Installing new windows in existing house
I’m looking to install a new vinyl window in an existing house with OSB sheathing and Hardiboard siding. There is no existing rough opening, I would be making that as part of the project. All of the existing windows were installed during initial construction with their nailing fins after the house was wrapped but before siding was installed. The siding was then butted right up to the vinyl window.
However, since I’m doing this with the siding already in place it’s not clear to me how I should properly seal a new window? I’ve read you can just buy the same windows but cut off the nailing fins and secure the window from the inside to the rough opening. But then how do I handle sealing the 1/2″ or so gap around the window and the rough opening of the exterior siding? The only thing I can think to do would be to cut back the siding a few inches around the window to allow me to do a proper window membrane and then trim it out with siding trim board.
But if I’m going through all that hassle why not just keep the nailing fins on as that seems like a much more watertight install anyway. How/why are people installing these windows by cutting off the nailing fins?
Thanks!
Replies
To properly seal a new vinyl window in an existing house with Hardiboard siding, consider keeping the nailing fins intact for a more watertight installation. If opting to remove the fins, ensure the rough opening is properly flashed with window membrane and trim out with siding trim board to prevent water infiltration. Cutting back the siding a few inches around the window allows for better sealing and a secure fit. Proper installation techniques are essential to prevent moisture damage and maintain the integrity of your home's exterior.
You buy replacement windows. They are custom made to fit inside your existing window frame with an exterior fin/casing that gets caulked to your existing exterior finish. Any home improvement store can help you. Don't be frightened by the idea of "custom". It's an economical solution. Very little labor involved.
I don't have an existing window frame. These will be completely new windows placed in newly framed openings in my wall. New headers and everything.
Since I originally created this thread I think I landed one getting new construction windows with the nailing fins and cutting back my siding a few extra inches to allow room for the fins and to do proper tape flashing. Then I'll trim out the window with standard Hardiboard trim material. Unless anyone has an alternative suggestion.
Yes, keep the nail fins! I've done this on a brick home and it worked great. The Pella rep told me I could cut off the bottom fin, which I did. You can fur in the RO a bit if needed...just depends on the window dimension vs. the RO and how much trim you want to add.
The nail fins really ensure a flush, tight installation. I use Simpson StrongTie #10 1.5" hex screws to secure the fin - these work great. With some good flashing tape and OSI Quad Max caulk (to handle the large thermal expansion/contraction of the PVC trim,) your windows cannot possibly ever leak.
your plan sounds good. Since this is a new installation and you're cutting the wall and siding, cutting back the siding to use the nailing flange is the correct way to do this job. Try to keep the house wrap when you cut the siding so you can use it in the installation.
good luck
When installing a new window in an existing house with siding already in place, it's important to seal the gap properly. One approach is to buy windows without nailing fins and secure them from the inside, but this leaves you with the challenge of sealing the gap around the window and the siding. One solution is to cut back the siding a few inches to apply a window membrane and then trim it out with siding trim board.
However, if you prefer a more watertight installation, keeping the nailing fins on might be a better choice. Ultimately, it depends on your preference and how much hassle you're willing to deal with!
Thanks everyone. My plan is to use the nailing fins, cut back the siding a few inches past the rough opening so I can properly flash and then trim out with matching Hardie trim that was used elsewhere on the house. I’ve got the windows on order and they should be here in about a month. I’ll report back here when I’m done - I always hate it when threads like this are left hanging!
I just did this, but the other windows on the home do not have trim, the siding is just butted up to the window. So, since I decided to keep the fins I have to take off a lot of Hardie siding, it's a real pain.
Sounds just like my house. Oof, sorry the siding was such a pain. What saw did you used to cut the siding? From what I've read a diamond blade on my angle grinder makes quick work of it. I'd of course be wearing a respirator and glasses.
Yeah, cutting back the siding a bit to properly seal and trim the new window sounds like the way to go. It might seem like extra work, but it'll give you a tighter seal in the long run.
Hey everyone, wanted to follow up on this, maybe it'll help someone down the road. I attached some pics below. Just finished the window install this past weekend. Overall went well, but the fact they these are 20' off the ground really complicated things. I wound up drilling 4 holes in the corners of each window rough opening to locate them on the outside. Then used an angle grinder with a diamond blade to cut the siding back 3" from the rough opening. My trim boards were 3.5" so this gave me some buffer to rip them to exact width later. I used a wedge to help hold the siding away from the sheathing so I wouldn't damage the house wrap with the diamond blade. Once all the siding was removed it was a standard window install process you can find detailed elsewhere (sill flashing, sealing around the window flange, flashing tape around the top and sides, drip cap up top, etc.) Once all the windows were installed, I took measurements and cut/ripped each trim board to fit. I also milled a 1 1/2"x1/8" rabbet on the back of the boards so they would sit flat when laid over the window nailing flange. If you don't, they'll sit at an angle and look a little sloppy.
This worked well, but it was definitely a hassle working up so high and trying to cut the HardiBoard. Ideally, you'll have some scaffolding set up, I just used an extension ladder and had to keep moving it around. Only other way I can see to do this job would be to pull all the siding off the area, back to the closest joint, install the windows and reinstall the siding butted right up to the window vinyl. That might have been overall less work as I could do most of the Hardie cutting on the ground and skipped all the hassle/expense of the trim. But that would have been a lot harder to do with just a ladder.