Blown Fiberglass and BIBS for Woodbridge, Montclair and Potomac Shores Homes

One material, three jobs. Fiberglass can be blown flat across an attic, cut into open cavities as batts, or blown behind fabric as BIBS, and which one applies depends on what you are looking at. Woodbridge itself grew after the war and sped up from the 1980s. Montclair filled in between the late 1960s and the 1990s. Potomac Shores, along the river south of town, has been adding homes from 2014.

We work the Richmond Highway corridor, Prince William Parkway, Gordon Boulevard (Route 123) and I-95, and reach Montclair and Potomac Shores from the south end of the county.

Three questions that pick the method

• Can you see the top of the joists? Then it is blown loose fill. It gives about R-2.2 to R-2.9 per inch, so R-38 to R-49 takes roughly 13 to 17 inches, and it flows around wiring and bracing that slow down cut batts. The attic floor is sealed first, because ENERGY STAR tells contractors to seal leaks before adding insulation.
• Can you see the studs? Then batts or BIBS. BIBS is a patented system: breathable fabric is stapled over open framing and fiber is blown through a slit, reaching about R-15 in a 2x4 wall and R-23 to R-24 in a 2x6. The fabric must be covered by drywall, so it belongs to additions and gut renovations.
• Is the wall closed? Then neither. Fiberglass can be dense-packed through drilled holes at a density that depends on the product, from about 1.6 to 2.3 pounds per cubic foot, but for old painted walls we usually quote cellulose.

Air leaks and damp are where fiberglass stops. Crawl space walls, rim joists and leaky knee walls do better with spray foam, and the fiberglass versus spray foam comparison lays out the trade-offs. A plain open wall is often a batt job.

Two jobs with the arithmetic shown

Montclair house from the 1970s: flattened R-19 under stored boxes

About 1,400 sq ft of 6.25 inch batts lie pressed flat, with gray streaks around the ceiling light fixtures. The crew clears a path, seals top plates and penetrations, sets eave baffles and blows roughly 10 to 14 inches of fiberglass over the old layer to reach R-49. At $0.90 to $1.60 per sq ft the cap is $1,260 to $2,240. The 22 by 30 inch hatch gets a dam and a gasketed lid, and depth rulers stapled to the joists let you read the finished depth yourself. One day, cleanup of the path and hatch included.

Dale City house from the 1960s: first floor taken to the studs

The owners are demolishing the kitchen and family-room walls, which exposes about 1,200 sq ft of 2x4 cavities while the electrician and plumber reroute. Permits apply, so insulation goes in after rough-in and before drywall.

• BIBS at $1.50 to $2.50 per sq ft: $1,800 to $3,000, filling to R-15.
• Fiberglass batts at $1.00 to $1.80 per sq ft would be $1,200 to $2,160.
• We choose BIBS when wiring and blocking would leave voids behind a batt, not to save money.

If knob-and-tube turns up in those walls, an electrician evaluates it before anything is blown, and it is never buried. The wiring and plumbing rough-in has to be finished and inspected before the fabric goes up, and drywall covers the fabric afterward, since it is never left exposed. A bay that cannot be filled from the front gets a batt instead. One day of installation.

Price bands by size of job

Blown fiberglass to R-49 is $0.90 to $1.60 per sq ft, which puts an attic of 1,200 to 1,500 sq ft at about $1,200 to $3,000. A garage ceiling in batts or blown fiber is $1,000 to $2,000, and a whole-wall BIBS retrofit on a gutted house is $3,000 to $7,500. Depth and density both count toward the final R-value, which is why the R-value guide is worth a read before you compare bids. Estimates are written and free.

Frequently Asked Questions