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I have a mid 90's Fleetwood with vertical (corrugated?) aluminum siding. I'm replacing a window and surrounding framing since it was rotten down to where the studs touched the bottom plate. I purchased a vinyl window from Lowe's it's listed as new construction and remodel. It has a nailing fin.

The window is about 1 inch wider and 2 inches taller than the stock window which means I'll be trimming the siding at the opening. My current plan is to pull enough siding panels off so that I can use the fins against the framing (I imagine I should run a bead of sealer there).

My question is how I should go about sealing/trimming out the window where it meets the siding. I'm considering having some J channel made for it but was unsure if this is the best way or is necessary.

Cut the aluminum the same size as the frame. I set our's up so that when I install the window it also overlaps the siding. Lots of sealer between the window and the frame, easier to wipe excess than add later.

Replace anything rotted now.

Greg

As to the rot since it got under the bottom plate and to the plywood subfloor (color me shocked I have plywood not OSB) my plan is to trim the bottom plate flush with the next studs past the rot which also happens to be about 1/2 inch from both edges of that sheet of plywood. Replace the whole sheet of subfloor, then replace the bottom plate there and the studs and window framing. Each end of my plate replacement will end up being a new stud attached to the stud left in place so it should marry my replacement section with the rest of the wall. Lucky for me the rim joist appears to be pressure treated and was in good shape.

I'm leaning towards doing a traditional stick built type header over the window instead of just the lone 2X4 flat across the top that was done at the factory. I figure it can't do anything but help structure wise and gives more surface to seal against. There is no sheeting under the siding so I'm going to take this opportunity to put some Tyvek in this section while the siding Is off as well to keep leaks running down and off the studs.

As to the window are you suggesting to use the nail flange and pretty much attach it from the outside like the old aluminum frame window was? I had considered this but my worry was piercing that many screws through the siding creating extra spots for more water intrusion again. And then how to hide the fin.

That was the way I did our's 10+ years ago, I have never had any leakage problems. Double top header (and bottom also) will always help with support.

You could slide the nail flange between the frame and aluminum, but I think it may turn into a lot of extra work. You may need to cut the corners and fold the edge back to get the window in, increasing the chance of leaks at the corner cuts.

Greg

The type of work you are doing in most areas requires a building permit. It is easy to get a permit but without one you will face a fine from the building inspector if you are reported.
Best to follow all rules to insure the work you are doing is to code.

Greg - I'm planning on pulling off the 2 full sheets of siding and two smaller pieces the manufacturer cut above and below the window entirely so shouldn't have to cut the ears. It seems that's one of the only benefits to this vertical siding is all the screws are exposed so easy on and off.

Actually had an idea today. One of my customers offered to make the J channel for me and I think I'll have them make it so the part under the siding extends at least long enough to go beyond the nail fins so it would be siding off, window wrap, put window in, fasten the J channel, then would slide the siding into the channel. Any pitfalls you notice in that thought process I may be overlooking?

Greg S- I'm out in an unincorporated area, all those inspections and such aren't an issue.

Apply butyl tape (Putty tape) to the back of the fins to seal, and caulk if you wish along the edges of the fins after install. I use 1x4 or 1x3 exterior trim to cover the fins; not necessary to seal the trim if you properly seal the fins, but it don't hurt. I've also ripped cedar fence boards lengthwise, used a clear stain and trimmed windows with that ; cheaper, and rustic looking.

Greg wrote:Cut the aluminum the same size as the frame. I set our's up so that when I install the window it also overlaps the siding. Lots of sealer between the window and the frame, easier to wipe excess than add later.

Replace anything rotted now.

Greg

After all my worrying I took another look at the window and went the way you suggested. Ended up using OSI Quad and ran it between framing and siding at the opening, around the perimeter of the opening on the siding, and a bead along the outer perimeter of the fin in line with the nail holes. Then used the low expansion door and window foam from the inside.

I was initially concerned the fins extended too far and would look funny but after another look they weren't as big as I remembered.

Ended up there was in fact rot (accompanied by some wood ants) in the rim joist right under the worst stud. Thought I had gotten lucky. I cut out a 4 foot section of the rim joist and replaced it using some blocking to sister it in.

Thanks for the advice. I'll probably have some after pictures when I get this nursery finished.