Blown Fiberglass and Blanket-Fill for Centreville Attics and Additions
Free Centreville Estimate
Book Phone Consultation
Centreville's median home was built in 1991, and about 73 percent of occupied homes are owner-occupied. Owners here hold on to their houses, and fiberglass is what most of them already have overhead, usually as thin batts. Loose-fill fiberglass is the upgrade that keeps the same material and fixes the depth, the gaps and the settled corners.
Our crews come in by Route 28 and Route 29 and work along Stone Road and Braddock Road, in London Towne and Sully Station. Stone Road runs through London Towne, and Sully Station belongs to Centreville. On this page, blown fiberglass means two jobs: loose fill across an attic floor, and a blow-in blanket system in walls that are open to the studs. Only one of them belongs in a finished house.
What the bag label says, and how to check it
- Per inch: about R-2.2 to R-2.9, so a few more inches than cellulose for the same R-value.
- By one manufacturer's chart: 13.25 inches for R-38, 16.75 for R-49 and 20 for R-60, with about 22 bags of 32 pounds per 1,000 square feet at R-49. Other products differ, so we read the label on the product we use.
- Settling: the same chart calls it negligible, which is the main reason people pick fiberglass over cellulose.
- Checking it yourself: we leave a ruler standing every few feet, so you can read the depth at any spot after we leave.
The rule for walls is simpler. BIBS is fabric stapled over open bays, and with the drywall off it reaches about R-15 in a 2x4 wall and roughly R-23 to R-24 in a 2x6. Once the wall is closed, the same fiber would have to be dense-packed through drilled holes, which is a separate method. Virginia's 2021 code asks for R-60 at the ceiling of new work, or R-49 where it is uncompressed at full height over the top plates. Our R-49 guide goes through the arithmetic.
Two fiberglass jobs, from a townhouse hatch to an addition's bare studs
1990s interior townhouse, 1,050 square feet of attic over old R-19 batts
The hatch in the upstairs hall is too small for bulky bales, so the hose runs up the stairs and a helper feeds it from the opening. We seal the plates, wire holes and fan housings, connect the bath fan to a roof vent, set baffles at the soffits and a dam around the hatch frame. Fiber goes over the batts to R-49. At $0.90 to $1.60 per square foot, 1,050 square feet is $945 to $1,680. A morning's work, with depth rulers left in the insulation. Because the floor is reached through a hatch, we check its weatherstripping on the way out, since an unsealed hatch leaks more air than any other single opening in the floor.
1980s colonial with a new two-story side addition, 2x6 walls open to the studs
The framing has passed and the wiring is roughed in, leaving about 540 square feet of exterior wall. Fabric is stapled across each bay, a slit is cut and fiber fills the cavity, which yields more than the 2021 code's R-15 wood-wall figure. At $1.50 to $2.50 per square foot the walls are $810 to $1,350. The addition's permit covers the inspection, so the fabric stays uncovered until the county signs off, and drywall then covers it, because the fabric is never left exposed. One day. If the addition also has a floor over a crawl space or a garage bay, that floor takes R-19 batts under the same permit.
When blown fiberglass is the wrong tool in Centreville
- The walls are closed. A finished wall gets dense-packed cellulose through small holes.
- The work is one basement room. Batts are less fuss there.
- Ductwork or an air handler sits in the attic. Spray foam brings the space inside the envelope.
- The floor is damp or the old fill is fouled. That gets cleared and repaired first. Our fiberglass versus spray foam post sets out where each one wins.
The permit office, and what triggers a permit
Centreville is in unincorporated Fairfax County. Land Development Services, 12055 Government Center Pkwy, Suite 324, Fairfax 22035, telephone 703-222-0801, issues permits. Blown attic insulation is usually not a permit item, but the code leaves the decision to the building official, so we confirm with LDS before we start.
An addition does need a permit, as do wall removal, wiring or mechanical changes and asbestos disturbance. On an addition, the insulation inspection is part of that permit.
Design review, parks and neighborhood limits
The Centreville Historic Overlay District takes in old Centreville near Braddock Road, Mount Gilead Road and Wharton Lane, along with Historic Centreville Park. If a permit-requiring exterior project lands inside it, design review applies. We check the parcel, because the boundary is not something we can state from memory.
Outside that core, Centreville is mostly subdivisions, and many have associations. We found no insulation rule, and exterior covenants matter only for roof vents and gable louvers.
Centreville owners ask about bag counts, old batts and design review
How many bags of blown fiberglass does an R-49 attic take in a Centreville townhouse?
One manufacturer's chart lists about 22 bags of 32 pounds per 1,000 square feet at R-49, which works out to roughly 23 bags for a 1,050-square-foot townhouse floor. Other products differ, so the count follows the label on the fiber we use, and the depth rulers confirm the result.
Can the fiberglass go over the old R-19 batts in my Centreville townhouse?
Yes, when the old batts are dry and intact. After sealing the plates and wire holes, loose fill goes over them to the target depth, which fills the low spots batts leave. Wet, fouled or collapsed batts come out first, and we pull back any that cover a fan housing.
What does the code require for the walls of a new Centreville addition?
The 2021 Virginia code lists R-15 in the cavity for wood-frame walls, or R-13 plus R-1 continuous. BIBS in a 2x6 wall gives roughly R-23 to R-24, which clears that. Existing rooms carry no mandatory retrofit level, so those upgrades are optional.
Does blown fiberglass settle the way cellulose does?
The chart we use lists negligible settling for blown fiberglass, while loose cellulose settles 10 to 20 percent. That is the main reason some owners prefer fiberglass in a hard-to-reach attic. It does need a few more inches than cellulose to reach the same R-value.
Does the Centreville Historic Overlay District affect an attic job in a Virginia Run house?
Most likely not. The district covers old Centreville, and the big 1980s and 1990s subdivisions are very unlikely to fall inside it, though the county lookup confirms any particular address. The review applies to exterior alterations that need a permit, and attic blowing is interior work.
Reading on R-values, and fiberglass pages for the next towns over
For what the numbers mean, read R-value decoded. The Centreville hub page and the service area list show the rest of what we do locally.
Fiberglass pages nearby: Chantilly, Fairfax, Manassas and Burke.
Other Insulation Options in Centreville
Fiberglass suits open attic floors and bare studs. For closed walls, tight basement rooms or ducts overhead, one of these Centreville pages will fit better:
Spray Foam Insulation in Centreville | Batt Insulation in Centreville | Cellulose Insulation in Centreville
