Home Remodeling in
Yelm, WA
Yelm is one of the few places around here where the size of your lot, not the size of your house, sets how big an accessory dwelling you can build.
Remodeling in Yelm
What building in Yelm actually involves
Yelm sits at the southeast corner of Thurston County, on the prairie between the Nisqually and the foothills, and it has grown fast. The population is now around 10,800, which is a very different town from the one many longer-standing residents bought into.
That growth shows up in the housing. Yelm has larger lots than Lacey or Tumwater in many neighbourhoods, older prairie properties on acreage, and newer subdivision stock built to much tighter footprints. What is possible on your property here depends heavily on which of those you own.
Lot size sets your ADU size in Yelm
This is the rule that makes Yelm different from its neighbours. In the moderate-density residential R-6 district, one secondary dwelling unit may be created on a single-family lot, and the size cap is tied to the lot rather than the main house.
For lots of record under one acre, the conversion or addition may not exceed 1,000 square feet. For lots of record of one acre or more, it may not exceed 1,500 square feet.
Compare that with Lacey, where the cap is the smaller of a fixed figure or half the size of the main house. If you own acreage in Yelm, you may have more room to work with than the same budget would buy you closer in.
The allowance is also subject to the availability of public utilities, and has to comply with building, plumbing, fire and other applicable codes. On larger prairie lots the utility question is not a formality.
Where Yelm permitting happens
Yelm's Planning and Building Division processes and issues the permits required under the Washington State Building Code and the Growth Management Act, with local rules set out in the Yelm Unified Development Code at Title 18 YMC.
Staff are in the Public Services building at 901 Rhoton Road NW, not at City Hall, and the phone number is (360) 400-5003. Business hours run 7:00am to 5:00pm Monday to Friday, which is an earlier start than most of the county and useful if you want to catch someone before a work day.
Yelm has also been amending its development code, including Ordinance No. 1154 which set design standards for unit lot subdivisions and accessory dwelling units.
State law still sits on top
HB 1337 requires jurisdictions planning under the Growth Management Act to allow two accessory dwelling units per lot inside urban growth areas, prohibits capping an ADU below 1,000 square feet, and prohibits owner-occupancy requirements. The compliance deadline is 31 December 2026.
Yelm's published R-6 standard describes one secondary unit. As with the rest of the county, the sensible move is to confirm the currently adopted standard with Planning and Building rather than designing to a figure found online.
City requirements on this page were last checked on 8 September 2026. Codes change, so confirm current standards with the city before you apply.
Common Questions
Remodeling in Yelm, answered
How big can an ADU be in Yelm, WA?
Yelm ties the cap to lot size. In the R-6 moderate-density residential district, a secondary dwelling unit on a lot of record under one acre may not exceed 1,000 square feet, and on a lot of one acre or more it may not exceed 1,500 square feet. The allowance is subject to public utility availability and applicable building codes.
Where is the Yelm permit office?
Yelm Planning and Building is in the Public Services building at 901 Rhoton Road NW rather than at City Hall. The phone number is (360) 400-5003 and hours are 7:00am to 5:00pm Monday to Friday.
Is Yelm different from Lacey for ADUs?
Yes. Lacey's published cap is a fixed square footage or half the size of the main house, whichever is smaller. Yelm's is based on your lot: 1,000 square feet under an acre, 1,500 square feet at an acre or more. If you own acreage in Yelm you may have more room than an equivalent property closer in.
Do you build in Yelm and the surrounding prairie?
Yes. KOI Build Co works across Yelm, Rainier, Tenino, Lacey, Olympia, Tumwater and the wider South Puget Sound region. Call (253) 348-1847 for a free estimate.
Planning a project in Yelm?
Free estimates, and a straight answer on what your project will cost and how long it will take.
Also serving Olympia, Tumwater and the wider South Puget Sound.