How to Install a Fiberglass Window

Lead Image
  • 4-6 hours
  • Advanced
  • 100-150
What You'll Need
Broad chisel
Reciprocating saw
Pry bar
Construction sealant
Fiberglass window
Spirit level
Wood spacers/shims
Finishing nails
Spray foam insulation
Tape measure
Protective eye goggles

Installing a fiberglass window is costly at the start, when compared to having vinyl or aluminum windows, but the benefits outweigh the cost. Fiberglass windows are the smart investment for your home because of their weather resistance, insulating properties, and energy-saving capabilities, thus low heating and cooling costs—not to mention their limitless color options. It also helps with keeping your home clean and free of pests. However, you must make sure that you install it well, to get good results.

Step 1 - Prepare

Before installing fiberglass windows, you need to take the measurements of the window’s rough opening. It must be of the window you are going to replace. Although windows may look to be the same size, they can often differ by an inch or two. To get the most accurate measurements for your fiberglass window, remove the inner trim so the window frame plus the opening can be measured. Using a tape measure, take the measurements of the window’s height and width.

Step 2 - Pre-Installation

To be able to uninstall the old window, pry the trim off of both the inner and outer sides of the window, with the help of the chisel and pry bar. Do not forget to wear a pair of protective eye goggles. The pry bar will help you in the removal of the trim board from the wall, while the claw will be used to free the frame of any nails. Use a reciprocating saw to cut through the framing nails holding the old window, and lift it out. Make sure that the rough opening where the window was is clean by removing all protruding nails and old sealant.

Step 3 - Install

Put a good amount of sealant on the windowsill bottom, then put the new fiberglass window into place. Make sure that the window is centrally placed by the help of the spirit level and the wood spacers/ shims.

It is these shims that help to keep the window in position as they fill up any spaces that the window has not covered to keep it from falling. Check to make sure that the window is at the desired level and that it is able to operate properly. After that is ensured, nail the new fiberglass window into the right place, using the finishing nails that are hammered through the frame. Place a spacer behind every nail so that warping does not occur.

Step 4 - Insulate

The window must be insulated, and this is done with the help of spray foam in the gaps around the window and the window frame. As you go about the insulation, make sure that it doesn’t push the window out of plumb. Put back the moldings/trims for the fiberglass window both on the inner and outer sides.

Step 5 - Finish Up

For the sake of beauty, you can paint the window, since one advantage of fiberglass is the color on the outside need not be the same as the inside. You can do this in accordance to match the look of your home.