Replacing single hung or double hung wood windows
If you’re in the market for basic, white vinyl replacement windows, you can save yourself a good deal of time by taking measurements yourself and shopping around over the phone. This guide will help you if you are replacing single or double-hung wood windows. Casement windows, hopper windows and other types of windows should be measured differently because the end frame deductions vary by type of window. You will be asked a number of questions but the measurements will be the most important. Please note that the actual measurements are to be taken by the person or company you hire to replace them.
Pick a few different size windows that are easily accessible. If you’re just shopping around for the best price you don’t need every window measured to see how the prices stack up.
Measuring:
Many houses have several windows of the same size in them and if you choose at least one window that has several in a particular size you’ll be able to get a quote for a handful of windows by measuring only one. You should also select at least one other window to measure plus a picture window if you have one.
First, identify the window opening perimeter. For instance, if you were to remove the existing window leaving the outermost framework in place, you would see the perimeter or rough opening. This is what we want to measure. Always measure from the inside of the house. The trim surrounding the window on your wall is a good starting point. Usually the trim surrounding the window is covering some percentage of the opening, and the rest of the trim’s width is covering the wall.
Width:
Open your window and see how deep the pocket is that the window slides inside. In other words, you want to identify where the outer window frame is on the left and right sides. When you look in the pocket and see wood behind it, measure how deep the pocket is. If you see wood framing behind the left and right side pockets you can measure the width directly from the space that spans from frame to frame left to right. If you see a metal or plastic covering in the back end of the pocket, you will need to assume the pocket depth is ¾” deeper than what you can see because the window balance mechanism is usually behind the metal or plastic.
In relation to the wall trim, determine how deep the window opening is on each side. If the trim lines up with the opening depth then the rest of your windows will be easy to measure. If the pocket turns out to be behind the perimeter of the trim, measure how much and use this as a guide. A common window trim or casing trim width is 2 ¼” so we’ll use this as our example. If we figure the left and right sides of the window opening is ½” behind the window trim on each side then 1 ¾” of the trim is left over. Now, we can measure the outside dimensions of the trim, and subtract 1 ¾” from each side or 3 ½” from the total outside trim width. This is your approximate width.
Height:
With the window still open, measure from the bottom of the opening to the inside edge of the trim at the top. The bottom of the opening will be the wood that your window sash rests upon when the window is closed. Note that most wood single or double hung windows have a bottom sill that slopes downward towards the outside. You will need to measure from the highest point nearest to the inside of the house up to the trim on the top of the window.
Take this height measurement and add the same amount to the height that you deducted from the trim width. Again, if you had 1/2” of the opening concealed on each side, then add that 1/2” to the height measurement taken to the inside edge of the same trim at the top. If you can lower the top sash and measure to the exact frame height this is best, but many old wood windows have a stationary upper sash or one that is painted closed from lack of use. Either measurement will give you a good “estimating” window height.
The most critical part of this process is what you are not to do with these measurements. Do not place an order for your windows from these measurements! If you are installing your own windows read the next paragraph. If someone else is installing the windows you must let the installer measure for them. If there is a measuring mistake, let it be their mistake and not yours so that you don’t wind up paying for a second set of windows in the correct size. Most installers have their own way of measuring them based on how they install windows. Your measurements will almost never exactly match the installer’s dimensions.
If you are installing your own replacement windows:
Do not order windows from these measurements unless you are 100% certain this is the exact frame size AND you are the one installing them. If you are planning to install your own windows, it is best that you remove one of the existing windows to see for yourself what the exact opening size is. For your dimensions, measure the width at the bottom, middle and top of the frame horizontally. Measure height the same way three times at left, middle and right positions vertically for every single window.
Use the smallest measurement found for width and height to define your opening size. Anything bigger than the smallest measurement won’t fit. Be clear about distinguishing between your “opening size” and the “replacement window frame size” when ordering your windows. You measured for the opening size. The replacement window frame size should be 1/4” to 3/8” inch narrower in width and 1/2” shorter in height. You’ll need the extra space to plumb the window and shim it into place before screwing it to the frame.
If you order from your own measurements, keep in mind that you're buying whatever you tell them to order whether they fit or not so measure carefully.
