Bay windows are structural work, not a window swap

Everyone else ranking for this is paid when you say yes. Here's when you shouldn't.

• What you actually want is light and a sense of space. A large picture window or a bow with shallower projection delivers most of that at a fraction of the structural work. The projection itself is the expensive part — if you do not specifically want the seat and the depth, you are paying for something you did not need.
• The wall is load-bearing and structural work is not in the budget. This is not a corner that can be cut later. If the header and support cannot be done properly now, do not start.
• The bay would sit above a walkway, a drive or a property line setback. A projection extends your building footprint outward, which can run into setback rules and can put the assembly where it will be hit or where snow and ice fall onto people.
• You are on a top floor with no framing above to hang cable supports from. It is solvable, but it means brackets, corbels or a built-up base, which changes both the appearance and the price. Find that out before you fall in love with a drawing.
• Your existing bay leaks and nobody has diagnosed why. If it is the roof-to-wall flashing, a new bay set into the same detail leaks the same way. Diagnose the water path first; a new window is not a repair for a roof junction.
• You are trying to add resale value specifically. Bays photograph well and buyers like them, but structural alterations are rarely recovered at full cost. Do it because you want the room to feel different, not as an investment.

• Is this a bay-for-bay replacement or a new opening? Price them differently.

  It is the fundamental question and it changes the trade you need. A window installation crew can do the first; the second needs a remodeler or carpenter comfortable with structural framing.

• Who specifies the header, and will an engineer be involved?

  On a widened opening in a load-bearing wall, the header size should come from a calculation or a code table, not from what was used last time.

• How will the projection be supported, specifically?

  Cables from above, knee brackets below, or a built-up platform — each has different appearance and different requirements. You want the answer before the wall is opened, in writing.

• Who pulls the permit and books the framing inspection?

  Structural alteration is almost always permitted work. Ambiguity here is how homeowners end up as the responsible party for unpermitted work on their own house.

• How is the seat platform insulated and air-sealed?

  The platform is exposed to outdoor temperature on three sides and underneath. Get a specific answer — insulation type and where the air barrier runs — because it cannot be improved later without dismantling the seat.

• How is the bay roof flashed into the wall?

  This is where bays leak. You want to hear step flashing, counter-flashing or a kick-out, integrated into the wall’s water barrier. If the answer is "we seal it", get another quote.

• Who repairs the siding, soffit and interior finishes, and is that in this price?

  A new opening leaves a scar in the siding and in the interior wall. Making good is real work, and it is the most common thing quoted vaguely or excluded entirely.

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