Deck permit in Somerville: when you need one, what to draw, and how long it takes
Deck permit Somerville guide: when a deck or porch needs a building permit and zoning review, what the drawings must show, inspections and timeline.
Mateus MagnoLicensed Construction Supervisor · October 20, 2026 · 4 min read
Plan on a building permit for almost any deck or porch in Somerville. The state's only deck exemption is a small, freestanding deck (200 sq ft or less, no more than 30 inches above grade, not attached, not serving a required exit door), and Somerville zoning treats a deck as a projecting porch that can't encroach into side or rear setbacks. Expect footing, framing and final inspections.
If you're asking whether you need a deck permit in Somerville, the answer is almost always yes. Most decks here are attached to the house, serve a back door and sit well above the yard, which rules out the state's only exemption. Zoning matters too, because on tight Somerville lots the setbacks decide how big your deck can be.
Here's how I walk my clients through it, from zoning to final inspection.
Do we need a permit for a deck in Somerville?
Somerville's ISD Building Division requires a building permit for all interior and exterior work except painting, tiling and flooring. The Massachusetts Residential Code (780 CMR 51, R105.2) exempts a deck only if it meets all four of these:
- 200 square feet or less;
- no more than 30 inches above grade at any point;
- not attached to the house;
- not serving a required exit door.
A low, freestanding platform in the yard might qualify. A back porch on a triple-decker never does.
Zoning: setbacks and lot coverage
The Somerville Zoning Ordinance calls a deck a synonym for a projecting porch, which is a building component. In the Neighborhood Residence (NR) district:
- A projecting porch may encroach 100% into the front setback but 0 feet into side and rear setbacks.
- Stairs can't encroach onto the sidewalk, and a porch roof can't rise above the main roofline.
- Porches can be screened, but not enclosed as living space.
- For a detached triple-decker in NR, the side setback is 5 feet (3 feet with front driveway access), the rear setback is 20 feet, and maximum lot coverage is 60%.
- Lot coverage counts covered porches and other building components.
Many older Somerville houses already sit closer to the lot line than today's rules allow. Under Article 14, you can maintain a nonconforming structure, but making the nonconformity bigger generally needs a Special Permit from a review board. That's why I check zoning before anyone draws.
Do I need a permit for a covered deck?
Yes, and the roof raises the stakes. It adds to lot coverage, must stay below the main roofline, and has to carry snow. Under IRC 2021 R507.1, decks are designed for the code live load (40 psf for decks) or the ground snow load, whichever is greater. The Massachusetts amendments list Somerville's ground snow load at 40 psf.
What the drawings need to show: a deck permit example
Here's what I put on a typical one- or two-family deck set. These are 2021 IRC sections as adopted in 780 CMR 51.
- Site plan (R107.2.9): the deck and existing buildings to scale, with distances to lot lines.
- Footings (R507.3): at least 12 inches below undisturbed ground. If the deck is attached to the house, footings must be frost-protected, typically by going below the frost line, which Massachusetts sets at 48 inches.
- Ledger (R507.9): at least a 2x8 pressure-treated ledger, never hung on stone or masonry veneer, with hot-dipped galvanized or stainless fasteners spaced per Table R507.9.1.3(1), plus corrosion-resistant flashing (R507.2.4).
- Lateral hold-downs (R507.9.2): with the Figure R507.9.2(1) detail, two devices rated at least 1,500 lb each, within 24 inches of each end.
- Guards (R312): required more than 30 inches above grade, at least 36 inches tall, with no opening that passes a 4-inch sphere.
- Stairs: Massachusetts limits risers to 8 1/4 inches and requires treads of at least 9 inches; handrails at 34 to 38 inches on flights with four or more risers; at least 36 inches wide.
Massachusetts also accepts the American Wood Council's DCA6 deck guide as an alternative. Three-family porches fall under the base building code rather than the residential code, so details differ. My porch and stair safety guide covers stacked triple-decker porches.
Inspections and timeline
| Step | What happens | Official timing |
|---|---|---|
| Apply | CitizenServe application, plans, cost estimate | ISD must issue or deny within 30 days of filing (R105.3.1) |
| Footing inspection | Holes dug, before concrete (R110.3.1) | Give 1 business day notice; inspection within 2 business days |
| Frame inspection | Framing, ledger and hardware visible (R110.3.4) | Same notice rule |
| Final | Guards, stairs and handrails complete (R110.3.10) | Before you use the deck |
Work must start within 180 days of the permit being issued, or the permit lapses (R105.5). Owner-occupants of one- and two-family homes may apply themselves; a three-family needs a licensed contractor. See my Somerville building permit guide for the paperwork.
Need a hand?
From Teele Square to Union Square, I've rebuilt plenty of Somerville decks and porches. Book a free walkthrough and I'll check zoning, sketch the permit set and send a written line-item budget, usually within 48 hours.
Frequently asked questions
Do we need a permit for a deck in Massachusetts?
Usually yes. The state code only exempts decks that are 200 sq ft or less, no more than 30 inches above grade, freestanding, and not serving a required exit door.
Do I need a permit for a covered deck in Somerville?
Yes. A covered deck needs a building permit, counts toward lot coverage, can't rise above the main roofline, and must be built for Somerville's 40 psf ground snow load.
How deep do deck footings need to be in Massachusetts?
At least 12 inches below undisturbed ground, and for a deck attached to the house, protected from frost, typically by going below the 48-inch Massachusetts frost line.
How close to the property line can I build a deck in Somerville?
A deck counts as a projecting porch, which can't encroach into side or rear setbacks. On an NR triple-decker lot that typically means 5 feet from the side and 20 feet from the rear.
Mateus Magno is the founder of Magno & Co — a licensed Massachusetts Construction Supervisor (CS-123658), registered Home Improvement Contractor (HIC #220484) and certified Lead-Safe Renovator Supervisor who has renovated and managed over $3 million in projects across Greater Boston.
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