How to Frame a Bay Window Roof

Installing bay windows are a gorgeous way to fill your house with natural light, but unfortunately for the do it yourselfer, every bay window must come with a bay window roof. On the bright side, the bay window roof can be an equally charming addition to the façade of your house, but on the downside, it certainly takes a little more labor and know-how to construct, especially in terms of laying out and installing the frame for the roof. However, it’s still a job that can be done by yourself, if you take the time to read the detailed instructions laid out below.

Step 1 – Plan and Install the Bay Window

Before you get started with the roof, the bay window itself needs to be in place. Plan carefully, consulting with the architectural plans, before commencing work. Once the window, the window frame and the window cap are all in place and have been secured and insulated, you can get started on framing the roof.

Step 2 – Plan the Roof

Part of your original plans for the bay window should have included planning for the bay window roof. A bay window roof is typically a hip roof (meaning it projects out with different facets) constructed using 45 degree angles. You should make the plan for the roof frame at this stage. Several handy framing calculators are available online for creating your plans. Simply plug in the dimensions and measurements that you’re working with, and then the calculator will give you a chart with the lengths and angles for the rafters for the roof.

Step 3 – Start Building the Frame

To get started building the bay window roof frame, take a 2 by 6 ledger board and nail it onto the back wall. You may also want to install long screws to affix the board even more securely. Then, create the perimeter of the roof using the 2 by 6 sub-fascia boards. Using your chart from the roof frame calculator as a guide, cut the rafters to size with your saw and nail them securely into place. Remember to always wear safety goggles and safety gloves while you use the saw for protection, and it isn’t a bad idea to wear them while nailing the boards into place, either. Finally, fill the frame in with fiberglass batt insulation and close the frame off with plywood.

Step 4 – Finish off the Bay Window Roof

Now that you’ve made the bay window roof frame, insulated it, closed it off and covered it with sheathing, it’s time to finish it off. Install a drip edge so that water and snow will safely run off the roof without sliding down the window panes, and install flashing as well. Finally, nail roofing shingles in single overlapping layers over the entire roof.