Blown-In Fiberglass and BIBS for Arlington Attics and Open Walls

Fiberglass turns up in Arlington attics in three forms: old batts, blown loose fill, and the blow-in-blanket system, BIBS, for walls that are open. The twins and small single-family houses of Aurora Highlands, the pre-war homes of Westover and the Cape Cods of Cherrydale mostly need the first two. This page is about the blown forms, reached along Langston Boulevard, Columbia Pike and Arlington Boulevard: what they do, when we use them over cellulose or foam, and what each costs.

The numbers behind a blown-fiberglass quote

• Depth. About R-2.2 to R-2.9 per inch, so it takes more depth than cellulose. One manufacturer chart lists 16.75 inches for R-49 and states that its product shows negligible settling.
• Target. Existing homes have no mandatory R-value. ENERGY STAR recommends R-60 for a bare attic and R-49 where three to four inches already sit there, and we work toward that.
• Air channel. The model residential code keeps 1 inch of airflow between insulation and roof sheathing at the vent, and baffles hold that space.
• Vent area. The model code sets net free vent area at 1 square foot per 150 square feet of attic, and only a balanced upper and lower split allows less, so we check yours and do not block it.
• Walls. BIBS is for open framing only, giving about R-15 in a 2x4 wall and up to about R-23 in a 2x6 because the fiber is blown denser than a batt.

Blown fiberglass is horizontal loose fill, laid over the attic floor with no fabric and no drilled holes, which suits attics with plenty of obstructions. Before blowing, we seal air leaks at the attic floor.

Two blown-fiberglass scopes for Arlington houses

Aurora Highlands twin, 700 sq ft attic at R-11

One half of a semi-detached house of about 1,100 sq ft has a low attic over about 700 sq ft with R-11 batts. Blown fiberglass to R-49, about 16.75 inches on the manufacturer chart quoted above, is $0.90 to $1.60 per sq ft, or $630 to $1,120. The shared wall between the two halves is where air tends to slip, so we seal along it and around the chimney before any fiber goes down.

The hatch is in a closet, so the hose goes through it and the crew never carries bags up. Bath fan ducts get checked and reconnected, and recessed cans that are not IC-rated get a dam so nothing sits within 3 inches of them. If we find vermiculite, the job stops there. Plan on half a day. Our row house guide covers what shared walls do in attached homes.

Westover cottage, gut renovation with 800 sq ft of open wall

A pre-war cottage of about 1,000 sq ft has been stripped to the studs. BIBS at $1.50 to $2.50 per sq ft on 800 sq ft of net wall is $1,200 to $2,000, and blown fiberglass on a 700 sq ft attic is another $630 to $1,120. The total is $1,830 to $3,120. If the owner picks wall batts instead, at $1.00 to $1.80 per sq ft, the walls drop to $800 to $1,440, and we say so plainly on the estimate.

The crew staples fabric across each bay, cuts a slit, blows to full density and trims the fabric flush to the studs. It must be covered by drywall, never left exposed. Plumbing and wiring rough-in is finished and signed off before the fabric goes up. Expect two days for the walls and a half day for the attic.

Where blown fiberglass is the wrong call

If the walls are closed, we drill and dense-pack with cellulose, and an open wall that only needs a standard fill is often cheaper with batts. Rim joists, crawl space walls and knee-wall slopes need an air barrier, which is spray foam territory. Our fiberglass and spray foam comparison explains why. For bigger scopes, expect $3,000 to $7,500 to retrofit BIBS through every wall of a gutted house, and $1,000 to $2,000 for a garage ceiling. Depth rulers stay stapled to the joists after any attic job, and the estimate is written and free.

Frequently Asked Questions