A new one- or two-family home in unincorporated Washington County, Wisconsin needs a building permit under the statewide Uniform Dwelling Code, issued by the municipality where authority is delegated and otherwise by Wisconsin DSPS1,2. General zoning comes from the town, village or city, while the county keeps shoreland, wetland and floodplain zoning3. Septic permits for every address, city or not, come from the county4,5.
Do you need a building permit in Washington County, Wisconsin?
Yes.
Yes. New one- and two-family homes in Washington County, including stick-built, modular and manufactured-home installations, require a building permit under Wisconsin's Uniform Dwelling Code1,8. Apply to the municipality when it has delegated building-permit authority; otherwise submit the application to Wisconsin DSPS with the plans, contractor-license information, required data and fee2. Requirements for additions and alterations vary by municipality, and construction begins only after plans are approved and the building permit is issued and posted2. County sanitary, erosion-control, stormwater or floodplain approval may also be required before work begins9.
How do septic permits work in Washington County?
Private onsite wastewater work in Washington County requires the applicable sanitary permit: the state permit covers installation or a major modification or addition, while the county permit covers reconnection, privies, minor repairs and components outside state permit requirements.
Private onsite wastewater work in Washington County requires the applicable sanitary permit: the state permit covers installation or a major modification or addition, while the county permit covers reconnection, privies, minor repairs and components outside state permit requirements5. Washington County issues county sanitary permits and inspects septic installations countywide, while state approval is required first for some systems4,5. County rules require domestic waste to go to an approved POWTS, restrict privies and generally prohibit holding tanks except in listed circumstances5. Only 15.4% of mapped soils lack severe limits for a conventional drain field, so obtain a site evaluation before treating a parcel as conventionally buildable10. Current sanitary-permit fees are published but vary by project11.
Can you live in an RV or tiny home on your land in Washington County?
We could not confirm a countywide private-land RV occupancy rule in Washington County, so ask the parcel's town, village or city about RV use.
We could not confirm a countywide private-land RV occupancy rule in Washington County, so ask the parcel's town, village or city about RV use3. The county's only confirmed RV rule covers campgrounds in floodplain districts: a camping unit may stay no more than 180 consecutive days before it must leave the floodplain for 24 hours, and stays beyond 30 days need the operator's written authorization12. That rule governs licensed campgrounds, not an RV on your own lot. A tiny home used as a covered new one- or two-family dwelling falls under Wisconsin's Uniform Dwelling Code1. In the county-regulated floodplain, a tiny home used as a dwelling is prohibited in the floodway and conditional in the floodfringe, general floodplain and flood-storage districts12. Ask County Land Resources which mapped district applies before choosing a site13. Off-grid living does not bypass sanitation rules: domestic waste must enter an approved POWTS, and county rules restrict privies and holding tanks5.
Building a home in Washington County: the steps, in order
Identify the municipality and ask its zoning office which local uses and setbacks apply.
- Identify the municipality and ask its zoning office which local uses and setbacks apply3.
- Ask County Land Resources about county shoreland, wetland, floodplain, erosion-control and stormwater approval9,13.
- For private wastewater, obtain the applicable county or state sanitary permit before the building permit2,5.
- Apply for the building permit through the municipality when it has delegated authority; otherwise apply to Wisconsin DSPS2.
- Call for an inspection of each construction phase before covering the work; the inspector has two business days after your request to inspect, and the county notes enforcement may be by a municipality, county or the state2.
- Occupy only after a final inspection finds no major health or safety violations2.
What should you check before buying land in Washington County?
Confirm the municipality and zoning authority first because Washington County does not administer general zoning countywide.
Confirm the municipality and zoning authority first because Washington County does not administer general zoning countywide3. A proposed land division may need township and extraterritorial approval as well as county review14. County approval applies when a plat creates 5 or more parcels of 1.5 acres or less within 5 years, or 3 or more parcels of 5 acres or less in the county shoreland area within 5 years; those are review thresholds, not a universal minimum lot size14. Check county mapping for shoreland, wetland and floodplain constraints, and contact Land Resources before work in a mapped floodplain9,13. Order a septic site evaluation because only 15.4% of mapped soils lack severe limits for a conventional drain field10. If access touches a County Trunk Highway, apply for the county access permit before installing the driveway15,16.
Watch-outs
- A town or village inside Washington County may issue its own building permits and set its own zoning, so confirm the municipality before relying on county rules3.
- Washington County does not administer general zoning countywide; confirm parcel-specific RV use, tiny-home standards and local setbacks with the municipality3.
- A new dwelling using private wastewater cannot receive its building permit until the sanitary permit is issued2.
- A new driveway in County Trunk Highway right-of-way requires the county access-permit process15.
Sources
16 official pages, each quoted and re-checked · written October 16, 2026
- One- & Two-Family Uniform Dwelling Code
- Wisconsin’s Uniform Dwelling Code
- County Land Information Plan 2024
- Septic Systems/POWTS
- Chapter 190: Private On-Site Wastewater Treatment Systems (POWTS)
- Instructions for Submitting a UDC Permit Application
- Well and heat exchange notification (Wisconsin statewide rule)
- UDC (Uniform Dwelling Code / One- and Two-Family Dwellings)
- Permits, Applications, and Grants
- Share of soils USDA rates "not limited" for a conventional septic drain field (SSURGO). A strict rating: the median county is about 6% and a tenth of counties are 0%, so a low figure means most lots need a site evaluation or an engineered system, not that septic is impossible. Cite it only with that caveat: Bolthole Index county data
- Septic Systems/POWTS
- Washington County Code, Chapter 275, Article IV: Floodplain Zoning
- Washington County Natural Resources Department — Land Resources (permitapp.washcowisco.gov)
- Land Division
- Permits
- Washington County Highway Department (washcowisco.gov)
Written October 16, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.
Off-grid gear
Going off-grid in Washington County means bringing your own water and power. The kit we’d start with:
- Water Crystal Quest Filter any source — well, rain, or creek — to drinking-clean.
- Power Bluetti Solar generators and home battery backup for living off the grid.
- Septic Soil percolation test kit Run your own perc test before paying an engineer — the first thing a septic office asks about.
- Water Well water test kit Bacteria, nitrates, hardness — know what the well on a parcel is really pumping.
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