Fiberglass Insulation in Alexandria, VA: Blown-In, Batts and BIBS

Fiberglass is not one product but three: batts cut to fit a cavity, loose fill blown across an attic floor, and blown fiber held behind fabric in an open wall. Each fits a different part of an Alexandria house, and mixing them up is how people overpay or end up with gaps. The city runs from the 1749 grid of Old Town to the townhouses of Cameron Station, and to Potomac Yard, a former rail yard now filling with new mixed-use buildings. Landmark and the Van Dorn Street area is another redevelopment site, on the grounds of the former Landmark Mall. Those sites are largely multifamily, so this page sticks to houses and townhouses.

Fiberglass by house type

Cameron Station townhouses. Built in five phases between 1999 and about 2007, with about 975 townhouses, 762 condos and 32 detached homes. An attic reached through a pull-down stair suits a hose better than carrying bags up, and blown fiber flows around the obstructions a cut batt fights.

Del Ray frame houses. The neighborhood was organized in 1894 on a grid. When a remodel takes a frame house to the studs, the open walls take batts or BIBS before drywall goes up.

Old Town brick rowhouses. Their closed plaster walls are not a fiberglass job. Fiberglass can be dense-packed through drilled holes at product-specific densities, but for older Alexandria frame walls we recommend dense-pack cellulose. Attic floors are another matter.

Blown fiberglass runs about R-2.2 to R-2.9 per inch, so R-38 to R-49 takes roughly 13 to 17 inches. Before any fill goes down we seal the attic floor, set baffles at the eaves so a 1 inch airway stays open under the roof deck, and keep insulation 3 inches from non-IC lights. BIBS, the Blow-In Blanket System, staples breathable fabric across exposed studs and blows fiberglass in behind it, for about R-15 in a 2x4 wall and up to about R-23 in a 2x6. The fabric has to be covered with drywall, and the method is for new construction or a gut renovation only. On regular 16 inch framing, batts usually cost less, and BIBS earns its price when a cavity is crowded with wiring or has an odd shape. Our R-value guide explains why depth and density both count.

Two fiberglass scopes, townhouse and frame house

A Cameron Station townhouse with R-19 batts in the attic

The attic floor is about 900 sq ft, reached through a pull-down stair in the upstairs hall, and holds the original R-19 batts. ENERGY STAR advises reaching R-49 when a house has some insulation already, so we add roughly 10 to 14 inches of blown fiberglass, or about R-30. Four small jobs matter: baffles at every eave bay, a bath fan duct run to a roof or wall cap, a weatherstripped and insulated hatch, and sealed wire holes. We work around the party-wall separation, since repair of a fire-rated assembly needs a permit. At $0.90 to $1.60 per sq ft the fill costs $810 to $1,440. Expect a half day, with hatch and baffle work as separate line items.

A Del Ray frame house gutted to the studs, with a 1,000 sq ft attic

A remodel near Mount Vernon Avenue has taken about 700 sq ft of exterior wall down to framing, with wiring running through the cavities, so BIBS fills around it better than batts. Walls at $1.50 to $2.50 per sq ft come to $1,050 to $1,750. On day two we blow the attic, about 1,000 sq ft at $0.90 to $1.60, or $900 to $1,600, for a combined $1,950 to $3,350. Because the remodel touches wiring, it is a permit job, and the walls stay open until the inspection the permit sets. Old knee walls at the attic edge are left for foam.

Where we point you elsewhere

Fiberglass is air-permeable, so a house with drafts needs sealing first. If a gas furnace or water heater sits in the basement below an attic you are sealing, have combustion safety testing done afterward. Crawl spaces are a different problem, covered in our crawl space guide, and rim joists belong to spray foam. For the full attic sequence, see our attic insulation page and the fiberglass versus spray foam comparison.