Home improvement property tax exemption in Washington (2026):
3 years of relief, if you file before you finish
IS A HOME IMPROVEMENT EXEMPT FROM PROPERTY TAX IN WASHINGTON?
Yes, for some improvements. Under RCW 84.36.400, the value an addition or remodel adds to a single-family home is exempt from property tax for three assessment years, up to 30% of the home's value before the work. You must file a claim with your county assessor before the work is finished. In King County, an application received after the project is completed is denied.
What qualifies and what doesn't
| Project | Status |
|---|---|
| Addition, remodel, renovation or structural improvement that adds value | Can qualify |
| Accessory dwelling unit (ADU) | Can qualify |
| Attached garage, carport or deck | Considered (King County) |
| Repairs and deferred maintenance | Does not qualify |
| Painting, new roof, gutters or siding | Normal maintenance (King County) |
| Pools, fences, landscaping, sheds, barns, shops | Does not qualify |
- The home must be a single-family dwelling. King County also requires it to be owner-occupied.
- The work has to add value. WAC 458-16-080 says repairs that only keep the home in its original condition don't count. In King County, appraisers decide whether the project adds value.
- Like-for-like roofs don't count. The rule's own example: replacing a composition roof with the same type of composition roof does not qualify. See roof replacement cost in Seattle for what a new roof costs.
- Once every five years. You can't claim the exemption on the same home more than once in a five-year period.
How much is exempt
- The added value, not what you paid. WAC 458-16-080 says the exemption is the difference between the home's value before and after the improvement, and "the cost of the physical improvements is not the basis for the exemption."
- Capped at 30%. The exempt amount can't be more than 30% of the home's value before the improvement. King County says that value generally means the assessed value of the structure for the year before construction started.
- For three assessment years. After that, the full value is taxed.
Example: what it could save in King County
| Structure value before | Value added | Exempt amount | Tax saved per year | Over 3 years |
|---|---|---|---|---|
| $300,000 | $50,000 | $50,000 | about $457 | about $1,370 |
| $300,000 | $120,000 | $90,000 (30% cap) | about $822 | about $2,465 |
The savings are modest compared with the cost of an addition or a kitchen remodel. A 2020 Department of Revenue review found about 1,062 participants a year statewide on average and concluded the exemption was not effective at encouraging improvements. Assessors pointed to the small benefit and to owners not knowing they had to file before construction.
How to apply in King County
- 1. Get the permit and plan the dates. The King County form asks which city or the county issued your building permit.
- 2. File before the work is finished. Send the Home Improvement Exemption application (DOA Form 400) to the King County Department of Assessments. King County says applications received after completion are denied.
- 3. Mind July 31. Applications received by July 31 start with the following tax year; later ones start with the second tax year after.
- 4. Report completion. WAC 458-16-080 requires a written notice of completion. The assessor then inspects and sets the exempt value.
King County Department of Assessments: 201 South Jackson St., Room 708, Seattle, WA 98104; HomeImp.DestProp@kingcounty.gov; 206-296-7300. Other counties use their own forms: ask your county assessor.
Before work starts
- File the exemption claim as soon as you have the permit, not at the end of the job.
- Keep the permit, the contract and the completion date together. You'll need them for the notice of completion.
- Budget for sales tax on the whole contract, labor included: see sales tax on home repairs.
- Check the contractor on L&I's Verify a Contractor tool. If a job goes wrong, see how a contractor bond claim works.
Frequently asked questions
Do home improvements raise property taxes in Washington?
They can, because the assessor values the improved home. Under RCW 84.36.400, the added value of a qualifying improvement to a single-family home can be exempt for three assessment years, up to 30% of the home's value before the work.
When do I have to apply for the home improvement exemption?
Before the improvements are completed. WAC 458-16-080 requires the claim to be filed with the county assessor before completion, and King County says applications received after the project is completed are denied.
Does a new roof qualify for the exemption?
Usually not. King County lists a new roof, gutters, siding and painting as normal maintenance, and Washington's rule says replacing a composition roof with the same type of roof does not qualify.
How long does the exemption last?
Three assessment years after the improvements are completed. You can't claim it again on the same home within five years.
Is the exemption based on what I paid the contractor?
No. Washington's rule says the cost of the work is not the basis. The exemption is the increase in the home's value, capped at 30% of its value before the improvement.
Sources
- RCW 84.36.400 — Improvements to single-family dwellings
- WAC 458-16-080 — Improvements to single-family dwellings
- King County Department of Assessments — Home Improvement Exemption application, DOA Form 400 (rev. 06/2024)
- Washington Department of Revenue — Tax exemption study: improvements to single-family dwellings (November 4, 2020)
- King County Assessor — 2026 taxes
All sources accessed November 8, 2026.
This guide summarizes Washington law and King County information. It is not tax or legal advice. Confirm eligibility and deadlines with your county assessor before work starts. See our disclosure and disclaimer.