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How to Build a Second-Story Bay in Three Days

It's a challenge to install, but a second-story bay window is a marvel of engineering and can do wonders for cramped dark spaces.

second-story bay window
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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.
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.
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Tom Silva slices through house wall with reciprocating saw to make opening for bay window
Photo by 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.
Even when secured to a header, a bay needs additional reinforcement to stop it from sagging. The best way to combat a bay's tendency to droop is with concrete piers or a foundation, but in most retrofits that's expensive, and it works only on ground floors. Exterior wood brackets, which builders once used to bolster bay bottoms, are structurally dicey because over time the window's weight will cause them to bend.

The third way is to suspend the bay from the wall. For years Tom hung his bays from steel strapping salvaged from lumber bundles. "It was a real challenge to get the straps taut and the whole thing level," he says. So he eagerly adopted a cable support system when it debuted in the late 1980s. This 150-pound factory-built bay will hang from two hidden quarter-inch steel cables, each rated for a 500-pound load, that snake up from the seat board, behind the two front corners and attach to a beam above the header. "The big advantage of the cables is adjustability," Tom says. "You can easily bring the whole unit up or down to make it perfectly level." Out on the scaffold, Tom clears a swath of shingles around the opening and covers the exposed sheathing on both sides with eight-inch-wide splines of 15-pound builder's felt. The felt offers protection should any rain sneak past the caulk, shingles and trim that Tom will install after the window is in place. With the opening framed and felted, Tom climbs down and turns his attention to the prefab bay. First, he and Dick remove the window sash to lighten their load. Then he snaps a chalk line across the headboard, the bay's plywood ceiling, to indicate just how far to shove the unit into the hole. Atop the headboard he builds a ladder-like framework of 2x4s to stiffen it against the cables' inward thrust. With the windowless bay loaded on the scaffolding, they slowly pump-jack the unit up to its new home and slide it into place. Unlike a typicalinstallation by mortals, it fits perfectly the first time. Tom quickly fastens the framework to the header with his cordless drill/driver to stabilize the window; cribbing on the scaffold takes most of the weight.
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Tom and Dick Silva pump-jacking the new bay window up to the opening
Photo by 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.
The bay's little hip roof is next. Using three 2-bys attached to the sheathing, Tom outlines the roof's shape on the wall. He makes sure the 2x6 ridge is screwed into an existing beam so he has a secure spot to anchor the cable tie-downs. Because the cables will pull mightily on the tie-downs, Tom drills a pilot hole for each screw. If the hole's diameter is slightly smaller than the screw shaft, "predrilling makes the screw grip better," he says. Tom pulls the cables taut, then Dick fine-tunes the window level by twisting nuts beneath the seat board. "I bring it one sixteenth above level," Dick says. "That allows it to settle." Tom takes the three short rafters, custom-cut to fit the undulations in the old wall, and quickly screws them down. He grins when asked how, exactly, he measured where to place them. "Measure? Measure?" he says in mock confusion as he arranges them into what appears to be perfect spacing. After 32 years of building, Tom doesn't have to measure everything. He lays a polyethylene vapor barrier on the headboard, then stuffs fiberglass insulation beneath the rafters. The roof is next: half-inch plywood sheathing covered with a sticky sheet of bituthane (a waterproof membrane that helps prevent ice dams), and flashed at the eave and peak with aluminum. As Tom nails down the asphalt shingles, he weatherproofs the wall next to the roof hips with painted aluminum step flashing. (He doesn't bother ventilating his bay roofs, and not one has ever failed.) To make space for the seat, Tom builds a plywood-sheathed box and mounts it to the window's underside. Once he nails up the new ranks of cedar shingles on this box and around the unit, the outside will be weathertight and paint-ready. Inside, to make the seat itself, Tom slices out the existing seat board with his reciprocating saw and drops a new one onto the short stud wall he built earlier. "Now it's 17 inches off the floor — that's the right height for a good chair." An angled skirt board covers the gap between seat and window bottoms. "The pillows will go against that, so you won't see them from the street," Tom says. As Burns predicted, the now sun-washed bedroom is transformed. Hot tea, good books, dozing cats, light-hungry plants and cabin-feverish people will no doubt jockey for position in this bright alcove. But watching Tom and Dick contend for three days with a staggering array of construction details leads to the conviction that installing a bay window is not for amateurs — a notion Tom confirms. "With a bay, particularly on an old place like this," he says with a sly smile, "it's useful to know what you're doing."
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Bay Window Styles

 

Bay Window Styles

sliding a new bay window into place
Photo by 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.
Some bay windows harmonize gracefully with the rest of the house. Too many others are the architectural equivalent of blisters-weird swellings that don't belong. Before installing one, "you must consider two things: the era of the house and the proportions," says Reneau de Beauchamp, a period design consultant in Decatur, Georgia. On Colonial homes of the mid- to late 19th century, bays "are mostly limited to commercial structures—you see them on the shop fronts of Williamsburg," de Beauchamp says. More common on residences was the box window, a bump-out with 90-degree corners (Image 9) versus the bay's 30, 45, or 60 degrees (Image 10). "Bays became popular in the early 1800s, mostly in rural areas," he says, and were confined to the sides and backs of houses.

Bays came into their own on Gothic and Second Empire homes of the late 1800s, and proliferated on gingerbread Queen Annes. The curved bow—rarer than the bay or box—was popular later (Image 11).

Bays were done in by the restraint of Colonial Revival. They survived, mostly as box windows, on Arts-and-Crafts homes in the early decades of this century, but not on postwar housing. Ranches and pseudo-Colonials were generally devoid of bay window flamboyance—and, to be true to their origins, should remain that way.

 
 

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