Batt Insulation for Rockville Remodels, Additions and Open Framing
Free Rockville Estimate
Book Phone Consultation
Roughly 13,300 of Rockville's 28,289 homes were built between 1950 and 1979, and the median house dates to 1979 (Census ACS 2020-2024). Nearly half of the homes are in buildings of two or more units, though, so the batt jobs we see are mostly owners of detached houses and townhouses who are opening walls: a kitchen gut, a rear addition, a bedroom over the garage, a finished basement. Those projects expose framing for a week or two, and that is the window for a batt.
We quote in Hungerford, Monroe-Lynfield and New Mark Commons, toward Rockshire and Fallsmead, and along Shady Grove Road, Norbeck Road, First Street and West Gude Drive. We always ask first what year the house was built and whether the framing is still visible.
Before batts: which office covers your street
In Rockville the permit office depends on the parcel. Check the list that matches your parcel, not your mailing address.
- Inside city limits (for example East Rockville, Hungerford, Woodley Gardens, College Gardens, King Farm and the original Twinbrook): the City's Inspection Services Division at Rockville City Hall, 111 Maryland Ave., phone 240-314-8240.
- Outside city limits (Aspen Hill, North Bethesda, Derwood and the Twinbrook area east of Twinbrook Parkway, whatever the mailing address says): Montgomery County's Department of Permitting Services, 2425 Reedie Drive in Wheaton, phone 240-777-0311.
Additions, finished basements, attic conversions, wall cutting and wiring, gas, plumbing or mechanical changes need a permit from whichever office applies. Neither office's list names insulation by itself, and both exempt ordinary repairs that stay clear of structure and building systems, so batts over an existing attic floor are usually not a permit item. The decision is theirs, and we confirm with the right one before we start.
Which batt goes in which Rockville cavity
| Batt | Thickness | Where it goes |
|---|---|---|
| Fiberglass R-15 | 3.5 inches | 2x4 walls opened to the studs |
| Fiberglass R-21 | 5.5 inches | 2x6 walls in additions |
| Mineral wool R-15 or R-23 | 3.5 or 5.5 inches | Same bays, denser fiber |
| R-30 or R-38 | About 8.25 to 10, or about 12 inches | Garage ceilings, attic floors in layers |
R-19 is 6.25 inches thick and will not sit right in a 3.5-inch bay. New work and additions follow the 2021 energy code, which Maryland adopted in 2023; the City adopted it effective May 29, 2024, and Montgomery County's permit office began requiring its 2021 codes on March 31, 2025. Your plans examiner sets the numbers. An existing house that nobody is altering has no retrofit minimum.
When we steer you away from batts
A closed wall cannot take a batt, so it is dense-packed instead, which is cellulose work. A cluttered attic floor is better filled with blown fiberglass or cellulose. Leaks at a rim joist, an overhang or attic ductwork need spray foam.
Two batt jobs, priced for Rockville houses
Kitchen and dining gut in a 1960s house in Woodley Gardens
- Walls: about 1,500 square feet of exterior wall, $2,000 to $4,500.
- Garage ceiling: 350 square feet at R-38 with an air barrier, $525 to $875.
- Total: $2,525 to $5,375, with the bath fan ducted outdoors and cans swapped for IC-rated ones while the ceiling is open.
- Notes: the house predates 1978, so we ask the general contractor who handles lead-safe practices on demolition. Two days.
Finishing the unfinished upstairs of a post-war house in the city part of Twinbrook
- Knee walls: two areas beside the dormers, $600 to $1,800 each, so $1,200 to $3,600.
- Attic floor: 500 square feet of the floor stays outside the new room and gets R-49 at $1.20 to $2.00 per square foot, $600 to $1,000.
- Total: $1,800 to $4,600.
- Notes: converting an attic is permit work with the City, so the batts stay visible until inspection. One day.
Historic districts, conservation areas and utilities
An addition changes the outside of a house. In a local historic district the City's Historic District Commission requires a Certificate of Approval for additions and other exterior alterations, and in the Lincoln Park Neighborhood Conservation District the review is limited to size and massing. The pages we read do not say whether interior work is reviewed, so we ask. Pepco and Washington Gas are the utilities around here, and Pepco's Maryland Home Performance with ENERGY STAR program works only through participating contractors, so ask us to check the current terms before you count on a rebate. We promise none. Where a gas furnace or water heater is in the space, a combustion safety test follows any air sealing.
Rockville Remodel Questions, Answered
My addition is in Twinbrook. Does the City or Montgomery County inspect it?
It depends which side of Twinbrook Parkway you are on. The original Twinbrook, annexed in 1949, is inside the City, which issues permits and inspects through Inspection Services at Rockville City Hall. The sector-plan area east of Twinbrook Parkway is outside city limits and belongs to Montgomery County Department of Permitting Services. Send the street address and we confirm the office before we schedule any work.
Is mineral wool thicker than fiberglass for the same R-value?
In a 2x4 wall they match: both R-15 batts are 3.5 inches thick. The gap opens in a 2x6 wall, where a 5.5-inch fiberglass batt is R-21 and a 5.5-inch mineral wool batt is R-23, because mineral wool runs about R-3.8 to R-4.3 per inch. Either product only performs when it is cut to the bay with no voids and no squeezing, so we price both on an open-wall job.
What do batts cost for a Rockville kitchen and dining room gut?
For a house of about 1,500 square feet, wall batts come to $2,000 to $4,500. Add a cleared 1,200-square-foot attic floor laid to R-49 at $1.20 to $2.00 per square foot, which is $1,440 to $2,400, and the two areas together run $3,440 to $6,900. A garage ceiling in R-30 or R-38 is extra at $1.50 to $2.50 per square foot. Every area is its own line, so any of them can come out.
Do I have to leave my basement walls open for an inspector?
Finishing a basement is permit work, and the inspector usually wants to see the insulation before drywall covers it. Which inspector depends on your parcel: the City of Rockville inside its limits, Montgomery County outside them. Ask the office what it needs to see, and we will time the crew so the batts stay exposed until that visit has happened.
Can batts go over the old insulation on my attic floor while the drywall stays up?
Yes, when the floor is clear. Batts can be laid across the joists over an existing layer, and two crossed courses are a common way to reach R-49. Laying them that way avoids demolition entirely. If the floor is crowded with wiring, duct boots or bracing, batts leave gaps around them and loose-fill cellulose or blown fiberglass is the better tool.
Background reading, and batt pages across Montgomery County
Two explainers fill in the details: what an R-value means for your home and Maryland attic insulation options. For the full list of what we do locally, use the Rockville hub page, and the service-area page shows where else we work.
Remodeling next door? Batt pages for Potomac, Bethesda, Kensington and Silver Spring.
Other Insulation Options in Rockville
Batts want open cavities and clear floors. If yours are closed or crowded, a Rockville house is usually better served by one of these:
Spray Foam Insulation in Rockville | Cellulose Insulation in Rockville | Fiberglass Insulation in Rockville
