How to Trim a Window with Metal Siding

Windows are an essential part of home design, they enhance a home’s style and boost your curb appeal. Much emphasis is placed on interior window finishes, however, it’s just as important to improve the look and function of your exterior windows. Trim is the best way to frame the exterior of your windows, and create an attractive finish.

Trim and siding function to protect a building from the elements, creating a stylish look at the same time. When it comes to residential sliding, it’s important to trim your windows properly, around the siding lap.

Metal siding is an alternative to cladding, used around the exterior of a home. It’s an attractive option for lots of people because it’s durable and easy to install. Usually, metal siding is made from steel or aluminum. If you’re looking to trim your windows with metal siding, read on to learn more.

Which type of trim?

If you’re trimming a window with the metal siding you’ll either use jamb trim or head trim. Both of these types have an inside primer and a color on the outside edge. The key difference is that if you choose jamb trim, you won’t be able to see the primer. For your vertical siding, jamb trim is probably your best bet. If you’re using horizontal panels, you won’t have the option of using jamb trim.

How to trim a window with metal siding?

To trim a window with metal siding there are several considerations that you’ll need to make. Firstly, you should find out the appropriate window trim codes. Building codes vary according to region. Before you start, you should learn the standard policies for your local area and climate.

Measure up your windows

First, take accurate measurements of your windows, once you have these you’ll be able to trim out the window perimeter. You’re going to need more trim than the measurement, approximately 2x the width of the trim (the face side).

Cut the trim

When you’re cutting the trim you should use a J-channel. Make a start using the side pieces. When it comes to marking reveals, a combination square is best. If you prefer, a compass can help you to scribe the markings. Alternatively, you can do the measuring by yourself and then mark the reveal parts.

Adjust the bottom trim

To fix the bottom trim you should square and clean the ends up. It’s incredibly important to ensure accuracy at this stage. Unless the trim is kept neat you’ll end up with unsightly windows!


When you’re installing the trim you’ll need to use caulk, start at the bottom and apply this along the perimeter of the window. Now you can push the bottom trim into the caulk, (this should help you to make a tight seal). Next, apply caulk to the side, and create a caulk bead that overlaps the bottom trim.

Steel siding

Once the steel siding is installed up to your window, you’ll need to measure the J-channel, (including the top, bottom, and from the sides). You might need to add some additional siding (so that it’s tight around the top of your window). From here, align the window frame and the siding, and nail it together at both sides. Once you’ve done this, you can add the J-channel for the top.

The top trim

Check your measurements to make sure the top trim is the right size. Add caulk just below where the trim is protruding, (this will prevent water from leaking in). The last thing you want are leaky windows!

General tips for installing window trim:

  • Ensure that you do not cut directly up to your pencil mark (most of the time, this will mean that your pieces are too long).
  • It’s a good idea to trim the largest windows first (you might be able to re-use any material that you cut improperly).
  • Take your trim by the thick side, and cut it against a miter saw (this can help you to avoid tearing the tapered edge).

To conclude 

With the help of this guide, it’s easy to trim your window with metal siding. Not only will you protect your property from the elements, but you’ll also improve the look of your home. The most important thing is taking accurate measurements, and ensuring that your workmanship is neat. If you’re not confident to complete the job by yourself, you may like to hire a professional.


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RPS Metal Roofing & Siding, Inc is a manufacturer and distributor of metal roofs. Located in Welaka, Florida, our company has state-of-the-art manufacturing equipment resulting in fine quality metal roofs for commercial, residential and agricultural use.

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