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Sealing off underneath siding... this one is a bit different...

Sealing off underneath siding... this one is a bit different...


Old 10-31-16, 10:37 AM
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Sealing off underneath siding... this one is a bit different...

So I'm putting in new construction windows and have to remove portions of the vinyl siding for the nailing flange, seems easy enough...

Well, whoever put this siding on my house never removed the original wood siding. Instead, they just put some foam over it and slapped the new stuff right over top of it.

Needless to say, this presents a bit of an issue with sealing around the area where I have to cut for the nailing flange, as it will now have wood exposed if water were to get back behind the siding around the windows. This means I either need to find a way to seal around this area, or I have to remove all my siding and redo the whole thing (I will probably do this later, but am not prepared to do so now). Luckily, the window I did yesterday is under an overhang, so water isn't an issue, but with all the other windows water will be a problem.

I was thinking of possibly using a spray type sealant for now, but wanted to know if anyone had a better idea.

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Old 10-31-16, 12:44 PM
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I dont think you understand how vinyl siding works... it wasnt really "sealed" before.

Its common to apply fanfold over existing siding prior to installing vinyl siding. Wont get into whether thats right or wrong as its immaterial at this point.

You will be removing some vinyl siding to install your windows. When you remove the windows, you will need to add plywood to the perimeter of the face of the opening that is equal to the thickness of your original siding. Then maybe put some housewrap over that, extending it out over your original siding. Put the window fin on top of that, tape it with flashing tape if you like. Then put the fanfold and siding back on. If the fanfold and siding together are too thick to fit inside your window j, your plywood perimeter would need to be thicker... equal to original siding plus fanfold thickness. Then install window, tape to fanfold, then install siding.
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