Detached ADUs

AN ACT Relating to establishing limitations on detached accessory 1
dwelling units outside urban growth areas; amending RCW 36.70A.696; 2
and adding a new section to chapter 36.70A RCW. 3
BE IT ENACTED BY THE LEGISLATURE OF THE STATE OF WASHINGTON:4
NEW SECTION. Sec. 1. A new section is added to chapter 36.70A 5
RCW to read as follows: 6
(1) Counties may allow detached accessory dwelling units outside 7
of urban growth areas if the county meets the requirements in 8
subsections (2) and (3) of this section, and such detached accessory 9
dwelling units are subject to development regulations that include 10
the following limitations: 11
(a) No parcel may have more than one attached or detached 12
accessory dwelling unit; 13
(b) The detached accessory dwelling unit is subject to the water 14
supply requirements of RCW 19.27.097 and any groundwater mitigation 15
requirements adopted by the county or the department of ecology;16
(c) The applicant must provide documentation that the existing or 17
proposed sewage or septic system is capable of handling the 18
additional demand placed upon it by the detached accessory dwelling 19
unit; 20
S-0588.1
SENATE BILL 5413
State of Washington 69th Legislature 2025 Regular Session
By Senators Lovelett, Nobles, and Saldaña
Read first time 01/22/25. Referred to Committee on Housing.
p. 1 SB 5413
(d) The gross floor area of the detached accessory dwelling unit 1
does not exceed the gross floor area of what could be authorized by 2
the county as an expansion of the primary dwelling to create an 3
attached accessory dwelling unit and is, in no case, greater than 4
1,296 square feet. Floor areas are exclusive of garages, porches, and 5
unfinished basements; 6
(e) The detached accessory dwelling unit must utilize the same 7
driveway as the principal unit; 8
(f) The detached accessory dwelling unit must be sited within 150 9
feet of the principal unit; 10
(g) The detached accessory dwelling unit may be the existing 11
principal unit if the existing principal unit meets the requirements 12
of this subsection, is a single-family dwelling unit, and a new 13
principal unit that is a single-family dwelling unit is constructed 14
on the same parcel; 15
(h) A parcel may not be subdivided for the purposes of avoiding 16
the limits on development regulations described in this subsection;17
(i) If the detached accessory dwelling unit is offered as a 18
short-term rental as defined in RCW 36.70A.696, the primary unit must 19
be owner-occupied; 20
(j) The combined water withdrawal for the detached accessory 21
dwelling unit, the primary unit, and any other domestic uses on the 22
parcel must not exceed the use limitations in RCW 90.44.050 for 23
domestic use; 24
(k) The detached accessory dwelling unit must be subject to the 25
water supply requirements in RCW 19.27.097; and 26
(l) Withdrawals of water by each dwelling unit on the parcel must 27
be metered. 28
(2) Counties may only allow detached accessory dwelling units 29
outside of urban growth areas if they have the following code 30
enforcement measures in place: 31
(a) A voluntary county code compliance process through which the 32
owner of an unpermitted detached accessory dwelling unit can bring 33
the unpermitted detached accessory dwelling unit into compliance with 34
applicable regulations. In such a case, a permit penalty of at least 35
double the normal permit fee applies. 36
(b) Owners who do not seek voluntary compliance and are found to 37
have constructed or placed a detached accessory dwelling unit without 38
all required permits are subject to a civil infraction of at least 39
$1,000 and are required to remove the detached accessory dwelling 40
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unit or ensure that it meets all existing development regulations, if 1
applicable. A penalty of at least triple the normal permit fee is 2
also required if the accessory dwelling unit remains and meets all 3
existing development regulations. 4
(c) Any owner who does not seek voluntary compliance and who 5
received a civil infraction for constructing or placing an accessory 6
dwelling unit without all required permits is prohibited from 7
receiving any permits for the placement or construction of new 8
accessory dwelling units for a period of at least three years.9
(3) Counties may allow detached accessory dwelling units outside 10
of urban growth areas if the county takes the following actions to 11
account for detached accessory dwelling unit development:12
(a) Tracks and reports to the department annually the number of 13
detached accessory dwelling unit permits completed;14
(b) Updates the county's comprehensive land use plan during the 15
county's next required review and all subsequent reviews according to 16
RCW 36.70A.130(5)(b) to properly account for the number of detached 17
accessory dwelling units completed since the effective date of this 18
section and the projected development over the next 20-year planning 19
period utilizing the data collected and reported in (a) of this 20
subsection within the overall underlying density outside of urban 21
growth areas; 22
(c) Makes future amendments to the county's comprehensive land 23
use plan accounting for actual and projected detached accessory 24
dwelling units within the overall underlying density outside of urban 25
growth areas no more than once every five years. 26
(4) Subsection (1) of this section is in addition to other county 27
authority enumerated in this chapter and does not:28
(a) Affect or modify the validity of any county ordinance 29
authorizing accessory dwelling units adopted prior to the effective 30
date of this section; 31
(b) Exclude other means of authorizing accessory dwelling units 32
in urban or rural areas, if consistent with this act; or33
(c) Exclude other innovative techniques under RCW 34
36.70A.070(5)(b), 36.70A.090, or 36.70A.177, if consistent with this 35
section. 36
Sec. 2. RCW 36.70A.696 and 2023 c 334 s 2 are each amended to 37
read as follows: 38
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The definitions in this section apply throughout RCW 36.70A.697, 1
36.70A.698, 36.70A.680, ((and)) 36.70A.681, and section 1 of this act 2
unless the context clearly requires otherwise. 3
(1) "Accessory dwelling unit" means a dwelling unit located on 4
the same lot as a single-family housing unit, duplex, triplex, 5
townhome, or other housing unit. 6
(2) "Attached accessory dwelling unit" means an accessory 7
dwelling unit located within or attached to a single-family housing 8
unit, duplex, triplex, townhome, or other housing unit.9
(3) "City" means any city, code city, and town located in a 10
county planning under RCW 36.70A.040. 11
(4) "County" means any county planning under RCW 36.70A.040.12
(5) "Detached accessory dwelling unit" means an accessory 13
dwelling unit that consists partly or entirely of a building that is 14
separate and detached from a single-family housing unit, duplex, 15
triplex, townhome, or other housing unit and is on the same property.16
(6) "Dwelling unit" means a residential living unit that provides 17
complete independent living facilities for one or more persons and 18
that includes permanent provisions for living, sleeping, eating, 19
cooking, and sanitation. 20
(7) "Gross floor area" means the interior habitable area of a 21
dwelling unit including basements and attics but not including a 22
garage or accessory structure. 23
(8) "Major transit stop" means: 24
(a) A stop on a high capacity transportation system funded or 25
expanded under the provisions of chapter 81.104 RCW;26
(b) Commuter rail stops; 27
(c) Stops on rail or fixed guideway systems, including 28
transitways; 29
(d) Stops on bus rapid transit routes or routes that run on high 30
occupancy vehicle lanes; or 31
(e) Stops for a bus or other transit mode providing actual fixed 32
route service at intervals of at least fifteen minutes for at least 33
five hours during the peak hours of operation on weekdays.34
(9) "Owner" means any person who has at least 50 percent 35
ownership in a property on which an accessory dwelling unit is 36
located. 37
(10) "Principal unit" means the single-family housing unit, 38
duplex, triplex, townhome, or other housing unit located on the same 39
lot as an accessory dwelling unit. 40
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(11) "Short-term rental" means a lodging use, that is not a hotel 1
or motel or bed and breakfast, in which a dwelling unit, or portion 2
thereof, is offered or provided to a guest by a short-term rental 3
operator for a fee for fewer than 30 consecutive nights.4
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