Franklin County, Idaho requires a building permit for a home, and zoning applies throughout unincorporated Franklin County12. Agricultural buildings have a code exemption, but they still must meet zoning placement rules3. Southeastern Idaho Public Health handles onsite septic permits, and the septic permit must come before the county building permit45.
At a glance
- Building permit
- Required for a home1
- Building codes
- Adopted by Franklin County6
- Zoning
- Yes in unincorporated Franklin County; cities maintain their own plans27
- Septic permits
- Southeastern Idaho Public Health4
- Agricultural buildings
- Exempt from adopted building codes, but zoning placement still applies3
- Manufactured homes outside parks
- At least 20 feet wide and 900 square feet, with a narrow older-unit exception8
- Septic soil suitability
- 5.3% of soils avoid a severe conventional drain-field limitation9
- Property taxes
- 0.5% effective rate; $1,512 median annual bill1011
Who to call
Building permits
Franklin County Building Department
Building permits and inspections for Franklin County; the county page says the septic permit must be completed before a building permit can be issued
561 West Oneida
Zoning
Franklin County Planning & Zoning
Planning, zoning, development-code materials, subdivisions and agricultural building-exemption materials
Septic permits
Southeastern Idaho Public Health — Franklin County Office
Local contact for the public health district that administers onsite septic permitting in Franklin County
42 West 1st South, Preston, Idaho 83263
Roads & driveways
Franklin County Road and Bridge
County right-of-way and approach permit materials
561 West Oneida Preston, ID 83263
Contact details are copied from each office’s official page and were checked against it on October 10, 2026.
Off-grid gear
Going off-grid in Franklin 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.
These are affiliate links — we may earn a commission, at no cost to you. As an Amazon Associate, Bolthole Index earns from qualifying purchases.
Do you need a building permit in Franklin County, Idaho?
Yes. Franklin County requires a written building permit from the County Building Inspector before anyone erects or constructs a new building, structure or mobile home, and before remodeling that changes a building's outside dimensions12. The county has adopted official building codes6. The county code sets the building permit fee at 1% of the assessed value of the proposed building, payable when the application is made12. Idaho also requires permits whenever electrical, plumbing or HVAC work is performed, although a local jurisdiction may administer some of those programs13. Agricultural buildings are the important exception: Franklin County exempts them from its adopted building codes, but zoning placement requirements still apply3. Do not treat that agricultural exemption as a general exemption for a farmhouse, cabin or other residence. The county's Building Department publishes the building-permit materials and tells applicants to send permits to that department5.
Who is the Franklin County building department, and how do you reach it?
Franklin County's Building Department is at 561 West Oneida in Preston; call 208-221-6149 or email randallh@fcidaho.us5. The department publishes building, mechanical and agricultural permit materials, along with a residential builders handbook and design criteria5. For land-use questions, contact Franklin County Planning & Zoning at 208-220-2120 or pandzadministrator@fcidaho.us14. The county's page does not publish a complete step-by-step process, and it states that a completed septic permit is required before a building permit can be issued15. The inspection sequence, certificate-of-occupancy process and other fees could not be confirmed. Ask the Building Department for the current application packet, fee total and required inspections before budgeting or scheduling construction.
Does Franklin County have zoning?
Yes. Franklin County zoning applies to land throughout unincorporated Franklin County2. Incorporated cities maintain their own plans, and city plans and zoning apply in an Area of City Impact only after annexation7. A listing described as rural or agricultural therefore does not establish what may be built. Ask Planning & Zoning to identify the parcel's jurisdiction and district and confirm permitted uses, setbacks, minimum lot size, building height and subdivision rules. The county's website lists zoning guidelines, a 2025 comprehensive plan and an amended development code, but the opened page does not give district names or the exact unincorporated boundary16. Franklin County publishes its development code, subdivision application and agricultural building-exemption material through Planning & Zoning14. The agricultural building-code exemption does not waive zoning placement requirements3.
How do septic permits work in Franklin County?
Southeastern Idaho Public Health administers onsite septic permitting for Franklin County under Idaho's district system41718. Start with the district's Franklin County office at 42 West 1st South in Preston, phone (208) 852-047819. Every application needs an onsite evaluation, test holes at least 8-10 feet deep depending on soil type, a plot plan, a deed or tax notice and the fee20. The district's published sewage disposal permit fee is $850 for a basic or complex system, $3,000 for a large soil absorption system and $300 for a tank only; fees may change21. Only 5.3% of county soils avoid a severe limitation for a conventional drain field, so make septic feasibility a purchase contingency rather than assuming a standard system will work9. The public health district conducts the site evaluations and issues the septic permits, and no system may receive wastewater until the final installation inspection is complete2223. Franklin County requires the septic permit before issuing the building permit5.
Can you live in an RV or tiny home on your land in Franklin County?
Franklin County's rules for long-term RV living, temporary camping on private land and tiny-home occupancy could not be confirmed. Zoning applies throughout unincorporated Franklin County, so ask Planning & Zoning whether the parcel permits the proposed dwelling or temporary occupancy214. A manufactured home outside a park must generally be at least 20 feet wide and contain at least 900 square feet; a narrow replacement exception covers qualifying units in place by January 26, 19988. The Building Inspector must inspect and certify the unit's bronze data plate before a building permit can issue, and the unit must meet county setbacks and other applicable rules8. Idaho also requires manufactured-home installation approval before occupancy24.
How do you build a home in Franklin County, step by step?
- Ask Franklin County Planning & Zoning to verify the parcel's zoning district, permitted dwelling type and dimensional standards2514.
- Have Southeastern Idaho Public Health evaluate the site and issue the septic permit; Franklin County requires that permit before the building permit205.
- Confirm water. Before drilling a private well, obtain an Idaho Department of Water Resources drilling permit and use a licensed well driller26.
- Apply to the Franklin County Building Department and confirm the current fee, plan requirements and inspection schedule15.
- Obtain separate permits for electrical, plumbing or HVAC work through the applicable Idaho or local program13.
- If access crosses county right-of-way, ask Road and Bridge about its approach permit; a connection to state-highway right-of-way requires an Idaho Transportation Department encroachment permit2728.
- Complete the required septic inspection before putting the system into service29.
What should you check before buying land in Franklin County?
Make septic feasibility the first physical-site check: only 5.3% of Franklin County soils avoid a severe limitation for a conventional drain field9. Confirm zoning and legal access next, including whether the parcel supports the intended dwelling and whether a county approach permit or state-highway encroachment permit is needed22728. Franklin County evaluates all development for its location within the National Flood Insurance Program before approval and may limit density or intensity in floodplain and floodway areas30. For a private well, budget for the required state drilling permit and licensed driller26. Franklin County has about 23.4 people per square mile, and 32.9% of its land is federally owned, so nearby public land does not establish private access or development rights3132.
Watch-outs
- A Franklin County agricultural building may be exempt from adopted building codes while still remaining subject to zoning placement requirements3.
- Franklin County requires the septic permit to be completed before it will issue the building permit5.
- Manufactured homes outside parks generally must be at least 20 feet wide and 900 square feet, and temporary permits last 12 months with one possible renewal8.
- Long-term RV living, private-land camping, tiny-home occupancy and an owner-builder exemption could not be confirmed; ask Planning & Zoning and the Building Department before relying on any of them33145.
Sources
- § 150.015 Building Permit Required (2026 county census)
- Franklin County Comprehensive Plan, quoted and re-checked
- franklincountyidaho.org, quoted and re-checked
- Southeastern Idaho Public Health - Septic Permits (2026 county census)
- Franklin County Building Department (franklincountyidaho.org)
- franklincountyidaho.org, quoted and re-checked
- Franklin County Comprehensive Plan, quoted and re-checked
- § 151.06 Manufactured Home Restrictions, quoted and re-checked
- 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
- Effective property tax rate: Bolthole Index county data
- Median property tax bill: Bolthole Index county data
- § 150.015 Building Permit Required, quoted and re-checked
- Frequently Asked Questions (FAQs) - Division of Occupational and Professional Licenses (Idaho statewide rule), quoted and re-checked
- Franklin County Planning & Zoning (franklincountyidaho.org)
- Building Department, quoted and re-checked
- Planning & Zoning, quoted and re-checked
- Building Department, quoted and re-checked
- Septic and Septage (Idaho statewide rule), quoted and re-checked
- Southeastern Idaho Public Health — Franklin County Office (siphidaho.org)
- Building Department, quoted and re-checked
- Septic Permits, quoted and re-checked
- Septic and Septage, quoted and re-checked
- IDAPA 58.01.03 – Individual/Subsurface Sewage Disposal Rules and Rules for Cleaning of Septic Tanks, quoted and re-checked
- Building Archives - Division of Occupational and Professional Licenses (Idaho statewide rule), quoted and re-checked
- Franklin County Comprehensive Plan (2026 county census)
- Wells Overview (Idaho statewide rule), quoted and re-checked
- Franklin County Road and Bridge (franklincountyidaho.org)
- Types of Right-of-Way Encroachment Permits (Idaho statewide rule), quoted and re-checked
- IDAPA 58.01.03 Individual/Subsurface Sewage Disposal Rules (Idaho statewide rule), quoted and re-checked
- Franklin County Comprehensive Plan, quoted and re-checked
- Population density: Bolthole Index county data
- Federal land share: Bolthole Index county data
- Homeowner Plumbing Permit Application (2026 county census)
Written October 10, 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.