How to Install a Fiberglass Window

A window.
  • 6 hours
  • Advanced
  • 150
What You'll Need
Broad chisel
Reciprocating saw
Hammer
Pry bar
Flashing
Construction sealant
Fiberglass window
Spirit level
Wood spacers/shims
Finishing nails
Spray foam insulation
Tape measure
Paint
Protective eyewear
Gloves
What You'll Need
Broad chisel
Reciprocating saw
Hammer
Pry bar
Flashing
Construction sealant
Fiberglass window
Spirit level
Wood spacers/shims
Finishing nails
Spray foam insulation
Tape measure
Paint
Protective eyewear
Gloves

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 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 pull 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

Install the window flashings around the frame and put a good amount of sealant on the windowsill bottom, then put the new fiberglass window into place. Make sure that the window is leveled and centered with 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 between the frame opening and the window frame, keeping the window in its proper positioning. Check to make sure that the window is at the desired level and that it is able to operate properly. After that is confirmed, nail the new fiberglass window into place or screw it in place using special fastening brackets that can be concealed behind the decorative trimming when you're done. If nailed into place, you should have shims placed directly behind to prevent any bowing in the window's frame.

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, be aware that an excessive application of the foam will result in the expanding material pushing against the window frame's styles and rails bowing them out of shape, and jam the sash shut or hamper its operation. 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, except for a few brands of fiberglass windows such as Pella, you can paint fiberglass windows, since one advantage of most fiberglass is the color on the outside does not need to be the same as the inside. You can do this in accordance to match the look of your home.