Blown Fiberglass and BIBS in Bailey's Crossroads: Attic Depths by Size, Fabric-Held Walls for Additions
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Bailey's Crossroads sits where Leesburg Pike meets Columbia Pike, and our crews also arrive by Sleepy Hollow Road. The houses and townhouses around that crossing were mostly built between 1960 and 1989, a span that covers about two-thirds of all the homes in the Census Bureau's 2020 to 2024 survey. The median build year is 1976, and survey margins are wide, so read those shares as a guide. Attic floors from those decades are often thin, and some of them have been disturbed by later wiring and duct work.
Fiberglass here means two different jobs. One is loose-fill blown across an attic floor to a measured depth. The other is BIBS, fiberglass held behind fabric in bare wall or ceiling cavities of an addition or gutted room. Everything else, including finished walls, is handled further down the page.
Attic size ladder: bags, inches and price for three Bailey's Crossroads attics
| Attic floor | Bags of 32 lb for R-49 | Installed depth | Price at $0.90 to $1.60 per sq ft |
|---|---|---|---|
| 600 sq ft | About 13 | About 16.75 in | $540 to $960 |
| 900 sq ft | About 20 | About 16.75 in | $810 to $1,440 |
| 1,200 sq ft | About 27 | About 16.75 in | $1,080 to $1,920 |
The bag figure is 22.2 bags per 1,000 sq ft, and the depth comes from one manufacturer's chart, which lists 13.25 in for R-38 and 20 in for R-60. Blown fiberglass delivers roughly R-2.2 to R-2.9 per inch, so it needs more height than cellulose, and that chart reports negligible settling. If 3 to 4 inches of old insulation already lie on the floor, ENERGY STAR advises adding enough to reach R-49, which lowers the bag count. We measure the old layer before we quote. The R-49 and Zone 4A article explains where these targets come from.
BIBS stays behind the drywall, so it needs bare studs
In a BIBS job, breathable fabric is stapled over the open cavities and fiberglass is blown in through a slit cut in it. That is why the method belongs to additions and gutted rooms, never to a finished wall. A 2x4 bay comes out near R-15 and a 2x6 bay at about R-23, because the fiber is blown denser than a batt. The fabric must be covered with code-approved board and never left showing, so inspectors see the framing first. Dense-pack for a closed wall is a separate method, usually with cellulose.
Sized and priced: a 1969 rambler attic and a bedroom over a garage
A 1969 rambler with 1,320 sq ft of attic under thin R-13 batts
The only way up is a pull-down stair in the hall, and flex duct wanders across the joists. The crew builds a dam around the stair opening, seals the plates and duct boots, sets baffles and boxes two can lights that are not insulation-rated. Fiberglass is then blown to the chart depth of about 16.75 inches, roughly 29 bags, and the depth is read with a ruler at several points. At $0.90 to $1.60 per sq ft, 1,320 sq ft comes to $1,188 to $2,112. One day, and the stair gets a gasket.
A 12 by 22 foot bedroom built over the garage of a 1977 split-level
The 2x6 walls are framed and open, with about 300 sq ft of wall after windows. BIBS fabric goes over each bay and fills them to about R-23. BIBS runs $1.50 to $2.50 per sq ft, so the walls cost $450 to $750. The flat ceiling is 264 sq ft and is blown to R-49 at $0.90 to $1.60 per sq ft, which adds $238 to $422. The total is $688 to $1,172. An addition is permit work, so the county inspector signs off on the framing before the fabric is covered. Two days with the inspection wait.
Who looks at a blown attic or a BIBS wall
Fairfax County Land Development Services issues permits for the Mason District, including Bailey's Crossroads, at 12055 Government Center Pkwy, Suite 324, Fairfax, VA 22035, 703-222-0801. Blowing an existing attic is typically not a listed trigger and the building official has the last word, so we check with that office before we book. A bedroom addition, a gutted room or new wiring is different, and then the inspector comes before the fabric or drywall closes the cavity. A Falls Church mailing address does not make a parcel part of the city, but we confirm the lot. A house built in 1976 is not required to reach the R-60 that new ceilings must meet.
Gray dust, damp fans and other reasons not to simply add fiberglass
Gray or black streaks on old batts near a bath fan or ceiling penetration are house dust caught where air leaks through. They point to a gap to seal, and they are neither mold nor a failed layer. Wet or matted material is removed first. Finished walls are drilled and packed with cellulose. Bare, regular bays in a small remodel are cheaper with batts. A furnace in the attic or a roof deck that needs sealing points to spray foam. Fairfax County's 15 historic overlay districts do not include Bailey's Crossroads, so no design review slows any of this.
Bag counts, fabric and gray batts: fiberglass answers for Bailey's Crossroads
My attic already has about 4 inches of old batts. Do you still bring the full R-49 bag count?
No. ENERGY STAR advises adding enough to reach R-49 when 3 to 4 inches are already down, so the load is smaller than for a bare floor. We measure the old layer at several points, check that it is dry and flat, and subtract what it already delivers. The estimate lists the old depth, the target and the bag count so you can follow the arithmetic.
Can the BIBS fabric in my new bedroom addition stay exposed like a wall finish?
No. The manufacturer's instructions require the fabric to be covered with a code-compliant building material, and the county inspects the framing before anything covers it. So BIBS goes in after the rough-in approvals and before drywall. The fabric is a holding layer for the fiberglass and it is not a finished surface.
The old batts around my bathroom fan vent are dark gray. Must I replace them?
Usually not. The gray is house dust filtered out where air leaks through, so it marks a gap and it is not mold. We seal the gap, duct the fan to a roof or wall cap if it ends in the attic, and blow new fiberglass over the layer. Damp or matted batts come out first, and pebbly fill that may be vermiculite is left alone.
I own a townhouse near the Minnie H. Peyton Community Center at Bailey's that I rent out. Who signs the estimate?
You do, as the owner. The tenant lives there but does not decide on insulation, so we quote you and arrange hatch access with the tenant. Attached homes can have association rules for roof work, so we ask for them. About half of households here rent, which makes this a routine request for us.
My house dates from 1976. Does code now force me to blow the attic up to R-60?
No. The R-60 number, or R-49 at full uncompressed height, is what the 2021 Virginia code asks of new ceilings and additions. An existing house has no mandatory retrofit. ENERGY STAR recommends R-49 when a few inches are already down, and R-60 for an empty attic, so we size your attic to what is there and to your budget.
Fiberglass pages for the places next to Bailey's Crossroads
Fiberglass pages cover Seven Corners, Falls Church and Annandale. The service areas page shows the wider reach.
If you are weighing materials, our fiberglass versus spray foam comparison is an even-handed read.
Other Insulation Options in Bailey's Crossroads
Finished walls, a gas furnace in the attic or a very small remodel may suit another material better, even for a house a short drive from Culmore Shopping Center. See the alternatives:
Spray Foam Insulation in Bailey's Crossroads | Batt Insulation in Bailey's Crossroads | Cellulose Insulation in Bailey's Crossroads
