Boston's deck building code requirements are derived from the Massachusetts State Building Code (9th Edition) and the International Residential Code. Understanding what the code actually requires helps Boston homeowners know whether a deck has been built correctly and what to expect from a new build.
Boston requires deck footings to extend below the frost depth — 42 inches minimum in Greater Boston's climate zone. Footings must be sized to distribute the load to bearing soil — for most residential decks, 12–18 inch diameter concrete footings are appropriate. In areas with soft soil (Allston, Brighton, East Boston), larger footings or greater depths may be required. The concrete must be formed and poured to prevent contamination with loose soil. Post bases must be rated for the connection type and corrosive environment — hot-dipped galvanized or stainless Simpson Strong-Tie hardware for above-ground applications. Massachusetts State Building Code →
The ledger — the board that attaches the deck to the house — must be positively attached to the house rim joist or band joist using lag screws or through-bolts of specified size and spacing per the IRC ledger bolt table. The ledger must be properly flashed to prevent water infiltration behind it — the most common cause of ledger rot and deck failure. Boston ISD inspectors specifically check ledger attachment during deck inspections. A deck ledger attached with nails rather than bolts, or without proper flashing, fails inspection. Boston ISD inspection requirements →
Decks more than 30 inches above grade require guardrails at least 36 inches high. Guardrail openings must not allow a 4-inch sphere to pass through (to prevent young children from slipping through or becoming trapped). Guardrails must resist a 200-pound lateral load applied at the top rail. Top rail connections to posts must be structurally adequate — a railing that looks solid but uses only wood screws into end grain will fail the load test. Bottom rail height is also specified — no opening at the base of the guardrail that allows a 4-inch sphere to pass. NADRA deck code compliance →
Deck stairs must have uniform rise heights (no more than 3/8" variation per stairway), minimum 36" stair width, handrails on stairs with more than three risers, and tread dimensions that meet the code minimums. Stair stringers must be properly sized for the span and must be attached at the top and bottom with code-compliant hardware. Open risers on deck stairs are permitted but require that the openings not allow a 4-inch sphere to pass through for decks attached to homes where young children are reasonably expected to be present. Verify MA contractor license →
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AURA Painting Inc serves all Boston neighborhoods. Licensed MA #193121, fully insured, 2-year warranty. Free estimates — most jobs scheduled within the week.
Call (617) 777-7700 ← Back to Deck Construction