Installing a Flanged Window to Replace an Old One

November 24, 2015

If you need to replace windows that are old, inefficient, leaky, or painted shut, maybe even rotted, this video’s for you


The start to finish steps to replace an entire window in your house (OFFICIAL TRANSCRIPT)

Remove the trim gently

The first step in removing those old windows is to score the trim on the inside and the out and use a small prybar to gently remove that. We want to try to use that trim later. 


Remove the window with a Sawzall

The window itself is going to come out pretty easily, you’re going to use a sawmill to cut down the jambs of that window, you’re going to cut those nails and the window will pop right off. If you have a flanged window, again, use that Sawzall, maybe even with a metal-cutting blade, and the window will come right out.


Install pan flashing

We’re going to protect the sill of this window with one of my favorite products, DuPont FlexWrap. Before we do this, though, we always want to slope the sill to get some positive drainage to the outside. Then when the FlexWrap goes in, we’re making a bathtub for that window to sit in. 

We're going to capture any water that might get in from that window and make sure it goes to the outside of the building and not inside where it could rot or mold on the inside of the framing.

This 1950s house when it was built didn’t have any insulation, and when the windows leaked into the wall cavity they could dry. But with today’s energy codes and the insulation and the air tightness we are doing on our houses, we have very little capacity for our homes to leak and not have mold or rot problems in the future. 


Put the window in the hole

Now that we’re got that sill in place on this opening, we’re going to pop in the new window. We’re using a flanged window in this case, which is similar to a new-construction window. If we didn’t have the room—let’s say if we were in a brick situation on the outside—we could fold those flanges in and screw through the jamb.

  • It is very important to pay attention to plumb and level, and square on these new windows. Make sure you check the operation as you’re installing them—very important,
  • On the outside of the window, we’re using a three-sided bead of caulk—basically an upside-down U—we’re not caulking the bottom side of this window so that if any water were to get in, it can find its way out. 
  • After the window is in place and nailed off, we’re going to go over that with another Tyvek product, called DuPont StraightFlash. If I didn’t have a one-story house like this, I’d make sure to add a metal head flashing. 

As you can see, its really not a difficult process, but you really need to be a good craftsman and make sure that you’re thinking about the waterproofing details.


One last thing:

In my 20 years of building and remodeling, 99 percent of the window leak issues I’ve seen are totally install errors. Pay attention to the waterproofing details that we talked about. 


—Matt Risinger is a custom builder, remodeler, and YouTuber in Austin Texas