Learn how to repair dry rot and install a new bay window to make your room more inviting.

An existing living room window admits beautiful morning light and frames a favorite scene, bringing the charm of the garden inside this home while leaving the weather and wildlife outside. As much as the view, however, a window's size and style can add ambience and grace to any room. Follow this project as we replace a flat window and its accompanying dry rot with a state-of-the-art bay window to make the room feel larger and more inviting. The new window provides more insulation, enhances the inside decor and compliments the other windows as seen from the outside of the house. On completion, it looks as though it has always been there.

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researching bay windows on the Web
Step 1

Determine What Is Involved in the Bay Window Installation

Take careful measurements and send dimensions for the custom-made bay window to the factory. Research what is involved in an installation. The size, weight, and complexity of this installation along with dry rot repair require help from a professional contractor.

removing the window frame during the bay window installation
Step 2

Remove the Wooden Trim Holding the Old Window and Screens

Remove the sash-stops, sashes and tracks, storm windows, and the large center pane for disposal. Pry off the interior sill and window casings. Take off the storm window frames and exterior trim. Lift the window frame from the rough opening.

prying off the damaged sheathing
Step 3

Pry off Shingles beneath the Window to Examine Dry Rot

Determine the extent of the dry rot beneath the shingles and plywood sheathing under the window. In this project, the dry rot is isolated. Cut away the damaged sheathing and replace it with a new section.

securing a leveled one-by-four for the bay window base
Step 4

Create a Stable Level Surface for the New Window Frame

Install a one-by-four base for the bay window frame to rest on, leveling it with shims and securing it with screws. Apply aluminum flashing tape to the bottom and sides of the rough opening to seal out moisture.

setting the bay window frame in place
Step 5

Position the New Bay Window in the Opening

Remove window panes and sashes from the bay window frame to reduce weight. Set it in place. Attach and tighten support cable clamps to the solid header above the window opening once the window is level. Add remaining window components.

leveling the bay window frame with shims
Step 6

Level and Secure the Bay Window Frame in the Opening

Insert shims between the top of the bay window frame and the rough opening to level it. Do this from the inside of the window. Secure the window permanently by driving screws through the shims and into the wall.

lifting the roof cap onto the bay window
Step 7

Frame and Install the Roof Cap for the Bay Window

Construct and install the bay window roof cap. Insulate the interior with fiberglass and waterproof it with drip caps, roofing felt, aluminum flashing tape, asphalt shingles, and step-flashing before replacing the wooden house shingles along the upper edge.

adding corbels to the bay window
Step 8

Finish the Bottom of the Bay Window with Insulation and Corbels

Use strips of wood trim to form a shallow tray for rigid foam insulation at the bottom of the bay window. Secure an outer plywood cover with nails. Add decorative wooden braces/corbels for additional support. Replace the wooden wall shingles.

spraying foam sealant into the framing crevice
Step 9

Insulate the Interior Space between the Bay Window and Wall

Insulate the space between the window frame and wall framing with spray foam sealant that expands to form a barrier against heat loss and cold intrusion. It will be hidden beneath trim when the bay window installation is complete.

nailing trim to the bay window edges
Step 10

Trim the Bay Window Interior and Add High-transparency Screens

Dress the bay window interior with a pre-finished top and bottom panel. Add trim at the sides and exposed joints and finish the edges with decorative casing. Finish with high-transparency window screens that block very little light and are nearly invisible.


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