Building a pergola or gazebo in New Hampshire

Every DIY pergola, gazebo, arbor, or pavilion built in New Hampshire has to contend with a deep frost line, high coastal wind exposure. Below is the practical, code-aware version of what those numbers mean for the way you build.

Footings: dig at least 60 inches

New Hampshire's frost depth is approximately 60 inches. Per IRC R403.1.4.1, every footing under a structural post must rest at least 12 inches below grade and below the local frost line. Because the frost line is 60 inches, every plan in our library — which defaults to 36-inch footings — needs to be deepened to at least 60 inches before pouring concrete in New Hampshire. Order one extra 60-lb bag of concrete per post to cover the additional volume.

Whichever depth you choose, always add 4 inches of crushed gravel at the bottom of the hole for drainage. Frost-heave damage is almost always caused by water freezing under a footing — gravel breaks the capillary path.

Wind load: 130 mph design wind

ASCE 7 / IRC R301 lists New Hampshire at a design wind speed of 130 mph. This is a high-wind zone. Hurricane ties at every rafter-to-beam intersection are required, and through-bolted post-to-beam connections are strongly recommended over lag screws.

Seismic: Low risk category

Seismic risk in New Hampshire is low. Standard lag-bolted post-base brackets and hurricane ties provide adequate lateral resistance for any structure in our library.

Permits: structures up to 200 sq ft are typically exempt

Most New Hampshire jurisdictions follow IRC R105.2, which exempts accessory structures up to 200 square feet of floor area from a building permit — but always confirm with your local building department. The exemption usually does not waive zoning setback requirements, even if no permit is needed. If your structure attaches to a habitable building (a house wall, garage wall, or porch ledger), a permit is almost always required regardless of size.

Recommended wood species for New Hampshire

Builders in New Hampshire typically reach for Eastern White Pine, Western Red Cedar, Pressure-Treated Pine. The cold climate puts the most stress on horizontal exposed surfaces from freeze-thaw cycles. Specify rot-resistant heartwood and finish horizontal surfaces every 2 years.

Plans recommended for New Hampshire

Every plan below is built from a wood species commonly stocked in New Hampshire lumber yards and sized to fit within the 200-sq-ft permit-exempt threshold (where applicable).