Picture two Layton listings in the same price range. One is a 1,600-square-foot rambler on a quarter-acre with a deep, empty backyard. The other is a 2,400-square-foot two-story on a lot just over 6,000 square feet. A buyer who wants room for aging parents, an adult child or a long-term tenant usually looks at that big backyard first.
Under Layton's code, the rambler on the bigger lot allows a cottage of up to 800 square feet. The two-story on the smaller lot allows up to 1,200. The difference comes from a rule tied to the house, and it rarely appears in a listing description.
October 1 Came and Went, and Layton Barely Moved
This fall, coverage of Utah's detached accessory dwelling unit law focused on the statewide requirement. Under Utah Code §10-21-304, which took effect October 1, 2026, a "specified municipality" has to allow a detached ADU, or DADU, on any lot of 11,000 square feet or more that holds a single-family home. Cities may also allow them on smaller lots.
Layton was already ahead of that floor. The city adopted Ordinance 21-23 on September 16, 2021, which set standards for internal, attached and detached ADUs. Detached units are allowed on lots of 6,000 square feet or larger.
The City Council unanimously adopted Ordinance 26-27 at its September 17 meeting to bring the code in line with the new state law. According to the staff report, the changes removed design controls the state no longer allows: matching building materials and colors, window type and placement, roof materials and minimum roof pitch, and door and entrance locations. One line from state code replaced them. Every ADU "must be designed consistent with the design of the primary single-family dwelling."
The new law relaxed how a cottage looks. The size cap and the height cap stayed the same, and both are still set by the main house.
The Size Cap Is Measured From the House
Layton limits a detached ADU to 50% of the main house's livable space, with a ceiling of 1,200 square feet. Garages and non-habitable storage areas don't count toward livable space. Lot size decides whether a DADU is allowed at all. After that, the house decides how big it can be.
| Example main house, livable space | Lot size | Largest DADU allowed |
|---|---|---|
| 1,600 sq ft rambler | About a quarter-acre | 800 sq ft |
| 2,000 sq ft home | 7,500 sq ft | 1,000 sq ft |
| 2,400 sq ft two-story | Just over 6,000 sq ft | 1,200 sq ft |
| 3,200 sq ft two-story | Half-acre | 1,200 sq ft |
| Any size | Under 6,000 sq ft | No detached unit |
These are example houses, not actual listings. The math works the same way on any detached single-family home. When a listing's square footage includes a big attached garage, the livable figure that counts may be well below the headline number. Check how a home's square footage is broken down before you assume a full 1,200-square-foot cottage will fit.
Height Follows the Roof, Setbacks Follow the Lot's Shape
Height is tied to the house too. A single-story DADU can reach 16 feet to the roof peak. A two-story DADU can reach 25 feet. In either case, a detached unit can never be taller than the main house's roof peak. So the 25-foot option only exists where the main roof is at least that tall. Behind a low-slung rambler, a two-story cottage may not be possible no matter how much yard there is.
Setbacks depend on where on the lot the cottage goes and how tall it is:
| DADU placement | Max height | Side setback | Rear setback |
|---|---|---|---|
| Side yard, single-story | 16 ft | Same as main house | Same as main house |
| Side yard, two-story | 25 ft | 10 ft | Same as main house |
| Rear yard, single-story | 16 ft | 5 ft | 10 ft |
| Rear yard, two-story | 25 ft | 10 ft | 20 ft |
Patios and other outdoor living space can't be within 10 feet of a side or rear property line. Balconies or decks built 4 feet or more above finished grade must sit 15 feet from the rear property line.
This is why a lot's shape matters as much as its size. When the Planning Commission reviewed the amendment on August 25, Chair Steenblik asked about side setbacks wider than 10 feet. Planner Whitney Black explained that the R-S, or Residential Suburban, zone has side setbacks of 8 and 12 feet. City Planner Brad McIlrath said it "would be tricky to fit a DADU with a 10' required setback in a 12' side yard." In practice, a two-story cottage in a side yard needs a much wider strip than most suburban side yards provide. A wide, shallow lot and a narrow, deep lot of the same acreage can give very different results.
Where Buyers' Assumptions Tend to Fall Apart
Ordinance 26-27 also made several rules clearer, and each one can come up after an offer is already written.
- Attached homes are excluded. ADUs are allowed only as an accessory use to a legally conforming detached single-family home in a primarily residential zone. The code says they are not allowed with attached single-family homes, "even when located in a primarily residential zone." A twin home or townhome with a nice yard doesn't qualify.
- An existing garage or shed only works if it was permitted. The new conversion process requires that the structure was legally built with a valid building permit. It must also meet current DADU setbacks for its spot on the lot, current height limits, and current building, health and fire codes. An older detached garage sitting 3 feet off the rear fence doesn't meet the 10-foot rear setback for a single-story cottage, even though it already stands.
- The owner has to live on the property. The owner listed with the Davis County Recorder's Office must live in either the main house or the ADU as a primary residence. Renting out both is not allowed. The owner signs a letter of agreement, and the city records it with the county. The requirement can be waived temporarily for a bona fide absence of three years or less for a job assignment, sabbatical or voluntary service. The home must have been the owner's primary residence right before leaving, and the owner must intend to move back.
- Short-term rentals are not allowed. The ADU must be rented to the same occupant for at least 30 consecutive days.
Taken together, these rules point toward an owner-occupied single-family lot where the cottage houses family or a long-term renter. For buyers who need that setup, the rules are workable. Buyers planning a property with two rental incomes should know before closing that Layton's code doesn't allow it.
What the Cottage Costs Before Anyone Moves In
The code shapes costs too. Every ADU has to connect to the same water, gas and sewer lines as the main house, and the two units share one address number. As a result, the distance from the house to the cottage site becomes a real budget item.
Utah law exempts ADUs built inside an existing home from impact fees. That exemption doesn't extend to a detached backyard unit.
There are no published, documented costs for completed Layton projects yet. A Davis County ADU guide from a builder-referral service, updated March 2026, estimates new detached ADUs at $150,000 to $350,000 or more, or about $190 to $250 per square foot. It estimates $8,000 to $35,000 for utility connections and $3,000 to $12,000 for permits and fees. It puts the full timeline from design to move-in at four to nine months. Treat these as planning ranges rather than bids. The service discloses that it may receive referral fees.
On the city side, Layton's ADU handout says permits are reviewed within 14 business days. The city also collects a $45 Davis County Recorder fee to record the owner-occupancy agreement. That handout was written before Ordinance 26-27. It still lists the roof-pitch and design-matching rules the council removed, so use the September 17 ordinance text for anything related to design.
Questions Worth Answering During Due Diligence
Does a 6,000-square-foot lot guarantee I can build a backyard cottage? No. Meeting the 6,000-square-foot minimum makes a lot eligible. Setbacks, the main roof's height, and the 50% livable-space cap then decide what will actually fit and how large it can be.
Is there time to check this before I'm committed? Statewide in August 2026, the Utah Association of REALTORS reported 65 days on market until sale, and the market had 4.6 months of supply. Those are statewide figures, not Layton-specific ones. Still, they describe a pace where buyers can often build a parcel review into their due diligence period instead of guessing.
Who confirms whether a specific lot qualifies? Layton Community & Economic Development at 437 N. Wasatch Dr., 801-336-3780. Bring the parcel's dimensions, its zoning, and the main home's livable square footage. Nothing here is legal advice, and the city's reading of a specific parcel is the one that counts.
If a backyard cottage is part of why you're shopping in Layton, Florencia Barrera can help you check each home's livable square footage, roofline and setbacks before you write an offer, in English or Spanish. Selling a Layton home that could host a detached ADU? Start with an instant home valuation, and we'll talk about how to show buyers that potential.
