Details For Lot Line Windows

By Frank Fortino

A long anticipated clarification has been issued regarding lot line windows and their protection requirements.

On June 30th of this year, Technical Affairs issued Buildings Bulletin 2015-017. The stated purpose of the memo was “To clarify Code requirements for lot line openings.” As is often the case with clarifications, all kind of questions are being raised.

Dating back to Table 3-4 of the 1968 Code, the size and amount of permitted openings in an exterior walls is a function of the walls distance from the lot line. BC Table 705.8 in the 2014 Code addresses the same issue. The further away from the lot line that a wall gets, the greater percentage of openings are allowed in the wall.

Openings in walls which are located on the lot line are not permitted except in R-3 and R-2 buildings. So called “lot line windows” must be protected and cannot be used to satisfy code requirements for natural light and air. They are also limited to 10% of the façade area per story.

The Building Bulletin does not make any changes to what is described above when the tax lot line in question coincides with the zoning lot line. To achieve the building bulk that many of today’s developments require, tax lots are aggregated to make larger zoning lots. It is these types of lots that are affected by the new Building Bulletin.

These zoning lots consist of multiple tax lots, most with existing buildings on them. Architects designing a new building on such a zoning lot must consider the conditions of the bulletin carefully. Prior to the bulletin’s issuance, once the new building rose above it’s neighboring buildings, the architect had relative freedom related to window placement and the ability to use the windows for light and air requirements.

Now, restrictions related to size of openings occur when neighboring construction is within 60 feet of the building measured in any direction. After the 60 foot point the windows can be larger but there are still restrictions to how much of the window can be used to meet light and air requirements.

The language used to explain all of these conditions gets a bit convoluted. The Department was kind enough to include illustrative diagrams that do help explain what will be allowed. To view them, and the Bulletin, please click here.