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How To Install A Window

Installing a new window into an existing opening can be done in as little as one hour or as long as perhaps four hours depending on a few things like correct sizing of the window to the existing opening, size and weight of the window, and accessibility to the area where the window is needed (e.g. working on the second story of the house).

Difficulty level: 7/12

Tools Required

Materials Required

To start this project you will need to determine the window size and style to be ordered. I would generally say that as a DIY home owner you should contact a local window supplier to help and advise you in these areas. In fact most will come to your home and measure up the sizes needed for your specific home. This is a great bonus because if they measure and order the wrong size on a window, they should be responsible for correcting their mistake.

I would not suggest changing the size of too many windows, but instead to order them to fit the openings you already have. I know that it is tempting to order smaller windows or “off the shelf “generic windows to save some money but the time and materials needed to adjust the hole size will usually outweigh the savings and making the window openings larger will have you getting into changing wall structural pieces like headers. Once you start changing structure you are no longer doing a DIY project that most can easily handle.

Once you have your window you will also need some insulation, wood shims, caulking and likely new interior trim. With all of the materials and tools that you will require ready, it is time to remove the old window.

Start by cutting any old caulking that maybe sealing the exterior of the window to the house exterior. Now remove any glass that you can easily remove to help make the window lighter, as well remove the interior trim. We will assume that your old window is wood and that it will be likely installed with nails through the exterior trim into the wall framing. So use a pry bar to pry it away from the wall and pull it out of the opening.

Now remove any old insulation or nails left behind. You are now ready to install the new vinyl window. I would recommend a vinyl window with renovation brick molding that will have a removable cap around the perimeter that allows you to install screws through the brick mold then re-install the cap to hide them, this gives a nice clean finish.

Once your opening is cleaned up and ready for the new window do a test fit to make sure the new one fits. Once you are sure it will fit remove it and apply a bead of exterior caulking around the opening onto the surface of the plywood sheathing this will form a seal onto the back of the new window, then reinstall new window into opening.

Center it in the opening and use the shims under the two outside bottom corners of the window jams to level the unit (this may require a helping hand). After the window is level place a screw through the brick mold at each corner.

TIP: At this point if you are installing a window that opens, try it to make sure it operates smoothly and correctly.

Now add more shims to the bottom sill about every 24" or so to help support the sill and window. Add more screws into the brick mold about 12" apart and reinstall the snap in cover to hide them. Install some insulation to the interior gap between the wall framing and the window jam (be careful not to stuff the space too tight with insulation as this reduces it's insulating R value).

TIP: You can use low expansion spray foam insulation to insulate, but be very careful to follow the manufacturers instructions and never over-fill the cavity around your window.

You can now cut and install your new interior trim, and seal the outside of the brick mold to the exterior finish with a bead of exterior caulking. When properly installed and sealed your new vinyl windows should last for years and never need painting.