Fiberglass Insulation in Sterling: Bag-Counted Attics and Fabric-Held Walls for Additions
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About 1,920 homes in the Sterling CDP date from the 1990s, roughly 19 percent, and newer ones sit around Dulles Town Center, which held its grand opening in 1999 and has its own CDP. Attics in houses of that age often hold only modest fill. Blown fiberglass is a good match because it is sized by the bag and the ruler: a number you can check.
Our crews come in by Route 7 and Loudoun County Parkway, or by the Dulles Greenway and Old Ox Road toward Loudoun Gateway, whose Metro station has a Sterling address but sits outside the Sterling CDP. Countryside, Cascades and Sugarland Run each have their own census place as well.
Depths, bags and code numbers for a Sterling fiberglass attic
- Per inch: blown fiberglass gives about R-2.2 to R-2.9, which is roughly 13 to 17 inches for R-38 to R-49.
- One published chart: R-38 needs 13.25 inches, R-49 needs 16.75 inches and R-60 needs 20.00 inches installed, and the maker lists negligible settling.
- Bags: R-49 is 22.2 bags of 32 pound fiber per 1,000 square feet.
- Code for new work: additions and new construction follow the 2021 code, which names R-60 for ceilings but accepts R-49 at full height over the top plates.
- Existing homes: no retrofit level is mandatory. ENERGY STAR suggests R-49 for an attic that already has a few inches and R-60 for a bare one.
Fiberglass is not the answer everywhere. Wet or matted fill that needs a settled-depth plan fits cellulose, bare framing that is already open is easy for batts, and leaky shells call for spray foam. The fiberglass and spray foam comparison lays out that trade-off.
Two fiberglass scopes: a 1,500 square foot attic in Countryside and an addition in Sugarland Run
A 1980s Countryside colonial with thin, patchy fill
Countryside's homes were built from 1981 to 1991, mostly colonials, and this scope assumes under 4 inches of tired fiber on a floor of about 1,500 square feet. The hatch is roughly 22 by 30 inches in the upstairs hall, so the hose runs up the stair. We seal the top plates, reconnect two bath fan ducts, set baffles at every soffit bay and swap or clear the cans. The chart says about 33 bags for a bare floor, and the old fill trims that slightly. At $0.90 to $1.60 per square foot that is $1,350 to $2,400, blown in a day to a 16.75 inch depth.
A rear addition on a 1970s Sugarland Run house, walls open
Sugarland Run was built out between 1970 and 1985. The new addition has about 900 square feet of 2x6 wall, open until drywall. We staple fabric over the bays and blow fiber through a slit, aiming for roughly R-23 to R-24. BIBS at $1.50 to $2.50 per square foot is $1,350 to $2,250. The ceiling is sized to current code, and an inspector sees the insulation before the drywall crew starts. Fabric on day one, fill and trim on day two. If the plans change a wall from 2x4 to 2x6, tell us before framing, because the fill and the R-value follow the stud depth.
Who decides what on a Sterling fiberglass job
Loudoun County Building and Development issues permits, takes applications through its LandMARC portal and answers at 703-777-0220. A loose-fill attic job is usually minor work, but the code leaves that to the building official, so we confirm with Loudoun before we start. Additions, wall removal, and electrical, mechanical or plumbing changes need permits, and so does asbestos disturbance. You decide the scope and the depth target. Your association sets its own approval rules; Loudoun tells applicants to ask it.
Utilities, old houses and what we will not promise
Dominion Energy and NOVEC both serve Loudoun, and your bill names yours. Dominion's Home Energy Evaluation covers attic insulation through participating contractors and publishes no dollar amounts. NOVEC shows audit tools and no insulation rebate. We quote no rebate. Loudoun has no county historic district in Sterling. In homes built before 1978 we do any drilling as lead-safe work, and vermiculite means we stop and leave it alone.
Sterling fiberglass answers: bag counts, BIBS walls, additions and vents
How many bags of fiberglass does a 1,500 square foot Countryside attic take at R-49?
One manufacturer's chart lists 22.2 bags of 32 pound fiber per 1,000 square feet for R-49, at a minimum installed depth of 16.75 inches. On 1,500 square feet that is about 33 bags over a bare floor. Existing fill that is dry and level trims the count a little. We verify by depth markers and a ruler rather than by bags alone, because the chart depth is the test.
Which fiberglass method goes into the new walls of a Sugarland Run addition?
While the studs are open, the fabric-held BIBS method fits: breathable fabric is stapled across the cavities and fiber is blown through a slit, reaching about R-15 in a 2x4 wall and up to about R-23 to R-24 in a 2x6 wall. The fabric must be covered with drywall. Dense-pack, drilled through finished walls, is a separate method, and we use it only where walls are already closed.
Does a rear addition in Sterling need a permit, and does the Dulles overlay apply?
An addition is permit work in Loudoun County, and the insulation is inspected before drywall goes up. Loudoun's Airport Impact Overlay District applies to new residential construction and additions, so we check your parcel for overlay rules before pricing. We have not verified which Sterling parcels are covered. Current code targets R-60 at the ceiling, with R-49 allowed at full uncompressed height over the top plates.
What keeps blown fiberglass from blocking the soffit vents on a Sterling colonial?
Baffles, set at every eave bay before any fiber goes in. Building code calls for at least a 1-inch space between the insulation and the roof sheathing at the vent, and baffles keep that channel open while the fiber banks up against them. Recessed lights that are not rated for insulation contact also get 3 inches of clearance or a replacement, so nothing is buried that should breathe.
What does blown fiberglass cost in Sterling for an attic cap or an addition's walls?
A blown attic cap to R-49 is $0.90 to $1.60 per square foot, so 1,500 square feet is $1,350 to $2,400. Typical 1,200 to 1,500 square foot attics run $1,200 to $3,000, and a garage ceiling is $1,000 to $2,000. BIBS in open walls is $1.50 to $2.50 per square foot, and whole-wall BIBS jobs run $3,000 to $7,500. Fiberglass batts in exterior walls are $1.00 to $1.80 per square foot.
More on fiberglass around Loudoun County
If you are weighing materials, see how we handled spray foam in Ashburn and Loudoun County next to the choices here. The Sterling page has our full service list, and service areas shows the region we cover.
Fiberglass pages for nearby towns: Ashburn, Leesburg, Herndon, Reston and Chantilly.
Other Insulation Options in Sterling
Blown fiberglass suits roomy 1980s and 1990s attics and open addition walls. Settled-depth questions or leaks near the Route 28 side of town may point elsewhere.
Batts for open joists | Cellulose for matted fill | Spray foam for air leaks
