Ask a Hollis homeowner how much room they have to expand and most will point to the acreage on their tax card. Ask the town's health officer the same question and he will walk the property with a soil probe, because in Hollis the number that actually caps your bedroom count, your addition, and eventually your resale price isn't the acreage. It's how much of that acreage sits outside a wetland buffer.
That distinction sounds like a technicality until you see it play out on a real lot.
What Happened on a 6.47-Acre Lot at the End of a Cul-de-Sac
In December 2024, the owners of a home on Southgate Road brought a request to Hollis's Zoning Board of Adjustment. They had lived on the property for more than 40 years, on 6.47 acres at the end of a cul-de-sac, with a house, a pool, a well, and a septic system. They wanted to downsize by splitting the parcel: keep roughly two acres around the existing house and create a new four-acre back lot behind it.
On paper, that looks simple. Six-plus acres is plenty of land to split in two. But the existing septic leach field sat close enough to a wetland buffer that the board had to work through whether redrawing the lot line would put that system out of compliance with today's setback rules, even though the system itself predated the current ordinance and had been legally grandfathered in as an existing use. The applicants' attorney argued the leach field's location wouldn't change just because a line moved. The board ultimately agreed the construction and existing systems fell outside the buffer, but only after real scrutiny of exactly where the septic sat relative to the wetland edge.
Nobody at that hearing was building a mansion. They were trying to divide a large, ordinary lot, and a decades-old septic system's position relative to a wetland buffer became the central question of the case.
The Building Area Is Smaller Than the Lot Line
Hollis's zoning ordinance, recodified in May 2025, defines what it calls a Building Area: the actual footprint available for a house and its utilities, which must fit inside a rectangle measuring 100 feet by 200 feet, or a circle 160 feet across. That Building Area cannot overlap a setback, a wetland buffer, or any slope steeper than 25 percent.
Layered on top of that is the town's Wetland Conservation Overlay Zone, which extends a 100-foot buffer around wetlands, surface waters, and hydric soils anywhere in town, not just around named water bodies like Rocky Pond. A lot doesn't need lake frontage to lose usable land to this rule. Plenty of interior parcels have a hydric soil pocket or an unmapped seasonal wetland that quietly eats into the buildable footprint.
To even qualify as a buildable residential lot, Hollis requires one and a half contiguous acres of what the ordinance calls "acceptable land," or one acre for lots in the town's open space and planned development overlay. The Planning Board can also require a site-specific soil map before approving a subdivision, precisely because acreage on paper and usable acreage in practice are two different numbers.
Put those pieces together and you get the real story: a five-acre lot with a wetland running through the middle can have less usable Building Area than a two-acre lot with none. The listing sheet doesn't show you which one you're buying.
Hollis Doesn't Just Take the State's Word for It
New Hampshire's septic approvals run through the Department of Environmental Services, but Hollis is one of the towns the state lists as requiring local approval on top of that. According to Select Board minutes from March 30, 2026, the town's health officer personally witnesses test pits during the design phase and will not sign off on a septic system until it has crossed his desk, checking setbacks and site conditions himself before construction proceeds.
That same meeting touched on how often bedroom-count changes drive new septic work. As homes change hands in Hollis, owners frequently want to expand a small cottage into a larger year-round home, and any increase in bedroom count requires a new septic design, not just a repair permit. As of those March 2026 minutes, the health officer had personally visited and inspected a number of these upgrades over the previous year.
The practical upshot for anyone buying or selling here: a septic timeline in Hollis runs through a local office, not just a mailed-in state form. Build that into your calendar before you assume a design or upgrade will move quickly.
Bedroom Count Is a Tank Size, Not a Preference
The number of bedrooms a septic system supports isn't a marketing choice. It's an engineering minimum tied directly to tank capacity.
| Approved Bedrooms | Typical Minimum Tank Size | Common Trigger |
|---|---|---|
| 1 to 2 | 750 gallons | Small home or camp |
| 3 | 1,250 gallons (state minimum) | Most single-family resales |
| 4 or more | 1,500 to 2,000+ gallons | Addition, finished basement bedroom, or accessory unit |
If you're buying a three-bedroom Hollis home with an eye toward a fourth bedroom or a finished basement suite, that isn't just a construction question. It's a septic redesign question, which loops back to how much acceptable land sits outside the wetland buffer on that specific parcel. A generous-looking yard doesn't guarantee the room to upsize the system. Only a site-specific soil map and test pit results tell you that for certain.
What the Price Spread in Hollis Is Actually Telling You
Hollis home prices don't cluster the way you'd expect for a small town. As of July 2026, one tracking source put the median list price at roughly $879,000 with homes spending a median of 34 days on market, while a separate home-value index put the typical Hollis home value closer to $729,000. One estimate of the full range of Hollis home values runs from roughly $200,000 to $2.2 million.
Some of that spread is condition and location, the same as anywhere. But part of it is exactly the mechanism above. Two lots of similar size can carry very different septic capacity once you account for wetland buffers and slope, and a buyer's appraiser or lender will eventually ask the same question the Zoning Board asked on Southgate Road: how much of this acreage is actually usable. A property capped at three bedrooms because of buffer geometry will not command the same price per acre as one with room to grow, even if the tax card acreage looks identical.
Zooming out, Hillsborough County's broader single-family median sat at $540,917 in the first quarter of 2026, down slightly from a year earlier, in a market where days on market have lengthened. In that kind of market, a property's real, verified building capacity is a stronger selling point than raw acreage on a flyer.
The Paperwork That Protects Both Sides
New Hampshire law puts real obligations on sellers here. Under RSA 477:4-d, before an offer is signed, a seller of a one-to-four-family home must disclose in writing the type, location, and any malfunctions of the private water supply, along with the date it was installed and last tested. The same statute requires disclosure of the septic system's location, any malfunctions, the date it was last serviced, and the name of the contractor who services it. If any of that information isn't available, the seller has to say so in writing rather than leave it blank.
For sellers, the smart move is pulling your Approval for Construction and Approval for Operation records before you list, since New Hampshire's environmental agency keeps these on file and buyers will ask for them anyway. For buyers, don't treat the disclosure form as the finish line. Request the actual state approval documents, and if the septic's age or bedroom rating isn't clearly documented, treat that gap as a real risk factor worth pricing into your offer, not a formality.
Well water deserves the same attention. New Hampshire's fractured bedrock is known for naturally occurring arsenic in groundwater, and testing isn't legally required to close, but most lenders insist on it anyway. A standard analysis panel is inexpensive relative to what a bad result can cost you in negotiating leverage, and most contamination issues found this way are treatable rather than deal-killing.
New Hampshire's environmental agency estimates that a full septic system replacement can run $25,000 or more depending on soil and site conditions, which is exactly why the acreage-versus-buildable-land question matters before you're the one paying for a redesign.
Questions Hollis Buyers and Sellers Ask Most
Can I add a bedroom without a new septic design? Not if it increases your home's approved bedroom count. That triggers a new septic design, which needs new test pits and has to fit within your remaining Building Area outside any wetland buffer.
What if my septic system predates the current wetland buffer rule? An existing, previously approved system is generally treated as a grandfathered use, as it was in the Southgate Road case. Problems tend to arise only when you change the lot line, expand the system, or increase bedroom count, at which point current setback rules apply fresh.
Does the local health officer's review add time to a straightforward sale? Not typically for a sale of an existing system with clean service records. It becomes relevant when a buyer's financing requires an inspection, or when a seller is upgrading the system before listing, since that work runs through both the state and the town.
If you're weighing a purchase or a sale in Hollis and want a straight read on what a specific lot's septic and wetland constraints actually mean for your plans, that's a conversation worth having before you write an offer or set a list price. Alex Betses works these details into every Hollis transaction, and you can start with a free home valuation to see where your property actually stands.
