How to Install Replacement Basement Windows


At, we know that the right windows can enhance your basement. Most existing basement windows were designed for utility rooms and storage areas, not living space. They were generally low-cost, stock, and cast-in-place units. Such old windows types often unnoticed until they have declined beyond repair. Fortunately, replacing them is cheap and straightforward and odern vinyl windows are airtight, more comfortable to operate, and require less maintenance than most existing basement windows. Although every home is different, our guide walks you through how to replace most old corroded, poured-in-place, basement windows with new and efficient units.

Houses built in the 1950s and later, usually have a metal basement windows of about 12 inches to 24 inches in height and between 30 inches to 36 inches in length. These units were made to be set into temporary wooden frames used to create foundation walls. Furthermore, the poured concrete would fill in around the window frames to lock the units in place.

Gray primer was the only coating usually applied to these frames or sashes. Due to this, they developed rust quickly once they were exposed to concrete on the sides. Since it is possible to replace windows with metal frames, recommends removing them instead of hiding them under new units. It is also possible to buy windows sized to fit the concrete opening. The most common replacement method is to install wood bucks into the rough opening and attach the new window to the wood. If custom-made basement windows are not needed, this is the best approach because its less expensive and basic stock windows can be used.

The bucks offer adjustable out-of-square and out-of-parallel openings, which makes it helpful when it comes to installing new basement windows. Because there are different types of metal basement windows, all of the steps described in our guide may not be needed. Nevertheless, these windows share similar qualities, and the steps for replacement are comparable. Simply take out the window, get the opening ready, measure and fit the new window, then affix and seal the window in place.

If your home is older you may have wooden windows. In most cases these windows were hinged at the top and sometimes held up by a hook. Although the process is slightly different than a metal frame removal, if anything it is easier and the steps are very similar.

Step 1: Remove Existing Sash & Cut Frame

First remove the existing window sash so only the frame remains in place.

, split the window down the midsection. After removing window sash, use an angle grinder with an abrasive cut-off wheel to create two front-to-back cuts across the metal frame. The cut on the frame includes one through the bottom and one through the top.

Then use a pry bar to twist the old frame. The bottom and top of the frame are bent towards the center, which allows the sides to be pulled inwards. After prying the frame top in a downward direction, you can use a reciprocating saw to divide the outmost portion of the top flange. This process can be done from the exterior part of the window.

Step 2: Get Rid of Excess Concrete:

The hollow sash stops filled with concrete when the basement was poured, leaving a ridge that necessitates chiseling out. A pneumatic chisel does a speedy job of cleaning up the opening. Still, a masonry chisel or hammer is also useful for the chisel work too. The whole process requires less than three hours.


Constructing the Bucks

Removing the Old Frame

The next step is to cut out the old window frame. Because of the concrete, it best to use a multipurpose metal-grinding wheel mounted in a 4 inches angle grinder. The structure doesn’t need to cut entirely through since the deteriorated metal usually breaks along the ground line when prying the mount out. Stop at the concrete if cutting entirely through the sash. That way, the grinding wheel won’t be damaged. The outer side of the window may have a top extension covered with siding and wall sheathing. For better access, cut this flange after starting to pry the frame out of the opening.

The main idea of prying the top and bottom sides of the frame along their centers is to create an X-shape from the detached frame parts. Most times, the bottom of the metal frame extends around an inch into the concrete. Forcing out the old window may be speedy or it may take much work. At Custom Basement Windows, we have found that the older windows were built using a stronger gauge of steel, which makes for more work.

With the old window removed, the next step is to clean and seal the opening for the new window. Use a siloxane sealer that penetrates deep into the substrate where it chemically reacts to form a barrier within the pores that decreases the absorption of water by up to 95%. This mixture is used for sealing the gaps to reduce the possibilities of freeze-thaw damage around the window. The siloxane material lessens the chance of efflorescence occurring on the window opening. It also helps to keep moisture from seeping up via the concrete to the wood sill, which will be installed.

Fitting Sills to the Bottom

Set up the new window on top of a sill cut from a 2×8 pressure-treated board. To reduce the possibilities of the wood warping, you can choose a knot-free piece of wood that has a relatively straight grain. Arrange the interior side of the window to sit flush with the inside edge of the 2×8 and make use of a table saw to set a 5° to 10° slope on the exterior side of the sill for draining water away. If the height of your opening or selected window doesn’t allow the use of the full thickness 2x sill, you can plane or saw the stock to a slimmer size. Also, if the opening is not level, you can shim or taper the ledge.

To seal the joint between the concrete and sill, lay three beads of adhesive sealant on the concrete at 1 inch from the long side of the sill edges and one in the middle. Then, apply a thick bead on each end before fitting the sill in place.

Fitting and Attaching the Sill

Now that the sill is in place situate the window in the center of the opening. At this time, the window can be used as a guide to size the buck pieces on the top and the sides. If there is no room for a buck piece above the window, then use the mudslide as a buck. The sill must fit tightly. Use a few taps of the hammer to fit in the right position. To join the sill, drill, and drive concrete screws in the concrete.

Measure the Opening

Using a window resting on the sill and centered in the opening, measure the width of the gaps at different points to each vertical side to check if the bucks require tapering.

Side Bucks Get Angled Clips

Mark the plumb lines on the rough opening to fit the bucks. Also, tape the side buck pieces in place, toe screw stainless-steel trim-head screws in the mudsill at the top, and sill at the bottom.

Maintain the Stops:

Fit the wooden stops with stainless-steel trim-head screws. The upper part can be secured on a mudsill, while side stops can be fastened to the side bucks using screws driven at the slight angle.


New Window Installation

Bucks offers attachment and adjustment options

With the sill in place, you can dry-fit the window at the center of the opening by guiding the buck pieces for the sides and top sizes. Most times, this installation process doesn’t require a buck above the window. Since the mudsill above window holds the buck.

Custom Basement Windows prefer the western red cedar for both the buck pieces and external window stops. When sawed into thin pieces, the red cedar is more stable and less prone to warping compared to the pressure-treated southern pine. The side pieces are ripped to fit the thickness of the window frame and then they are planed or resawn to fill the gap between the concrete and window.

If the opening for the window is out of square by more than ¼ inch, then the buck pieces can be cut to a tapered thickness. If the buck pieces on the window are off by 1/16 inches or more, both pieces can be cut to the smaller dimension of the tapered gap on every side of the window. It is a good idea to subtract an added 1/16 inches from your initial measurement to allow for the thickness of the sealant, which will be applied. Doing this helps to tight-fit the window but not so tight the window unit needs to be forced in.

The exterior side of the new window requires stops around the top and down each side for the unit to seal. After refining the bucks and stops, apply a wood sealer, primer, stain, and paint to all sides of each piece and use a sealant to the perimeter.

Installing the Window

To install the window, Custom Basement Windows recommends applying a sealant to the internal surface of the window stops before sliding the window into the opening. If the window fits tightly between the bucks, don’t force it into place. To avoid damage, you can use a block plane to shave down the side channel of the vinyl frame.

Screw into the side of the window and through the sides of the buck pieces. Use screws that are long enough to fit into the wood but do not go into the concrete.

As an extra precaution, complete the job with a bead of sealant around the external and internal region of the window frame, except the outer part of the sill, which is left open for drainage.


The Bottom Line

Custom basement replacement windows offer a wide range of bucked opening. Due to this, they are undersized to provide an installer for some wiggle room during the installation process. If the opening is squared, Custom Basement Windows offers custom windows that are sized and fit in the opening and use concrete screws without bucks. Custom replacement windows are durable and cost-efficient. A custom window provides many benefits, which include labor savings and increased in the glazing region. So, do not hesitate to call Custom Basement Windows about your basement window needs today!



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