Attic Insulation & Air Sealing in Washington, DC

Attic insulation and air sealing is usually the first fix for a top floor that bakes in July. On a summer afternoon, the air in an attic or roof cavity can be much hotter than outside. Thin insulation lets that heat pour down into the rooms below, and gaps around light fixtures, chases and top plates let hot attic air leak in directly. In winter the same gaps run in reverse, carrying warm air up and out.

Seal first

We seal the openings before adding insulation: around plumbing and vent stacks, wiring holes, recessed lights rated for contact, chimney chases (with proper clearances), duct boots and the attic hatch. Then we bring the insulation to depth.

How much

DC's code, based on the 2017 IECC for Zone 4A, lists R-49 for ceilings. ENERGY STAR suggests R-60 for an uninsulated attic in Zone 4A, or R-49 added to an attic with 3 to 4 inches already. With blown fiberglass around R-2.2 to R-2.9 per inch and cellulose R-3.1 to R-3.8 (HomeGuide), that is more than a foot of loose fill.

Rowhouse roof cavities

Many rowhouses have a low-slope roof with a shallow space above the top-floor ceiling, sometimes reachable only through a small hatch. Where there is room, we blow in loose fill. Where there is not, foam may be the only way to get meaningful R-value. We look before recommending either.

Ductwork in the attic

Many suburban homes have air handlers or ducts in the attic. Leaky ducts in a hot attic waste a lot of cooling. Sealing them, or foaming the roof deck to bring the attic inside, can be part of the plan.

Recessed lights and old fixtures

Older recessed lights are often not rated for insulation contact and leak a lot of air. We identify them and either cover them with an approved enclosure or note them for an electrician, before blowing insulation around them.