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Video Series: Exterior Insulation Retrofit — How to Flash Windows Over Rigid Foam

This video is only available to GBA prime members

Finish off your exterior-insulation project right
by managing water at all window and door openings

with David Joyce


David Joyce: Now that we have the window opening all prepped and ready to go, the first thing we do is wrap the opening with Ice & Water Shield.


Insulation Retrofit Complete

1. Introduction (free)

2. Strip Siding and Roofing (free)

3. Install Housewrap and Roof Underlayment

4. Install Rigid-Foam Over the Walls

5. Install Rigid-Foam on the Roof

6. Flash Windows Over Rigid Foam

7. Choosing Details and Materials (free)


Remodel Project: Deep Energy Retrofit

Podcast: What Is a Deep Energy Retrofit?

The History of the Chainsaw Retrofit

Roofing and Siding

Jobs Are Energy-Retrofit Opportunities

Narrator: The first part of the window install is pan flashing. In this case, Dave is using peel-and-stick membrane. The existing window stool acts as a back dam, and the sill already slopes toward the outside. Corners are the trickiest spot. It’s important to fit the flashing tape right into the corners so that the window frame won’t puncture them later. Stretch the flashing past the corner so that it covers the critical spot in the bottom corner of the sill.

David Joyce: We want to make it to that wood framing and to the foil face. I put an inch or two onto that foil face so that I can get the rest definitely back to the wood. I’ve just got to cut straight across. I don’t try to be right on the edge like I would for most windows. I really want to stretch the Ice & Water Shield.

Narrator: Realistically, this is probably fine. But to be sure, Dave adds a butterfly patch at the bottom corners. The side pieces overlap the bottom piece, and the top…


  1. lowelllodesign | | #1

    These videos can be more
    These videos can be more useful than the articles. I just finally discovered them.

    Architect from Toronto

  2. AKHandyman | | #2

    Where can you get those metal
    Where can you get those metal washers for getting the foam in place? Does anyone know the manufacturer?

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