Lot line window closure requirements

Also, apologies for the lack of paragraphs in my original post. StreetEasy doesn't seem to respect my line breaks.

Yes, you will have to brick up the openings to meet the required fire rating (Building Code Chapter 7). The window assembly generally will not suffice. Lot line window openings are not generally code complaint but the City lets them slide if they’re “exiting conditions” and nothing changes substantially on the subject or neighboring lots.

It’s sort of alluded to in this bulletin, section V. An architect may be able to provide some additional insight:

https://www1.nyc.gov/assets/buildings/bldgs_bulletins/bb_2015-017.pdf

A "lot line" window means that your building (usually sides) is built right up to the lot line. If it is set back, it is not a lot line window. A lot line window needs to be fire resistant (usually wired glass or (much more expensive) ceramic glass). If a building is built next door but not adjacent to the building, you need not do anything to the lot line window. If the building is adjacent, the envelope needs to be closed with fireproof enclosure (i.e., bricked) at your expense. A poorly kept secret is that many people don't do the required bricking, but simply insulate and drywall over the window. This is a disaster waiting to happen.

"A "lot line" window means that your building (usually sides) is built right up to the lot line."

I'm not sure this is exactly right. According to:

https://www1.nyc.gov/site/planning/zoning/glossary.page

It says:

Window, Legally Required*
Legally required windows are mandated in dwelling units to provide necessary light, air and ventilation. Legally required windows cannot be located on or closer than 30 feet to a lot line.

I believe this means that any window within 30 feet of a lot line (which doesn't face the street) is a lot line window.

The short answer is that if you have a window that is directly on the lot line, you could have to enclose it. Whether this is at your expense depends on the declaration of condominium, which (in newer buildings) will describe the presence of lot line windows and who pays (you or the condo association.) Windows facing a street or a courtyard that your building owns are NOT lot-line windows.

If windows are within 30 feet of a lot-line, they need to be fire rated to prevent fires from jumping. But to be clear: lot line windows are those that are directly on the lot line, not those that are 29 feet back.

The key question is what restrictions exist on the neighboring property to prevent them from building on the lot line and whether closing the window causes the loss of a legal bedroom. Years of construction next door could be far more bothersome than losing a window.

As George said, lot line windows and windows that count for ventilation/light are two different concepts. A "lot line " window is one that (a) must be fire resistant and/or sprinklered, and (b) is susceptible to being lost if the adjacent lot is developed. You have to brick in a lot line window if the adjacent building is within a few feet (I believe 3 feet) of the window. Otherwise it is fine, but lot line windows technically don't ever count as a legally required window even if there is no similar height building for miles. So, you could have a "lot line" window overlooking a cemetery with no obstruction in sight that legally cannot be a bedroom, but on the other side have windows facing a shaftway or tiny rear "yard" that qualify as windows and bedrooms.

Thanks all, very helpful.