Until August 7, 2026, a detached accessory dwelling unit in the Town of Chevy Chase had to sit at least 20 feet from the rear lot line, or 15% of the lot's depth if that was greater. Since that date, the same structure on an interior lot can sit 5 feet from the rear and side lines if it is under 12 feet tall, and 7.5 feet if it is 12 feet or taller. On a 150-foot-deep lot, the old rule required 22.5 feet. The new one can require 5.
That one change says something about the whole area. Chevy Chase, Maryland, is made up of several incorporated municipalities that sit on top of Montgomery County zoning. Most of them moved on their ADU rules this year, each on its own schedule and with its own formulas, and the public record still shows gaps for some. Two houses that look the same in listing photos can now have quite different rights to add a second home in the backyard, depending on which town line they sit inside. Backyard potential has become a separate question from the house, and it needs its own due diligence.
Why so many towns moved at once
The trigger was in Annapolis. House Bill 1466 and Senate Bill 891, enacted as Chapter 196 of the Laws of Maryland in 2025, required every local legislative body to adopt an ADU law on or before October 1, 2026. That deadline is today. The state law also says local setbacks for an ADU cannot be stricter than the setbacks that already apply to ordinary accessory structures like sheds and detached garages.
That requirement explains the Town of Chevy Chase change above. The town could no longer hold backyard cottages to a stricter standard than garages, so it deleted the separate ADU setbacks. The same ordinance keeps the rest of its accessory-building rules. Accessory buildings on interior lots must still sit in the rear yard, take up no more than 25% of it, and stand at least 60 feet back from the front lot line. Taller and longer structures still trigger extra setback: 1.5 feet for each foot of height over 12 feet with a flat roof or 15 feet with another roof type, and 1.5 feet for each foot of length over 24 feet along a lot line. Those increases stack. An ADU there also cannot exceed 75% of the size of the main building.
The county acted under the same deadline. The Montgomery County Council adopted Zoning Text Amendment 26-06 on September 15, 2026, and it takes effect October 5, 2026. It deletes the old size caps for detached ADUs, which had limited a unit to the smallest of 1,200 square feet, 50% of the main house's footprint, or 10% of the lot. In their place, an ADU can be no larger than 75% of the primary single-family home and must meet the setback, height, and lot coverage standards for an accessory structure in the underlying zone. The rule allows only one ADU per lot.
So a Chevy Chase lot now answers to two layers. The county sets the use rules: whether an ADU is allowed, licensing, occupancy, and parking. The municipality sets the physical envelope: how close to the lot line, how tall, and how much of the yard.
Same state deadline, different math by town
The municipalities that acted each took their own route to the state's floor. The table compares what the 2026 records show.
| Municipality | Status in 2026 | Detached ADU setback approach | Other notable terms |
|---|---|---|---|
| Town of Chevy Chase | Ordinance 26-03, effective Aug 7, 2026 | 5 ft under 12 ft tall, 7.5 ft at 12 ft or taller on interior lots; +1.5 ft per foot over height and length thresholds | 25% of rear yard max; 60 ft from front lot line; ADU no more than 75% of main building |
| Section 5 | Resolution 12-25-1, effective Feb 3, 2026 | 5 ft baseline; +2 ft per foot over 12 ft flat roof or 15 ft other roof, and +2 ft per foot over 24 ft of length | Accessory height cap of 15 ft to highest point or 12 ft to mean roof height; 30% building coverage cap |
| Chevy Chase View | Ordinance 105, adopted 5–0 on July 15, 2026 | Accessory-building setbacks; +1.5 ft modifier above 15 ft tall and 24 ft long | Extra ADU parking requirement removed; detached ADU capped at 75% of principal dwelling's floor area |
| Martin's Additions | Adopted 4–1 in July 2026 | CitizenPortal reports a 5 ft default; +1.5 ft per foot over 12 ft height or 24 ft width | Parking flexibility kept pending a study |
| North Chevy Chase | Introduced June 16; adoption on Sept 15 agenda | The North Chevy Chase September 15 agenda proposed 5 ft; +2 ft per foot over height threshold, +1 ft per foot over 24 ft of length | Draft removed on-site parking; final adoption not yet confirmed in the public record |
| Section 3 | July 8, 2026 council action | The Section 3 newsletter says the exception allowing small sheds within 5 ft of side or rear lines was removed | Town newsletter says this also keeps ADUs from being built that close |
| Chevy Chase Village | No ADU ordinance found in 2026 Board records | Not established | Confirm directly with the Village |
The gap between a 1.5-foot and a 2-foot modifier looks small on paper. On a narrow lot it adds up quickly. Take a 16-foot-tall cottage with a pitched roof. It is one foot over the 15-foot threshold, which adds 1.5 feet of setback in the Town of Chevy Chase and 2 feet in Section 5. Make that structure 30 feet long against the rear line and the length modifier adds 9 more feet in the Town and 12 in Section 5. The same backyard building can fit in one town and need redesigning a few blocks away.
The Martin's Additions figures come from a published summary of the July meeting, not the ordinance text itself. Anyone planning a project there should work from the adopted ordinance. North Chevy Chase's September 15 agenda listed "ADU ordinance adoption," but minutes confirming the vote were not posted at the time of writing.
The parking rule follows the Purple Line
The county layer has a variable that municipal boundaries don't control: distance to rail. Under ZTA 26-06, a licensed ADU generally needs one on-site parking space beyond what the main house requires, unless a hearing examiner grants a waiver. Lots within one mile of any Metrorail, Purple Line, or MARC station are exempt. The new text also lets the examiner waive parking when a lot's size or shape makes another space impractical.
That is why the Purple Line's Connecticut Avenue station matters for backyard plans in Chevy Chase. The line is not open yet. The Maryland Transit Administration reported on September 3, 2026, that the project was 92% complete, with testing on more than half of its 16-mile alignment. The agency did not give a passenger-service start date. The project's own site still projects construction through 2027 and lists ongoing work at the Connecticut Avenue station. Whether a station under construction counts for the one-mile exemption is a question for the county before you rely on it. Several municipalities, including Chevy Chase View, have also dropped their own extra ADU parking requirements, which is a separate local layer.
Some county rules apply no matter which town you're in. The ADU must be licensed by the Department of Housing and Community Affairs and share the main house's street address. No more than two occupants aged 18 or older may live in it. An ADU is not allowed on a lot with a licensed short-term rental.
What the county is still deciding this month
The rules are still changing. On September 15, 2026, Councilmember Andrew Friedson and Council President Natali Fani-González introduced Bill 41-26. It would remove the owner-occupancy requirement for ADU rental licensing and waive certain county fees when an owner agrees with DHCA to keep rent affordable to households earning 65% of area median income or less for at least 10 consecutive years. A public hearing is set for October 6, followed by a Planning, Housing & Parks Committee worksession on October 26.
The same county announcement gives a measure of how the old rules performed. Department of Permitting Services data shows 222 ADUs permitted countywide since 2019. That is a small number for a county of Montgomery's size. The 2026 changes target the barriers that kept it low: setbacks, size caps, parking, and owner occupancy. If Bill 41-26 passes, a buyer who later moves out could rent both the main house and the ADU, which changes how a backyard unit fits into long-term plans for the property.
An order of operations for a lot you might build on
The county market is moving quickly. Montgomery County's median days on market was 15 in August 2026, with 2.5 months of inventory, according to Maryland Realtors' monthly report using data current as of September 4. Those are countywide figures, but they suggest that ADU homework done after you find the house may come too late. A practical sequence:
- Confirm the municipality. A "Chevy Chase" mailing address can sit in the Town, a numbered Section, Martin's Additions, Chevy Chase View, North Chevy Chase, the Village, or an unincorporated area. Each one sets its own setbacks.
- Get the rear yard dimensions. In the Town of Chevy Chase, the 25%-of-rear-yard cap and the 60-foot front setback can limit you before the side and rear setbacks do.
- Look for an existing structure built before May 31, 2012. The county lets a legally built pre-2012 structure become a detached ADU without regard to setbacks or floor area, as long as it isn't enlarged, isn't made taller, and doesn't get new windows on the wall nearest a neighbor. An old garage can be worth more than its square footage suggests.
- Measure the distance to the nearest station. The one-mile line decides whether the county ADU parking requirement applies.
- Check for short-term rental licenses. A licensed short-term rental on the lot rules out an ADU.
- Watch Bill 41-26. The owner-occupancy question may be settled after the October 26 worksession.
This list is a starting point for conversations with the municipality, DPS, and your own legal and tax advisors. It doesn't replace them.
Quick answers
Does the county rule override my town's setbacks? The county ZTA defers to the accessory-structure setback, height, and coverage standards that apply to the lot. Municipalities like the Town of Chevy Chase and Section 5 set those physical standards under their own building authority, and the state law caps how strict they can be.
Can I put an ADU in a basement instead? Yes. The county rules cover attached ADUs too. The separate entrance must generally be on the side or rear of the house, unless a front entrance existed before May 20, 2013, or the unit shares a single front door with the main house.
What if I'm buying in Chevy Chase Village? No 2026 ADU ordinance appeared in the Village's Board records or its September Crier. Ask the Village office which standards apply before you count on a backyard unit.
If you're weighing a Chevy Chase home partly for what the backyard could become, I'm happy to check the municipality, the lot dimensions, and the current ordinance text with you before you write an offer. Reach out to Jen Goroff and let's connect.
This article is general information, not legal, tax or financial advice. Consult a qualified professional about your situation.
