Preston sits about twenty five miles north of Logan, close enough that Franklin County is officially part of the Logan metropolitan area. People shop in Logan, work in Logan, and often assume that building a house up there works the same way. It mostly does, right up until the paperwork. Idaho runs its own building code, on a different edition than Utah, adopted a different way, and enforced under a different structure. We have drafted plans on both sides of the line since 1997, and the surprises are always administrative rather than structural. Here is what actually changes.
Key Takeaways
- Idaho and Utah are both on the International Residential Code, but different editions of it
- Utah amends the IRC in ways Idaho does not, and the reverse is also true
- Idaho law limits local jurisdictions from adopting codes stricter than the state code
- Preston City and unincorporated Franklin County are separate permitting offices, so confirm which one governs your parcel
- A complete, code-compliant plan set works on either side of the line, but the details on it should match the correct jurisdiction
Same Model Code, Different Edition
Both states build residential work off the International Residential Code, which is why a Utah drafter and an Idaho builder can speak the same language. The difference is which edition. Utah adopted the 2021 IRC as the Utah Residential Code, effective July 2023. Idaho’s residential standard is the Idaho Residential Code, based on the 2018 IRC with Idaho amendments.
That gap exists partly because of how Idaho adopts codes. Building codes there are adopted by state statute, which means moving to a newer edition requires legislative approval rather than an agency rule change, and that process tends to run slower than in states where a board can update administratively. The practical effect for a homeowner is small but real: a few requirements that apply in Logan may not apply in Preston, and a plan set should be drawn against the correct one.
The Amendments Are Where It Gets Specific
Neither state adopts the model code word for word. Utah, for example, amends the IRC to remove the mandatory residential fire sprinkler requirement, and amends it to require passive radon control in new residential construction. Idaho carries its own set of amendments collected into the Idaho Residential Code. If you have built in Utah before and are now building in Idaho, do not assume the checklist carries over. We cover the Utah side in detail in our guide to Utah building codes for homeowners.
One more Idaho-specific point worth knowing: state law prevents local jurisdictions from adopting building codes more stringent than the state code. That is a meaningful difference from the patchwork of local amendments homeowners often expect, and it makes the state code the reliable baseline. Zoning, setbacks, and land use are a separate matter and remain very much local.
Who Actually Issues Your Permit
This is the question that saves the most time, and it has two answers depending on where your parcel sits. Inside Preston city limits, the City of Preston has its own building department and its own city code. Outside city limits in unincorporated Franklin County, permitting and inspections run through the county building department in Preston, with planning and zoning handled separately.
Idaho’s enforcement model is a hybrid: local jurisdictions can choose to enforce the state code, and where none does, the state Division of Occupational and Professional Licenses handles permitting and inspections. So the first call in any Franklin County project is simply confirming which office has your address. Everything else follows from that.
- Confirm city limits versus unincorporated county before you assume which office reviews your plans
- Ask what the plan review timeline currently looks like, since small offices run on real schedules
- Ask about permit validity, since Franklin County residential permits have required work to commence within 180 days with the permit expiring in one year
- Ask which fire district, highway district, and health district also touch your parcel, because in Idaho those are frequently separate authorities
The Site Questions That Matter More Than the Code
Much of Franklin County is rural, and rural means the lot itself drives the budget. Water rights, well permitting, and septic approval are common on parcels outside the cities, and each one carries its own timeline that runs in parallel with your building permit. Power distance, driveway length, and access during spring runoff belong in the conversation before you buy, not after.
Snow load is set locally by the building official rather than by a statewide number, and frost depth in Idaho is likewise determined by the local official based on local conditions. Both go on your plan set, so both need to be confirmed for your specific address rather than borrowed from a nearby project.
What Does Not Change
The house itself. Framing practice, truss spans, roof design for heavy snow, foundation approaches, and the way a good floor plan works are the same in Preston as they are in Smithfield. So is what it costs to build in Cache Valley, allowing for local labor and material differences. Contractors work across the line in both directions all the time, and a plan drawn for a Cache Valley climate is drawn for Franklin County too.
That is why we are comfortable working on both sides. Our drafting services produce a complete plan set with the correct code references, snow load, and jurisdiction details for wherever the house is going, and being twenty five miles away means we can visit the lot rather than working from a satellite image.
Frequently Asked Questions
Which building code applies in Preston, Idaho?
The Idaho Residential Code, based on the 2018 IRC with Idaho amendments, is the state residential standard. Confirm the current adopted edition with the permitting office for your address before plans are finalized, since adoption cycles do move.
Do I need different house plans for Idaho than for Utah?
The design itself carries over. What changes are the code references, snow load and frost depth figures, and any jurisdiction-specific details noted on the drawings. A plan set drawn for a Utah address should be reviewed and updated before it is submitted in Idaho rather than submitted as is.
Can a Utah drafting firm do plans for an Idaho build?
Yes. Drafting a residential plan set is not a state-restricted activity the way contracting is, and Franklin County sits within our normal service area alongside Logan, Smithfield, and Box Elder County. Contractor registration and licensing rules do differ between the states, so your builder should confirm their own standing in Idaho.
How long does it take to build in Franklin County?
Plan on several months of design and permitting followed by roughly nine months to a year of construction for a typical custom home, with rural site work and septic approval capable of adding time up front. Our realistic building timeline post walks through the stages in order.
Is it cheaper to build in Idaho than in Utah?
Land is often less expensive north of the line, which is a large part of why people look there. Construction costs track closely because the same trades and suppliers serve both sides of the valley. Fees and impact charges vary by jurisdiction, so compare those specifically rather than assuming a general savings.
Twenty Five Miles, One Phone Call
Building in Preston is not complicated. It is just different in a handful of administrative ways that are easy to handle when you know about them in advance and expensive to discover during plan review. Confirm your jurisdiction, confirm the code edition, confirm your snow load and frost depth, and then get on with designing the house.
Poulsen Home Design has drafted custom plans for families across Cache Valley, Box Elder County, and Franklin County since 1997. Mont and Mary-Ellen Poulsen worked as general contractors before moving to design and drafting full time, so the plans we produce are built to get approved and built to get built.
Building north of the line? Call Poulsen Home Design at (435) 512-5852 or visit poulsenhomedesign.com to get your plans started, and bring your parcel number if you have it.