Renovation-Headquarters Banner

Replacement Windows - Installation - Part 1

Part 2

Replacement windows are a worthwhile home improvement. Replacement windows, providing they are better than your current windows will save you energy and increase the value of your home.

There are many levels of quality of replacement windows. The glass can be single, double or triple glazed. There can be inert gases or sheets of plastic for UV protection, placed between window panes. The replacement window frame materials can be vinyl, aluminum, wood and combinations.

No matter which replacement windows you purchase, the method of installation is basically the same. That being said, you should always follow the replacement window manufacturer’s specific installation instructions.

Note: Some manufacturers sell replacement windows that mount inside existing window jambs. While the installation may at first glance to be somewhat easier, there are some inherent problems with these types of window replacements.

  1. The biggest air leakage and hence energy losses come from the outside of the window frame where it meets the lumber or framing that it is to be mounted too. With replacement windows that mount inside existing window framing it is very difficult to properly insulate and seal between the outside of the window frame and the inside of the old window frame.
  2. If you are replacing old windows, it is more than likely that the old window frames are not plumb or square and that they are damaged or have some rot problems.
  3. No matter what the manufacturers say in their literature, new window trim both inside and out is almost always necessary to make the installation look professional and to protect the home from the ingress of water.

tape measure tip and rivets

Figure 1 - Tape measure - damaged parts

Note: Check the tip of your tape measure and make sure that it reads accurately. The small rivets that hold the tip on the tape measure, as shown in Figure 1, will wear and over time the tip can become bent and hence, create measurement errors.

Measuring the size your replacement windows:

The outside frame of the replacement window should be 1 inch smaller than the width and height of the rough window opening. The gap is necessary to ensure that the windows are mounted square and level as rough-in openings for windows are not constructed using a level or a square!

When you pick-up the replacement windows or when the replacement windows are delivered, measure them to make sure they are the correct dimensions prior to ripping out the old windows. When you have a hole in your home, the old window has been removed, is not when you want to find out that the replacement windows that you have purchased are the wrong dimensions.

Prior to installing the replacement windows:

  1. Remove the outside and inside trim surrounding the old window, the old window and its frame.
  2. Remove any insulation that may be stuck to the rough-in lumber.
  3. Remove any nails, screws, staples or other fasteners that may be left in the rough-in lumber.
  4. Inspect the rough-in lumber and the trim lumber to ensure that it is not rotting and is sound. Any pieces of lumber that are soft and/or rotting should be removed and replaced with new lumber.
  5. Check the new windows for square.

Your new vinyl, wood or aluminum replacement windows can go out of square during shipping. It is important that the replacement windows be perfectly square prior to installation. To check if the replacement windows are square, measure diagonally from the bottom of the left corner to the top of the right corner, and from the bottom of the right corner to the top of the left corner, as shown in Figure 2, both dimensions must be identical. If they are not identical the window is not square.

squaring replacement window

Figure 2 - Checking the replacement window for square

Note: The actual number that you measure is not important, as long as both numbers are identical.

Installation of the replacement window:

Place the replacement window into position in the rough-in opening.

Note: The installation of replacement windows is usually a 2 person project! It is generally wise to have someone on the outside and on the inside of the room to make sure that when the replacement window is placed in position it does not fall in or out, while it is being leveled and plumbed, prior to being secured.

The replacement windows should sit square in the hole with an equal distance of spacing on both sides and top and bottom.

Once the replacement window is in position, level the bottom using cedar or composite material shims.