Twin Falls building department

The City of Twin Falls Building Safety Department reviews plans, issues building and trade permits, inspects new and existing structures, and issues certificates of occupancy inside city limits. Its office is at 203 Main Avenue East (mailing address P.O. Box 1907). The department works with Planning & Zoning, Fire and Engineering on plan approvals and change orders.

When a permit is required

The City’s Permit Requirements page lists:

• additions of any kind, such as sunrooms, garages and pools
• all electrical, plumbing, mechanical and gas work
• every new single-family home
• residential detached accessory buildings over 200 sq ft, and commercial accessory buildings over 120 sq ft
• fences over 7 feet tall
• most alterations, including new built-up roofs or trusses and new windows
• new commercial buildings, remodels and additions
• signs, including temporary event banners
• starting a home-based business

Twin Falls lists interior painting, reroofing and carpet replacement as work that doesn’t need a permit. For everything else, the City follows the exemption lists in Section 105.2 of the 2018 IRC (residential) and 2018 IBC (commercial). Properties in the historic preservation district must go before the Historic Preservation Commission before a permit is issued. Arrange that through Planning & Zoning, 208-735-7267.

Applying

Residential building permits can be filed online. The City’s newer ArcGIS-based Building Permit Portal and the Cityworks portal both accept applications, and Cityworks also handles mechanical, electrical and plumbing permits. The Applications & Forms page has PDF applications for:

• new homes
• enclosed and non-enclosed additions
• detached accessories (shed, garage, deck, pool)
• interior remodels
• demolition, moving a building, temporary structures and manufactured or modular homes
• an ag-exempt permit
• a 2026 repair permit guide

Commercial projects follow the Commercial Development Guide (August 18, 2025) and the City’s electronic plan submission standards.

Since October 1, 2024, plan review fees for commercial, industrial and multifamily projects are due when you apply, and review doesn’t start until they’re paid. That rule doesn’t yet apply to single-family and duplex projects. Commercial submittals are reviewed by four departments, and revisions aren’t accepted until all four first reviews are done.

Published plan review timelines (to first review)

Project	Time
New single-family home	2 weeks
Residential fence, deck or pool	2 weeks
Commercial new building, addition, tenant improvement or multifamily	5 weeks
Commercial miscellaneous (signs, pools, fences)	3 weeks
Mechanical plan review	3 weeks

Incomplete submittals don’t enter the review queue.

Fees

Building permit fees follow the City’s 2024 Building Permit Fee Schedule and the Master City-Wide Fee Schedule. Impact fees (effective January 1, 2025), sewer connection and water connection fees are published separately. According to the fee schedule footnotes:

• Applicants declare the project value. For one- and two-family homes, the declared value must be within 20% of the average per-square-foot value of homes permitted in Twin Falls the prior fiscal year.
• New-home mechanical, electrical and plumbing permits are flat fees based on the home’s floor area, including basements but not garages or covered patios. Each trade needs its own permit.
• A small-work MEP permit covers jobs of $500 or less. Regardless of cost, it also covers residential water heaters up to 100 gallons, water softeners, bath fans, dryer ducts and duct extensions up to 25 feet.
• Escalating penalties can be added for work done without a permit.

Adopted codes and design criteria

For one- and two-family dwellings and townhouses, Twin Falls enforces the 2018 IRC (with Appendices A, B and G), the 2018 IECC, the 2023 National Electrical Code and the 2017 Idaho State Plumbing Code, all with Idaho amendments. Under Idaho Code 39-4116 and a November 26, 2024 City policy, a project is governed by the codes in effect on the date the building permit application is received. That includes the related electrical, mechanical, plumbing and fire permits.

Criterion	Twin Falls value
Ground snow load	15 psf
Minimum roof design load	25 psf (local ordinance)
Frost depth	24 inches
Climate zone	5B
Wind	115 mph, Exposure B (C in some areas)
Seismic design category (IRC)	B
Presumptive soil bearing	1,500 psf
Minimum crawl space depth	30 inches below floor joists

Local amendments require a 40 psf live load in habitable attics and sleeping rooms, plus specific rebar in stem walls and basement walls: #4 bars top and bottom, vertical bars at 6 feet on center, and reinforcement around openings. Unvented fuel-burning appliances aren’t allowed.

Inspections

Request inspections in the Cityworks portal or by phone:

Line	Number
Building inspection	208-735-7333
Electrical inspection	208-735-7235
Plumbing inspection	208-735-7299
Mechanical inspection	208-735-7289
Fire Department	208-735-7338
Engineering inspection	208-735-3446

• Portal requests made by 7:00 a.m. get a same-day inspection. Phone requests for building inspections made after midnight go to the next business day.
• Inspections normally run 8 a.m. to 4 p.m. and aren’t done on City holidays.
• Concrete inspections get priority. You can book AM (8–12) or PM (1–4), and the work must be ready by 8 a.m. or noon. Property lines must be strung and footings at least 12 inches deep.

The residential sequence is:

1. footing and setback
2. foundation, including shear hold-downs
3. shear
4. MEP rough-ins
5. framing, with truss engineering on site
6. insulation
7. gypsum, for fire-rated assemblies only
8. MEP finals
9. building final

You can’t request framing until all rough-ins are signed off, or the building final until all trade finals pass. A re-inspection fee of $50 applies only after a second failure for the same issue and must be paid before rescheduling. Certificates of occupancy can take up to 3 business days to process.

Contractors and owners

Contractors must hold Idaho registration through DOPL, which is required for jobs over $2,000 in materials and labor. Owners doing work on their own property can file the City’s Contractor Registration Exemption Declaration. The City also has a Change of Contractor application for switching contractors mid-project.