How To Install Replacement Windows

installing replacement windowsInstalling windows is a mid-range home improvement project in terms of the time, skill and price required to undertake it. Once you have a little bit of education and knowledge about what needs to be done to remove the old window unit and install the new one, you should be able to do it confidently with small simple windows such as picture or casement installations. However, if you intend on installing a larger and more complex window unit, a bay or bow window for example, we would recommend you find a local registered contractor who has the experience to complete the work to a higher standard and quality.

Many people pay thousands of dollars for a professional to install replacement windows; however, you can do it yourself for as little as $300, depending on the type of window you want to install. Whether you’re looking for a single/double hung window, a more extensive bay or bow window set, an elegant casement or awning window, a fixed frame, or a sliding window, the same general rules apply.

Installing Your Replacement Windows

Step 1 – Gather Your Materials

This project will take about 4-6 hours, so be sure you have an afternoon set aside for your work. Additionally, you should set aside your necessary tools and materials, which will include:

Tools & Items Required For Window Replacement
Utility knife
Small pry bar
Caulking gun
Tape measure
Wood shims
Caulking tubes
Sandpaper or sanding device
Wood putty
(optional) Expanding polyeurethane foam

The video below shows how to install replacement windows.

As you can see, you should only try to install replacement windows if you already have a substantial toolbox as well as significant experience with home improvement or DIY projects. If you foresee yourself doing more home improvement projects in the future, you may want to invest in these items anyway.

Step 2 – Measure for the Replacement Window

No matter what type of window you install, you need to make sure your measurements are as accurate as possible. All of the above mentioned windows use the same general structure, with the structure of the house creating a hole for the replacement window hardware to fit in.

You are getting two measurements when you measure for the replacement window: the height of the window hole and the width of the window hole. Height and width are measured from jamb to jamb, which is a fancy way of saying from inside edge to inside edge of the non-movable frame.

Be sure to take width and height measurements at the top of the window, the middle of the window and the bottom of the window. Use the smallest measurements when choosing a window frame. If the sill is not flat, you may also want to measure the angle of the sill to ensure that your replacement window fits.

Finally, check to see if the window is square. If it isn’t, you may need to get a full frame replacement window, which will be a more expensive operation.

Purchase your desired window based on these measurements.

You can see our full guide with detailed diagrams on how to measure for replacement windows.

Step 3 – Remove the Old Window

The first step is to remove the interior stops from the old wooden frame. You may want to reuse these if your replacement window kit doesn’t come with a set of stops, so be careful as you take them off. The stops keep the movable window sashes from falling in or out. Every window is different, this may be as simple as unscrewing the stops from the wall or as complex as carefully using your utility knife to cut away any paint, wood chisel to create a space and prybar to carefully pry out the stops from where they’ve been nailed into the wall.

Once the inside stops are removed, you need to pull out the interior sash. “Sash” is just a fancy term for the part of the window that moves up and down. This is as simple as pulling the sash out of the window where the stops used to hold it in.

A thin piece of wood known as the parting bead separates the exterior sash from where the interior sash used to be. You may need to pull the exterior sash down before you can get at the parting beads, also known as the parting stops. Use whatever means you need to remove them. You may be able to simply pull them out, but if your home is older, it may take a chisel, prybar, pliers, hammer and elbow grease to remove the beads. You will not be reusing these parts, so feel free to utilize all of your aggression to get them out of the wall. If there are any obvious sash weights or cords, remove these as well.

Once the parting bead has been removed, you will be able to free the exterior sash. Pull it down if you haven’t done so already and pull it out of the window frame. Do not remove the outside stops.

Finally, make sure the inside of the window jambs are clean, clear and smooth. Scrape off any splinters and fill any small holes with wood putty. Large holes may be patched and filled as well, either with wood putty or with polyurethane expanding foam. Let the patching and filling material dry, then sand the entire jamb surfaces smooth. If you’re looking to insulate your window frames, use

Step 4 – Install the New Window

Lay a continuous bead of caulk along the inside of the outside stops where the replacement window will rest against. Mark, caulk and install the sill angle. Then, place and install the header from your window replacement kit on the top jamb.

Now comes the moment of truth. Insert the replacement window into the square hole. If it isn’t square, tap your wood shims into place until it is. Your replacement window will likely come with a set of screws. Once it’s square, use a drill or screwdriver to screw these into the top and bottom of the inside jamb. Don’t screw them in so tightly that they deform or destroy the jamb. When in doubt, just go loose enough to allow the window to open and close. Move the expanding header up to close any gaps between the top of the frame and the top of the replacement window.

Finally, check to make sure your replacement window works. Open and close any casements or awnings and move the hung sashes up and down. Make any precise adjustments that you need to make to ensure that the window operates smoothly. Once you are satisfied with how it works, trim any shims flush with your utility knife and lay a bead of caulk along the edge between the window frame and the replacement window both inside and outside. If the gaps are larger than 1/4″, you will need to purchase backer rod, stuff it in, and fill the gap with expanding polyurethane foam. Re-install the inside stops, and you’re done!

If you’d rather not install your own windows after reading that tutorial then we recommend you go ahead and receive a free window quote from a contractor in your area.

More Window Installation Guides

How To Measure For Replacement Windows

If you're looking at installing replacement windows yourself then understanding how to measure for replacement

Understanding Basic Replacement Window Terminology

Some of the main window terms you will come across are shown below, however you

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