Except for its additional weight and larger size, a garden window can be as easy to install as a regular window — just be sure to have a few friends on hand to help with lifting. We worked with Simonton Windows on this project, but the basic installation steps are similar with any brand. However, it’s essential that you follow any instructions supplied by the window manufacturer. The International Residential Code (R613.1) requires windows to be “installed and flashed according to manufacturers’ instructions,” so as long as you meet the specific requirements for your window, you’ll be well on your way not only to a successful installation, but to creating a space that’s filled with sunlight and greenery.
Before purchasing a window, first remove the interior trim and measure the width and height of not only the rough opening but also the casing of your current window. You’ll need to know these dimensions when placing your order.
Garden Window Installation
Begin the process by taping over the panes of the old window to help secure the glass in case it breaks. Remove the window’s casing trim and cut through any mounting screws or jamb nails — we used a multitool outfitted with a metal-cutting blade.
Remove as many of the window’s components as possible to reduce its overall weight; then carefully pull the window from the framed opening.
Asphalt-based flashing tape can damage certain types of vinyl, so check the window’s specs. Butyl tape is easier to work with, and although it initially isn’t as tacky, its adhesive strength increases over time.
Apply window flashing tape to the sill, running the tape about 12 in. up each side. Use a putty knife or a small pry bar to tuck the flashing tape behind the siding, being careful not to disturb the underlying house wrap (if present).
Have a friend help you lift the new window into the opening. From inside, have a third person drill a countersunk hole (for the supplied mounting screws) on each side of the window 6 in. from the top. Make sure the unit is flush; then drive the mounting screws into the framing to secure the window.
Check that the window is both plumb and level, measure the diagonals to make sure that the unit is square, and shim where necessary. Drill two more countersunk holes in each side and three holes in both the top and bottom; then drive the remaining mounting screws into the framing.
To conceal the screwheads, first apply a small amount of glue to each of the 12 screw holes; then tap the supplied matching wood plugs into the holes.
If your window has mounting flanges, install flashing tape over the flanges and beyond both the top and bottom edges; then apply tape along the top, allowing it to run past the side tape by a couple of inches. Our unit did not have flanges, so instead we folded the tape 90 degrees and ran it along the seams where the window case met the revealed underlayment.
Cut the new window trim to length; then nail it in place. To minimize maintenance and better match the finish of the new vinyl window, we opted for PVC trim boards that are impervious to rot.
From inside, spray low-expansion foam into any voids to completely seal the window. After you install the interior trim, all that’s left is to stain or paint the woodwork and enjoy the natural light your garden window provides.