How to Install Window Trim

You don’t even need a tape measure!

Most trim carpenters don't even use a tape to trim windows. It's all done by eye, with a sharp pencil, a miter saw and an 18-gauge nailer. Here's how they do it.

By the DIY experts of The Family Handyman Magazine

Step 1: Mark the length

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Step 2: Get the spacing right

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Step 3: Check the fit, then cut to length

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Step 4: Glue and pin for a solid miter

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Step 5: Trim the other side

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Step 6: Fit the first bottom miter

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Step 7: Fit the opposite miter

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Step 8: Scribe for length

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Dealing with problem drywall

If you have drywall that's "proud" (sticking out past the jamb) or recessed behind the jamb, you have to deal with it before trimming or the trim won't lie flat. Here's what to do:

Avoiding Trim-induced Headaches

Here are a few tips to help you avoid a few trim hassles:

  • Whenever you can, cut with the thick side of the trim against the miter saw fence. You’ll be less likely to tear out the narrow tapered edge that way.
  • Cutting right up to the pencil mark almost always leaves pieces too long, so remove the pencil line with the blade. You’ll most likely still have to shave off more.
  • Sneak up on cuts by starting long and dipping the saw blade into the wood while you work your way to the cutoff mark.
  • Trim out the biggest windows first. That way, you can reuse miscuts for the smaller windows and not run out of material.
  • When nailing 3/4-in.-thick trim, use 15-gauge 2-1/2-in. nails for the framing and 18-gauge 2-in. brads for nailing to the jamb.
  • To prevent splitting, avoid nailing closer than 2 in. from the ends.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Hammer
  • Miter saw
  • Air compressor
  • Air hose
  • Brad nail gun
  • Caulk gun
  • Safety glasses
  • Utility knife
  • Wood glue

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • Trim
  • Wood shims
  • Extra pencils