Fiberglass Insulation in Reston: Blown-In Attics, BIBS for Open Walls, and How It Compares with Cellulose
Free Reston Estimate
Book Phone Consultation
Detached houses are the minority in Reston, about 20 percent of the roughly 30,485 homes the census counts, but they are where blown fiberglass does the most. Big attics, long runs of joists and few wiring obstacles suit loose fill, and Tall Oaks, beside Lake Fairfax Park, and North Point both list single-family homes among their types. Townhouse attics are smaller, and condo spaces may not be yours to insulate, so ask your association first.
We drive Hunter Mill Road, Fairfax County Parkway and the Dulles Toll Road corridor to reach these jobs. Each one starts with air sealing, because ENERGY STAR says to seal the attic floor before adding insulation.
Blown fiberglass beside cellulose in the same Reston attic
| Question | Blown fiberglass | Loose-fill cellulose |
|---|---|---|
| R-value per inch | About 2.2 to 2.9 | About 3.2 to 3.8 once settled |
| Depth for R-49 | Roughly 13 to 17 inches | About 3 to 4 inches less |
| Settling | Negligible on one manufacturer chart | 10 to 20 percent over time |
| Installed cost | $0.90 to $1.60 per square foot | $1.00 to $1.80 for a cap to R-49 |
Fiberglass suits a tall attic with few bypasses. A shallow attic under a low roof or beside a knee wall may take cellulose better, since it reaches the same R-value in less depth.
Three installs that all get called fiberglass
Loose fill is blown horizontally over an attic floor. BIBS, the Blow-In-Blanket System, blows fiber behind fabric stapled across open stud cavities, so it needs a new build or a gut renovation, and it gives about R-15 in a 2x4 wall and R-23 or R-24 in a 2x6. Dense-pack fiberglass is a separate drill-and-fill method for closed walls, with a density set by the product data sheet, from about 1.6 pounds per cubic foot in Department of Energy guidance to 2.2 or 2.3 for two manufacturers. The fabric in BIBS always ends up behind drywall.
Walls open to the studs in a renovation are cheaper in batts, closed walls are a cellulose job, and EPA says to assume vermiculite contains asbestos and leave it alone, so no fiber goes over it.
Reston fiberglass estimates: a South Lakes attic and a house down to the studs
A 1,500 square foot attic in a detached South Lakes house with 4 inches of old fill
A gas furnace stands in the attic along with two bath fan ducts, and the hatch is a 24-inch square in the hallway. The scope is sealing the top plates and duct penetrations, baffles at every soffit vent so a 1-inch air space stays open, blown fiberglass to R-49 at about 17 inches and depth rulers on the rafters. The furnace gets a combustion safety test after the sealing. At $0.90 to $1.60 per square foot the floor is $1,350 to $2,400. The crew finishes in a day, and the hatch gets a weatherstripped, insulated cover.
A detached house stripped to the studs, 1,250 square feet of 2x4 wall
After a whole-house renovation the walls are open, so BIBS applies. Fabric goes across each bay, fiber is blown through a slit, and drywall covers it. Wall removal and framing are permit work with the county, and painted surfaces cut or demolished in a pre-1978 house bring in lead-safe rules. BIBS lands near R-15 in a 2x4 wall, matching the 2021 code's R-15 cavity value, though the manufacturer's chart sets the exact number. At $1.50 to $2.50 per square foot the walls are $1,875 to $3,125, and the work takes two days.
County permits and the gas-appliance test
Fairfax County Land Development Services, 12055 Government Center Pkwy, Suite 324, Fairfax, VA 22035 (703-222-0801), handles building permits for Reston. Virginia's code does not name insulation, and a minor, ordinary job is usually not a permit item, though the building official decides, so we confirm before starting. Gut renovation, wall removal, framing and any electrical, plumbing or mechanical change is permit work. A gas furnace or water heater near the attic gets a combustion safety test after air sealing, and knob-and-tube wiring needs an electrician first.
Associations, Town Center and Lake Anne
Reston Association is a covenant association and not a permit office, and its design review covers exterior changes only. A new ridge vent or altered siding is visible, so we ask RA at 703-435-6530 when the exterior is involved, while fiber blown into an attic from inside is interior work. Reston Town Center reviews exterior changes through its own board. Lake Anne Village Center, a county Historic Overlay District dating to 1983, sends exterior changes to the Architectural Review Board, and it covers the village center, not every Lake Anne home. Dominion Energy, Washington Gas and Fairfax Water are the utilities.
Reston fiberglass questions, answered plainly
What does blown fiberglass cost for a Reston townhouse attic versus a detached house?
Blown fiberglass to R-49 runs $0.90 to $1.60 per square foot. An 850 square foot townhouse attic comes to $765 to $1,360, and a detached 1,400 square foot attic to $1,260 to $2,240. Our band for a typical 1,200 to 1,500 square foot attic is $1,200 to $3,000. BIBS in open wall cavities is $1.50 to $2.50 per square foot, or $3,000 to $7,500 for a whole-wall retrofit.
What if my Reston attic is too shallow for 17 inches of fiberglass?
Then cellulose may fit the space better. It reaches the same R-value in about 3 to 4 fewer inches, at the cost of settling 10 to 20 percent over time. A low roof or a knee wall often makes the attic shallow. We measure the clearance at the eaves first, because baffles have to keep a 1-inch air space open whichever material goes in.
What separates BIBS from dense-packed fiberglass in a Reston house?
BIBS stands for Blow-In-Blanket System. Breathable fabric is stapled over open stud cavities and fiberglass is blown through a slit, so it needs exposed framing. Dense-pack drills holes in a closed wall and uses no fabric. The two should not be confused, and finished Reston walls only ever get the drilled method, with cellulose or fiberglass.
Is it safe to blow insulation in an attic that has a gas furnace?
Yes, with care. ENERGY STAR says to have combustion safety testing done after any air sealing when fuel-burning appliances are in or near the space. We seal first, keep clearances, then the furnace or water heater gets tested. Knob-and-tube wiring is a separate stop: an electrician looks at it before any fiber goes near it.
Does a fiberglass attic job ever involve Reston Association?
Only when the exterior is touched. RA design review covers exterior alterations, and blowing fiber into an attic from inside is interior work. A new ridge vent or altered siding is visible and may need an application, so we call RA at 703-435-6530 in those cases. Not every Reston property belongs to RA, and Reston Town Center has its own exterior-only review.
Fiberglass reading, and pages for towns near Reston
The fiberglass versus spray foam comparison and the Reston spray foam article show where each material wins. The Reston page lists every service, and the service areas show the wider map.
Fiberglass pages for neighboring towns: Herndon, Great Falls, Tysons Corner, Sterling and Chantilly.
Other Insulation Options in Reston
If your Reston attic is shallow, your walls are closed or the problem is leaks, a different material may fit. These pages cover each one.
Batts for open framing and basements | Cellulose for shallow attics | Spray foam for drafts
