Committee weighs how to count attics, basements and height in FAR calculations

At the Sept. 30 meeting the committee reviewed proposed wording for measuring attic space, the interaction of building‑code “habitable” definitions and what should count toward floor‑area ratio (FAR).

Why it matters: Counting attic and third‑floor area toward FAR changes the effective marketable square footage that can be sold on a lot and affects both visual bulk and developer design choices.

Committee members discussed two primary approaches used by neighboring towns: a simple attic threshold (count attic space above a 5‑foot interior height) and a more complex building‑code‑based test that requires a minimum percentage of the attic area to meet a higher ceiling threshold. Joe (committee member) explained the distinction: building code determines whether attic area is “habitable” for life‑safety and habitability purposes, but zoning FAR measurement is a separate calculation and can adopt a simpler numeric threshold for practical administration.

Several members argued for retaining the simpler 5‑foot rule used in Wellesley and many nearby communities to avoid creating an avenue for builders to “game” the system by designing just‑below‑threshold spaces. Others cautioned a 5‑foot rule could incentivize different roof profiles (for example, flatter roofs or more dramatic massing) that may change neighborhood character. Paul (committee member) said he needed more analysis to determine whether the combination of a 5‑foot attic threshold and a lowered ridge height would drive an undesired shift to flat roofs.

The committee also discussed how basements are treated and whether light‑and‑air or exposed basement area should be counted for FAR — members noted stormwater and impervious surface effects even when a space is unenclosed. Members asked the building inspector to advise how plan review would change if the bylaw explicitly counted attic and certain third‑floor areas.

Ending: The committee agreed to keep the 5‑foot threshold as an option in working drafts, ask staff and the building inspector for implementation implications and for the consultant to model likely design responses in the fiscal analysis.