Nashua, NH Building Setbacks & Zoning: Setback Rules (2026)

Nashua's Land Use Code Sec. 190-16 (Dimensional Regulations) contains the city's Dimensional Matrix — the table of minimum lot area, frontage, front yard, side yard, rear yard, maximum lot coverage, and maximum building height for each zoning district. Residential districts in Nashua include: R-40 (40,000 sq ft minimum lot — large-lot single-family, typically rural-edge); R-30 (30,000 sq ft); R-18 (18,000 sq ft); R-9 (9,000 sq ft minimum lot — Nashua's most common single-family district); R-A (medium-density two-family); R-B (higher-density two- and three-family); and R-C (high-density urban). Specific front/side/rear setbacks vary by district per the Dimensional Matrix — typical Nashua residential standards are roughly 30 ft front / 15 ft side / 30 ft rear in R-40 and R-30, 25 ft front / 10 ft side / 25 ft rear in R-18, 20-25 ft front / 8-10 ft side / 20-25 ft rear in R-9, and reduced setbacks (10-15 ft front, 5-8 ft side, 15-20 ft rear) in R-A, R-B, and R-C. Confirm exact values with the Nashua Department of Building Safety because the matrix is revised periodically. Corner lots must provide a front yard along each street frontage. Detached accessory structures (sheds, carports, ADUs) follow Sec. 190-31 (Accessory Buildings) and Sec. 190-32 (Accessory Dwelling Unit), with a 4 ft side and rear setback for ADUs and a 10 ft minimum separation between principal dwelling and detached ADU (with an exception allowing reduction if needed to fit an up to 800 sq ft ADU). Critically, NH RSA 674:72 (effective 7/1/2025, HB 577) preempts Nashua from imposing additional lot size or setback requirements on ADUs beyond the single-family district standards — Nashua cannot impose a larger lot or wider setbacks than the underlying district requires for the principal single-family home. Existing structures (garages, barns) may be converted to ADUs even if they violate current setbacks. Fences are exempt from the standard setback rules but must meet sight-distance requirements at corners. Decks, porches, eaves, and other projections are governed by encroachment provisions in Sec. 190-16. Variances from dimensional standards are obtained through the Zoning Board of Adjustment under Sec. 190-180 and RSA 674:33 (hardship variance standard).