What Nantucket zoning actually lets you build
Six things the bylaw decides before you do
Ground cover decides how much house the lot will hold
If you learn one Nantucket number, learn this one. Ground cover ratio is the horizontal area of your lot covered at grade by structures, divided by the lot's area, expressed as a percentage. It is the ceiling on your house's footprint, and it varies enormously by district.
Run the arithmetic and the island's logic becomes visible. A 5,000-square-foot lot in the R-5 district carries a 40% ratio — 2,000 square feet of footprint. An 80,000-square-foot lot in Limited Use General 2, nearly two acres, carries 4% — 3,200 square feet. Forty times the land, sixty percent more house. That is not an accident; it is the town deliberately keeping the outer island open and concentrating density near town.
What counts toward the number matters as much as the number. The bylaw's definition of ground cover excludes a long list of things buyers assume would count: decks, unenclosed porches, exterior in-ground pools, hot tubs, chimneys, bay and bow windows, roof eaves, generators, ground-mounted solar, and detached sheds or greenhouses up to an aggregate 200 square feet and 16 feet tall. Overhangs count only where they enclose interior space. That list has been amended repeatedly — most recently at the 2025 Annual Town Meeting — so a builder working from a five-year-old assumption is working from the wrong list.
A practical consequence: on a small lot, the difference between a screened porch and a conditioned sunroom is the difference between a project that fits and one that needs relief from the town. When you're looking at raw land, multiply lot area by the district's ratio before you fall for the view.
What your zoning district actually controls
Nantucket has more than thirty districts. Most residential buyers encounter a handful. Here are the ones that come up most, from § 139-16A of the bylaw as amended through the 2024 Annual Town Meeting:
| District | Min. lot (sq ft) | Front setback | Side / rear | Frontage | Ground cover |
|---|---|---|---|---|---|
| ROH — Residential Old Historic | 5,000 | none | 5 ft | 50 ft | 40% |
| SOH — Sconset Old Historic | 5,000 | none | 5 ft | 50 ft | 50% |
| R-1 | 5,000 | 10 ft | 5 ft | 50 ft | 30% |
| R-5 | 5,000 | 10 ft | 10 ft one side, 5 ft after; rear 5 ft | 50 ft | 40% |
| R-10 | 10,000 | 20 ft | 10 ft | 75 ft | 25% |
| R-20 | 20,000 | 30 ft | 10 ft | 75 ft | 12.5% |
| R-40 | 40,000 | 30 ft | 10 ft | 75 ft | 10% |
| V-R — Village Residential | 20,000 | 20 ft | 10 ft | 100 ft | 10% |
| LUG-1 | 40,000 | 35 ft | 10 ft | 100 ft | 7% |
| LUG-2 | 80,000 | 35 ft | 15 ft | 150 ft | 4% |
| LUG-3 | 120,000 | 35 ft | 20 ft | 200 ft | 3% |
| CDT — Commercial Downtown | 3,750 | none | side none, rear 5 ft | 35 ft | 75% |
"LUG" stands for Limited Use General — the low-density districts covering much of the moors and outer island, and the zoning counterpart to the island's large holdings of protected open space. Sconset and other outlying areas carry their own S- and V- prefixed districts, which generally track their in-town equivalents. Overlay districts sit on top of the base district and add requirements rather than replace them.
Two wrinkles worth knowing. First, when a district boundary runs through a single lot, the bylaw splits the difference: if the line falls within 30 feet of a lot line, the less restrictive rules govern the whole lot; otherwise each portion follows its own setbacks, and your total allowable ground cover is the sum of what each portion earns. Second, the official Zoning Map lives with the Town Clerk. Third-party map layers are a starting point, not an answer.
Setbacks, height, and the shape the lot has to keep
Setbacks are the easy part — the table above gives you the buildable envelope. Height is where people get surprised. Nantucket measures building height as the average height of all sides from average mean grade to the single highest point, not from one corner to the ridge. Thirty feet is the cap in every residential district, with a hard rule that no individual side may exceed 32 feet. Chimneys, cupolas, roof walks, and lighthouses are permitted to exceed it; a taller roofline is not.
Then there is the rule nobody expects: the regularity formula. Every lot must have a regularity factor of at least 0.55, calculated as 16 times the area divided by the perimeter squared. In plain terms, the town will not accept long spaghetti-shaped lots — the shape has to be reasonably compact. Lots recorded or endorsed before April 15, 1980 are exempt. This rule quietly kills a lot of otherwise-tempting subdivision arithmetic.
How many houses one lot can hold
A secondary dwelling is a detached second house on the same lot as the primary. Its footprint must differ from the primary house by at least 20% — the town wants one of the two clearly subordinate — and the two must stand at least 10 feet apart, connected only by a breezeway if at all. The Use Chart makes it a by-right use in most residential districts — R-1, the Old Historic districts, R-20, R-40, Village Residential, and the three LUG districts among them — and a Planning Board special permit matter in R-5 and R-10. The stated purpose is year-round rental housing.
A tertiary dwelling is a third unit, capped at 900 square feet of floor area, permitted in R-5, R-10, R-20, R-40 and the LUG districts but not their L- and S-variant neighbors — and it is not a free income unit: the bylaw ties it to owner-occupancy on the lot or restricts it to year-round use. In the denser districts, bedroom density also caps at eight per lot, scaled to lot area. It is currently the most unsettled corner of the bylaw: in 2024 Massachusetts made accessory dwelling units under 900 square feet a by-right use in single-family districts statewide, and Nantucket responded with a temporary moratorium on new tertiary dwellings while it works out how the two systems fit together. The moratorium's stated end date has passed. Anyone counting on a third unit needs the current answer from Planning and Land Use Services, not last year's.
The covenant lot is the mechanism almost nobody outside town government has heard of: where a lot carries a Nantucket Housing Needs Covenant — the island's own year-round housing instrument, reaching up to 150% of county median household income — the Planning Board can divide one lot into two or even three by special permit. A real density entitlement, administered under Chapter 100 of the Town Code, and worth knowing exists before you rule a property out.
And a separate, newer point that matters to almost every buyer: as of the November 2025 Special Town Meeting, the bylaw defines short-term rental and states that principal use includes renting a dwelling unit, short-term or long-term — permitted in every district except Commercial Industrial. That settles a question the island argued over for years.
What to do when the rules don't fit your plan
Two different doors, and buyers routinely confuse them.
A special permit is the ordinary one. It is relief the bylaw itself anticipates — reducing a setback, exceeding ground cover on a lot that already exceeds it, adding a secondary dwelling. The granting authority is usually the Zoning Board of Appeals, and the Planning Board for a defined list including secondary and tertiary dwellings and most commercial work. The board must find the proposal is in harmony with the purpose of the bylaw, and it can attach conditions. Procedurally: a hearing within 65 days of filing, a decision within 90 days of the hearing, four of five votes to approve, a 20-day appeal window, and expiration after three years if you never build.
A variance is the rare one, and it is much harder than most buyers assume. The ZBA must find that soil conditions, shape, or topography specific to your land and not shared by the district generally make literal enforcement a substantial hardship, that relief does no substantial detriment to the public good, and that it doesn't derogate from the bylaw's intent. Critically, a variance can never authorize a use the district doesn't allow. If a seller or listing implies "you can just get a variance," treat that as an unpriced risk until a land-use attorney says otherwise.
Older houses that would be illegal to build today
A large share of Nantucket's housing stock predates the modern bylaw and sits closer to a lot line, or covers more ground, than today's rules permit. Those houses are lawful — the town protects a structure that has stood 10 years without a recorded enforcement action, and they can generally be altered or extended so long as the existing violation isn't made worse and no new one is created. Increasing an already-over-limit footprint requires a special permit with specific findings, and if you plan to demolish and rebuild, the permit must be in hand before the structure comes down. That sequencing has cost people real money.
There is also a floor for legally undersized lots. A protected lot under 5,000 square feet gets the greater of 30% ground cover or its district ratio; one of 5,000 square feet or more gets the greater of 1,500 square feet or its district ratio — 2,000 square feet in LUG-2 and LUG-3 for lots of at least 40,000 square feet. On a small grandfathered parcel, that floor is frequently far more generous than the district percentage, and it is routinely missed. The same grandfathering logic runs through the island's antique-home stock.
Zoning, the HDC, and Title 5 are three separate gates
Zoning answers how much and where. It does not answer what the building looks like, and it does not answer how many bedrooms you get.
Appearance belongs to the Historic District Commission. Under the 1970 act that created it, the entire island is a historic district, and no structure may be built, altered in its exterior features, or razed without a certificate from the HDC. Shingles, windows, massing, and paint are their conversation, not the Zoning Board's. The full HDC walkthrough is here.
Bedrooms belong to your wastewater system. Massachusetts Title 5 sizes a septic system at 110 gallons per day per bedroom with a 330-gallon minimum, which means the septic permit — not the floor plan, not the listing sheet — establishes the legal bedroom count. A five-bedroom house on a three-bedroom permit is a problem you inherit at closing. The septic guide covers the pre-offer checks.
Three gates, three timelines, and a construction schedule that runs on island terms. Sequence them badly and a two-year project becomes four.
What to check before you make an offer
Pull the district and confirm it on the town's official map. Multiply lot area by the district ratio and compare it to the existing footprint — that gap is your entire expansion budget. Ask for the septic permit and read the bedroom count. Ask whether any prior special permits or variances were recorded, and whether their conditions bind you. If the plan depends on a second dwelling, get the current word from Planning and Land Use Services in writing.
None of this is exotic. It's just specific, and it's all knowable before you commit. Want this run on a particular property before you write an offer? I'll pull the district, the ground cover math, the septic permit, and the HDC file, and tell you honestly what the town will and won't allow. Call or text 508-228-4578, or start with the complete buyer's guide.
Nantucket zoning — frequently asked questions
What is ground cover ratio on Nantucket?
It's the footprint of all structures on your lot divided by the lot's area, expressed as a percentage, and it's the single most important number in Nantucket zoning. It ranges from 75% in Commercial Downtown to 3% in LUG-3 and 0.5% in the Moorlands district. Decks, unenclosed porches, in-ground pools, and roof eaves are excluded from the calculation.What is the minimum lot size on Nantucket?
It depends entirely on your zoning district. Commercial Downtown allows 3,750 square feet; the in-town residential districts start at 5,000; R-10 requires 10,000, R-20 requires 20,000, and the Limited Use General districts require 40,000, 80,000, or 120,000 square feet. The Moorlands Management District requires ten acres.How tall can a house be on Nantucket?
Thirty feet in every residential district, with no individual side exceeding 32 feet. Height is measured as the average height of all sides from average mean grade to the highest point — not from one corner to the ridge. Chimneys, cupolas, and roof walks may exceed the limit. A few overlay districts set different caps.What's the difference between a variance and a special permit?
A special permit is relief the bylaw already anticipates, granted by the Zoning Board or Planning Board when the proposal fits the bylaw's purpose. A variance is far harder: the board must find that soil, shape, or topography unique to your land makes literal enforcement a substantial hardship. A variance can never authorize a use the district prohibits.Does the HDC control how big my house can be?
No. The Historic District Commission governs exterior appearance — shingles, windows, massing, demolition — across the entire island, which is one historic district. How much you can build is zoning's job, and how many bedrooms you get is your septic permit's job. All three approvals are separate, and clearing one says nothing about the others.Can I build a second house on my Nantucket lot?
Often, yes. The bylaw's Use Chart makes a detached secondary dwelling a by-right use in most residential districts — R-1, the Old Historic districts, R-20, R-40, Village Residential, and the three LUG districts among them — and a Planning Board special permit matter in R-5 and R-10, with size and separation requirements keeping it subordinate to the main house. A third unit is currently unsettled while the town reconciles its tertiary-dwelling rules with the 2024 Massachusetts accessory-dwelling-unit law. Confirm the current position before you buy on that basis.Know what the lot will hold before you offer
Sean Kalman is a sixth-generation Nantucketer, a Nantucket REALTOR®, and the founder of The Kalman Co., brokered by eXp Realty. He runs the zoning math before his buyers fall for the view, because the district decides what the view costs. Reach him at sean@thekalmanco.com or 508-228-4578. Zoning figures cited to Chapter 139 of the Nantucket Code as of August 2026; Town Meeting amends the bylaw, so verify current requirements with Planning and Land Use Services before relying on them. Equal Housing Opportunity.