Straight answers
How big can a granny pod be?
There is no standard size, because the ceiling is set by the jurisdiction rather than by the builder. Three real examples show the range: New Hampshire protects at least 750 square feet of living space and caps a unit at 950 unless the town allows more, Surrey permits a garden suite between 35 and 75 square metres, and a Vancouver laneway house can reach 0.25 of the site area to a ceiling of 186 square metres. So the same building is generous in one city and over the limit in the next, and the size question is really a zoning question.
Figures verified against the sources below · September 9, 2026
01 — The longer answer
What actually decides the size
The cap is a floor-area rule, a lot-coverage rule, or both
Some jurisdictions publish a flat maximum, which is the easy case: Surrey's garden suite range of 35 to 75 square metres is a number you can design against on day one. Others tie the cap to your parcel, so a larger lot earns a larger building. Vancouver does this, allowing 0.25 of the site area up to 186 square metres, which means two neighbours on different-sized lots have different ceilings. Where both a ratio and a flat maximum exist, the smaller of the two governs.
A minimum size can also be protected
The rule can work in your favour. New Hampshire's accessory dwelling unit law prevents a municipality from restricting living space below 750 square feet, with 950 square feet as the cap unless the town authorises more, so the floor is protected by statute rather than left to local preference. If your town's guidance predates the current law, check the statute itself before accepting a smaller number.
Height and setbacks decide the size as much as the cap does
A floor-area maximum is rarely the binding constraint. Setbacks from the rear and side property lines, height limits, separation from the main house, and the space a municipality requires for access all shrink the usable footprint before floor area does. That is why two lots with the same published cap support different buildings, and why the honest answer to how big yours can be starts with your parcel rather than with a catalogue.
Transport limits are separate from all of this and apply only to the factory build: a home on wheels is capped at 8 ft 6 in wide by highway rules, while a modular ships as a volume and is craned into place, so its width is a delivery-route question rather than a fixed limit. KYRAX modular sizes run from 10 ft by 32 ft to 12 ft by 44 ft.
03 — Sources
Each figure above links to the authority it came from.
New Hampshire RSA 674:72 and 674:73: one accessory dwelling unit, attached or detached, as of right where single-family dwellings are permitted; municipalities cannot restrict total living space below 750 sq ft; 950 sq ft cap unless the municipality authorizes more
gc.nh.govSurrey Zoning By-law 12000, consolidated 27 July 2026: garden suite floor area minimum 35 sq m and maximum 75 sq m
surrey.caVancouver Zoning and Development By-law Section 11, laneway house regulations at s.11.3.8: floor area the lesser of 0.25 times the site area and 186 sq m
bylaws.vancouver.ca
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