Flashing Code Requirements in New Hampshire

New Hampshire frost depths range from 48 inches in southern counties to 60+ inches in the White Mountains and North Country. Foundation footings must extend below the local frost line per IRC R403.1.4, typically 48 inches minimum statewide. Coos County and White Mountains communities above 2,000 feet elevation require the deepest foundations. Frost-protected shallow foundations per IRC R403.3 are an accepted alternative.

New Hampshire falls within Seismic Design Categories A and B per ASCE 7-22. Northern New Hampshire near the Quebec border has the highest seismic risk in the state. The 1940 Ossipee earthquake (magnitude 5.5) caused damage across the state. All structures must meet minimum seismic detailing per IBC Chapter 16. Post-glacial rebound stress in bedrock contributes to occasional seismic activity.

New Hampshire has extensive wetlands protected under RSA 482-A. The Wetlands Bureau administers permits for all activities within jurisdictional wetlands and their 100-foot buffers. Prime wetlands designated by municipalities receive enhanced protection with 100-foot undisturbed buffers. Foundation design near wetlands must account for high water tables and saturated soils.

New Hampshire is subject to remnant tropical storms that bring heavy rainfall and river flooding. The 1938 Great New England Hurricane devastated the state. Hurricane Irene (2011) caused significant flooding. While wind speeds are lower than coastal areas, saturated soils and steep terrain create mudslide and washout risk during tropical events. Rockingham County coast has the highest wind vulnerability.

New Hampshire's 18-mile Atlantic coastline in Rockingham County including Hampton Beach, Rye, and Newcastle experiences coastal erosion. The Coastal Zone Management Program under DES administers development setbacks. Hampton Beach and Seabrook experience erosion from nor'easters and coastal storms. Construction within the coastal erosion zone requires state permits and compliance with NHDES Shoreland Water Quality Protection Act.

New Hampshire has 18 miles of Atlantic coastline, entirely within Rockingham County. Coastal communities include Portsmouth, Rye, Hampton, Hampton Falls, Seabrook, New Castle, and North Hampton. Subject to coastal storms, nor'easters, storm surge, wave action, and sea level rise. Tidal rivers and estuaries extend the coastal influence zone inland. Great Bay National Estuarine Research Reserve adds environmental sensitivity.

New Hampshire is predominantly EPA Radon Zone 1 (highest risk — predicted average indoor level >4 pCi/L). The state's granite bedrock is a significant source of radon gas. Hillsborough and Rockingham counties have the highest measured indoor radon levels, but elevated levels have been found in every NH county. Approximately 40% of homes tested in NH have radon levels above the EPA action level of 4 pCi/L. NH ranks among the highest radon risk states in the US.

Ice barrier underlayment is REQUIRED statewide on all roof eaves per IRC R905.1.2. Mean January temperature is well below 25°F throughout the entire state. Heavy snowfall (60-80+ inches/year) and extreme freeze-thaw cycling create severe ice dam risk. White Mountain region is particularly susceptible due to wind-driven snow and extreme cold.

Ground snow loads range from 40 psf in the southern Merrimack Valley to 80+ psf in the White Mountains and northern tier. Annual snowfall averages 60-80 inches, with 100+ inches in the White Mountains. Coos County and Grafton County (White Mountains) have the highest snow loads in the state. Many mountain locations exceed IRC prescriptive table limits and require site-specific engineering.

New Hampshire has numerous National Register Historic Districts and locally designated historic districts. The most significant is Portsmouth's historic downtown, which includes some of the oldest structures in New England (17th-18th century). Other notable districts include Concord (state capital historic district), Exeter, Hanover, Keene, and numerous small town centers throughout the state. The NH Division of Historical Resources maintains the state historic registry.

Areas designated as Zone A, AE, V, or VE on FEMA Flood Insurance Rate Maps. New Hampshire has significant riverine flood risk along the Connecticut River (western border), Merrimack River (central corridor), Pemigewasset River, Saco River, and Androscoggin River. Coastal flood zones along the 18-mile Atlantic coastline in Rockingham County. Major flood events in 2005, 2006, 2007, and 2017 caused widespread damage. Local jurisdictions participate in National Flood Insurance Program (NFIP).

The White Mountain National Forest and forested areas of northern New Hampshire create WUI conditions. Communities in Coos, Grafton, and Carroll counties adjacent to national forest land are designated WUI areas. While lower risk than western states, drought conditions combined with pine forest create significant fire hazard. New Hampshire Division of Forests and Lands identifies at-risk communities.