Replacing New Construction Windows

Old 05-03-21, 12:22 PM
johnam's Avatar
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Replacing New Construction Windows

A friend of mine has vinyl, new construction, double hung windows with a built-in J Channel. He now wants to replace them with double hung replacement windows. Any suggestions on how to remove the old windows and install the new? Thanks in advance.

Old 05-03-21, 03:23 PM
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You don't replace new construction vinyl windows with replacement windows that have no fin. The nailing fin is what flashes the opening and prevents water from leaking into the rough opening.

You would replace it with another new construction vinyl window that is exactly the same size. To cut the old window out you would take a short 2" wide board put it against the outside perimeter of the window and trace a line on the siding. Then cut on that line, exposing the nailing fin. Then you would take out the old window and put in the new window in. You would tape it to the WRB, and then apply a new trim around the opening to cover that 2" gap.

The details may vary depending on what kind of siding it is.

But putting a replacement window (with no fin) into a rough opening is a sure way to create a leak that will rot the framing in no time.
Old 05-03-21, 04:23 PM
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I remove the siding instead of cutting it. Short pieces get removed completely but long strips I only free up the end around the window. Then you can remove the old window and put in a new, new construction window. If you are lucky then the siding is the right size to go back into the channel of the new window.

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