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The ptc@home Continuous Exterior Insulation Detail

The process for installing continuous exterior insulation over 1x6 T&G sheathing with existing windows
March 28, 2023

In the video series, ptc@home, Editor Dan Morrison (me) replaces the siding on his 1950s cape-style house. Because replacing the siding is a once-in-a-generation opportunity to improve the insulation in an old house SERIOUSLY, Dan (I) also added two inches of continuous exterior insulation—Styrofoam, in this case—to the outside of the walls.

I added Tyvek, sealed at window and door openings, as part of the air barrier system before adding two layers of Styrofoam, over which I added new TruExterior siding.

The continuous insulation retrofit process

  • I removed the clapboard siding to reveal 1x6 T&G sheathing. The windows had been replaced from the inside and the original 1957 brick molding was intact.
  • Removing it revealed a lucky break. 1x3 sub casing circumscribed the window and acted as the window stops for the tilt-in replacement windows installed recently.
  • They also provide a continuous surface for flashing tape to seal off that window opening.
  • I cut off the sill flush with the wall sheathing and sealed the sides and top with DuPont flashing tape.
  • At the bottom, I installed a wide strip of [Flexi flash] tight to the replacement window and leaving the release sheet on the outer section.
  • Now I installed Tyvek over the wall, cutting out at the windows.
  • Sealing the edges to the flashing tape that seals the 1x3s around the opening.
  • In this assembly, the Tyvek is really mostly for air control. The outer face of the Styrofoam will shed any water that gets behind the siding.
  • Now the foam goes on.
  • And the sill flashing tape can be folded down and stuck to the fact of the styrofoam.
  • At the bottom of the wall is site-bent coil stock to keep the bugs out. The whole thing is covered with a rainscreen product called DrainVent.
  • Finally, I added new exterior trim and siding from TrueExterior.

The result has been about a 40% drop in energy use and a lot fewer free weekends.

More videos about continuous exterior insulation:

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