How to Install a Bay Window Step-by-Step

Windows rank amongst the fundamental architectural features of a house, allowing daylight to filter in. With that in mind, bay or bow windows are a sure asset in all homes. 

They’re essentially multi-purpose features, notably doubling as a reading nook, breakfast area, or lounge area (the window seat).

Moving forward with a bay window installation project requires one to be knowledgeable in construction, so if you’re a novice in the matter, recruit as many experienced individuals as you can, to lend you a helping hand with your project. With a bit of confidence and a decent skill set, we’re sure you can install the bay window of your choosing. Keep reading for step-by-step guidelines.

How to Install a Bay Window

Preliminary Stage

Source: Canva

First things first, you’ll need to determine the shape and size of the bay window you’re looking to install. If you want your bay window to be rather striking, you’ll need to build one that protrudes way out, in a sort of cantilevered fashion. Choose the angle of your window. Angles range from 45, 30, or 10 degrees; the smaller of the lot is often referred to as a bow window.

A bay window is made up of three separate window panes, which are joined to make a single, larger unit. Although the installation is similar to that of a flanged window, some significant differences should be accounted for.

We suggest asking yourself some preliminary questions prior to moving forward with such an installation project, such as: what kind of side window to use; what type of sash; and how you plan on holding the window in place. In some cases, additional support will be necessary from above or below the window, and it may be that both are required.

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

Required Materials

Bear in mind that, depending on the manufacturer, you may need more or less material than listed here:

• Tape measure

• Drill

• Sledgehammer

• Level

• Caulk and caulk gun

• Screwdriver

• Flat pry bar

• Brackets

• Circular saw
  

• Window

• Flashing

• Roof structure

• Roofing felt

• Sheathing

• Roofing

• Roofing and finishing nails

• Interior trim

• Casing nails

• Insulation

Once you’ve collected all of the necessary tools and materials, you can begin installing your new bay window.

How to Cut Out a Bay Window Opening

Prior to cutting a hole directly in your wall, properly prepare the space in which the project will unfold. This includes removing any furniture you wish to keep dust-free or simply covering items with a tarp or two, or an old bedsheet. Also, don't forget to seal any ducts or air vents located in the room to prevent dust from seeping into them. The first step will consist of cutting the opening where your bay window will be installed.

This process will mostly depend on where in your home you plan on installing the window, the surrounding surfaces, the wall's material, as well as whether there's already a window in the spot where you’re planning to install said bay window. You may need a sledgehammer to knock down any studs found in the wall. If sheathing and siding nails are secured, cut them off using a reciprocating saw. Next, remove the sill that’s in place, as this will help you determine the window's rough opening width.

Then, frame the opening in such a way that it can accommodate the flashing. The window jambs should be fastened directly to the window's framing. Note that your bow window may have flanges. If so, temporarily position the window in the hole. Next, wedge into place using shims and mark the sides to then cut the siding.

Now, cut the siding according to the measurements taken. Make sure that the area where you will be installing the window has a levelled, flat surface. Grab a level to ensure the surface is actually level. If the space is not level, you will have to build a frame on which the window will rest.

Bay Window Installation

Source: Canva

Once you’ve prepared the area, mark the location where the brackets will be secured according to the manufacturer's instructions. Drill a few holes to wedge and level the unit. This can be completed by inserting shims between the top of the frame and the rough opening. Once completed, you can temporarily position the window in the cut-out. You’ll definitely need someone to help out during this process, so rally up friends or loved ones.

However, before temporarily installing the window, cut a couple of temporary supports to fit directly underneath it. This part of the installation process is meant to check whether the unit is level, and lays flat across. Next, drive screws into the holes you’ve made so that the window can be upheld temporarily. Make sure the window's individual panes can 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 build it. It will be much easier to make adjustments when working at 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 make it. During this phase of the process, make sure to drill holes that are big enough for the support cables should you require additional overhead support. Cut out the structure's outline in the sheathing and build the roof.

Once the roof is ready to be installed, position it and mark the spot where you'll cut the siding to allow for flashing. Once secured in place, you’ll want to form a shallow gap to add foam insulation. Make sure to insulate the space between the window frame and the wall. If you’re working with a spray foam sealant, note that it will expand to form an air barrier to keep cold air in and hot air out. Now, your bay window is ready to be finished in any way you’d like, whether that be adding decorative trim or casing.

How much does a bay window cost?

Bay windows are considered high-end features in terms of window designs. They’re appreciated on account of their ability to provide panoramic views. Furthermore, they automatically make a room feel and look bigger. The only hitch rests in its installation cost and the fact that its installation is restricted to select areas of a home.

A bay or bow window usually costs around $2,500 and $4,000.

Find more information on different window models in our tailored guide.

Do you need a permit to install a bay window?

There are standards relating to windows and other opening types per the Civil Code of Quebec. Indeed, it is illegal to have an unobstructed view, such as a clear-glass window or door, within 1.50 metres from your and your neighbour’s property line.

If you’re planning on installing new doors and windows or altering their size, you should request a work permit. Furthermore, you will have to abide by the regulations regarding natural lighting, ventilation, and security. The latter may not be necessary if your project solely entails replacing or repairing an identically sized window or door. 

Inquire with your town hall representatives to fully understand the guidelines to follow before undertaking your renovation project.

Bay Window Installation Guideline Summary

1. Determine the size and shape of the window

2. Gather tools

3. Prepare the work area (remove furniture, seal ducts)

4. Cut out the bay window opening

5. Insert wedges (shims)

6. Secure the jambs

7. Cut the siding

8. Make sure everything is level

9. Build the frame (if needed)

10. Mark the spots where the brackets will be secured

11. Drill the holes to wedge and level the unit

12. Temporarily install the window (install temporary supports)

13. Build the roof

14. Insulate the gap between the window frame and the wall

15. Permanently affix the bay window

16. Carry out the final details