An addition is the biggest project in this set of guides, and the one where permits are not a question. Almost every town requires building permits and zoning approval for an addition, and many require drawings from a design professional. The real questions are what your zoning allows, what the plans need to show, and how long the review takes.
This guide covers what to decide, measure and ask before you hire a designer or a builder. General guidance only. Your permit office and zoning office decide.
Start with zoning
Before anyone draws a plan, find out what your lot allows. Zoning rules commonly limit:
- Setbacks, the distances from the front, side and rear lot lines.
- Lot coverage, the share of the lot covered by buildings and sometimes pavement.
- Height, and sometimes the number of stories.
- Floor area, in some places as a ratio to lot size.
- Use, for example whether a separate living unit is allowed.
If your addition doesn't fit, the options are to change the design or apply for a variance, which is a separate process with its own hearing, timeline and no promise of approval. Knowing this first can save the cost of a design you can't build.
When permits come up
For an addition, expect most or all of these:
- Zoning approval.
- A building permit with plans.
- Electrical, plumbing and mechanical permits for the trades.
- Sometimes a grading, stormwater or driveway permit.
- Septic review if bedrooms or bathrooms are added on a septic system.
- Historic-district or HOA approval where they apply.
What to decide first
- What the space is for. A bedroom, a family room, a kitchen expansion, a garage. Use drives requirements.
- Where it goes. Rear, side, or up. Going up means checking the existing structure.
- Rough size. Enough to test against zoning.
- Who designs it. An architect, a designer, or a design-build contractor. Many towns require plans prepared or sealed by a licensed professional for additions.
- Budget and timeline. Including a contingency, and the time for permits.
What to measure and gather
- Your survey or plot plan, showing lot lines and existing structures.
- Distances from the house to each lot line.
- The footprint of the house and any accessory buildings, for lot-coverage math.
- Where utilities enter the house and where septic components sit.
- Photos of the walls where the addition will attach.
Questions to ask your zoning office
- What zoning district is my property in, and what are the setbacks, coverage and height limits?
- Does my planned addition fit, roughly? If not, what's the variance process?
- Are there any overlays, like a floodplain or historic district?
Questions to ask your building department
- What do you require in an addition application: site plan, floor plans, elevations, structural details, energy compliance?
- Do the plans need to be prepared or sealed by a licensed design professional?
- How long does plan review typically take?
- Which inspections are required, and in what order?
- Does the existing house need any upgrades because of the addition, like smoke alarms?
The review and inspection sequence
Additions usually go through plan review before a permit is issued, then a series of inspections as the work proceeds: footings, foundation, framing, rough trades, insulation, and final, among others. Each inspection has to pass before the work is covered. A good builder plans the schedule around this. If you're managing the project yourself, put every inspection on the calendar with the trades.
Common reasons addition applications get sent back
- The design doesn't meet setbacks or coverage.
- Plans missing structural details or energy compliance information.
- Plans not prepared by a licensed professional where required.
- The site plan doesn't match the survey.
- Septic capacity not addressed when adding bedrooms.
Choosing the people
The team for an addition usually includes a designer or architect, possibly a structural engineer, a general contractor and licensed trades. Ask each for their experience with additions in your town specifically, because local familiarity with the review process saves time. Get written proposals that say who prepares the drawings, who submits the permit application, who responds to plan-review comments, and who schedules inspections. Those four responsibilities are where addition projects most often stall, usually because each party assumed someone else was handling it.
Living through it
An addition usually means opening an exterior wall of a house you're still living in. Ask your builder how the opening will be protected from weather and security risks while it's open, where the dumpster and deliveries will go, what happens to the yard and driveway, and which days utilities may be shut off. Ask your town whether there are working-hours limits for construction noise. And plan for dust. A sealed temporary wall between the work and your living space is worth asking for by name. None of this is a permit question, but it shapes how the months of construction feel, and a builder who has good answers to it usually has good answers about the permit side too.
Do it yourself or hire a pro?
Most additions need professional design and a general contractor or licensed trades. Experienced owner-builders do take them on, but the structural, zoning and coordination demands are serious. Sully's report says so plainly, and highlights where your town requires licensed professionals.
How Sully helps with an addition
Sully won't design your addition, and doesn't replace the architect, engineer or the office. What Sully does is get you ready. Sully asks about the use, location and size, then reads your town's zoning and building pages first, then county and state, labeling every rule with its source. The report lays out the permits and reviews your town lists, setbacks and limits it publishes, who to call, what the application should include, and common rejection reasons, so your first meeting with a designer starts from facts. If the town doesn't publish something, the report says so plainly.
Related reading: What the permit office wants in an application and Site plans and sketches the office accepts.