Do you need a permit for a sauna, hot tub or shed?

What the model codes say

3 points for a sauna: 2 from the code text, 1 our reading. Details and code text below.

Permit likely needed. 3 points for a sauna: 2 from the code text, 1 our reading. Exempt. Building permit: exempt in the model code up to 200 sq ft. Depends. Your city may use a lower limit, such as 120 sq ft. Permit likely. Electrical work: a permit under the model code.

1. Exempt: Building permit: exempt in the model code up to 200 sq ft

   A one-story detached sauna building of 80 sq ft falls under the exemption. It only waives the permit: the building must still meet the code and local rules such as zoning.

   Limit 200 sq ft You 80 sq ft

   120 sq ft under the limit

   Other than storm shelters, one-story detached accessory structures, provided that the floor area does not exceed 200 square feet (18.58 m2).

   Code text, IRC 2021 and 2024, R105.2, Building item 1; IRC 2021 and 2024, R105.2

2. ? Depends: Your city may use a lower limit, such as 120 sq ft

   States and cities adopt the codes with their own changes. The International Building Code (IBC) exempts only tool and storage sheds, playhouses and similar uses up to 120 sq ft. Some cities use 120 sq ft for homes too, each with its own scope: Durango, Colorado, for any one-story detached accessory structure; Urbandale, Iowa, only for sheds, playhouses and similar uses without a permanent foundation.

   One-story detached accessory structures used as tool and storage sheds, playhouses and similar uses, provided that the floor area is not greater than 120 square feet (11 m2).

   Code text, IBC 2021 and 2024, 105.2, Building item 1; Durango, Colorado, 2024 IRC Amendments, R105.2 (1); Urbandale, Iowa, Code of Ordinances, 150.03(B)(2)(a)

3. Permit likely: Electrical work: a permit under the model code

   R105.1 asks for a permit to install any electrical system the code regulates. The electrical exemptions in R105.2 cover only small jobs, such as replacing lamps or plugging approved portable equipment into an existing receptacle. A hard-wired heater or a new dedicated circuit is not among them.

   Any owner or owner’s authorized agent who intends to construct, enlarge, alter, repair, move, demolish or change the occupancy of a building or structure, or to erect, install, enlarge, alter, repair, remove, convert or replace any electrical, gas, mechanical or plumbing system, the installation of which is regulated by this code, or to cause any such work to be performed, shall first make application to the building official and obtain the required permit.

   Our reading, IRC 2021 and 2024, R105.1; IRC 2021 and 2024, R105.2, Electrical item 5

Check with your city or county building department

They decide, under the code edition your state or city has adopted and its local changes.

1. Find it: search for your city's name and "building permit". Outside city limits, ask your county. USA.gov lists the local governments of every state.
2. Ask which edition of the IRC applies there and whether it changed the permit exemptions in R105.2.
3. Ask about zoning as well: distance to the property line, height and lot coverage are local rules, with or without a building permit.
4. Have the floor area, the heater's power and voltage, and the installation manual at hand.

This guide quotes the model codes and marks our own reading of them; it is not legal advice.