How Can I Install a Window in an Existing Wall?

Most windows are always assembled and made with a frame that hung on the window spaces. These are called “pre-hung” windows and are simpler to install on than building a wall frame and hanging a window in it. However, having a window installed in an existing wall is more difficult than installing one in a wall that is newly built. Yet, you actually don’t need to be a professional to install a window in an existing wall. This blog discusses how you can do that. 

  •  Open up the wall 

Since there might be no window openings in an existing wall, you need to make a rough opening through the wall at the place and position you want to place your window. Depending on the size of the window to be installed, do the following to make an opening in the wall; 

  • Drive nails at the four corner positions of your window. This should be done from the inside part of the wall. With the nails marking the four window corners, make an outline on the outside of the house to mark the wall opening. You will have to measure the size of the window opening correctly.   
  •  Make the opening by cutting in through the wall. Now that you have your correct opening measurements, it is vital to be careful as you cut through your wall to make the opening. This will depend on the type of wall you are dealing with. Some walls might need even the whole day to cut through while others like wooden are likely easy. So for this article, we consider a wooden wall. The steps, however, apply to all wall types. Make sure the opening is cut more significantly than the rough opening measurements. Cut and do away with the studs.  It is good to follow the instructions from the manufacturer.  
  • Framing the window 

After making the opening, you will need to verify if your window will fit. This will involve a series of framing to check whether it fits. Cut the opening siding again to create more space if necessary. Framing the window properly will help you ensure that the window is structurally stable and prevent any sagging in the future.  

  • Below the opening, add bottom wall cripples stud to support the sill of the window. Install the sill at an inch slope to drain water. Ensure you level the window on both sides. 
  • Place a king stud to the right side of the opening while leaving it loose to contain the header. Place a window trimmer, and then the header having 2×4 cripples stud above it. Mark the bottom and top of the header using a level. At 1/8 inch below and above the marked lines, make cutlines. If need be, fill any gaps with shims.  
  • Connect the window trimmers to the sill by installing angled brackets. Lastly, notch the studs. 
  • Now that the framing is complete, you can line the window opening with strips of sealed moisture 8-inch in length while tucking them into the window sides. Trim the strips to make them extend inside the interior frame of the opening and fix them by stapling. Place spacers at the bottom of the frame.  
  • Mount the window 

Now that we are done creating an opening and a frame for our window, it is time to mount the window to the wall. This should be done from the outside of the house. Have the window rest on the spacers at the bottom of the frame/opening and then gradually push the top part to fit into the opening. The window should be placed in a way that the right side is up. Check and recheck to ensure the window is level, thereby making any necessary corrections. Once that is done, drive a nail halfway at any of the upper corners through the trim. Check from the inside of the installation is okay, then drive the pins around the window’s perimeter and corners. Check whether the window is operational and apply sealant and flashing according to the instructions of the manufacturer.  

  • Finish the window 

Once the window is mounted, fasten the trim on the outside, and according to the instructions in the manual, fill the space between the siding of the opening and the window. Check the window for level from the inside while adding shims at the sides till the window becomes comfortable in the opening. Between the studs and the jambs, cut the shim to flush them with the wall and glue them to the interior trim. Lastly, finish by applying a suitable molding from the inside. 

  • The Bottom Line 

You can do a window replacement in an existing wall and make it work. All you need is to follow the steps, instructions provided by the manufacturer, and use appropriate tools. However, if you cannot do so, contact a professional and a qualified carpenter to install it for you. My advice is, don’t do it if you feel you cannot!