Detached ADU rules in Renton's Residential-1 zone: corner lot, alley behind the lot

A detached ADU (backyard cottage) in Renton's Residential-1 zone needs at least 30 ft from the front lot line, no rear setback, at least 25 ft from the side lot line, and at least 30 ft from the secondary front lot line. It can be up to 1,000 sf. All buildings together can cover up to 25% of the lot.

Rules last updated 2026-11-05 · This page quotes the Renton Municipal Code. It is a reading aid, not the official code. The City's published code governs. Read the code

Your lot

Detached ADU

Narrow it to your lot

Corner lot

Alley behind the lot

Setback: no building hereWhere a detached ADU (backyard cottage) can goA typical lot, not to scale. Your lot's shape, size and conditions change these lines.

Visualize these on your property

Enter an address and Feasy draws these rules on your actual lot.

What the code allows

Setbacks

iWhat is a setback?

The distance a building has to stay back from a lot line. How the code defines each line ›

A setback is a distance a building has to stay back from a lot line. Here is what the code calls it, and how far a detached ADU (backyard cottage) has to stay back from each line.

Front

30ftminimum

At least 30 ft.

How close to the front lot line can a detached ADU (backyard cottage) be?

What the code says: Renton Municipal Code 4-2-110A

Rear

Nonenot required

No rear setback is required.

How close to the rear lot line can a detached ADU (backyard cottage) be?

What the code says: Renton Municipal Code 4-2-110C.4

Side

25ftminimum

At least 25 ft.

How close to the side lot line can a detached ADU (backyard cottage) be?

What the code says: Renton Municipal Code 4-2-110C.4

Secondary front

30ftminimum

At least 30 ft.

How close to the secondary front lot line can a detached ADU (backyard cottage) be?

What the code says: Renton Municipal Code 4-2-110A

What the code says · 4-2-110A, 4-2-110C.4

(Ord. 4869, 10-23-2000; Amd. Ord. 4963, 5-13-2002; Ord. 5100, 11-1-2004; Ord. 5132, 4-4-2005; Ord. 5153, 9-26-2005; Ord. 5306, 9-17-2007; Ord. 5355, 2-25-2008; Ord. 5383, 6-2-2008; Ord. 5387, 6-9-2008; Ord. 5401, 7-14-2008; Ord. 5450, 3-2-2009; Ord. 5473, 7-13-2009; Ord. 5518, 12-14-2009; Ord. 5526, 2-1-2010; Ord. 5528, 3-8-2010; Ord. 5529, 3-8-2010; Ord. 5531, 3-8-2010; Ord. 5590, 2-28-2011; Ord. 5649, 12-12-2011; Ord. 5650, 12-12-2011; Ord. 5675, 12-3-2012; Ord. 5702, 12-9-2013; Ord. 5726, 10-20-2014; Ord. 5744, 1-12-2015; Ord. 5759 (Att. C), 6-22-2015; Ord. 5790, 4-25-2016; Ord. 5791 (Att. A), 4-25-2016; Ord. 5798 (Att. A), 4-25-2016; Ord. 5841 (Att. A), 6-12-2017; Ord. 5867 (Att. B), 12-11-2017; Ord. 5899 (Att. B), 11-19-2018; Ord. 5960 (Att. B), 12-9-2019; Ord. 5981 (Att. A), 10-12-2020; Ord. 6048, 12-13-2021; Ord. 6049, 12-13-2021; Ord. 6076 (Att. A), 8-8-2022; Ord. 6091 (Att. A), 11-28-2022; Ord. 6128 (Att. C), 12-11-2023; Ord. 6154 (Att. A), 12-9-2024; Ord. 6160 (Exh. B-1), 6-16-2025) Please see Section 4-2-110I, Conditions Associated With Residential Development Standards Tables, for explanation of table footnotes.
8
RC
Minimum Net Density (per Net Acre)¹, 2, 15 None {spans 3 columns}
Maximum Net Density (per Net Acre, Except per Net 10 Acres in RC)², 14, 15 1 dwelling unit
Maximum Number of Dwellings (per Legal Lot)² Single-family dwellings and cottage house dwelling units: 1 per legal or unit lot. / Accessory dwelling units (attached or detached): 2 per legal lot. / Middle housing See RMC 4-2-110F, Development Standards for Middle Housing Developments. {spans 5 columns}
Minimum Lot Size², 28, 31 10 acres
Minimum Lot Width³¹ 150 ft
Minimum Lot Width³¹ (Corner Lots) 175 ft
Minimum Lot Depth³¹ 300 ft
Minimum Front Yard⁴, 5, 31 30 ft
Minimum Rear Yard⁴, 22, 31 35 ft
Minimum Side Yard⁴, 31 25 ft
Minimum Secondary Front Yard⁴, 5, 31 (applies to Corner Lots) 30 ft
Maximum Building Coverage (including Primary and Accessory) 10%
Maximum Impervious Surface Area 15%
Maximum Number of Stories 3 {spans 3 columns}
Maximum Wall Plate Height⁸, 9, 10, 12, 18, 19 32 ft. {spans 3 columns}
Maximum Number of Units per Building² 4 dwelling units {spans 5 columns}
Minimum Freeway Frontage Setback 10 ft. landscaped setback from the street property line. {spans 5 columns}
Maximum Wireless Communication Facilities Height (including Amateur Radio Antennas) See RMC 4-4-140, Wireless Communication Facilities. Amateur radio antennas are allowed a maximum height of 6 feet without a Conditional Use Permit. Larger structures will have a maximum height determined by the Conditional Use Permit process, RMC 4-9-030, Conditional Use Permits. {spans 5 columns}
Design Standards See RMC 4-2-115, Residential Design and Open Space Standards. {spans 5 columns}
Landscaping See RMC 4-4-070, Landscaping. {spans 5 columns}
Exterior Lighting See RMC 4-4-075, Lighting, Exterior On-Site. {spans 5 columns}
Screening See RMC 4-4-095, Screening and Storage Height/Location Limitations. {spans 5 columns}
Exception for Pre-Existing Legal Lots See RMC 4-10-010, Nonconforming Lots. {spans 5 columns}
Renton Municipal Code 4-2-110A · DEVELOPMENT STANDARDS FOR RESIDENTIAL LOW DENSITY AND MEDIUM DENSITY ZONES – PRIMARY STRUCTURES^1

		RC
Minimum Net Density (per Net Acre)¹, 2, 15		None {spans 3 columns}
Maximum Net Density (per Net Acre, Except per Net 10 Acres in RC)², 14, 15		1 dwelling unit
Maximum Number of Dwellings (per Legal Lot)²	Single-family dwellings and cottage house dwelling units: 1 per legal or unit lot. / Accessory dwelling units (attached or detached): 2 per legal lot. / Middle housing	See RMC 4-2-110F, Development Standards for Middle Housing Developments. {spans 5 columns}
Minimum Lot Size², 28, 31		10 acres
Minimum Lot Width³¹		150 ft
Minimum Lot Width³¹ (Corner Lots)		175 ft
Minimum Lot Depth³¹		300 ft
Minimum Front Yard⁴, 5, 31		30 ft
Minimum Rear Yard⁴, 22, 31		35 ft
Minimum Side Yard⁴, 31		25 ft
Minimum Secondary Front Yard⁴, 5, 31 (applies to Corner Lots)		30 ft
Maximum Building Coverage (including Primary and Accessory)		10%
Maximum Impervious Surface Area		15%
Maximum Number of Stories		3 {spans 3 columns}
Maximum Wall Plate Height⁸, 9, 10, 12, 18, 19		32 ft. {spans 3 columns}
Maximum Number of Units per Building²		4 dwelling units {spans 5 columns}
Minimum Freeway Frontage Setback		10 ft. landscaped setback from the street property line. {spans 5 columns}
Maximum Wireless Communication Facilities Height (including Amateur Radio Antennas)		See RMC 4-4-140, Wireless Communication Facilities. Amateur radio antennas are allowed a maximum height of 6 feet without a Conditional Use Permit. Larger structures will have a maximum height determined by the Conditional Use Permit process, RMC 4-9-030, Conditional Use Permits. {spans 5 columns}
Design Standards		See RMC 4-2-115, Residential Design and Open Space Standards. {spans 5 columns}
Landscaping		See RMC 4-4-070, Landscaping. {spans 5 columns}
Exterior Lighting		See RMC 4-4-075, Lighting, Exterior On-Site. {spans 5 columns}
Screening		See RMC 4-4-095, Screening and Storage Height/Location Limitations. {spans 5 columns}
Exception for Pre-Existing Legal Lots		See RMC 4-10-010, Nonconforming Lots. {spans 5 columns}

4. Development Standards: The following development standards are established for ADUs: Please see Section 4-2-110I, Conditions Associated With Residential Development Standards Tables, for explanation of table footnotes.
1
GENERAL REQUIREMENTS⁴, 10 {spans 2 columns}
Maximum Number of Units²⁴ Two (2) ADUs are allowed per legal lot as an accessory use to a principal dwelling
Configuration Either one (1) attached ADU and one (1) detached ADU, two (2) attached ADUs, or two (2) detached ADUs. ADUs may be established within or as an addition to the principal dwelling. / In RC, R-1, R-4, R-6, and R-8 zones, when two (2) ADUs are proposed, the second ADU shall comply with the location and setback requirements applicable to the principal dwelling
Maximum Gross Floor Area⁴⁰ 1,000 sq. ft
Maximum Building Area²⁶, 41 1,000 sq. ft
Conversions²⁵ If a conversion unit occupies an entire single floor of the primary dwelling, it may be allowed to increase the maximum unit size to efficiently use all the floor area. Conversion units greater than 1,250 sq. ft. shall be classified as an attached dwelling rather than ADU
Parking²⁰ A minimum of 1.0 parking space per dwelling unit. / No off-street parking required for ADUs located on lots within a one-half mile walking distance of a Major Transit Stop (Area A)
Design Standards See RMC 4-2-115, Residential Design and Open Space Standards
ATTACHED AND INTERNAL ADUs {spans 2 columns}
Setbacks and Building Height ADUs shall comply with the standards applicable to primary structures, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures, and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures
DETACHED ADUs {spans 2 columns}
Front Yard and Secondary Front Yard Setbacks ADUs shall comply with the location and front yard setback requirements of the underlying zone, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures. / Detached ADUs shall be located at least 4 ft. from any residential structure otherwise the structure shall be considered an attached ADU
Side Yard Setbacks RC and R-1 zones: 25 ft. / R-4, R-6, and R-8 zones: 5 ft. / R-10 and R-14 zones 4 ft
Rear Yard Setbacks 5 ft. When located within 10 ft. of the rear property line, at least 25% of the lineal length of the rear yard shall remain unoccupied from accessory dwellings. / ADUs may be sited at the rear lot line where an alley is present
Building Height²³, 42 24 ft. measured to the highest point of a flat roof or the highest ridge of a pitched roof
Renton Municipal Code 4-2-110C.4 · DEVELOPMENT STANDARDS FOR ACCESSORY DWELLING UNITS^1

GENERAL REQUIREMENTS⁴, 10 {spans 2 columns}
Maximum Number of Units²⁴		Two (2) ADUs are allowed per legal lot as an accessory use to a principal dwelling
Configuration		Either one (1) attached ADU and one (1) detached ADU, two (2) attached ADUs, or two (2) detached ADUs. ADUs may be established within or as an addition to the principal dwelling. / In RC, R-1, R-4, R-6, and R-8 zones, when two (2) ADUs are proposed, the second ADU shall comply with the location and setback requirements applicable to the principal dwelling
Maximum Gross Floor Area⁴⁰		1,000 sq. ft
Maximum Building Area²⁶, 41		1,000 sq. ft
Conversions²⁵		If a conversion unit occupies an entire single floor of the primary dwelling, it may be allowed to increase the maximum unit size to efficiently use all the floor area. Conversion units greater than 1,250 sq. ft. shall be classified as an attached dwelling rather than ADU
Parking²⁰		A minimum of 1.0 parking space per dwelling unit. / No off-street parking required for ADUs located on lots within a one-half mile walking distance of a Major Transit Stop (Area A)
Design Standards		See RMC 4-2-115, Residential Design and Open Space Standards
ATTACHED AND INTERNAL ADUs {spans 2 columns}
Setbacks and Building Height		ADUs shall comply with the standards applicable to primary structures, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures, and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures
DETACHED ADUs {spans 2 columns}
Front Yard and Secondary Front Yard Setbacks		ADUs shall comply with the location and front yard setback requirements of the underlying zone, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures. / Detached ADUs shall be located at least 4 ft. from any residential structure otherwise the structure shall be considered an attached ADU
Side Yard Setbacks	RC and R-1 zones: 25 ft. / R-4, R-6, and R-8 zones: 5 ft. / R-10 and R-14 zones	4 ft
Rear Yard Setbacks		5 ft. When located within 10 ft. of the rear property line, at least 25% of the lineal length of the rear yard shall remain unoccupied from accessory dwellings. / ADUs may be sited at the rear lot line where an alley is present
Building Height²³, 42		24 ft. measured to the highest point of a flat roof or the highest ridge of a pitched roof

How the code defines each line

SETBACK: M. SETBACK: The minimum required distance between the building footprint and the property line and any private access easement or tract. For lots containing private access easements, setbacks are the minimum required distance between the building footprint and the easement. A setback is measured perpendicularly from a lot line or private easement access to the outer wall of the structure. In the case where a structure does not have an outer wall, such as a carport, the measurement shall be to the posts of such structure, unless otherwise determined by the Department of Community and Economic Development.Renton Municipal Code 4-11-190.M
LOT LINES: LOT LINES: The property lines bounding a lot; the designation of lot lines (front, rear, and side) shall be based on the yard designations (see YARD REQUIREMENT).Renton Municipal Code 4-11-120.[LOT LINES]
Lot, Corner: A. Lot, Corner: A lot abutting upon any combination of two (2) or more streets, including private streets (e.g., unit lot drives), access easements, or shared driveways, but excluding alleys, at their intersection, or upon two (2) parts of the same street, such streets or parts of the same street forming an interior angle of less than one hundred thirty-five degrees (135) within the lot lines.Renton Municipal Code 4-11-120.[LOT TYPES].A
Lot, Interior: C. Lot, Interior: A lot that generally abuts or has frontage on only one (1) street (or other means of access that may be permitted).Renton Municipal Code 4-11-120.[LOT TYPES].C
Lot, Through: D. Lot, Through: A lot that has two (2) opposing ends each fronting on a street.Renton Municipal Code 4-11-120.[LOT TYPES].D
YARD REQUIREMENT: YARD REQUIREMENT: An open space on a lot unoccupied by structures, unless specifically authorized otherwise. The Planning Division shall determine the various yard requirements for uniquely shaped lots and flag lots. (See also SETBACK.)Renton Municipal Code 4-11-250.[YARD REQUIREMENT]
Front Yard: A. Front Yard: The yard requirement that separates the structure(s) from public right-of-way, private access easement, or shared driveway. For through lots, corner lots, and lots without street frontage, the front yard will be determined by the Planning Division Director.Renton Municipal Code 4-11-250.[YARD REQUIREMENT].A
Secondary Front Yard: B. Secondary Front Yard: The yard requirement for corner lots and through lots that serves as a second front yard abutting a street right-of-way, private street, or shared driveway.Renton Municipal Code 4-11-250.[YARD REQUIREMENT].B
Rear Yard: C. Rear Yard: The yard requirement opposite the front yard. Where a lot abuts an alley, the rear yard shall always be the yard abutting the alley. For irregularly shaped lots, the rear yard shall be measured from an imaginary line at least fifteen feet (15') in length located entirely within the lot and farthest removed and parallel to the front lot line or its tangent.Renton Municipal Code 4-11-250.[YARD REQUIREMENT].C
Side Yard: D. Side Yard: The yard requirement which is not a front yard, a secondary front yard, or a rear yard.Renton Municipal Code 4-11-250.[YARD REQUIREMENT].D

How setbacks are measured

Height

iWhat is the height limit?

How tall a detached ADU (backyard cottage) can be, measured the way the code measures height.

Height

24ftmaximum

to the highest point of the roof

Renton measures from the average ground level along the building's walls. Check with a design professional to confirm your height.

Up to 24 ft. to the highest point of the roof.

How tall can a detached ADU (backyard cottage) be?

What the code says · 4-2-110C.4

4. Development Standards: The following development standards are established for ADUs: Please see Section 4-2-110I, Conditions Associated With Residential Development Standards Tables, for explanation of table footnotes.
1
GENERAL REQUIREMENTS⁴, 10 {spans 2 columns}
Maximum Number of Units²⁴ Two (2) ADUs are allowed per legal lot as an accessory use to a principal dwelling
Configuration Either one (1) attached ADU and one (1) detached ADU, two (2) attached ADUs, or two (2) detached ADUs. ADUs may be established within or as an addition to the principal dwelling. / In RC, R-1, R-4, R-6, and R-8 zones, when two (2) ADUs are proposed, the second ADU shall comply with the location and setback requirements applicable to the principal dwelling
Maximum Gross Floor Area⁴⁰ 1,000 sq. ft
Maximum Building Area²⁶, 41 1,000 sq. ft
Conversions²⁵ If a conversion unit occupies an entire single floor of the primary dwelling, it may be allowed to increase the maximum unit size to efficiently use all the floor area. Conversion units greater than 1,250 sq. ft. shall be classified as an attached dwelling rather than ADU
Parking²⁰ A minimum of 1.0 parking space per dwelling unit. / No off-street parking required for ADUs located on lots within a one-half mile walking distance of a Major Transit Stop (Area A)
Design Standards See RMC 4-2-115, Residential Design and Open Space Standards
ATTACHED AND INTERNAL ADUs {spans 2 columns}
Setbacks and Building Height ADUs shall comply with the standards applicable to primary structures, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures, and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures
DETACHED ADUs {spans 2 columns}
Front Yard and Secondary Front Yard Setbacks ADUs shall comply with the location and front yard setback requirements of the underlying zone, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures. / Detached ADUs shall be located at least 4 ft. from any residential structure otherwise the structure shall be considered an attached ADU
Side Yard Setbacks RC and R-1 zones: 25 ft. / R-4, R-6, and R-8 zones: 5 ft. / R-10 and R-14 zones 4 ft
Rear Yard Setbacks 5 ft. When located within 10 ft. of the rear property line, at least 25% of the lineal length of the rear yard shall remain unoccupied from accessory dwellings. / ADUs may be sited at the rear lot line where an alley is present
Building Height²³, 42 24 ft. measured to the highest point of a flat roof or the highest ridge of a pitched roof
Renton Municipal Code 4-2-110C.4 · DEVELOPMENT STANDARDS FOR ACCESSORY DWELLING UNITS^1

GENERAL REQUIREMENTS⁴, 10 {spans 2 columns}
Maximum Number of Units²⁴		Two (2) ADUs are allowed per legal lot as an accessory use to a principal dwelling
Configuration		Either one (1) attached ADU and one (1) detached ADU, two (2) attached ADUs, or two (2) detached ADUs. ADUs may be established within or as an addition to the principal dwelling. / In RC, R-1, R-4, R-6, and R-8 zones, when two (2) ADUs are proposed, the second ADU shall comply with the location and setback requirements applicable to the principal dwelling
Maximum Gross Floor Area⁴⁰		1,000 sq. ft
Maximum Building Area²⁶, 41		1,000 sq. ft
Conversions²⁵		If a conversion unit occupies an entire single floor of the primary dwelling, it may be allowed to increase the maximum unit size to efficiently use all the floor area. Conversion units greater than 1,250 sq. ft. shall be classified as an attached dwelling rather than ADU
Parking²⁰		A minimum of 1.0 parking space per dwelling unit. / No off-street parking required for ADUs located on lots within a one-half mile walking distance of a Major Transit Stop (Area A)
Design Standards		See RMC 4-2-115, Residential Design and Open Space Standards
ATTACHED AND INTERNAL ADUs {spans 2 columns}
Setbacks and Building Height		ADUs shall comply with the standards applicable to primary structures, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures, and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures
DETACHED ADUs {spans 2 columns}
Front Yard and Secondary Front Yard Setbacks		ADUs shall comply with the location and front yard setback requirements of the underlying zone, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures. / Detached ADUs shall be located at least 4 ft. from any residential structure otherwise the structure shall be considered an attached ADU
Side Yard Setbacks	RC and R-1 zones: 25 ft. / R-4, R-6, and R-8 zones: 5 ft. / R-10 and R-14 zones	4 ft
Rear Yard Setbacks		5 ft. When located within 10 ft. of the rear property line, at least 25% of the lineal length of the rear yard shall remain unoccupied from accessory dwellings. / ADUs may be sited at the rear lot line where an alley is present
Building Height²³, 42		24 ft. measured to the highest point of a flat roof or the highest ridge of a pitched roof

How Renton measures height: Pitched roof — How Renton measures height

How Renton measures height: Flat roof — How Renton measures height

Square footage

iWhat counts as square footage?

The floor area of a detached ADU (backyard cottage), counted the way the code counts it.

Square footage

1,000sfmaximum

Up to 1,000 sf.

How big can a detached ADU (backyard cottage) be?

What the code says · 4-2-110C.4

4. Development Standards: The following development standards are established for ADUs: Please see Section 4-2-110I, Conditions Associated With Residential Development Standards Tables, for explanation of table footnotes.
1
GENERAL REQUIREMENTS⁴, 10 {spans 2 columns}
Maximum Number of Units²⁴ Two (2) ADUs are allowed per legal lot as an accessory use to a principal dwelling
Configuration Either one (1) attached ADU and one (1) detached ADU, two (2) attached ADUs, or two (2) detached ADUs. ADUs may be established within or as an addition to the principal dwelling. / In RC, R-1, R-4, R-6, and R-8 zones, when two (2) ADUs are proposed, the second ADU shall comply with the location and setback requirements applicable to the principal dwelling
Maximum Gross Floor Area⁴⁰ 1,000 sq. ft
Maximum Building Area²⁶, 41 1,000 sq. ft
Conversions²⁵ If a conversion unit occupies an entire single floor of the primary dwelling, it may be allowed to increase the maximum unit size to efficiently use all the floor area. Conversion units greater than 1,250 sq. ft. shall be classified as an attached dwelling rather than ADU
Parking²⁰ A minimum of 1.0 parking space per dwelling unit. / No off-street parking required for ADUs located on lots within a one-half mile walking distance of a Major Transit Stop (Area A)
Design Standards See RMC 4-2-115, Residential Design and Open Space Standards
ATTACHED AND INTERNAL ADUs {spans 2 columns}
Setbacks and Building Height ADUs shall comply with the standards applicable to primary structures, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures, and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures
DETACHED ADUs {spans 2 columns}
Front Yard and Secondary Front Yard Setbacks ADUs shall comply with the location and front yard setback requirements of the underlying zone, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures. / Detached ADUs shall be located at least 4 ft. from any residential structure otherwise the structure shall be considered an attached ADU
Side Yard Setbacks RC and R-1 zones: 25 ft. / R-4, R-6, and R-8 zones: 5 ft. / R-10 and R-14 zones 4 ft
Rear Yard Setbacks 5 ft. When located within 10 ft. of the rear property line, at least 25% of the lineal length of the rear yard shall remain unoccupied from accessory dwellings. / ADUs may be sited at the rear lot line where an alley is present
Building Height²³, 42 24 ft. measured to the highest point of a flat roof or the highest ridge of a pitched roof
Renton Municipal Code 4-2-110C.4 · DEVELOPMENT STANDARDS FOR ACCESSORY DWELLING UNITS^1

GENERAL REQUIREMENTS⁴, 10 {spans 2 columns}
Maximum Number of Units²⁴		Two (2) ADUs are allowed per legal lot as an accessory use to a principal dwelling
Configuration		Either one (1) attached ADU and one (1) detached ADU, two (2) attached ADUs, or two (2) detached ADUs. ADUs may be established within or as an addition to the principal dwelling. / In RC, R-1, R-4, R-6, and R-8 zones, when two (2) ADUs are proposed, the second ADU shall comply with the location and setback requirements applicable to the principal dwelling
Maximum Gross Floor Area⁴⁰		1,000 sq. ft
Maximum Building Area²⁶, 41		1,000 sq. ft
Conversions²⁵		If a conversion unit occupies an entire single floor of the primary dwelling, it may be allowed to increase the maximum unit size to efficiently use all the floor area. Conversion units greater than 1,250 sq. ft. shall be classified as an attached dwelling rather than ADU
Parking²⁰		A minimum of 1.0 parking space per dwelling unit. / No off-street parking required for ADUs located on lots within a one-half mile walking distance of a Major Transit Stop (Area A)
Design Standards		See RMC 4-2-115, Residential Design and Open Space Standards
ATTACHED AND INTERNAL ADUs {spans 2 columns}
Setbacks and Building Height		ADUs shall comply with the standards applicable to primary structures, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures, and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures
DETACHED ADUs {spans 2 columns}
Front Yard and Secondary Front Yard Setbacks		ADUs shall comply with the location and front yard setback requirements of the underlying zone, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures. / Detached ADUs shall be located at least 4 ft. from any residential structure otherwise the structure shall be considered an attached ADU
Side Yard Setbacks	RC and R-1 zones: 25 ft. / R-4, R-6, and R-8 zones: 5 ft. / R-10 and R-14 zones	4 ft
Rear Yard Setbacks		5 ft. When located within 10 ft. of the rear property line, at least 25% of the lineal length of the rear yard shall remain unoccupied from accessory dwellings. / ADUs may be sited at the rear lot line where an alley is present
Building Height²³, 42		24 ft. measured to the highest point of a flat roof or the highest ridge of a pitched roof

Structure coverage

iWhat counts as coverage?

How much of the lot buildings can cover, counting every structure on the lot together.

Structure coverage

25%of the lot, maximum

BuildingsOpen

Up to 25%.

How much of the lot can buildings cover?

What the code says · 4-2-110A

(Ord. 4869, 10-23-2000; Amd. Ord. 4963, 5-13-2002; Ord. 5100, 11-1-2004; Ord. 5132, 4-4-2005; Ord. 5153, 9-26-2005; Ord. 5306, 9-17-2007; Ord. 5355, 2-25-2008; Ord. 5383, 6-2-2008; Ord. 5387, 6-9-2008; Ord. 5401, 7-14-2008; Ord. 5450, 3-2-2009; Ord. 5473, 7-13-2009; Ord. 5518, 12-14-2009; Ord. 5526, 2-1-2010; Ord. 5528, 3-8-2010; Ord. 5529, 3-8-2010; Ord. 5531, 3-8-2010; Ord. 5590, 2-28-2011; Ord. 5649, 12-12-2011; Ord. 5650, 12-12-2011; Ord. 5675, 12-3-2012; Ord. 5702, 12-9-2013; Ord. 5726, 10-20-2014; Ord. 5744, 1-12-2015; Ord. 5759 (Att. C), 6-22-2015; Ord. 5790, 4-25-2016; Ord. 5791 (Att. A), 4-25-2016; Ord. 5798 (Att. A), 4-25-2016; Ord. 5841 (Att. A), 6-12-2017; Ord. 5867 (Att. B), 12-11-2017; Ord. 5899 (Att. B), 11-19-2018; Ord. 5960 (Att. B), 12-9-2019; Ord. 5981 (Att. A), 10-12-2020; Ord. 6048, 12-13-2021; Ord. 6049, 12-13-2021; Ord. 6076 (Att. A), 8-8-2022; Ord. 6091 (Att. A), 11-28-2022; Ord. 6128 (Att. C), 12-11-2023; Ord. 6154 (Att. A), 12-9-2024; Ord. 6160 (Exh. B-1), 6-16-2025) Please see Section 4-2-110I, Conditions Associated With Residential Development Standards Tables, for explanation of table footnotes.
8
RC
Minimum Net Density (per Net Acre)¹, 2, 15 None {spans 3 columns}
Maximum Net Density (per Net Acre, Except per Net 10 Acres in RC)², 14, 15 1 dwelling unit
Maximum Number of Dwellings (per Legal Lot)² Single-family dwellings and cottage house dwelling units: 1 per legal or unit lot. / Accessory dwelling units (attached or detached): 2 per legal lot. / Middle housing See RMC 4-2-110F, Development Standards for Middle Housing Developments. {spans 5 columns}
Minimum Lot Size², 28, 31 10 acres
Minimum Lot Width³¹ 150 ft
Minimum Lot Width³¹ (Corner Lots) 175 ft
Minimum Lot Depth³¹ 300 ft
Minimum Front Yard⁴, 5, 31 30 ft
Minimum Rear Yard⁴, 22, 31 35 ft
Minimum Side Yard⁴, 31 25 ft
Minimum Secondary Front Yard⁴, 5, 31 (applies to Corner Lots) 30 ft
Maximum Building Coverage (including Primary and Accessory) 10%
Maximum Impervious Surface Area 15%
Maximum Number of Stories 3 {spans 3 columns}
Maximum Wall Plate Height⁸, 9, 10, 12, 18, 19 32 ft. {spans 3 columns}
Maximum Number of Units per Building² 4 dwelling units {spans 5 columns}
Minimum Freeway Frontage Setback 10 ft. landscaped setback from the street property line. {spans 5 columns}
Maximum Wireless Communication Facilities Height (including Amateur Radio Antennas) See RMC 4-4-140, Wireless Communication Facilities. Amateur radio antennas are allowed a maximum height of 6 feet without a Conditional Use Permit. Larger structures will have a maximum height determined by the Conditional Use Permit process, RMC 4-9-030, Conditional Use Permits. {spans 5 columns}
Design Standards See RMC 4-2-115, Residential Design and Open Space Standards. {spans 5 columns}
Landscaping See RMC 4-4-070, Landscaping. {spans 5 columns}
Exterior Lighting See RMC 4-4-075, Lighting, Exterior On-Site. {spans 5 columns}
Screening See RMC 4-4-095, Screening and Storage Height/Location Limitations. {spans 5 columns}
Exception for Pre-Existing Legal Lots See RMC 4-10-010, Nonconforming Lots. {spans 5 columns}
Renton Municipal Code 4-2-110A · DEVELOPMENT STANDARDS FOR RESIDENTIAL LOW DENSITY AND MEDIUM DENSITY ZONES – PRIMARY STRUCTURES^1

		RC
Minimum Net Density (per Net Acre)¹, 2, 15		None {spans 3 columns}
Maximum Net Density (per Net Acre, Except per Net 10 Acres in RC)², 14, 15		1 dwelling unit
Maximum Number of Dwellings (per Legal Lot)²	Single-family dwellings and cottage house dwelling units: 1 per legal or unit lot. / Accessory dwelling units (attached or detached): 2 per legal lot. / Middle housing	See RMC 4-2-110F, Development Standards for Middle Housing Developments. {spans 5 columns}
Minimum Lot Size², 28, 31		10 acres
Minimum Lot Width³¹		150 ft
Minimum Lot Width³¹ (Corner Lots)		175 ft
Minimum Lot Depth³¹		300 ft
Minimum Front Yard⁴, 5, 31		30 ft
Minimum Rear Yard⁴, 22, 31		35 ft
Minimum Side Yard⁴, 31		25 ft
Minimum Secondary Front Yard⁴, 5, 31 (applies to Corner Lots)		30 ft
Maximum Building Coverage (including Primary and Accessory)		10%
Maximum Impervious Surface Area		15%
Maximum Number of Stories		3 {spans 3 columns}
Maximum Wall Plate Height⁸, 9, 10, 12, 18, 19		32 ft. {spans 3 columns}
Maximum Number of Units per Building²		4 dwelling units {spans 5 columns}
Minimum Freeway Frontage Setback		10 ft. landscaped setback from the street property line. {spans 5 columns}
Maximum Wireless Communication Facilities Height (including Amateur Radio Antennas)		See RMC 4-4-140, Wireless Communication Facilities. Amateur radio antennas are allowed a maximum height of 6 feet without a Conditional Use Permit. Larger structures will have a maximum height determined by the Conditional Use Permit process, RMC 4-9-030, Conditional Use Permits. {spans 5 columns}
Design Standards		See RMC 4-2-115, Residential Design and Open Space Standards. {spans 5 columns}
Landscaping		See RMC 4-4-070, Landscaping. {spans 5 columns}
Exterior Lighting		See RMC 4-4-075, Lighting, Exterior On-Site. {spans 5 columns}
Screening		See RMC 4-4-095, Screening and Storage Height/Location Limitations. {spans 5 columns}
Exception for Pre-Existing Legal Lots		See RMC 4-10-010, Nonconforming Lots. {spans 5 columns}

Some cases depend on details a drawing can't show. Check with a design professional for: 4-2-110I.5, 4-11-190.M, 4-2-110C.4

5. The minimum front yard and secondary front yard setback for lots that abut required turnarounds (cul-de-sacs and hammerheads) may be reduced, excluding garage setbacks, to no less than five feet (5'), subject to the following:
Renton Municipal Code 4-2-110I.5 · CONDITIONS ASSOCIATED WITH RESIDENTIAL DEVELOPMENT STANDARDS TABLES

M. SETBACK: The minimum required distance between the building footprint and the property line and any private access easement or tract. For lots containing private access easements, setbacks are the minimum required distance between the building footprint and the easement. A setback is measured perpendicularly from a lot line or private easement access to the outer wall of the structure. In the case where a structure does not have an outer wall, such as a carport, the measurement shall be to the posts of such structure, unless otherwise determined by the Department of Community and Economic Development.
Renton Municipal Code 4-11-190.M · DEFINITIONS S:

4. Development Standards: The following development standards are established for ADUs: Please see Section 4-2-110I, Conditions Associated With Residential Development Standards Tables, for explanation of table footnotes.
1
GENERAL REQUIREMENTS⁴, 10 {spans 2 columns}
Maximum Number of Units²⁴ Two (2) ADUs are allowed per legal lot as an accessory use to a principal dwelling
Configuration Either one (1) attached ADU and one (1) detached ADU, two (2) attached ADUs, or two (2) detached ADUs. ADUs may be established within or as an addition to the principal dwelling. / In RC, R-1, R-4, R-6, and R-8 zones, when two (2) ADUs are proposed, the second ADU shall comply with the location and setback requirements applicable to the principal dwelling
Maximum Gross Floor Area⁴⁰ 1,000 sq. ft
Maximum Building Area²⁶, 41 1,000 sq. ft
Conversions²⁵ If a conversion unit occupies an entire single floor of the primary dwelling, it may be allowed to increase the maximum unit size to efficiently use all the floor area. Conversion units greater than 1,250 sq. ft. shall be classified as an attached dwelling rather than ADU
Parking²⁰ A minimum of 1.0 parking space per dwelling unit. / No off-street parking required for ADUs located on lots within a one-half mile walking distance of a Major Transit Stop (Area A)
Design Standards See RMC 4-2-115, Residential Design and Open Space Standards
ATTACHED AND INTERNAL ADUs {spans 2 columns}
Setbacks and Building Height ADUs shall comply with the standards applicable to primary structures, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures, and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures
DETACHED ADUs {spans 2 columns}
Front Yard and Secondary Front Yard Setbacks ADUs shall comply with the location and front yard setback requirements of the underlying zone, pursuant to RMC 4-2-110A, Development Standards for Residential Low Density and Medium Density Zones – Primary Structures and RMC 4-2-110B, Development Standards for Residential High Density Zones – Primary Structures. / Detached ADUs shall be located at least 4 ft. from any residential structure otherwise the structure shall be considered an attached ADU
Side Yard Setbacks RC and R-1 zones: 25 ft. / R-4, R-6, and R-8 zones: 5 ft. / R-10 and R-14 zones 4 ft
Rear Yard Setbacks 5 ft. When located within 10 ft. of the rear property line, at least 25% of the lineal length of the rear yard shall remain unoccupied from accessory dwellings. / ADUs may be sited at the rear lot line where an alley is present
Building Height²³, 42 24 ft. measured to the highest point of a flat roof or the highest ridge of a pitched roof
Renton Municipal Code 4-2-110C.4 · DEVELOPMENT STANDARDS FOR ACCESSORY DWELLING UNITS^1

Detached ADU rules in Renton's Residential-1 zone: corner lot, alley behind the lot

Your lot

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What the code allows

Setbacks

How close to the front lot line can a detached ADU (backyard cottage) be?

How close to the rear lot line can a detached ADU (backyard cottage) be?

How close to the side lot line can a detached ADU (backyard cottage) be?

How close to the secondary front lot line can a detached ADU (backyard cottage) be?

Height

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Square footage

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Structure coverage

How much of the lot can buildings cover?

Other structures in Renton's Residential-1 zone