A bay window relates to an exterior wall in much the same
way that a dormer relates to a primary roof. Like a dormer, a
bay window captures extra space and daylight for the primary
volume. Also like a dormer, it can enliven an exterior
elevation. If formed, scaled, and positioned appropriately, it
can contribute to a favorite interior space while creating a
unique exterior feature.
There are essentially three types of bay windows —
entrance bays, novelty accent bays, and expanded footprint
bays. An entrance bay serves two primary purposes: providing
cover for and calling attention to the entrance below. A
novelty accent bay is generally trimmed underneath with
brackets or corbels — rather than extending to the
foundation — and punctuates the elevation, giving it
personality. An expanded footprint bay can be a single- or
multiple-story component; it extends to the foundation and
increases interior square footage while remaining subordinate
to the overall mass of the structure.
Each type of bay can take a variety of forms —
rectangular, triangular, multifaceted, semicircular, bowed
— and can be capped with any of a number of roof types:
flat, hipped, shed, domed. The challenge is to select a form
and a roof type compatible with the bay itself and with the
building in general. As with dormers, combining too many
different forms or roof configurations on one structure will
result in a confused hodgepodge.
Rectangular Entry Bay
Placing a bay on an otherwise flat continuous exterior wall can
announce an entry while providing shelter for the doorway. Such
bays offer prized views down the street as well as across it,
while admitting daylight from several directions.
Because these bays are rectangular, they create interior niches
well suited to a desk or built-in bench.
This bay type needn't be restricted to traditional homes. By
changing the window type, trim, and post configuration, you can
create a more contemporary bay. In the case shown here, the
flat roof is appropriate to the bay's rectangular form and the
building type it adorns.
Rectangular Entry Oriel
The bracketed bay at left is also known as an oriel: It doesn't
extend down to a foundation or supporting columns. This bay
uses supporting brackets instead of columns, probably because
it isn't quite deep enough to accommodate a generous entry
porch below; columns might have resulted in a more confined and
formal entry. The brackets allow unencumbered, open space
The angled oriel below punctuates a playful faade. Its
hipped roof and hipped wood corbeling complement its angled
The decision to place the bay off-center may have resulted from
an interior floor-plan requirement, or it may have been an
effort to create a counterpoint to the entry door beneath.
However, it appears a little too large to function as a
counterpoint to the rather modest entry.
If we could take it back to the drawing board, it might work
better in its current location if it were scaled down with
smaller windows. This would result in a smaller bay that would
relate better to the scale of the entry. Or we could relieve
the balance issue by shifting it, at its current size, to the
center of the gable.
The semicircular novelty oriel at left provides an otherwise
austere elevation with whimsical visual relief. The domed roof
and curved corbeling underneath are well suited to the
cylindrical form, and together create a jewel-like
From within, this bay creates a peekaboo 180-degree view and
welcomes omnidirectional daylight.
Both of these oriels — angled and semicircular —
grow more organically out of the exterior wall than rectangular
bays would. Their shape helps keep them clearly subordinate to
the primary volume while furnishing an animated visual
Offset Two-Story Expanded Footprint Bay
The two-story rectangular bay below adds considerable floor
space and daylight to the interior without overwhelming the
exterior elevation. The roof skirt between the first and second
floor relates nicely to the bracketed entry roof overhang;
without the skirt, the bay might have seemed towering. The flat
roof keeps the bay from visually interfering with the
triangular pediment suggested by the eaves returns and is
stylistically appropriate for this Greek Revival hybrid.
Repeated One-Story Expanded Footprint Bay
Angled bays with hip roofs add rhythm to this elevation and
work well with the hipped roof of the entry porch. The bay to
the left lends the entry a touch of privacy, too, without
obscuring it. And, because the bays extend down to the
foundation, they bring space and light into the basement.
The hip roofs allow the bays and the porch to appear more
integral to the main volume. The hips are perhaps more informal
than flat roofs, which also would have worked stylistically
with the Greek Revival hybrid.
Bays That Don't Work
The bowed bay at right fails functionally, in both type and
form. For one, the angle of the segmented windows is too
shallow to provide additional interior space or even to admit
light from multiple directions. Plus, the window type isn't
compatible with the primary windows. Even worse, the bay cuts
awkwardly into the rake fascia. Although perhaps meant to be a
novelty bay, the result is more of a blemish on the gable end
than a desirable accent. If the goal was to admit light within
this pediment, a small oval window may have done the
The stock bay unit below is too small for the overall gambrel
end elevation. An enlarged bay surround with wider mullions,
taller head trim, and panels or shingles underneath — as
well as beefier brackets — would look better. This
better-articulated, larger bay would "mediate" between the
scale of the garage door and the upper windows. Also, swapping
the blank center picture window for a pair of double-hungs and
replacing the flanking casements with one double-hung each
might further improve the bay's relationship to the windows
Last, the shutters on this bay have got to go. For shutters to
work visually, they need to be sized as if they could actually
close over a window to fully protect it. Closed, these little
shutters would leave the center window completely vulnerable.
Though the shutters may have been included to help the bay look
larger, they're not effective.
Bays present an opportunity to create a distinctive feature.
Rather than opting for an off-the-rack bay-window unit,
consider assembling stock window sizes within a custom
surround. Stock units generally lack the charm of a carefully
designed one-of-a-kind bay.
Start by focusing on what you hope a window bay will help you
achieve, then select the appropriate type — entry,
accent, or expanded footprint — to accomplish your goal.
Next, look to the overall house to shape the bay form and roof
Katie Hutchisonis an architect
and the owner of Earthlight Design in Salem,