Fiberglass Insulation in Chevy Chase: Blown Attic Depth, Old Wiring and BIBS for Gutted Floors
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The big detached houses of the Town, the Village and Sections 3 and 5 tend to have big attics, often with irregular floors, old duct runs and a few bath fan hoses. Blown fiberglass suits that kind of space, because the machine stays at the truck and the hose reaches corners where a person holding a batt cannot. The other half of this page is about who has to be asked first: in Chevy Chase that changes from one street to the next, so the table below comes before the depth numbers.
Who decides before the first bag is blown, by Chevy Chase address
| Where the house is | Office beside the County | What the written rules say |
|---|---|---|
| Town of Chevy Chase | Town Office, 4301 Willow Lane | Five Town permit categories; interior-only work is not one of them |
| Chevy Chase Village | Village Hall, 5906 Connecticut Avenue | No Village building permit for interior-only work; letter needed before a County permit |
| Section 3 | Section 3 office | Interior work exempt unless it breaks an exterior wall; acknowledgement letter still required |
| Section 5, Martin's Additions, North Chevy Chase | Each village office | Texts we read exempt interior-only work; none names insulation |
| Somerset, Chevy Chase View | Each town office | We could not confirm the interior wording, so we ask |
| Drummond | Village of Drummond | Regulates exterior changes; no-objection letter before a County permit |
| Unincorporated blocks, Friendship Heights | None; County DPS only | Friendship Heights is listed as County permit only |
The County's Department of Permitting Services (2425 Reedie Drive, 7th floor, Wheaton, 240-777-0311) issues the building permit for every row. None of these lists names insulation, so blowing fill across an existing attic floor is usually not a permit item, but the building official makes that call and we confirm with DPS and the local office before we start. Rewiring, framing changes and wall removal are permit work. On the DC side of Western Avenue, a different system applies, and our Washington, DC page explains it.
Reading the bag label in a large, awkward attic
Blown fiberglass delivers about R-2.2 to R-2.9 per inch, so the depth has to be generous: one manufacturer's chart calls for 13.25 inches at R-38, 16.75 at R-49 and 20 at R-60, and notes negligible settling. At R-49 that is 22.2 bags of 32-pound fiberglass per 1,000 square feet. The bag you are sold carries the governing chart. ENERGY STAR suggests R-49 where a floor already holds 3 to 4 inches and R-60 where it is bare; for an existing house these are recommendations, since Maryland sets no retrofit level. Cellulose needs 3 to 4 fewer inches for the same R-value, so a shallow attic over a bedroom wing may call for cellulose instead.
Two fiberglass jobs, sized and priced for Chevy Chase
A 1920s house with a 1,900-square-foot attic, two bath fans and a few runs of cloth-covered wiring
The floor is irregular, the hatch is about 22 by 30 inches, and two fan hoses end in the old fill. After an electrician clears the wiring, we seal the plates and duct holes, connect both fans to roof caps, set baffles at the soffits and blow to about 16.75 inches, roughly 42 bags. At $0.90 to $1.60 per square foot the floor costs $1,710 to $3,040. Rewiring, if the electrician recommends it, is priced separately and is a County permit item. Expect one long working day after the wiring is cleared, and a weatherstripped, insulated hatch cover at the end.
A 1960s Chevy Chase View house with the first floor gutted to 1,000 square feet of 2x4 wall
Everything inside is down to studs, so fabric-held BIBS fits. At $1.50 to $2.50 per square foot the walls run $1,500 to $2,500, reaching about R-15 in the 3.5-inch bays. Fabric is stapled after rough-in, fiberglass is blown through slits, and drywall must cover the fabric, so the builder schedules the board. If the work carries a County permit, the inspector sees the framing before we start. The job takes two days, stapling first and blowing second. Because Chevy Chase View is its own town, we also ask its office what it wants to see before the County acts.
Where blown fiberglass stops: old wiring, vermiculite and plaster that stays
If an attic holds vermiculite, EPA says to assume asbestos and leave it undisturbed, so we stop at the hatch. Loose fill never goes over knob-and-tube. Finished plaster walls get dense-pack through drilled holes, not fabric, and small open areas are easier with batts. A rim joist that leaks air needs spray foam. If a gas furnace or water heater stands in or near the space, ENERGY STAR asks for a combustion safety test after air sealing, and we book it.
Attic, Wiring and Boundary Questions From Chevy Chase Homeowners
Roughly how much blown fiberglass goes into the attic of a large Chevy Chase house?
One manufacturer's chart lists 22.2 bags of 32-pound fiberglass per 1,000 square feet at R-49, so a 1,900-square-foot attic takes about 42 bags at roughly 16.75 inches deep. Sound old fill on the floor counts toward the total. At $0.90 to $1.60 per square foot, that attic prices at $1,710 to $3,040.
My house is near Friendship Heights and Western Avenue. Which side of the line am I on?
Western Avenue is the boundary street, so an address on it can be in Maryland or in the District. Maryland addresses go to Montgomery County DPS, and the County lists Friendship Heights as County permit only. DC addresses go to the DC Department of Buildings at 202-671-3500. We check the parcel first.
Can you blow fiberglass over the old cloth-covered wiring in my attic?
No. The National Electrical Code does not allow concealed knob-and-tube wiring to be enveloped by loose, rolled or foamed insulation, because the wires rely on open air to shed heat. An electrician evaluates the runs first, and rewiring is a County permit item. We return once the wiring is cleared.
Who do I contact in Chevy Chase Village before an attic job?
Village Hall, at 5906 Connecticut Avenue. The Village's 2022 guide says interior-only work needs no Village building permit, recommends a pre-design meeting and requires a Village letter before DPS will issue a County permit. A blown attic floor is usually not a permit item, but we confirm with both offices.
We are gutting the first floor of a 1930s house to the studs. Should it get BIBS or batts?
Either fits open bays. BIBS stretches breathable fabric across the studs and blows fiberglass behind it, reaching about R-15 in a 2x4 wall, and the fabric must be covered with drywall. Batts are simpler for a small scope. Finished walls elsewhere in the house get dense-pack instead, because BIBS needs exposed framing.
More on attics, and fiberglass pages for addresses around Chevy Chase
Our comparison of spray foam against fiberglass and the complete fiberglass and spray foam guide go into the trade-offs. The Chevy Chase hub lists local work, spray foam in Chevy Chase covers air sealing, and service areas shows the wider map.
Fiberglass for nearby places: Bethesda, Kensington, Silver Spring, Rockville and Washington, DC.
Other Insulation Options in Chevy Chase
A house by Wisconsin Avenue with closed plaster, or a small remodeled room with bare studs, is better served elsewhere. The other pages are here:
Spray Foam Insulation in Chevy Chase | Batt Insulation in Chevy Chase | Cellulose Insulation in Chevy Chase
