Fiberglass Insulation in Silver Spring: Blown Attic Depth and BIBS for Gutted Walls
Free Silver Spring Estimate
Book Phone Consultation
With a median build year of 1964, many Silver Spring houses, in neighborhoods off roads like Georgia Avenue and Colesville Road, are ramblers and split-levels where a single low-slope attic floor covers most of the house. Those attics suit blown fiberglass: the machine sits at the truck, a hose runs to the hatch, and the fill lands evenly over wiring, duct boots and plates that batts would have to be cut around. Fewer than 4 in 10 units here are houses, so we also spend time on townhouse attics, and on the occasional gutted house where fiberglass goes in behind fabric instead.
Inches and bags: what an R-number means in a Silver Spring attic
| Target | Minimum installed depth | Where it fits |
|---|---|---|
| R-38 | 13.25 inches | Attics that already hold a few inches of sound fill |
| R-49 | 16.75 inches | The usual goal for a 1960s house, about 22 bags per 1,000 square feet |
| R-60 | 20 inches | Uninsulated floors, where ENERGY STAR suggests the highest level |
These depths come from one manufacturer's blown-fiberglass chart, which notes negligible settling. Fiberglass delivers roughly R-2.2 to R-2.9 per inch, and the chart on the bag you are sold governs the final depth. Cellulose reaches the same R-value in 3 to 4 fewer inches, which matters in a shallow attic over a bedroom wing.
Who decides, by kind of Silver Spring address
| Your address | Who has a say | What we do |
|---|---|---|
| Detached house in the unincorporated area | You, and Montgomery County if a permit is triggered | Confirm with the County before starting |
| House inside Takoma Park | You, the City, then the County | Check for a Municipality Letter on permit work |
| Townhouse in an HOA | You for the attic floor, the HOA documents for the roof | Read your covenants first |
| Condo or garden apartment | The association, usually for ceilings and roof | Work only where the owner controls it |
The County's Department of Permitting Services is at 2425 Reedie Drive, 7th floor, in Wheaton, 240-777-0311. Its lists of permit and no-permit work do not name insulation. Blowing fill over an existing attic floor is usually not a permit item, but the building official makes that call, so we confirm with DPS before we start. If the house sits inside Takoma Park and the project grows into permit work, the City's Municipality Letter comes before the County permit. Townhouse and condo owners should read their association documents first, because those, not the County, usually decide who may open a roof or common ceiling.
Two fiberglass scopes, priced for Silver Spring
A 1960s split-level off East-West Highway: 1,250 square feet of attic and the garage ceiling
About 4 inches of flattened batts lie on the attic floor. Blowing to R-49 at $0.90 to $1.60 per square foot is $1,125 to $2,000. The ceiling over the garage, under a bedroom, is its own line at $1,000 to $2,000, making $2,125 to $4,000 in all. The bath fan hose that ends in the fill gets a duct to a roof cap, baffles go in at the soffits, and the hatch is weatherstripped. A gas furnace or water heater in the house means a combustion safety test after air sealing. Plan one day, plus a few hours for the garage. The estimate shows the attic floor, the garage ceiling and any duct work as separate lines, so you can drop one without redoing the rest.
A gutted house in Lyttonsville with 1,600 square feet of exterior wall open
With the first floor down to studs, fabric-retained BIBS fits. At $1.50 to $2.50 per square foot the walls run $2,400 to $4,000, a little under our whole-house band because only one floor is open. A 2x4 wall reaches about R-15 and a 2x6 addition wall about R-23 or R-24, from the same denser fill. Fabric goes up after rough-in approval, the fiberglass is blown through slits, and drywall must cover the fabric. Two days: stapling first, blowing second.
BIBS stays in open walls; closed walls go another way
Blow-in-blanket fiberglass needs exposed stud bays, because the fabric is stapled across them before anything is blown. If your walls are finished, the same fiber can be dense-packed through drilled holes, or dense-pack cellulose can be used, with no fabric in either case. Studs that are open but small in scope are often simpler with batts, and air leaks belong to spray foam.
Older homes bring two more checks. Paint from before 1978 makes drilling lead-safe work, and concealed knob-and-tube wiring cannot be covered by insulation. Forest Glen, which has a Silver Spring mailing address, and Linden share a small County historic district, designated in 1993, and the County exempts interior insulation from its historic permit. Pepco, Washington Gas and WSSC Water commonly serve the area.
Attic, Garage and Energy Code Questions From Silver Spring Owners
How many bags does a 1,300-square-foot Silver Spring attic take to reach R-49?
One manufacturer's chart calls for 22.2 bags of 32-pound fiberglass per 1,000 square feet at R-49, so 1,300 square feet is about 29 bags, at a minimum installed depth near 16.75 inches. Old batts on the floor count toward the total, so the bag count drops when they are in decent shape. At $0.90 to $1.60 per square foot, this attic prices at $1,170 to $2,080.
Will blown fiberglass warm the bedroom over my split-level's garage?
It helps, but cold floors over garages usually come from air leaking at the rim joist as much as from thin insulation. We price the garage ceiling as its own line at $1,000 to $2,000 and tell you if the rim joist needs spray foam as well. Fiberglass alone will not stop a draft.
My townhouse attic hatch is only about 22 by 30 inches. Is blown fiberglass a good fit?
It is a better fit than batts, because the fiberglass travels through a hose and only a person has to fit through the hatch. We run the hose from the truck, work the floor from the opening, and weatherstrip and insulate the hatch cover afterward. A very shallow attic may limit the depth we can reach, and we measure that before quoting.
Does Montgomery County's 2021 energy code make me add R-60 to my existing attic?
No. Maryland adopted the 2021 IECC on May 29, 2023, and the County's Department of Permitting Services has required the 2021 codes for permit applications since March 31, 2025. Those targets apply to new construction, additions and altered areas. An existing house has no mandatory retrofit level, although ENERGY STAR suggests R-49 to R-60 for attics.
I think my 1950s attic holds Zonolite vermiculite. Can you blow fiberglass over it?
No. The EPA says to assume vermiculite insulation contains asbestos and to leave it undisturbed, and it does not list burying it as acceptable. A licensed asbestos contractor should handle it first. Removal is specialist work, so we stop at the hatch and help you plan the order of jobs.
Further reading, and fiberglass for neighboring towns
Two guides cover the trade-offs: Maryland attic insulation options and the spray foam and fiberglass guide. The Silver Spring hub shows everything we do locally, spray foam in Silver Spring handles the air sealing, and service areas maps the rest.
Fiberglass pages nearby: Kensington, Chevy Chase, Laurel and Rockville.
Other Insulation Options in Silver Spring
A plaster-walled house near Jesup Blair Park, just off Georgia Avenue, or a leaky rim joist over a garage, calls for something else. Those jobs are covered here:
Spray Foam Insulation in Silver Spring | Batt Insulation in Silver Spring | Cellulose Insulation in Silver Spring
