Cambridge, MA Permit Requirements: Deck & Patio Permits (2026)

The Massachusetts State Building Code (780 CMR) governs deck permits uniformly across Middlesex County's 54 municipalities. Decks are exempt from building permits if they meet all of these criteria: floor area does not exceed 200 square feet, the deck is not more than 30 inches above grade at any point, the deck is not attached to a dwelling, and the deck does not serve a required exit door. Decks exceeding any of these thresholds require a building permit. This means most practical backyard decks — especially those attached to the house, elevated above 30 inches, or larger than 200 square feet — will need a permit. Plans must be submitted to the local building department showing structural details, footings, guard rails (required when the deck is more than 30 inches above grade — minimum 36 inches tall), and setback compliance. Concrete or paver patios at grade level generally do not require building permits. Covered porches, screened porches, and three-season rooms are treated as additions and always require permits. In flood zones along Middlesex County waterways (Concord River, Charles River, Assabet River), decks may need to comply with FEMA and local flood plain regulations. Some municipalities may require Conservation Commission review if the deck is within a wetland buffer zone. Plan review timelines vary by municipality: smaller towns may issue permits within 1–2 weeks, while larger cities like Cambridge or Lowell may take 3–6 weeks.