Gap Width Between Vinyl Window Frames and Trim
I have a question about the suitable width of expansion joint between window frame and trim.
I’m renovating my sunroom back wall, replacing what was 6 doors with 1 door and 5 windows. I have repaired wood rot here many times over the last 26 years, but am now going with vinyl windows and fiber cement siding. I am a rookie at using these kinds of non-wood construction materials., so I could use your help, please. The windows are 31.5 x 71.5 picture type, made by Jeld-Wen. Their advice on this is, “Maintain a gap of 1/4″-3/8″ between window frame and final exterior wall surface (siding, stucco, etc.).” This is from their literature. They have no tech support.
On my neighborhood walks, I see a lot of similar construction materials being used, and the frame/trim gaps are way smaller than what Jeld-Wen specifies. I have read that vinyl expands and contracts a fair bit, but it looks like the manufacturer’s spec could be overstated to ward off warranty claims.
Before becoming aware of this spec, I started my layout on this project with 1/8″ gaps, and because I’m using a board and batten siding style, it does matter. My plan was to use standard 5 1/2 ” wide fiber cement trim. If I need to increase all the gaps another 1/8″, I could switch to PVC trim and rip the boards down 1/4″. This would be more expensive and would not look as good, but it would work.
I did see a 3 year old video on here – How To Install Exterior Window Trim, and the windows were vinyl. The advice given was to provide 1/16″ gaps, measured from the “nibs, ” or tops of the welded corners, which, in effect, would be about 1/8″ from the frames.
I sure don’t want to screw up my project, so I’d appreciate any input on whether or not it’s safe to use a smaller gap than Jen-Weld specifies.
This joint is considered a "beauty joint", meaning its there for overall esthetics. It will assist with shedding bulk water, but not a concern if it cracks or fails. 1/8" -1/4" should be sufficient, but double check with the siding manufacturer and pick a middle ground. I would pay attention to the orientation of the house and if it will be shaded or in direct sunlight. More sun = more gap for expansion and contraction.
I'm in San Antonio, and the wall is south facing, so it gets tons of sun. Whether that really warrants a 1/4-3/8 inch gap is what I'd like to know. Fiber cement does not move much, from what I've read. The contractors around here are installing Hardie siding and trim around vinyl windows and are leaving 1/8 inch gaps or less between the window frames and trim. I don't know if they know from experience that that's all that's required or not.
Hardie defers to the window manufacturer's requirements on the gap size, so if Jeldwen is stating to hold off 1/4-3/8" from the window, then you have your answer. I would choose 1/4". I've attached a snippet from Hardie's installation instructions for trim and highlighted the note I mention above.
Thanks for your help!