Spray Foam Insulation in Washington, DC

Spray foam insulation in Washington, DC has to handle both ends of the year. Summers average 79.8F in July with relative humidity around 66 percent, and the city sees about 37 days a year at 90F or hotter. Winters bring about 64 nights at or below freezing. A rowhouse with a hot, leaky roof cavity and an open basement fights the air conditioner all summer and the furnace all winter. We seal and insulate those spaces with closed-cell or open-cell foam, blown-in cellulose or fiberglass, or a combination chosen for each part of the house.

Old houses are the rule here

Rowhouses are prominent in the parts of the city built after the Civil War, many with Federal or late Victorian fronts. Capitol Hill's historic district is mostly 19th-century rowhouses. Petworth's brick rows date from the 1920s and 1930s. Georgetown predates the District. None of these were built with modern air sealing, and many have thin or missing insulation in the roof and none in the brick walls.

Closed cell vs open cell

Closed-cell foam is dense, about R-5 to R-7 per inch in HomeGuide's figures, and slows water vapor at typical thickness. It suits basement walls, rim joists, crawl spaces and shallow roof cavities where every inch counts. Open-cell foam runs about R-3.5 to R-3.7 per inch, costs less, and seals air well; it is common under roof decks when an attic is brought inside the conditioned space. In DC's humid summers the moisture details matter, and we explain which foam goes where.

What the code asks for

DC's residential energy code is based on the 2017 IECC and covers Climate Zone 4A. Its prescriptive table lists R-49 for ceilings, and new homes must test at 3 air changes per hour at 50 pascals. ENERGY STAR suggests R-60 for an uninsulated attic in Zone 4A, or R-49 added where there is already 3 to 4 inches.

Spray foam insulation cost

HomeGuide's 2026 guide puts installed spray foam at $1.50 to $5.00 per square foot: open cell $1.50 to $3.50 and closed cell $3.00 to $5.00. Fixr lists $3.15 to $7.50 per square foot in existing walls. Those are national figures. We measure first, and the written quote is the price.

Hot summers, cold snaps

The DC area's summers drive most of the energy complaints we hear: top floors that will not cool down, and basements that feel clammy. Winter brings drafts at baseboards and cold floors over basements and crawl spaces. Air sealing helps with both.

Comparing insulation companies

When you talk with spray foam insulation contractors or insulation companies in the DC area, ask each for the same details in writing: foam type and thickness for each area, target R-value, how air sealing is handled, and whether removal and disposal are included. That makes quotes comparable. If you searched for spray foam insulation near me, we cover the District plus close-in Maryland and Virginia. Get a free estimate

In the District we work across Capitol Hill, Georgetown, Petworth and the rest of the city's rowhouse and detached-home neighborhoods. In Maryland we cover Silver Spring, Takoma Park, Bethesda and Rockville in Montgomery County and Hyattsville, College Park and Bowie in Prince George's County. In Virginia we work in Arlington, Alexandria, Falls Church and McLean. The housing changes a lot across that area: 19th-century rowhouses, Victorian commuter-suburb houses, interwar bungalows, garden apartments, postwar subdivisions and newer infill. We plan each job around the house in front of us.