New Window, Old Wall 2: How to Surgically Remove An Old Window Without Destroying the Air Barrier

February 7, 2022

Replacing a 30-Year old replacement window in a 100-year-old wall that was upgraded with exterior foam insulation 25 Years ago (part 2 of 4)

"Shove a flat bar in and just hammer on something..."

The first step of replacing the window is removing the exterior trim. Sometimes it pops right off, but when the camera is rolling...

"Not all trim is equal. You know, some of it pops right off for you...

So David breaks out his cat’s paw.

Other ones you have to ask really  nice…

Removing the exterior trim begins to reveal the construction layers below

Behind the casing is ¾-inch plywood, which is unusual. 

The ¾ inch plywood planes out with the 1x3 wooden strapping used to create a rainscreen and also for fastening the siding into.

Removing the exterior extension jambs reveals the 2-inches of Styrofoam blanketing the house.

David cuts back the plywood to the edge of the siding, and then he cuts back the Styrofoam and saves the pieces so he can put them back in later.

Break the foam by prying it sideways

"One key thing that I do here is because of this foam.I know that there's house wrap on the other side of it and I want to take care of it, but I've gotta cut my foam back.

That's difficult to do, but I'll set my blade a little short and then I'll pop the foam off."

Keep the blade about a half-inch short of the foam depth—an inch and a half in this case—and slice around where you need to cut.

The foam now will break easily by prying it sideways.

"Just pop that in and break the last half inch or so. It doesn't always break nice, but then it;s like a puzzle piece when you're putting it back."

With the foam cut back and the Tyvek intact, the original window jamb is exposed. 

"So all of this time I've been talking care of the house wrap and I'm just gonna cut it apart now.

I cared about the house wrap on that connection, because I didn't want to cut a line there. I know I'm going to flash into it, but now I have to open the weight pockets."

The Tyvek had been taped to that jamb, and now it needs to be cut back — so that the jamb can be removed.

As long as an inch or so of Tyvek sticks past the foam, he can tie the new window into the existing Tyvek. 

"Exposing now our original window."

So David cuts around the perimeter.

After removing the screws holding the replacement window in place, he begins prying it out of the hole.

Now, the old window frame is visible, as are the layers that need to be re-flashed into the window/wall interface.

Again, there is a weight pocket with some yellow fiberglass stuffed in the existing Tyvek, which will be integrated into the new window flashing. You can see the styrofoam and plywood backing behind the siding.

Remove the original window frame

Inside, he removes the trim so that he can remove the old window jamb.

It turns out some water had been leaking in. Sloping the sill forced excess water to run out and away. 

We know it worked because there is no water damage in this window opening.

With the old jambs and sill removed, he cleans up the opening, cutting back the old pan flashing and prying off the old canned foam that sealed the inside perimeter.

Now that the old window is out and the opening is cleaned up, it’s time to put the new window in the wall — after framing the opening to the correct size.

We’ll look at that process in the next installment.

 

—David Joyce is a high-performance builder and remodeler in Central Massachusetts. He cut his high-performance teeth doing deep energy retrofits for Building Science Corporation.

 


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