How to Build a Second-Story Bay in Three Days

By: Brad Lemley, This Old House magazine (Page 1 of 4)

second story bay window brings light and life

Photo Keller & Keller

Although a challenge to install, this second story bay turned the dark bedroom behind the paired windows, into a brighter, lighter space and added visual interest to an austere, flat wall.

Tom Silva slices through house wall with reciprocating saw to make opening for bay window

Photo Keller & Keller

Tom Silva's reciprocating saw slices through shingles, sheathing and studs. He frames out the rough opening with 2x4s and a club sandwich header with alternating layers of plywood and 2x8s.

Tom and Dick Silva pump-jacking the new bay window up to the opening

Photo Keller & Keller

Tom and brother Dick pump-jack the bay, minus windows, to the second floor. Taking out the sash "makes it light and removes the risk of breaking the glass," Tom says.

Photo Keller & Keller

The men slide the bay into the opening with the help of a 2x4 handle tacked across one window. Once the window is leveled, Tom steadies it in place by screwing it to the header.

Tom Silva ties cable to bay window to keep it from sagging

Photo Keller & Keller

Tom ties thin steel cables to zigzag anchors on the bay's roof frame. The cables support the window corners and make leveling a cinch.

Photo Clancy Gibson

A bay window will droop if there's nothing to hold it up. With a steel-cable suspension system, a bay can be installed just about anywhere.

Tom Silva threaded the stainless wire (1) through metal eyes (2) on the bay's ceiling and seat and bolted one end to the seat bottom. He laced the other end through a zigzag tie-down (3) and pulled it tight. Interior trim nailed over the mullions hides the cables.

sheathing the extension of the bay's bottom for the window seat addition

Photo Keller & Keller

The addition of a window seat gives this prefab bay a custom touch. Here, in preparation for lowering the factory installed seat board, Tom sheathes the extension of the bay's bottom.

the view is now expansive with the second-floor bay window

Photo Keller & Keller

From their bedroom, the owners now have a panoramic, bird's-eye view of their property.

Photo: Clancy Gibson

Box window

Photo: Clancy Gibson

Bay window with 45-degree angles

Photo: Clancy Gibson

Bow window

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In this how-to video, learn the correct way to install a window with This Old House general contractor Tom Silva

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A bay window protruding from a house is a sweet revolt against flat, stark walls, an exuberant endorsement of old-fashioned pleasure over modern minimalism. In its cozy, three-sided embrace, we can enjoy the majesty — and ignore the wrath — of howling winds and driving rain. In an older house, where a picture window might be a desecration, a bay is often the only appropriate way to enlarge the window. Although a bay window adds just a half-dozen square feet to the room's footprint, sunlight spraying through it can make the space seem a third again as large.

Gaining those gentle blessings requires violent remodeling. To create space for a new bay at an 1880 carriage house in Ipswich, Massachusetts, Tom Silva jabs and slashes his reciprocating saw into the shingled east wall. Standing on a metal platform 15 feet in the air, following a pencil line that defines the window's rough opening, he roars through a hodge-podge of the dimension lumber added when this post-and-beam stable was converted to a residence. "This wall has been Mickey Moused around over the years," he grumbles, but the blade, oblivious to any structural vagaries, plows on.

This second-story job is a particular challenge, but for Tom's client it's essential. Homeowner Michael Burns, a former actor given to theatrical expression, says his master bedroom was "terribly long, low and dark." He believes the bay will be "absolutely transforming," enlarging the vista of the east lawn and its surrounding ring of spruce and pine.

Tom is up to the task, having installed more than 60 bay windows in the last 32 years. Fifteen minutes after he begins sawing, a 7 1/2-by-5 1/2-foot hole yawns, flooding Burns's bedroom with light. Along the bottom of this opening, Tom erects a short stud wall, which will support a window seat. Across the top of the hole, Tom and his brother Dick wedge a new header made of three 2x8s and two pieces of half-inch plywood. In this case, the header doesn't support the wall above; the gable-end studs Tom cut carried no significant load. It's the header's job to resist the outward pull of a window thrust a foot and a half from the wall. Laden with one or two lounging humans and a half-dozen potted plants, a bay without such reinforcement "can really make an old wall bulge," Dick says.