Fiberglass Insulation in Ashburn, VA: Blown-In, Batts and Blow-In-Blanket
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Fiberglass shows up on our Ashburn jobs in three forms: batts, loose-fill blown over attic floors, and blown fiberglass held behind fabric in open walls. Choosing the form that matches the cavity matters more than the brand on the bag. A batt jammed into a closed wall or loose-fill spilled into a stud bay both fail for the same reason, which is that the material never fills the space.
Broadlands, Belmont Country Club and Moorefield Station mix townhomes with single-family houses, and Ashburn Farm and Brambleton do too, so attic size varies from a few hundred square feet to well over a thousand. Crews cross town on Route 7 (Leesburg Pike), Waxpool Road, Claiborne Parkway and Loudoun County Parkway, and the estimate is measured attic by attic, not by neighborhood.
Which Fiberglass Goes Where
- Blown loose-fill on attic floors. Roughly R-2.2 to R-2.9 per inch, with one manufacturer chart calling for 16.75 inches at R-49 and reporting negligible settling. We seal the plates and hatch, place baffles at the eaves, and blow to marked depth.
- BIBS in open walls. Fabric is stapled across bare studs and fiber is blown in through a slit, giving about R-15 in a 2x4 wall and up to R-23 or R-24 in a 2x6 wall. It suits additions and gut renovations only, and the fabric gets covered with drywall.
- Dense-pack fiberglass in closed walls. A separate method, drilled and filled to the product's data sheet density, which ranges from about 1.6 to 2.3 pounds per cubic foot depending on the fiber.
- Batts. Best for regular open bays and garage ceilings, covered on our Ashburn batt page.
Limits of Fiberglass in Ashburn Houses
Loose fiberglass is air-permeable, so it does not stop leaks on its own; the sealing underneath does the work, and gray streaks on old attic insulation show where that sealing is missing. Wind can also push fiber back from the soffits if baffles are missing, and recessed cans below must be IC-rated or boxed in before fiber goes over them. For attics with tight spots, irregular framing or many wires, cellulose packs more evenly. For a bonus room with cold roof slopes, foam is the right tool, described on the Ashburn spray foam page.
On code, existing houses have no retrofit mandate. New walls in an addition follow the 2021 Virginia code, which is R-15 in a wood wall, so 2x6 BIBS clears it comfortably. The ceiling target is R-60, and R-49 is accepted only if it is uncompressed at full height over the top plates.
Ashburn Fiberglass Scopes and What They Cost
Our ranges here are $0.90 to $1.60 per sq ft for a blown attic cap to R-49, and $1.50 to $2.50 per sq ft for BIBS in walls.
2000s townhome attic in Belmont Country Club
A townhome here has about 700 sq ft of attic floor with settled R-19 batts, a 22 by 30 inch hatch, and a gas water heater in the closet below. The scope is air sealing, baffles, a blown cap to R-49 over the batts, and an insulated hatch cover. Combustion safety testing follows the sealing. The job is a half day.
At $0.90 to $1.60 per sq ft, 700 sq ft costs $630 to $1,120.
520 sq ft family-room addition on a 1990s Ashburn Farm house
The addition has 2x6 walls with about 800 sq ft of exterior wall to fill. The scope is BIBS in every bay after electrical rough-in and before drywall, then loose-fill to R-49 in the ceiling once the drywall is up. We check the truss heel height, since R-49 only counts as R-60 at full height over the plates. Two visits, a day each.
BIBS at $1.50 to $2.50 per sq ft is $1,200 to $2,000. The ceiling at $0.90 to $1.60 per sq ft is $468 to $832, so the total is $1,668 to $2,832.
Zoning and Permit Notes for Fiberglass Work
Ashburn has no town government, so Loudoun County does zoning approval, permits, plan review and inspections. Its Department of Building and Development takes permits at 1 Harrison St. SE in Leesburg and answers at 703-777-0220. An attic cap alone is usually not a permit item, but the code leaves that to the building official, so we confirm with the county first. A new addition needs zoning approval and a building permit, and the county inspects the insulation before drywall covers it.
Loudoun asks applicants to contact their homeowner association too. Ashburn is normally outside the county's historic overlays, such as Aldie, Waterford and Goose Creek, and we confirm the parcel.
Frequently Asked Questions
How many inches of blown fiberglass does R-49 take?
Blown fiberglass gives about R-2.2 to R-2.9 per inch, so R-38 to R-49 takes roughly 13 to 17 inches. One manufacturer chart lists 13.25 inches for R-38, 16.75 inches for R-49 and 20 inches for R-60. The bag label carries the exact chart, and we mark depth across the floor to match it. Existing homes have no required R-value, but ENERGY STAR suggests R-49 to R-60 for this area.
Our Ashburn Farm addition is framed but not drywalled. Is that the right moment for BIBS?
Yes, that is the window. With the studs bare and the wiring and plumbing roughed in, fabric goes across each bay and fiberglass is blown through a slit, reaching about R-15 in 2x4 framing and up to R-23 or R-24 in 2x6 framing. Once drywall is up the option is gone, and a closed wall can only take dense-pack through drilled holes. Loudoun inspects insulation before the drywall, so we schedule our visit ahead of that inspection.
What do the gray streaks on my attic insulation mean?
Gray or dark streaks are dust and soot that air carried through the fiberglass and left behind, called filtration soiling. They mark where warm house air leaks into the attic, along top plates, duct boots and wire holes. They are not mold, and they do not show the insulation cleaning your air. The fix is air sealing before more insulation goes down.
Is fiberglass or cellulose better for an Ashburn attic?
Both reach R-49 when installed well. Blown fiberglass is priced lower per square foot in our Ashburn range, at $0.90 to $1.60 against $1.00 to $1.80 for a cellulose cap, but it needs several more inches of depth. Cellulose settles 10 to 20 percent, so bids should compare settled depth. If your attic has odd shapes and many wires, ask us to price both.
Does a gas furnace or water heater change how you insulate?
It adds a step. If a fuel-burning appliance is in or near the space we seal, ENERGY STAR advises combustion safety testing after the air sealing, since a tighter house can change how flue gases move. That means the venting gets checked before the job is called finished. Attic hatches under a furnace closet also get an insulated, gasketed cover.
Ashburn Fiberglass: Guides and Sister Pages
Read the Ashburn insulation overview and browse all service areas. Our fiberglass versus spray foam comparison is candid about both, and R-value decoded explains the numbers. Budget with the attic insulation cost guide. Fiberglass work is also available in Sterling, Leesburg, Herndon and Reston.
Other Insulation Options in Ashburn
Loose-fill fiberglass is one of four ways we fill a cavity in Ashburn. A townhome attic in Belmont Country Club and a new family-room addition call for different products, so compare the other pages too:
Spray Foam Insulation in Ashburn | Batt Insulation in Ashburn | Cellulose Insulation in Ashburn
