Easy Guide on Trimming Vinyl Windows with PICTURES!

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Trimming vinyl windows can be done by:

  • Ripping some 1×4 #1 pine to 1”
  • Stepped off about ¼” for the extension reveal if the vinyl frame has a serious radius on its edges
  • Countersink 1-5/8 trim head screws deep into the jamb extensions. You could use hot glue with it if you like.
  • Use a power planer to get the jambs even to the undulating drywall.
  • Attach the trim as usual with a 3/16” reveal off the jamb extension.


Of course, some solutions will depend on the size, type and/or brand of window.

Here are other ways to trim vinyl windows by yourself:

Method One

  • Pre-assemble the whole window trim assembly.
  • Then attach the return, rip to the proper depth, to the inside edge of the casing.
  • Next, run a bead of adhesive caulk before installing. I use a bead of adhesive caulk (White Lightning) along the back edge of the jam extension (the edge that will contact the window) and place shims at 2 or 3 locations on the jack stud.
  • Once that is done, I place the whole unit in place and then begin to nail it in place. The idea of drywalls screws is great! They’re much easier to adjust than shims!
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Trimming Vinyl Windows

Method Two

  • You should rip your 5/8” jamb extensions long.
  • Then glue and nail the casing (also cut long) to these jamb extensions
  • That way, you end up with a built-up casing/jamb.
  • Now, cut this built up casing/jamb to fit, use a sacrificial 5/8″ strip against the fense to keep the built-up jamb/case flat when you cut the miters.
  • Drive some drywall screws into the trimmer studs, header and sill before you begin the process of nailing the jamb/case to the wall.
  • Then adjust these screws to provide backing for the 5/8 jamb extensions.
  • Now, put a gob of CSR adhesive on each screw head, and nail everything in place.
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Method Three

  • Pre-assemble the jamb frame. If the window features a stool (sill), you should include this with pre-assembly.
  • Now, hold the jamb frame assembly in place and mark for whatever scribes and cut to fit.
  • Next, run a bead of caulk on the vinyl so you’re able to keep to the side of your pencil margins that way.
  • Now, place a few spots of hot melt along all edges and then position it in place.
  • Your frame profile, and vinyl will determine the level at which you’ll drill pilot holes for screws through the edge (into the vinyl). A Jamb depth too wide for screws won’t allow the screws settle in. Instead, try to shim to the framing and nail through the sides. Remember to insulate the perimeter before you case it out.
  • For a stain grade wood extension, you should back cut (bevel) the edge contacting the vinyl to get the joint tight. The edge of the jamb will help receive the casing as it gets a bevel too.
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window trim interior

Method Four

  • Make the extension jamb into a box
  • Then, center it over the window with shims
  • Shoot nails into the studs (at an angle with 5/8” jambs)
  • For windows with an accessory grove around the edge, You can cut the outside of the extension jambs to the measurement build the box and then put a skinny flatbar in the grove and shoot into the studs.
  • That way there is no need to caulk or nail to the vinyl in case it does move.
  • if you do paint the extension jambs color matching to the vinyl is a key to a good looking trim job

Author: Howard S. Baldwin

My name is Howard S. Baldwin. I am a work-at-home dad to three lovely girls, Jane + Hannah + Beauty. I have been blogging for the last 3 years. I worked for other Home and Lifetsyle blogs, did hundreds of product reviews and buyers’ guides. Prior to that, I was a staff accountant at a big accounting firm. Needless to say, researching and numbers are my passion. My goal is to be an informative source for any topic that relates to DIY life and homemaking.

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