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Cutting siding to install new construction windows without cutting through tyvek

Jeremy Swanson's Avatar

Join Date: Jul 2015
Posts: 2

07-16-15, 05:17 PM   #1  
Cutting siding to install new construction windows without cutting through tyvek

I'm in the process of cutting the cedar beveled siding around my old window so that I can remove and replace it with a new construction window. I've screwed a guide to the siding and made the cut with a circular saw, but I haven't found a way to not cut the Tyvek in the process.

I'd really like to keep it intact to get a good seal. Is it possible to do this?

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XSleeper's Avatar
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07-16-15, 09:15 PM   #2  
When you say you screwed a guide onto the siding, you mean the saw is sliding on top of the guide, right? Not on top of the individual clapboards? A guide should have a board that lays on top of the siding (this is what the saw slides on and you set the depth of the saw to the thickness of the siding plus the thickness of the guide), and if you like, a stop on the far side of the saw that keeps the saw running straight.

Assuming that is the kind of guide you mean, you would need to take those screws out, remove any nails, and pry the siding out enough so that you can slip a shim behind the siding. As long as the siding is shimmed out 1/8" or 1/4" you should be able to set the saw depth so that it doesn't cut it. If it does cut it, it's not the end of the world. You can slip a thin strip of tyvek behind the siding. IMO, easiest way is to cut a strip, say 8" wide. Fold it in half so that it's 4" wide. Place it next to the siding. Then put a 6" putty knife between the fold and use the putty knife to shove it behind the siding. After the window is installed, use flashing tape to cover what is exposed. Someday when the siding gets replaced they can address the rest then.

Probably a simpler method would be to set the saw until it almost cuts through the siding but not quite, then snap the siding off. Clean up the cut with a sharp utility knife, protecting the tyvek of course, with a wide putty knife or similar.

chandler's Avatar
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07-17-15, 03:20 AM   #3  
Newer methodology does not wrap Tyvek in the window frame anyway. It is cut about 1" short of your window flange. The flange is caulked and Window tape is applied over the existing Tyvek, touching the OSB and onto the window flange. So cutting the Tyvek isn't a game ender at all.

Jeremy Swanson's Avatar

Join Date: Jul 2015
Posts: 2

07-23-15, 08:30 AM   #4  
Thanks for the help!

I've done 4 windows now and finally got a system down. I've been doing 2 cuts. The first is just passed the nailing fin on the old window. The wrap gets cut a little, but it doesn't matter. Once the old window is removed, wedges are slid under the siding and the second cut is made. Works great!

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