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How to Install a Bay Window

Last modified: 2020-02-27 | Approximate reading time 5 mins

Amanda Harvey

A home is defined by its windows, with the ability to soak up natural light as an integral element to how it feels inside. Regardless of its purpose, a bay window is a big and beautiful addition to any household. Bay windows can be used for a variety of things, including a reading nook, a snack space alongside a table or just a casual spot to hang out.

This installation project requires a bit of preliminary construction knowledge, so if you’re a beginner, make sure to enlist friends or family that have a little bit of experience. With some confidence and the right skill set, we’re sure you’ll be able to install your very own bay window in no time. Keep reading for our step-by-step instructions!

How to install a bay window

Preparing for this project


source: unsplash

First things first, you’ll need to determine the shape and size of the bay window you’re crafting. If you want your bay window to have an extremely dramatic effect, you’ll need to build one that protrudes further away from your house.

Choose the angle of your window between 45-, 30-, or 10-degrees, the smaller angle is often referred to as a bow window. A bay window is composed of three separate windows which are joined to make a single, larger unit. Although the installation has similar installation steps to that of a flanged window, there are some significant differences that should be recognized.

We’re suggesting that you ask yourself some preliminary questions before moving forward with this installation project, including what side window, what type of sash, how you intend on supporting the window. In some cases, additional support will be necessary from above or below the window, and even further both may be necessary.

If you’re planning on installing a compact bay window, it likely won't require additional support. It’s also important to consider how the bay window will be finished, including whether these will be an eave above the window or whether you’ll be building or purchasing a custom-made roof.

The materials required for your bay window installation project are as follows. Though bear in mind that as dependant on the manufacturer, you may need less or more than listed:

  • Tape measure;
  • Drill;
  • Hammer;
  • Level;
  • Caulk and caulk gun;
  • Screwdriver;
  • Flat pry bar;
  • Circular saw;
  • Window;
  • Exterior casing;
  • Drip cap;
  • Flashing;
  • Plywood;
  • Roofing and roofing felt;
  • Roofing and finishing nails;
  • Interior trim;
  • Casing nails;
  • Insulation.

Once you’ve collected all of the necessary items and materials, you can begin the installation process.

Begin preparing the opening of your bay window

Before you start cutting a hole directly in your wall, make sure you prepare the room for the project. This will include removing any furniture that you don’t want to become dusty or simply covering items with a cloth or two. Also, think about sealing any ducts or air vents located in the room so that the excess dust doesn’t find its way into them.

The first step will involve cutting the opening where your bay window will live. This process will greatly depend on where in your home you will be installing the window, the surrounding surfaces, the wall materials as well as whether a window already exists in the spot where you’re planning to place your bay window.

A sledgehammer may be necessary to knock any studs and trimmers away from their place in your walls. If sheathing and siding nails are attached, they will need to be cut away using a reciprocating saw. Next remove the sill that’s in place, as this will help you to determine the rough opening width of the window.

Next, the opening will need to be framed and ready to be flashed. The jambs of the windows should fasten directly to the framing members of the window. In some cases, your bay window may have flanges, and with these, it will be necessary to set the window in place temporarily. Next, shim it into place and mark the sides to prepare for cutting the accommodating siding. Now, cut the siding accordingly to the measurements you’ve taken. Make sure that the area where you will be installing the window has a level surface, and this can easily be tested with the level itself. If the space is not level, it will be necessary for you to build a frame to rest on.

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bay window

source: unsplash

Once you’ve prepared the area, mark the locations where the fasteners will live by following the manufacturer's instructions. Drill a few holes to allow for shimming and levelling of the unit you’re installing. This can be completed by inserting shims between the top of the frame and the rough opening. After this, you can temporarily fit the window. You’ll definitely need someone to help out during this process, so rally up friends or loved ones.

However, before putting the window in place temporarily, cut a pair of temporary supports to live directly underneath it. This part of the installation process is to check if the unit is level, plumb and can be flush in place. Next, drive screws into the holes you’ve cut so that the window can be temporarily held, make sure that the windows are able to open and close as smoothly as possible.

If you haven’t had a roof cap for your bay window manufactured, now is the time to construct it. It will be much easier to make adjustments when working at the ground level. If you haven’t done so already, make a template for your roof or take down the measurements so that you’re able to prefabricate it. During the construction process, make sure that if you require support from above, you drill holes that are big enough for the support cables.

Cut out the sheathing pieces and construct the roof. Once the roof cap is good to go, you can set it in place and mark where you’ll cut the siding to allow for flashing. Once secured in place, you’ll want to form a shallow tray for foam insulation to be inserted. Make sure to insulate the space between the window frame and the wall.

If you’re working with a spray foam sealant, it will expand to form an air barrier to keep cold air in and hot air out. Now, your bay window can be finished in any way you’d like, whether that be adding decorative trim or casing.

Recap of the steps for a bay window installation project

  1. Determine the size and shape of the window
  2. Gather the tools
  3. Prepare the room (remove the furniture, block the ducts)
  4. Create the opening for the window
  5. Fix the jambs
  6. Shim the window
  7. Cut the siding
  8. Check if everything is levelled
  9. Build a frame (if necessary)
  10. Mark the places where the fasteners are placed
  11. Drill holes to wedge and level the unit
  12. Install the window temporarily (put temporary supports)
  13. Build a roof covering
  14. Insulate the space between the window frame and the wall
  15. Place the bay window permanently
  16. Complete the finishing step

Get 3 renovation quotes for your bay window installation project can help you get quotes for your window project. If you submit your project to us, we’ll put you in contact with top-rated contractors. Fill in the form on the homepage (it only takes a few minutes), and you will get estimates from trusted professionals. 

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