-in insulation to an attic it’s recommended to have a barrier to prevent insulation from accumulating above the attic hatch. Without this insulation dam the next person who enters the attic will surely be covered by inches, if not feet, of fiberglass.

Here’s how I built mine from plywood to serve as inspiration for your own building efforts.

I Don’t Give a Dam Permalink

The existing blown-in insulation was highly compressed (by me, mostly) to a depth of 5.5”, which is the actual height of a 2×6 stud. Between the ceiling joists there were formerly a couple of pieces of cardboard holding back the insulation that I replaced with a stud cut-to-fit.

A Short Barrier Permalink

Initially I cut two 2×6 studs to lengths of 14.5” inches, which is the distance between ceiling joists set 16” on center. This kept the old insulation from falling through the entrance to the attic, while also allowing me easy passage.

A Taller Barrier Permalink

I built my dam with sheets of 2’x4’ plywood that I secured together with wood screws. I also added a bead of caulk along the inside seams, which was probably unnecessary, but I figured why not.

Obviously your dimensions differ from mine, but take care to exceed the desired height of your insulation. In my case the plywood is 24” tall, which is in addition to the 5.5” height of the ceiling joists. My goal was to increase the blown-in insulation by a depth of 20”, so the height of my dam leaves a small margin for drifts.

I built the taller insulation dam when I was near the end of my prep work. It was a bit of an acrobatic act to climb out of it, so I was glad that I delayed the installation.

View from Above Permalink

As you can see I added a lot of insulation to my attic. I’m pleased with the volume that I added, but as you can see I failed to distribute it evenly. It’s possible that some of the insulation may drift with the wind. I’m hopeful that will level out the peaks and valleys, although it may also breach my dam and accumulate above the attic hatch. We shall see!

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