Idaho Building Codes, Permits and Contractor Rules
Here’s every rule from our 50-state guides for Idaho on one page: the residential building code, frost depth, retaining wall permits, the 811 dig law, drainage law, contractor licensing, deposit limits, mechanics lien deadlines, workers’ comp, planting zones and frost dates. Each section links the official source and the full 50-state comparison.
Idaho at a glance
- Building code: 2018 IRC (applies where locally enforced)
- Frost depth: Set locally; often 24-30 in.
- 811 notice: Not less than 2 nor more than 10 business days before excavation
- Contractors: State registration required
- Deposits: No statewide cap
- Liens: 90 days from last furnishing
- Workers’ comp: 1+ employees
- Drainage rule: Civil law (natural flow)
- Planting zones: 3b to 8a
| Topic | Idaho | Compare |
|---|---|---|
| Residential building code | 2018 IRC (applies where locally enforced) | All states |
| Frost line depth | Set locally; often 24-30 in. | All states |
| Retaining wall permit | Exempt if not over 4 ft from bottom of footing to top of wall, unless supporting a surcharge or impounding Class I, II or IIIA liquids (2018 IRC R105.2 as… | All states |
| 811 notice before digging | Not less than 2 nor more than 10 business days before excavation | All states |
| Contractor license | State registration required | All states |
| Deposit limit | No statewide cap | All states |
| Right to cancel | 3 business days, credit sales at home | All states |
| Lien filing deadline | 90 days from last furnishing | All states |
| Workers’ comp required | 1+ employees | All states |
| Drainage between neighbors | Civil law (natural flow) | All states |
| Planting zones (2023 USDA) | 3b to 8a | All states |
| Frost dates (NOAA) | Last frost early Apr (Lewiston) to late Jun (McCall); first frost early Sep (McCall) to late Oct (Lewiston) | All states |
Idaho residential building code
- Code
- 2018 International Residential Code (Parts I-III and IX) with Idaho amendments (Idaho Residential Code, 2020 Edition)
- How it applies
- Statewide, applies only where locally enforced
- In effect since
- January 1, 2021
- Code agency
- Idaho Division of Occupational and Professional Licenses (Idaho Building Code Board)
- Who enforces it
- Cities and counties that issue building permits must adopt the Idaho Residential Code and cannot make it stricter; local building programs are optional, so some rural areas have no residential permits. Sprinklers cannot be required in one- and two-family homes.
- Good to know
- Idaho uses the 2018 IRC with state amendments, and local codes can't be stricter. Some rural counties don't issue residential building permits, so check with your county.
Compare building codes in all 50 states
Frost line depth in Idaho
- Who sets it
- Local building department
- Local examples
- City of Idaho Falls: 30 in. (finished grade to bottom of footing)
City of Meridian: 24 in. minimum
City of Coeur d'Alene: 24 in. minimum - Typical range
- 24-30 in.
Frost line depth in every state
Retaining wall permits in Idaho
- Permit exemption
- Exempt if not over 4 ft from bottom of footing to top of wall, unless supporting a surcharge or impounding Class I, II or IIIA liquids (2018 IRC R105.2 as adopted; Idaho amends only R105.2 items 7 (pools) and 11 (flag poles)).
- Who decides
- Cities and counties don't have to enforce a code. If yours does, it decides and can amend some parts by ordinance.
- Good to know
- Height is measured from the bottom of the footing to the top of the wall. A 2026 law (H0643) revised how cities and counties adopt the code, effective July 1, 2026.
Retaining wall permit rules in every state
811 dig law in Idaho
- One-call center
- Idaho 811 one-call services: Dig Line, Inc. (southern Idaho) / North Idaho 811 / Dig Safe North Idaho 811
- Notice before digging
- Not less than 2 nor more than 10 business days before excavation
- Ticket good for
- Markings valid no longer than 4 consecutive weeks after notification; renotify if work hasn't started within 3 weeks
- Hand-dig zone
- 24 in. horizontally from the outside dimensions of the facility ('reasonable accuracy'); hand dig within 24 in. of a mark
- Homeowners
- Partial exemption: digging less than 15 in. deep on private property outside any recorded underground facility easement needs no notice (also farm tilling under 15 in.), unless facts would reasonably indicate a facility within that depth. Deeper work requires a call.
- The law
- Idaho Code § 55-2201 et seq. (Underground Facilities Damage Prevention)
- Good to know
- Three separate one-call services operate in Idaho. If work hasn't started within 3 weeks, notify again.
Drainage law and stormwater permits in Idaho
- Rule
- Civil law (natural flow)
- The rule
- Civil law: a natural servitude of drainage means the lower owner must accept surface water that naturally drains onto it; the upper owner may not release water in unnatural concentrations that increase harm to the lower owner.
- Leading case
- Olson v. Moulton. Idaho S. Ct. Docket No. 44498, Opinion No. 24 (Mar. 13, 2018); quoting Dayley v. City of Burley, 96 Idaho 101, 524 P.2d 1073 (1974) and Burgess v. Salmon River Canal Co., 119 Idaho 299, 805 P.2d 1223 (1991)
- What it means for your yard
- Your downhill neighbor has to accept natural runoff, but you can't regrade or pipe water so that it lands on them in unnatural concentrations that cause more harm.
- Construction stormwater permit
- Idaho Department of Environmental Quality (DEQ), IPDES program: 1 or more acres of disturbance that discharges stormwater, or smaller sites that are part of a larger common plan (IPDES CGP IDR100000)
- State rules below 1 acre
- No statewide rule below the 1-acre permit found; check your county and town.
- Local rules
- Idaho cities and counties often have their own grading, drainage and erosion control ordinances.
- Good to know
- Idaho requires the lower property to accept natural runoff, but you can't concentrate water onto a neighbor in a way that does more harm. State construction stormwater permits start at 1 acre.
Contractor licensing in Idaho
- Statewide rule
- Registration
- Agency
- Idaho Division of Occupational and Professional Licenses (DOPL) – Idaho Contractors Board
- Who needs it
- Anyone doing a construction job over $2,000 must register with the Idaho Contractors Board unless exempt (e.g., wage employees, owners working on their own property).
- When it applies
- Construction jobs over $2,000 (labor + materials)
- Check a contractor
- Official lookup
- Licensed separately
- Licensed electrical contractors, plumbers and similar licensees generally need not register for work within their license.
- Good to know
- Registration does not test a contractor's skill.
Contractor license requirements in every state
Contractor deposits and your right to cancel in Idaho
- Deposit limit
- No statewide cap.
- Right to cancel
- Home solicitation sales on credit: until midnight of the third business day after signing (Idaho Code §§ 28-43-401, 28-43-402; limited to regulated consumer credit sales). For cash sales at your home, the federal 3-day Cooling-Off Rule applies.
- Written contract
- No general written-contract statute found. For residential jobs over $2,000, the general contractor must give a signed disclosure before the contract is signed covering the owner's right to lien waivers, proof of liability and workers' comp insurance, extended title insurance, and a surety bond at the owner's expense (Idaho Code § 45-525).
- The law
- Idaho Code § 45-525 (residential disclosure); §§ 28-43-401 to 28-43-405 (home solicitation sales)
- Good to know
- On Idaho residential jobs over $2,000, ask for the required disclosure form: it tells you that you can demand lien waivers and proof of insurance before paying.
Contractor deposit limits in every state
Mechanics lien deadlines in Idaho
- Lien deadline (prime)
- File the claim of lien with the county recorder within 90 days after completion of the labor or services or furnishing of materials, and serve a copy on the owner within 5 business days after filing (Idaho Code § 45-507).
- Lien deadline (sub/supplier)
- Same as prime.
- Preliminary notice (sub/supplier)
- Not required.
- Notice of intent
- Not required.
- Enforce within
- Proceedings within 6 months after the claim is filed; a payment or credit extension endorsed on the lien record restarts the 6 months (Idaho Code § 45-510).
- Homeowner rules
- Before signing a residential contract over $2,000, the homeowner must get the contractor's disclosure of the right to require lien waivers from subs, insurance proof, extended title insurance and a surety bond (Idaho Code § 45-525).
- The law
- Idaho Code Title 45, Ch. 5 (Liens of Mechanics and Materialmen), § 45-501 et seq.
- Good to know
- In Idaho, a lien must be filed within 90 days after your last work and served on the owner within 5 business days. Homeowners signing a contract over $2,000 should receive the contractor's lien and insurance disclosure.
Mechanics lien deadlines in every state
Workers' comp requirements in Idaho
- Who must carry it
- Most employers with any employees must carry coverage; exemptions are listed in Idaho Code § 72-212 (e.g., household domestic service, casual employment) (Idaho Industrial Commission). No separate construction threshold.
- Owners and officers
- Exempt unless they elect coverage: the owner of a sole proprietorship; working members of a partnership or LLC; and corporate officers owning at least 10% of voting stock (who must also be directors if the corporation has directors). Family members living in the household of a sole proprietor or single-member LLC owner are exempt; non-resident family members can file form IC53 to be exempt (Idaho Code § 72-212(4)-(6); Idaho IIC).
- Subcontractors
- An employer is liable for compensation to the employees of a contractor or subcontractor under it who has not secured coverage, and can seek reimbursement from that contractor (Idaho Code § 72-216).
- Homeowners
- Household domestic service is exempt unless coverage is elected (Idaho Code § 72-212(1)). Section 72-216 contains no express homeowner exception.
- Penalties
- Failure to insure is a misdemeanor, and responsible officers or LLC managers can be personally liable for benefits; civil penalty of the greater of $2 per employee per day or $25 per day (up to 3 years), plus $500 for a second and $1,000 for a third failure within 3 years; a court can bar the business from operating while uninsured (Idaho Code § 72-319).
- The law
- Idaho Code Title 72, Ch. 2-3; §§ 72-212, 72-216, 72-301, 72-319
- State agency
- Idaho Industrial Commission, Employer Compliance
- Good to know
- Idaho has no minimum employee count: if you have employees, you need coverage. Owners, partners, LLC members and 10%+ officers are exempt unless they choose to be covered.
Workers' comp requirements in every state
Planting zones in Idaho
- 2023 USDA zones
- 3b to 8a
- Coldest-night range
- −35°F to 15°F
- Warmest area
- Deep canyon bottoms along the lower Salmon and Snake rivers
- Example cities
- Boise: 7a, Idaho Falls: 5b, Coeur d'Alene: 6b, Lewiston: 7b
- Good to know
- Idaho's zones follow elevation. Boise stayed 7a on the 2023 map, the low river valley around Lewiston is milder at 7b, and Hailey in the Wood River Valley moved two half-zones warmer.
Frost dates in Idaho
| Station | Last spring frost | First fall frost | Frost-free days |
|---|---|---|---|
| Boise Treasure Valley, southwest | April 24 | October 21 | 179 |
| Lewiston North-central, low elevation | April 6 | October 26 | 200 |
| Pocatello Snake River Plain, southeast | May 23 | September 18 | 117 |
| McCall West-central mountains | June 22 | September 2 | 72 |
- Typical range
- Last frost early Apr (Lewiston) to late Jun (McCall); first frost early Sep (McCall) to late Oct (Lewiston)
- Good to know
- These are typical (50%) dates from NOAA's 1991–2020 climate normals, so about half of years still bring a 32°F night after the listed spring date. In Idaho, the last spring frost at the stations listed ranges from early April around Lewiston to late June around McCall.
- Local frost or planting guide
- University of Idaho Extension
Frequently Asked Questions
What building code does Idaho use?
2018 International Residential Code (Parts I-III and IX) with Idaho amendments (Idaho Residential Code, 2020 Edition). It applies as follows: statewide, applies only where locally enforced. Your local building department can confirm the edition and amendments for your address.
How deep is the frost line in Idaho?
Frost depth is set by local building departments. Typical local values: 24-30 in.. Footings for houses, additions and attached decks go below it.
How much can a contractor ask for up front in Idaho?
No statewide cap. Cancel rights: Home solicitation sales on credit: until midnight of the third business day after signing (Idaho Code §§ 28-43-401, 28-43-402; limited to regulated consumer credit sales). For cash sales at your home, the federal 3-day Cooling-Off Rule applies.
How long does a contractor have to file a mechanics lien in Idaho?
File the claim of lien with the county recorder within 90 days after completion of the labor or services or furnishing of materials, and serve a copy on the owner within 5 business days after filing (Idaho Code § 45-507). Subcontractors and suppliers may have different notice rules; see the section above.
What planting zone is Idaho?
On the 2023 USDA map, Idaho runs from zone 3b to 8a. Examples: Boise 7a, Idaho Falls 5b, Coeur d’Alene 6b. Enter your ZIP on the USDA map for your exact zone.
Do contractors need workers' comp in Idaho?
Most employers with any employees must carry coverage; exemptions are listed in Idaho Code § 72-212 (e.g., household domestic service, casual employment) (Idaho Industrial Commission). No separate construction threshold. Owner exemptions and subcontractor rules are in the workers’ comp section above.
When is the last frost in Idaho?
At the NOAA stations we list: Last frost early Apr (Lewiston) to late Jun (McCall); first frost early Sep (McCall) to late Oct (Lewiston). These are typical (50%) dates from the 1991–2020 climate normals, so about half of years still bring a 32°F night after the spring date.
This page is general information, not legal or tax advice. Rules change; the agencies and statutes linked above have the final word.
Idaho in each 50-state guide: Frost line depth · 811 dig laws · Retaining wall permits · Contractor licensing · Contractor deposit limits · Building codes · Planting zones · Mechanics lien deadlines · Workers' comp · Frost dates · Drainage laws · Noxious weed laws · Rainfall and snowfall · Landscaper pay · Pesticide applicator licensing · Landscaping sales tax · All state guides
Last checked October 31 and November 1, 2026 against official state and local sources for this state. Rules change; your state agency or local building department has the final word. Spot something out of date? Email info@muthlerlandscaping.com and we’ll fix it.
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Cite as: Muthler Landscaping & Construction, “Idaho Building Codes, Permits and Contractor Rules,” https://muthlerlandscaping.com/state-guides/idaho/ (last checked November 9, 2026).
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