TL;DR
- 200 square feet is the line. Under it, a detached accessory building generally doesn't need a building permit. Over it, it does.
- Exempt from a permit does not mean exempt from the rules. Setbacks still apply, and if you put it in the wrong place you can be required to move it.
- In the City of Twin Falls, the exemption has conditions: under 200 square feet, single story, under 15 feet tall, and storage only with no habitable space.
- Separation distances differ by jurisdiction. The County requires 6 feet between structures. City guidance calls for 10 feet between accessory buildings and other structures.
- Watch three other size thresholds: the County's zoning definition of a detached garage caps at 1,600 square feet, the City treats accessory buildings over 1,000 square feet as a separate land use category, and anything pushing total roof area past 4,500 square feet triggers fire district review in the County.
- Your slab and footings still have to meet real design criteria: a 24 inch frost line, a 30 pound snow load, and 115 mph wind.
- Power and plumbing are separate permits, and out in the county they come from the State, not the County.
- If you might finish part of it later, plan for that now. Retrofitting a shop into habitable space is far more expensive than building with it in mind.
Half the properties in this valley have a shop, and the other half want one. It's one of the most common projects we get asked about, and one of the easiest to get wrong on paper before a single post goes in the ground.
Most of the trouble comes from three places: assuming a permit isn't needed, putting the building where it can't legally go, and building something that can't become what you eventually want it to be.
Here's how it actually works locally.
Do I need a permit?
The threshold is 200 square feet, and it applies in both jurisdictions.
In unincorporated Twin Falls County, a building permit is not required for accessory buildings under 200 square feet accessory to the residence. But permits are required for carports, garages, covered decks and patios, and any deck with a floor more than 30 inches above the ground.
Read that carefully. A garage is called out specifically. So a detached garage generally needs a permit regardless of how modest it is, because it's a garage rather than a shed.
In the City of Twin Falls, a permit is required for any residential detached accessory building over 200 square feet.
For a sense of scale: 200 square feet is about 14 by 14. Any real shop or garage is several times that. This exemption is for garden sheds, not for the building you're actually picturing.
The exemption has conditions, and setbacks are not one of the things you get out of
This is where people get burned, and the City is explicit about it.
To qualify for the City's exemption, the building has to be under 200 square feet, single story, under 15 feet tall, and used for storage only with no habitable space allowed. Miss any one of those and you're back to needing a permit.
And here's the part that matters most: the property owner remains responsible for following setback requirements, and the City reserves the right to require an owner to move or relocate any accessory building found to be in violation.
So a permit exemption is not a placement exemption. You can build a shed without a permit, put it three feet from the property line where the setback requires more, and be told to move it. That's an expensive lesson for a building that's already sitting on a gravel pad.
Before you decide where it goes, confirm your setbacks with the office that covers your address. Not your neighbor, not the guy who sold you the kit.
Which office covers your address?
A Twin Falls mailing address does not mean you're inside city limits, and the two jurisdictions have different rules.
Inside Twin Falls city limits | Unincorporated Twin Falls County | |
|---|---|---|
Building permit | City of Twin Falls Building Safety, (208) 735-7238 | Twin Falls County, (208) 734-9490 |
Electrical, plumbing, mechanical | The City handles these itself | State of Idaho, through DOPL |
Separation from other structures | 10 feet per City accessory building guidance | 6 feet minimum per County |
Height cap for the small-shed exemption | Under 15 feet | Confirm with the County |
If you're in Kimberly, Filer, Buhl, Hansen, or Murtaugh, check with your city office, and expect trade permits to route to the State.
The size thresholds nobody mentions
Beyond 200 square feet, three more numbers can change your project. These are the ones that surprise people planning a large shop.
1,600 square feet, in the County. Twin Falls County's zoning code defines a detached garage as a building not more than 1,600 square feet in area used for storing vehicles belonging to the occupants. Go bigger than that and what you're building may no longer fit the zoning definition of a detached garage, which can change how it's classified and reviewed. If you're planning a large shop in the county, ask how it will be classified before you design it.
1,000 square feet, in the City. Twin Falls's land use matrix treats accessory buildings over 1,000 square feet, including garages, as a distinct category from smaller ones. What that means in practice depends on your zoning district, so confirm the requirements for your specific zone rather than assuming a big shop is permitted outright.
4,500 square feet of total roof area, in the County. If the total floor area within the roof line exceeds 4,500 square feet, the County requires comment or plan review from your local fire district, which is a separate agency with its own timeline. That number counts everything under the roof, so a large shop on a property that already has a substantial house can cross it sooner than you'd expect.
Where it can go
Four constraints, and they compound.
Setbacks. Front, side, and rear, per your zoning district. The front setback is measured from the property line, not from the edge of the road, which is a distinction that has moved more than one building.
Separation from other structures. The County requires that no building or structure be placed within 6 feet of another structure. City guidance for accessory buildings calls for at least 10 feet of separation. Check which applies to you.
Easements. Nothing may be placed within an easement area. Pull your plat map and look before you pick a spot, because utility and irrigation easements are common on parcels around here and they rarely run where you'd guess.
Access and drainage. You need to get vehicles to it, and you need water to run away from it rather than toward the house.
One practical warning. When your setback inspection happens, property pins must be located and property lines clearly marked. If there's any question about where the boundary is, the inspection will not be approved, and a survey may be required. Find your pins early. This is the single most common avoidable inspection failure.
It still has to be built for this climate
A shop is not exempt from structural reality just because nobody lives in it.
Twin Falls County publishes its design criteria: 115 mph wind loading, a 30 pound per square foot ground snow load, seismic design category C, a zero degree design temperature, a frost line of 24 inches below finished grade, and a maximum soil bearing pressure of 1,500 pounds per square foot unless a soils investigation says otherwise.
What that means for a shop:
Footings go below frost. Twenty-four inches is a requirement, not a guideline, and it applies to post embedment in a post-frame building as much as to a poured foundation.
The roof has to carry snow. A 30-pound ground snow load is a real number, and clear-span buildings are exactly where undersized trusses show up. A kit engineered for a milder region is not automatically acceptable here.
Wind matters on open ground. Most shops around here sit on open lots with no windbreak. Uplift and lateral bracing are design questions, not afterthoughts.
Ask who engineered the package and whether it reflects Twin Falls County criteria. "It's engineered" and "it's engineered for your county" are different statements, and the second one is what the building department needs.
Power, plumbing, and heat
Almost every shop ends up with power, and many end up with a slop sink, a floor drain, or a heater. Each of those is a separate permit.
Inside Twin Falls city limits, the City handles electrical, plumbing, and mechanical permits and inspections itself. Outside city limits, the County issues your building permit and those trade permits come from the State through DOPL. Two agencies, two schedules.
Worth knowing: as of July 1, 2026, Idaho law puts a clock on trade inspections. Under HB 585, if a requested electrical, plumbing, or HVAC inspection isn't performed within 48 business hours, the permit holder can hire a qualified third-party inspector and get the inspection fee refunded. It doesn't cover building inspections, but it does cover exactly the trades a shop needs.
On heat specifically: decide early. Insulating and heating a shop built for it is straightforward. Retrofitting a building that was framed and sheeted with no thought to insulation is not.
Don't accidentally build an ADU
This is the mistake with the most expensive consequences.
The moment a building has its own cooking, sleeping, and sanitation facilities, it stops being an accessory building and becomes an accessory dwelling unit under Idaho law. That brings in the entire residential code: ceiling height, egress windows, energy compliance, smoke and carbon monoxide alarms, and occupancy approval. It also brings in septic, because a second dwelling adds wastewater load that your existing system may not be sized for.
A shop with a bathroom and a sink is still a shop. A shop with a bathroom, a kitchenette, and a bed is a dwelling, whatever you call it on the application.
That's not a reason to avoid it. ADUs are legitimate and, in Twin Falls, Jerome, and Burley, now protected by state law. It's a reason to decide deliberately, because the two projects have very different requirements and very different costs.
If there's a real chance you'll finish part of it later, build for that now:
- Get the ceiling height right. Habitable space needs 7 feet finished, and you cannot add height later.
- Run conduit while the walls are open.
- Put the plumbing stub where the bathroom will go, before the slab is poured.
- Insulate, or at least frame so insulating later is straightforward.
- Talk to the health district about septic capacity before you build, not after.
Doing those five things during construction costs a fraction of what retrofitting costs, and none of them commit you to anything.
What goes wrong
Building first, asking later. In the County, the minimum penalty for work started without a permit is an amount equal to the permit fee. The City can assess an escalating penalty on top of the permit fee, payable before work continues.
Placing it wrong. Setbacks, easements, and separation distances. This is the one that requires physically moving a building.
Undersized structure. Kit buildings engineered for other regions, and trusses that don't carry a 30 pound snow load.
No plan for power. Running a service to a building 200 feet from the house is a real cost that people leave out of the budget entirely.
Drainage. A slab poured without thought to grade turns into a shop that takes on water every spring.
Unpermitted work surfacing at resale. A shop with no permit record shows up in inspections and appraisals, and it becomes a price concession at exactly the wrong moment.
Planning a shop or detached garage?
We build shops, detached garages, barndominiums, ADUs, additions, and custom homes across Twin Falls, Jerome, Kimberly, Buhl, Filer, Burley, Rupert, and unincorporated Twin Falls County.
We'll tell you what your setbacks allow, how your building should be engineered for local snow and wind, whether the size you want crosses a threshold that changes the process, and what to do now if you might finish part of it later.
We're a registered Idaho contractor, RCE-65510, insured and warrantied. One point of contact, and an itemized estimate you can actually read.
Tell us what you're planning → or call (208) 731-1729
Frequently asked questions
Do I need a permit for a detached garage in Twin Falls County? Almost certainly yes. The County requires permits for garages specifically, along with carports and covered patios. The under-200-square-foot exemption applies to accessory buildings generally, and any real garage is well over that.
How big can a shed be without a permit? Under 200 square feet in both the City and the County. In the City it also has to be single story, under 15 feet tall, and used for storage only with no habitable space. Miss any condition and you need a permit.
If I don't need a permit, do setbacks still apply? Yes. The City is explicit that the owner is responsible for meeting setbacks, and that the City can require a building found in violation to be moved or relocated. A permit exemption is not a placement exemption.
How far does it have to be from my house? Depends on jurisdiction. The County requires that no building be placed within 6 feet of another structure. City accessory building guidance calls for at least 10 feet of separation. Confirm which applies at your address.
How tall can it be? For the City's small-shed exemption, under 15 feet. Above that threshold, height is governed by your zoning district, so confirm for your zone.
Is there a maximum size? Effectively there are several thresholds. In the County, the zoning definition of a detached garage caps at 1,600 square feet. In the City, accessory buildings over 1,000 square feet are treated as a separate land use category. And in the County, total roof area over 4,500 square feet triggers fire district review. None of these are hard bans, but each changes the process.
Do I need a separate permit for electrical? Yes. Inside Twin Falls city limits the City handles it. Outside city limits it comes from the State through DOPL, on a separate schedule from your County building permit.
Can I put a bathroom in my shop? Generally yes, with the appropriate plumbing permit and, on septic, confirmation that your system can handle it. A bathroom alone doesn't make it a dwelling. Adding cooking and sleeping facilities does, and that changes everything.
Can I finish part of it into an apartment later? Possibly, but that makes it an accessory dwelling unit, which brings in the full residential code and septic capacity questions. If it's a real possibility, build for it now: correct ceiling height, conduit in the walls, plumbing stubbed before the slab, and insulation planned.
What happens if I already built it without a permit? Call the department. The County's minimum penalty is an amount equal to the permit fee, and the City can add an escalating penalty. Coming forward voluntarily is a much better position than having it found during a resale inspection.
Why would my setback inspection fail? Most often, unmarked property lines. Pins must be located and boundaries clearly marked, and if the boundary is in question the inspection won't be approved and a survey may be required. Find your pins before you call.
Sources: Twin Falls County Community Development Services published permit information and design criteria; Twin Falls County Code Title 8 zoning definitions; City of Twin Falls Building Safety Department accessory building guidance and land use matrix; Idaho House Bill 585 (2026). Verified September 2026. Codes, thresholds, and zoning district requirements change, so confirm current requirements with the department covering your address before you build.
