Keith wrote:
If you read the Certainteed website install instructions, you will see
that installation into a rough opening is one of the options....in fact
when I ordered the windows, they asked for the rough opening size....

Keith, I don't know what to tell you, but those instructions are
entirely ****ed up. There's no mention of any flashing whatsoever -
they want you to caulk the window to the wood framing! That is simply
insane. Your framing will rot instead of the window frame. Rule one
in weatherproofing - don't rely on caulk.

I thought you were missing something, but nope, the instructions do say
to do exactly what you have done. I've never seen such lame
instructions from such a quality company.

You are now in for a rather large learning experience. Having been in
the business for a while, I would have ignored those instructions and
either inserted the windows into the existing window frame after
pulling the sashes and stops, or have allowed for quite a bit of
flashing work.

You are now firmly in damage control territory. I don't see any simple
options. I would not be happy about doing it because it is so much
more work and money, but I'd probably cut back the siding to allow for
an exterior casing of 1x4 Azek, then flash around the window with a
metal top (required by code even though it is frequently omitted) and
self-adhesive 4" or 6" Bituthene type flashing. After that's done I'd
probably install the siding channel to the Azek casing and install
those pieces as an assembly (you won't be able to nail standard
J-channel as the leg will be behind the existing siding).

I'd contact Certainteed's tech department and ask them to fax you some
detail sketches of how they suggest you do it. They might have a way
that is easier than mine, but I can't see it from here.

R