Ada County Development Services - Building Division

Ada County, Idaho

county

200 W. Front St., 2nd Floor, Ada County Courthouse, Boise, ID 83702

Not required

Required

Ada County Code Title 7, Chapter 2, Section 7-2-5 opens: "The International Residential Code, 2018 edition, as adopted, is hereby amended as follows," and the chapter's own section index (7-2-4 through 7-2-11) names the County's amendments to the 2018 editions of the International Building, Residential, Mechanical, Fuel Gas, Energy Conservation, Wildland-Urban Interface, Swimming Pool and Spa, and Existing Building Codes, current through Ordinance 1018, passed 3-24-2026. This matches the State of Idaho's own mandatory floor: IDAPA 24.39.30 adopts Parts I, II, III and IX of the 2018 IRC for one- and two-family dwellings statewide, and a local jurisdiction may not be ahead of the state board's adopted edition. Ada County's Section 7-2-5 amendments were read in full and reach nothing above Section R602, so IRC Chapter 9, Roof Assemblies, applies to unincorporated Ada County in its base 2018 form.

Required — Sourced to the base 2018 International Residential Code, not to any Ada County text. Ada County's own amendments to the 2018 IRC (Ada County Code 7-2-5, read in full) do not touch Section R905, and the State of Idaho's building code rule (IDAPA 24.39.30, read in full) does not touch it either -- zero occurrences of "R905" or "drip" in either instrument. So the base 2018 IRC's drip edge requirement at Section R905.2.8.5 governs unincorporated Ada County unmodified, with no local text to quote in its place. About drip edge

Not required — Sourced from Ada County's own climatic and geographic design criteria, not inferred from climate. The County's amendment to the 2018 IRC (Ada County Code 7-2-5) states that "Table R301.2(1) Climatic and Geographic Design Criteria" shall be deleted "in its entirety and replace[d] with the following Table R301.2(1)," and the replacement table the County publishes carries "No" in the column headed "Ice Barrier Underlayment Required." Idaho's state rule does not answer this question either way: IDAPA 24.39.30 amends nothing in Chapter 9 of the 2018 IRC, and Table R301.2(1) is the one part of Part III of the residential code that Idaho Code leaves a county free to amend for local conditions. Nothing in the County's entry stops a shingle manufacturer's printed installation instructions, or a particular roof's exposure and history of ice damming, from calling for eave protection anyway. About ice & water barrier

Not required — Neither Ada County's own amendments to the 2018 International Residential Code (Ada County Code 7-2-5, read in full) nor the State of Idaho's building code rule (IDAPA 24.39.30, read in full) contains any impact-rating provision: both were searched and neither carries an occurrence of "impact," "hail," "Class 4," "Class IV" or "UL 2218." No UL 2218 or Class 4 impact-resistance mandate appears in the county's adopted code, its amendments, or the state rule that frames them.

Ada County's own amendment to Section R105.2, Work exempt from permit (Ada County Code 7-2-5), read in full, deletes and replaces the "Building" exemption list and its item 12 reads, verbatim: "Roof repair, including complete replacement of roof coverings, in association with one- and two-family dwellings and their accessory structures." Item 13, immediately after it, exempts siding repair or replacement "when fire resistance is not reduced" on the same class of structures. Neither item carries a dollar figure or a square-footage threshold -- the exemption is categorical, covering everything from a small patch repair to a full tear-off and replacement, for a one- or two-family dwelling or its accessory structures. Section 7-2-2, Exceptions to Regulations, was read and adds only one qualification to the whole of Title 7, Chapter 2: the chapter "does not apply to agricultural buildings" as Title 8 of the County's own code defines them, and it says nothing that narrows or conditions the roofing exemption. Work that falls outside item 12 -- a new roof on new construction, or reroofing on a multi-family or commercial building -- still needs a permit, and the County's general building permit fee is calculated from the project's valuation under its own fee schedule rather than a flat per-inspection figure.

Take these from Ada County's own table, which the County publishes filled in as its replacement for the 2018 IRC's Table R301.2(1). The County states that the table "shall be" deleted "in its entirety and replace[d] with the following Table R301.2(1)," and the table it prints reads across its columns: Ground Snow Load -- ground snow load Pg 20 pounds per square foot, with a minimum roof snow load of 25 pounds per square foot and no reduction below that permitted; Wind Speed 115 mph, Topographic Effects No; Seismic Design Category C; Weathering Severe; Frost Line Depth 24 inches; Termite Slight to Moderate; Winter Design Temp 10 degrees F; Ice Barrier Underlayment Required No; Flood Hazards date of adoption 1/30/1980, date of current FIRM 6/19/2020; Air Freezing Index 894; Mean Annual Temp 51.1 degrees F. CHECK THE BASIS BEFORE YOU APPLY THE WIND NUMBER. The County prints 115 under a column headed only "Wind Speed" and states no basis for it in the table itself. A nominal wind speed (the older allowable-stress basis) and an ultimate design wind speed are two different numbers for the same wind loading and are not interchangeable, so confirm which basis your design method, your engineering or your product listing expects before you use the figure. One related fact belongs beside these: Ada County's own amendment separately deletes "R301.2.1.2 Protection Of Openings... in its entirety," and the State of Idaho's building code rule independently deletes the same section statewide ("Section R301.2.1.2 Protection of Openings. Delete."). That is a wind-borne-debris opening-protection (window and door) provision rather than a roofing one, and it is removed at both the state and the county level.

Ada County's own amendments to the 2018 International Residential Code, Ada County Code 7-2-5, were read in full (all twelve numbered sections of Title 7, Chapter 2, covering the IBC, IRC, IMC, IFGC, IECC, IWUIC, ISPSC and IEBC), and they touch nothing above Section R602 -- Chapter 9, Roof Assemblies, is not amended, deleted or excepted anywhere in the County's ordinance. The State of Idaho's own building code rule, IDAPA 24.39.30, was independently read in full and likewise amends nothing in Chapter 9 (zero occurrences of any R9xx section number). So the base 2018 IRC governs roof recovering in unincorporated Ada County unmodified. Section R908.3.1.1, Roof recover not allowed, reads: "A roof recover shall not be permitted where any of the following conditions occur: 1. Where the existing roof or roof covering is water soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing. 2. Where the existing roof covering is slate, clay, cement or asbestos-cement tile. 3. Where the existing roof has two or more applications of any type of roof covering." A roof that already carries two layers of any covering may not be recovered with a third layer -- it must be torn off to the deck first. This is a Chapter 9 "roof recover" rule and is a separate question from the County's own permit exemption for roof repair and replacement described in repair_permit_threshold.

Neither Ada County's own amendments to the 2018 International Residential Code (Ada County Code 7-2-5, read in full) nor the State of Idaho's building code rule (IDAPA 24.39.30, read in full) amends anything in Sections R802 or R803, the IRC's roof framing and roof sheathing provisions -- both instruments were searched for "sheath" and the only hits in either document are wall-sheathing and insulation terms unrelated to a roof deck. So the base 2018 IRC roof sheathing requirements apply in unincorporated Ada County unmodified, and neither instrument states its own sheathing thickness, span or fastening schedule for a roofer to rely on in place of the base code.

6.0% -- the Idaho state rate, with no local add-on, and for a county record covering only unincorporated territory that is itself the finding: Idaho counties levy no sales tax at all, so nothing is added at the county line, and unincorporated Ada County has no city sales tax layered on top of it either. Idaho Code 63-3619 imposes the state sales tax "at the rate of six percent (6%)... of the sales price of all retail sales." HOW A ROOF IS TAXED, which matters more than the rate: the Idaho State Tax Commission's own contractor guidance states that "Idaho sales tax law says contractors are the consumers (end users) of all the goods they use. As a result, they must pay sales tax on all purchases, including all the equipment, tools, and supplies they use to build, improve, repair, or alter real property," and that "a contractor doesn't charge sales tax to the customer." The roofer pays the 6% on materials at the supply house; the homeowner's invoice carries no sales tax line at all, on materials or on labor, because the tax is absorbed into the bid rather than itemized.