Batt Insulation in Chevy Chase: Rear Additions, Rebuilt Houses and Third-Floor Knee Walls
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Chevy Chase is a string of separate communities that share a name and a ZIP code, and the batt work we are asked to do depends on which one you live in. All 1,008 homes in the Town of Chevy Chase are detached, and about two thirds were built before 1940. Census estimates also count roughly 140 homes from 2000 or later, which points to rebuilds and large additions. Those projects, plus older houses with a finished room under the roof, are where batts do their best work: the framing is open, every bay can be seen and each batt is cut to its cavity. Closed plaster is another job, covered near the end of this page. Our crews work along Connecticut Avenue, East-West Highway and Brookville Road.
Seven steps from first call to last batt at a Chevy Chase address
- Name the entity. A Chevy Chase, MD 20815 address can belong to the Town of Chevy Chase, Chevy Chase Village, Section 3, Section 5, Chevy Chase View, North Chevy Chase, Martin's Additions, Somerset, Drummond or unincorporated land. We ask for the parcel, not just the mailing address.
- Call two offices. Montgomery County's Department of Permitting Services issues the building permit for all of them, and the town or village rules sit on top. Batts alone are usually not a permit item and the building official has the last word, so we confirm with DPS and the local office before we start.
- Collect the letter. Section 3 and Chevy Chase Village want a notice or acknowledgement letter before DPS will process a permit, and Drummond wants a no-objection letter. If an addition already has a permit, the letter belongs to that file and the insulation goes in under it.
- Check the framing with your builder. Wiring, plumbing, duct runs and fire-blocking should be complete, since batts are the last trade in and nobody wants them pulled back out.
- Seal, then cut. Gaps at plates, window openings and wire holes are foamed or caulked first. ENERGY STAR says to seal before insulating, and a batt does not stop moving air. Each piece is trimmed to the bay and left uncompressed.
- Take pictures of every bay. Before the board goes up, you, the drywall crew and any inspector have a record of what sits behind it.
- Leave the exterior alone. Interior work is not reviewed in the Chevy Chase Village Historic District, but cladding changes need a Historic Area Work Permit. Batts never touch the outside wall.
Batt thickness against bay depth in old and new framing
A 2x4 wall bay is 3.5 inches deep, which is exactly the thickness of an R-13 batt or its high-density R-15 cousin. A 2x6 addition wall takes R-21 at 5.5 inches. R-19 is 6.25 inches thick, so it is squeezed in a 2x6 bay, and squeezing a batt returns less R, not more. The thicker sizes belong to joist bays: R-30 runs about 8.25 to 10 inches and R-38 about 12 inches. Mineral wool reaches roughly R-3.8 to R-4.3 per inch, so an R-23 piece at 5.5 inches is worth pricing where a shallow bay needs more.
Nothing in Maryland makes you raise an existing attic to a set level. ENERGY STAR suggests R-49 where 3 to 4 inches of insulation already lie on the floor and R-60 where there is none. New construction follows the County's adopted 2021 energy code with local amendments, and the plans name the target.
Two batt scopes for older Chevy Chase houses
A 1940s house with a two-room rear addition and a flattened attic floor
The new rooms are framed with 2x6 studs, so R-21 goes in the walls and the ceiling gets a thicker batt. Each room sits inside our single-room band of $800 to $2,500, which makes $1,600 to $5,000 for both. Over the original part of the house, 700 square feet of attic floor holds paper-faced R-11 pressed flat. We seal the plates, run the bath fan duct out through the roof and lay unfaced batts crosswise to about R-49 at $1.20 to $2.00 per square foot, or $840 to $1,400. The total is $2,440 to $6,400. The addition has its own permit, so if the County inspector wants to see the framing first, the batts wait for that visit. Plan one long day for the rooms and a half day for the attic, which has a 22-by-30-inch hatch.
A 1920s house with a finished room under the roof
Two knee-wall areas flank the room, each priced at $600 to $1,800, so $1,200 to $3,600 together. The attic side of each gets a rigid air barrier before the batt is fitted. Beyond the room sits a flat section of about 520 square feet of attic floor, which at $1.20 to $2.00 per square foot adds $624 to $1,040, for a total of $1,824 to $4,640. Access is a small door about two feet wide, so bundles go through one at a time. Cloth-covered wiring found behind a knee wall is left uncovered until an electrician looks at it. The job is one day. Batts do not cut painted plaster, so the lead-safe rule is not part of this scope.
Offices, letters and the line at Western Avenue
The Town Office is at 4301 Willow Lane and Chevy Chase Village Hall is at 5906 Connecticut Avenue. Several local codes say interior-only work needs no local building permit, but none of them mentions insulation, which is why we ask instead of assuming. Framing changes, wall removal, new wiring, plumbing or ductwork, and a newly finished attic are permit work in any entity. DPS is at 2425 Reedie Drive, 7th floor, Wheaton, 240-777-0311.
On the far side of Western Avenue, Chevy Chase, DC is a different permit system run by the DC Department of Buildings. We have a Washington, DC page for those addresses.
Plaster that stays on the wall is not a batt job
Where the original plaster is staying, dense-packed cellulose is blown through small holes. A wide, clear attic floor goes faster with blown fiberglass, and a leaking rim joist is a spray foam problem. Around Chevy Chase Circle, where the first Village houses went up, a single address can need all three.
Questions From Chevy Chase Owners Planning a Wing or a Finished Attic
My address is on Kensington Parkway. Which office do I call before batts go in?
A Kensington Parkway address can sit inside Chevy Chase View, which is its own incorporated town, so we confirm the parcel before anything else. We have not found that town's wording on interior work, so we ask the town office and Montgomery County DPS together and schedule only after both answer.
We are adding a two-story rear wing with 2x6 walls. Which batt fills it, and who sets the R-value?
A 2x6 bay is 5.5 inches deep, which is the size of an R-21 batt. The target for a new addition follows the 2021 energy code as Montgomery County has adopted it with local amendments, so your architect's plans set the number for the wing. The older part of the house has no required retrofit level.
What do batts cost for the knee walls of a finished third-floor room?
A knee-wall area runs $600 to $1,800, depending on its length and how hard the space behind it is to reach. The attic side gets a rigid air barrier first, because a batt fills the bay but does not stop moving air. We list each knee wall as its own line on the written estimate.
Does the Chevy Chase Village Historic District limit insulation work in an open attic?
The 1998 amendment that expanded the district to 327 properties says interior alterations are not subject to review under the preservation ordinance. Changes to exterior cladding do need a Historic Area Work Permit. Batts stay inside the envelope, so the district is not an obstacle, but we check whether your parcel is listed.
The plaster is already off the walls of our 1930s house. Does lead-safe work still apply?
Fitting batts into bare bays does not cut painted surfaces, but the demolition that exposed them does. In a house built before 1978, paid work that disturbs paint must be done by a certified firm, which is your builder's responsibility. We schedule after that work is finished and cleaned.
Reading before the drywall order, and batt pages for the neighbors
Our Maryland attic insulation guide compares the materials for Montgomery County houses, and R-value decoded explains the number on a batt wrapper. The Chevy Chase page lists everything we do locally, and service areas shows where else crews work.
Batts for nearby addresses: Bethesda, Kensington, Silver Spring, Rockville and Washington, DC.
Other Insulation Options in Chevy Chase
A house off Bradley Boulevard with plaster that is staying put, or a rim joist that leaks, wants a different material. Those pages are below:
Spray Foam Insulation in Chevy Chase | Cellulose Insulation in Chevy Chase | Fiberglass Insulation in Chevy Chase
