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Deck Permits and Code Basics in NH

Updated 2026-10-10 · 5 min read

Building a deck in NH? How permits work, what inspectors check (footings, ledger, guards, stairs), Dig Safe, shoreland rules, lumber and fasteners.

The code is statewide, the permit is local

New Hampshire's State Building Code applies to decks like any other construction. Under RSA 155-A:1, the code for homes is the 2024 International Residential Code (IRC) with New Hampshire amendments. The IRC has a section specifically for decks, plus rules for guards, stairs and footings that apply to them.

Permits are handled by your city or town, and each one sets its own process and exemptions. Many towns require a building permit for a new deck. Rochester, for example, asks for a permit application, footing and framing plans, elevations, and a site plan showing setbacks (Rochester deck handout). Zoning setbacks can apply to decks too. Call your building department before you design. Our building permit guide explains how NH permits work and who should pull them.

A free design reference: AWC's DCA 6

The American Wood Council publishes DCA 6, the Prescriptive Residential Wood Deck Construction Guide. It's free to download. Two cautions apply. The current edition is based on the 2015 IRC, and it says the IRC governs where the two differ. It also doesn't cover decks with snow loads over 40 psf or decks carrying heavy loads such as hot tubs. Ask your building official what design snow load applies in your town and whether they accept DCA 6 details.

Footings and frost

DCA 6 says footings must bear on undisturbed soil at least 12 inches below grade or below the frost line, whichever is deeper. It also says the building official sets the frost line and checks the holes before concrete goes in. Frost depth is set locally, so get the number from your town. Rochester's handout, for example, shows footings at least 4 feet below finished grade.

Other DCA 6 footing rules worth knowing:

Deck footings closer than 5 feet to the house foundation must bear at the same elevation as the house footing.
Don't put footings over septic tanks or leach fields, utility lines or enclosed meters.
The IRC has limited exceptions for some freestanding decks that aren't attached to the house. Ask your inspector before you rely on one.

Call Dig Safe before you dig footings

Digging footing holes counts as excavation. Under RSA 374:51, anyone excavating within 100 feet of an underground facility must notify the damage prevention system at least 72 hours ahead, not counting weekends and legal holidays. In New Hampshire that's Dig Safe. Call 811 or submit a request online. The service is free, and Dig Safe says property owners as well as contractors are required to notify it before digging. Mark the area you plan to dig with white paint, stakes or flags first. In New Hampshire, work has to start within 30 days of the ticket. Member utilities mark only the lines they own or maintain, so Dig Safe says it's up to you to find any privately owned lines, such as a buried line to a garage or shed.

The ledger connection

If the deck is attached to the house, the house side is usually carried by a ledger board fastened to the house framing. DCA 6 and Rochester's handout cover these points:

Remove the siding where the ledger goes, and flash the connection with corrosion-resistant flashing so water can't reach the house band joist.
Fasten the ledger with 1/2-inch lag screws or bolts in the spacing and staggered pattern the code tables call for. Rochester's handout notes a minimum 2x8 pressure-treated ledger.
Don't attach a ledger to brick, stone or other veneer, to hollow masonry, or to a cantilevered floor or bay window. Those cases need a deck with its own support beam and posts next to the house.
Provide lateral load connections to the house framing. Rochester's handout calls for hold-down tension devices in at least two places.

Guards and stairs

These are the numbers homeowners most often ask about. The ones below come from DCA 6 and Rochester's handout. Confirm them with your inspector under the 2024 IRC.

Guards: required on decks more than 30 inches above grade. Rochester requires guards at least 36 inches high, with openings small enough that a 4-inch sphere can't pass through.
Stairs: at least 36 inches wide. Rochester's handout lists a maximum riser height of 7 3/4 inches and a minimum tread depth of 10 inches.
Handrails: required on stairs with 4 or more risers, on at least one side, between 34 and 38 inches high measured above the tread nosings.
Lighting: DCA 6 calls for a light at the top landing that lights all the stairs, switched from inside the house. A motion sensor or timer switch is acceptable.

Lumber and fasteners

According to DCA 6:

Lumber must be preservative-treated or a naturally durable species such as heartwood redwood or cedar. Wood in contact with the ground must be treated for ground contact.
Field cuts in treated lumber should be treated with an approved preservative, such as copper naphthenate.
Nails, screws, bolts and washers used with treated wood must be hot-dip galvanized, stainless steel, silicon bronze or copper. Joist hangers and other connectors must be galvanized or stainless steel.
Within 300 feet of salt water, fasteners and connectors must be stainless steel (grade 304 or 316). That matters on the Seacoast.
Don't let aluminum flashing touch lumber treated with copper-based preservatives.

Near a lake, river or the coast

Under RSA 483-B:4, the protected shoreland is generally the land within 250 feet of public waters. That includes lakes and ponds over 10 acres, tidal waters and larger rivers. RSA 483-B:5-b requires an NHDES permit before construction, excavation or filling there, with a faster permit-by-notification route for qualifying small projects. A deck near the water may need one. See our shoreland and wetlands guide.

Before you build

Ask your building department which inspections it requires and schedule them before anything gets covered. DCA 6 says a deck shouldn't be used until it passes final inspection. If you're hiring, look for deck builders or carpenters who will pull the permit in their name, and use our hiring checklist.

This guide is general information, not a substitute for the code or your inspector. Town requirements differ and codes change, so confirm details with your local building official before you build.