Most buyers who tour a teardown-ready lot in Hillsborough run the same math before they ever call an agent. Lot size times the town's floor area formula equals the house they assume they can build. That number is real, but it is only one part of the review: in Hillsborough, a five-member volunteer board reviews exterior design and decides whether most projects clear design review; its meeting schedule is one factor in a project's timeline.
The board is called the Architecture and Design Review Board, and its own application materials say plainly that meeting the technical maximums does not guarantee approval. It reviews new houses, additions, fences, gates, and landscaping changes along the street, essentially anything visible from outside the property line. In a town with no commercial zoning and no downtown to absorb change, nearly every exterior decision gets made in a public hearing room instead of at a permit counter.
The Formula Everyone Runs First
Hillsborough does not hand you a flat percentage. It uses a sliding formula tied to net lot area. On smaller lots you are generally looking at a percentage set by the formula. Once a lot crosses a threshold, the allowable percentage steps down for everything above that threshold. The Town of Hillsborough's floor-area rules set a floor as well as a ceiling: a new house has to reach at least 2,500 square feet of floor area, and a lot has to meet a minimum size to subdivide in the first place.
Run that formula on a specific lot and you get a specific number. Buyers treat that number like a permit. It is closer to an opening bid.
Where the Spreadsheet Stops Being the Answer
The Architecture and Design Review Board's own checklist tells applicants that compliance with the town's Residential Design Guidelines does not ensure project approval. The board evaluates neighborhood compatibility, massing and proportion, exterior material quality, privacy impact on adjoining lots, landscaping integration with the tree canopy, and how driveways and grading sit on the site. None of that is on the zoning sheet. All of it is decided by five appointed residents, typically people with design, architecture, or construction backgrounds, voting project by project.
That is the gap that catches buyers who priced a lot off the formula alone. The math tells you what the town will let you build. The board tells you what the town will let you build on your specific street, next to your specific neighbors, given your specific roofline.
| On the zoning sheet | In the ADRB hearing room |
|---|---|
| Maximum floor area ratio | Whether that floor area reads as too large for the block |
| Setbacks and lot coverage | Window and balcony placement facing neighbors |
| Height limit | Whether story poles reveal a massing problem once they go up |
| Subdivision rules | Whether a project clears in two hearings or five |
What the Process Actually Looks Like
The path from purchase to permit runs through a set sequence, and each step adds real weeks to a project.
- A pre-application meeting with a town planner.
- Neighbor outreach. The town recommends contacting everyone within 500 feet before plans are finalized, and projects that arrive with unresolved neighbor objections face a harder path.
- Preliminary review by the board. This is a public meeting but not a public hearing. There is no project presentation and no testimony, just board feedback the applicant is expected to take notes on.
- A formal application, which for any project 22 feet or taller, or any new two-story house or second-story addition, requires story poles installed on site so the board and neighbors can see the actual bulk and height before a decision is made.
- Public hearings. Most new custom homes need two to four of them.
- A board decision to approve, approve with conditions, deny, or continue to a future meeting for redesign.
- A 15-day appeal window, during which the story poles have to stay up. If nobody appeals, the poles come down within 20 days.
The board meets roughly once a month, about 11 times a year, and the schedule is not evenly spaced, so two to four hearings can stretch review alone across two to five months before a building permit application is even submitted. Initial plan check for a major project runs four to five weeks, and a full custom home submittal typically needs six to twelve weeks including correction cycles, each of which adds another two to four weeks. Add construction, commonly 12 to 30 months for a full teardown and rebuild, and the realistic span from design kickoff to move-in lands at 18 to 30 months.
The Second Gate: 8,000 Square Feet
There is a second approval layer that catches buyers who assumed the board's sign-off was the finish line. Any dwelling of 8,000 square feet or larger, whether new construction or the result of an addition, requires a final decision from the Town Council, not just the board. That threshold can be waived, but only if the Building and Planning Director and the Council's planning liaison agree there is no unresolved public opposition and the board approved the project unanimously. On larger Hillsborough lots, where the floor area formula naturally produces bigger numbers, this is not a rare edge case. It is a possible second hearing that a buyer's timeline needs to account for from the start.
What a Recent Agenda Reveals
A Hillsborough ADRB agenda from earlier this year shows how differently the same formula plays out lot to lot. One application proposed demolishing a 3,031-square-foot California Ranch home and replacing it with a 4,012-square-foot Modern-style house on an 87,088-square-foot lot, a floor area ratio of just 6.4 percent, far under what the formula would allow on a parcel that size. Another, on a 28,378-square-foot lot, proposed tearing down a 3,831-square-foot 1955 Ranch home for a 7,087-square-foot Contemporary Spanish structure at 24.9 percent, essentially maxing out the available envelope. A third application on a vacant 28,648-square-foot lot proposed a 6,929-square-foot Modern home at 24.2 percent, against a maximum of 24.4 percent allowed, leaving almost no cushion. A separate item from Klopf Architecture involved something far smaller: a ground-floor addition and interior renovation adding roughly 1,050 square feet to an existing 1953 Ranch home, still required to go through the same formal design review as the larger new builds.
The agenda shows four different proposals under the same town formula. The examples vary by lot, and the board reviews each proposal in relation to its site and surroundings.
If You're Buying the Lot, Not Just the House
Treat the formula's number as a starting proposal, not a promise. Before writing an offer on a teardown-ready parcel, budget for the application fee structure, currently $2,308 for a first submittal and $1,198 for each additional round, and build two to five months into your financing plan for board review alone, separate from construction. If the lot's size puts your project anywhere near 8,000 square feet, plan for the possibility of a Town Council hearing on top of the board's decision. And start neighbor conversations before your architect finalizes drawings. A project that shows up to its first hearing with unresolved neighbor concerns may get continued to a future meeting instead of approved.
If You're Selling a Teardown-Ready Lot
A lot's floor area number is worth stating in a listing. It is not worth stating as a guarantee. If a prior owner already went through a preliminary review, has story pole certifications on file, or has any documented ADRB feedback, that paper trail is a real asset and worth disclosing, since it can shave real time off a buyer's path to a hearing. Sellers who market raw teardown potential honestly, formula plus process, timeline and all, tend to attract buyers who show up prepared rather than buyers who walk away frustrated six months into a process they did not know existed.
A Few Questions Worth Asking Before You Write an Offer
Does hitting the maximum floor area ratio guarantee approval? No. The board's own application materials state that compliance with the design guidelines does not ensure approval. Board members can ask for redesigns that bring a project below the mathematical ceiling.
How long does design review take on its own, separate from construction? Most new custom home projects need two to four hearings, and given the board's roughly monthly, unevenly spaced calendar, that typically works out to two to five months before a building permit can even be submitted.
When does a project need a Town Council final decision? Any dwelling of 8,000 square feet or larger needs a Town Council final decision, unless the Building and Planning Director and the Council's planning liaison agree there is no unresolved public opposition and the ADRB approved the project unanimously.
A Hillsborough teardown is a real estate decision and a civic process at the same time. Buyers and sellers who understand both come out of the transaction with fewer surprises and a lot more patience for the calendar in front of them.
If you are weighing a teardown lot, a major remodel, or a listing that needs the right story told before it goes to market, Debbie Elowson has spent years walking Hillsborough clients through exactly this process. Work with Debbie.
This article is general information, not legal, tax or financial advice. Consult a qualified professional about your situation.
