Fiberglass in Dunn Loring: Blown Attic Floors and Blanket-Fill Walls
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A Dunn Loring house from the 1960s or 1970s usually has a plain rectangular attic floor, and that is the easiest place to add loose-fill fiberglass. The Census Bureau puts the median home here at 1979 and counts 2,926 homes, nearly all detached. The fiber is light, it goes down quickly and one crew can move a great deal of it through a 22-by-30-inch hatch in a day.
Fiberglass comes in more than one form, and this page is about picking among them. Homes off Gallows Road and along Cedar Lane have their share of all three situations we describe below. Many carry Vienna, VA 22180 mailing addresses but sit in unincorporated Fairfax County, ZIP 22027, and the Dunn Loring Metro station in the Interstate 66 median is placed in Merrifield. Before quoting a house we ask when it was built, how the attic is reached and whether any wall is open, because those three answers decide almost everything else.
Three questions that pick the method
Is the attic floor open and dry?
Then blown loose-fill is the answer, and it is also the least expensive loose-fill we offer. It delivers about R-2.2 to R-2.9 per inch, so R-38 to R-49 is roughly 13 to 17 inches. One manufacturer chart lists 13.25 inches for R-38, 16.75 for R-49 and 20 for R-60, with negligible settling.
Are the studs bare?
Then BIBS, the blow-in blanket system. Breathable fabric is stapled across the open bays, fiber is blown through a slit, and drywall covers the fabric, which is never left exposed. A 2x4 wall reaches about R-15 and a 2x6 wall roughly R-23 to R-24.
Is the wall finished?
Then it is not BIBS, and we will not pretend it can be. Closed, empty walls are dense-packed through drilled holes, and for that we usually choose cellulose. A cluttered attic floor is easier with cellulose too, a single open room with batts, and a furnace in the attic with spray foam.
Fiberglass estimates for a 1966 family-room gut and a 1980s ranch attic
1966 house, family room stripped to 2x4 studs
The owners have removed the old plaster from the family room and kitchen, leaving about 820 square feet of exterior wall, with the electrician and plumber done. Fabric goes across every bay, a slit is cut for the hose, and fiber fills each cavity until it is firm. At $1.50 to $2.50 per square foot for BIBS the walls come to $1,230 to $2,050. The general contractor holds the permit, and the fabric stays uncovered until the county inspector signs off. Two days: fabric first, fiber second.
1980s ranch with a thin attic, 1,150 square feet and a pull-down stair
Matted R-13 batts cover the floor, the stair frame leaks and a bath fan ends in the attic. After sealing the frame, the plates and the wire holes, and running the fan duct to the roof, we set baffles at each soffit and blow fiberglass to R-49. At $0.90 to $1.60 per square foot the floor is $1,035 to $1,840. One day, plus an insulated stair cover and a depth ruler left standing. If a flue from a gas water heater passes through the floor, it keeps its required clearance and gets a dam, and we suggest a combustion safety test afterward.
Code numbers behind the quotes
Virginia's 2021 code asks for R-60 at the ceiling of new work, and accepts R-49 when it is uncompressed at full height across the attic, top plates included. It lists R-15 in the cavity of a wood-frame wall. Nothing in it forces an existing house to catch up. Our fiberglass versus spray foam comparison puts prices beside trade-offs, and the blown-in attic guide explains depth, sealing and baffles.
A 1-inch airway at each eave, non-IC cans kept 3 inches clear and a bath fan that exhausts outdoors are part of every attic job, not extras.
Who issues permits for Dunn Loring fiberglass work
Fairfax County Land Development Services, 12055 Government Center Pkwy, Suite 324, Fairfax 22035, telephone 703-222-0801, issues permits here. Blowing an attic is usually not a permit item, but the building official decides, so we confirm with LDS first.
A gut renovation is another matter. Wall removal and new electrical, plumbing or mechanical work need permits, and so does disturbing asbestos. On a renovation the general contractor carries the permit and we fit the insulation into their schedule.
Overlay districts, covenants and utilities
We found no historic overlay or National Register district in Dunn Loring. The Dunn Loring Woods civic association is voluntary and not an HOA, and we know of no insulation rule from it.
Dominion Energy supplies electricity, Washington Gas supplies gas and Fairfax Water supplies water. Dominion's Home Energy Evaluation covers attic and wall insulation through participating contractors, with no published dollar amounts.
Dunn Loring answers on depth rulers, BIBS and attic fans
Does blown fiberglass cost less than cellulose in a big, clean Dunn Loring attic?
Often a little. Both go down fast, and fiberglass is priced at $0.90 to $1.60 per square foot against $1.00 to $1.80 for a cellulose cap. It needs more inches for the same R-value, and it does not settle in the chart we use. If the floor is cluttered, cellulose may fit better despite the price.
What does a depth ruler in the attic actually tell me?
It lets you check our work. R-49 in blown fiberglass is about 16.75 inches by one manufacturer's chart, so a ruler reading near 17 inches at several spots tells you the blanket is even and deep enough. We leave the rulers standing when we finish.
Can my family-room walls get BIBS if only the plaster has been removed?
Yes, once the studs are bare, wiring and plumbing are roughed in and any moisture problem is fixed. BIBS is fabric stapled over open bays, so it belongs to gut renovations and new framing. The fabric is then covered by drywall, because it is never left exposed.
Why are bath fans and recessed cans part of a fiberglass attic quote?
Because they can ruin it. A fan that exhausts into the attic puts moist air into the fiber, and a non-IC can needs 3 inches of clear space. We run the duct outdoors and build covers or swap the fixtures, since insulation is not allowed to smother either.
Do I need a permit from Fairfax County to have my attic blown?
Usually not, because insulation is not on the state's list of permit triggers and minor, ordinary work is left to the building official. We call Land Development Services, 703-222-0801, before we start. A renovation that includes wiring or wall changes carries its own permit.
More reading, and fiberglass pages for nearby communities
The Dunn Loring hub page lists everything we do here, and the service area list shows the wider region. Our Tysons Corner contractor guide covers the market next door.
Fiberglass pages nearby: Vienna, Merrifield, Falls Church, Tysons Corner and Oakton.
Other Insulation Options in Dunn Loring
Fiberglass is one of four materials we use in Dunn Loring. If your attic is crowded, your walls are closed or ducts run overhead, compare these pages:
Spray Foam Insulation in Dunn Loring | Batt Insulation in Dunn Loring | Cellulose Insulation in Dunn Loring
