Where Class 4 Shingles Are Required by Code — Colorado’s Impact-Resistant Belt

“Required by code” is not the same as “your insurer likes it”

Two different things get called a “Class 4 requirement,” and confusing them costs money in opposite directions.

The common one is an insurance matter: many carriers in hail country offer a premium credit for a documented Class 4 roof. That is a discount you negotiate, not a rule you must follow — and Colorado law does not compel carriers to offer it. That subject has its own guide: Class 4 Roof Insurance Discounts in Colorado.

The rarer one is a code matter: a jurisdiction amends its adopted building code so that asphalt shingles must be Class 4, tested to UL 2218. Where that amendment exists, Class 4 is not an upgrade you can decline. It belongs in the bid, and the inspector can fail the roof without it.

This guide is only about the second kind. Every jurisdiction below is listed because its own adopted amendment says so, quoted on its record.

The eight jurisdictions that require it

Across the six states this directory covers, these are the permitting authorities whose own adopted codes mandate Class 4 impact-resistant asphalt shingles. All eight are in northern Colorado.

• Fort Collins — a 2024 IRC local amendment adds R905.2.4.2: “Asphalt shingles shall be Class 4 impact resistant, tested in accordance with UL 2218.” Applies to re-roofs via R908.1.
• Loveland — “Class 4 shingles required effective June 1, 2022,” per the city’s Roofing Affidavit, and listed as a requirement for replacements covering 50% or more of the roof.
• Larimer County (unincorporated) — “Class ‘4’ impact resistant asphalt shingles are required for all new construction, repairs over 25%, and roof replacements.”
• Boulder County (unincorporated) — “Asphalt shingles shall be Class 4 impact resistant, tested in accordance with UL 2218,” via the Boulder County Building Code amendment to IRC R905.2.4.2.
• Berthoud — “Impact Resistance Asphalt Shingles required per R905.2.4 (Amended): Asphalt shingles shall be Class 4 impact resistant, tested in accordance with UL2218.”
• Johnstown — the same amendment text, effective with the town’s adoption of the 2024 IRC on January 1, 2026.
• Timnath — Ordinance No. 19, Series 2025 amends R905.2.4.2: “Asphalt shingles shall be Class 4 impact resistant and tested in accordance with UL 2218.”
• Lafayette — a 2021 IRC/IBC local amendment requiring Class 4, with documentation or shingle packaging posted on site for inspection (effective March 15, 2021).

Seven of the eight sit in or against Larimer and Boulder counties; Lafayette is the outlier, in Boulder County but well south of the cluster.

Where the belt stops — in the neighbours’ own words

The most useful thing about this belt is that the towns immediately outside it say so themselves, in print.

Windsor and Dacono both publish a residential re-roofing guide — through SAFEbuilt, the contract administrator they share — containing this line:

“IMPACT RESISTANT SHINGLES ARE NOT REQUIRED EXCEPT IN THE TOWN OF TIMNATH.”

A shared administrator’s own handout naming the single neighbouring town where the rule flips is about as clear a boundary marker as building code produces. Windsor borders Timnath directly.

Weld County carries the other explicit negative: a read of the full text of the county’s IRC (Sec. 29-2-30) and IBC (Sec. 29-2-20) adoptions confirms no amendment mandates Class 4.

An important limit on this map: only jurisdictions with an explicit sourced statement are characterised here in either direction. Many Front Range cities — Denver, Longmont, Boulder, Broomfield, Erie, Superior, Louisville and others — carry no recorded finding on this question yet. That means we have not established one, not that they have no requirement. Check the individual record, or the building department, before relying on silence.

How the belt spread: shared codes and shared documents

The eight are not eight independent inventions. Two mechanisms are visible in the documents themselves.

First, counties and their municipalities adopted separately but alike. Larimer County’s unincorporated amendment sits alongside Fort Collins, Loveland, Berthoud and Timnath — four municipalities inside or bordering it — each with its own ordinance. Boulder County does the same alongside Lafayette. A homeowner does not need to know which authority they fall under; in this corner of the state, they land on the requirement either way.

Second, the amendment text itself travels. Berthoud’s and Johnstown’s published requirements are word-for-word identical, down to the “R905.2.4 (Amended)” phrasing and the closed-up “UL2218.” The two towns adjoin each other across the Larimer–Weld line. Identical language in adjacent jurisdictions is evidence of a shared template rather than parallel drafting — though the documents record the text, not the reason a given council adopted it.

The contrast with north Texas is instructive. There, the same regional sharing produces the opposite result: cities across the Dallas–Fort Worth metro adopt the North Central Texas Council of Governments’ recommended amendment package, and that package contains no impact-resistance provision at all. McKinney, for one, incorporates the NCTCOG amendments by reference as an attachment to its own ordinance. One region’s shared template puts Class 4 in; another’s leaves it out.

The threshold matters as much as the mandate

“Is Class 4 required here?” has a second half: how much of the roof are you touching? Most of these jurisdictions trigger the requirement only past a stated repair size, and the numbers are not the same.

• Larimer County — new construction, roof replacements, and repairs over 25%. Exceptions for repairs or additions not exceeding 100 sq ft.
• Fort Collins — exceptions for repairs not exceeding 49% of roof area (or additions not exceeding 50% of original building size).
• Loveland — required on replacements covering 50% or more; repairs up to 49% may match the existing non-Class-4 shingle.
• Boulder County — the owner may request a code modification where the work is no greater than 200 sq ft and no greater than 25% of total roof area.

Two jurisdictions fifteen miles apart flip at 25% and 50%. On a partial repair that difference decides whether the job carries a Class 4 line item.

Nearly every one of these ordinances also carries a colour-match escape hatch: where no Class 4 product matches the colour or style of the existing shingles, Fort Collins, Larimer County, Timnath and Boulder County each allow relief — Timnath by letting the Building Official approve the highest impact class available, Boulder County on a written statement from a roofing contractor or supplier that no matching Class 4 shingle exists. These are administrative approvals, not automatic exemptions: get them in writing before the roof goes on.

What this means when you bid or buy

Inside the eight, Class 4 is a permit condition. Price it into the bid, keep the wrapper or spec sheet for the inspection, and check the repair threshold before assuming a partial job escapes the rule.

Outside them, Class 4 is an economics question rather than a legal one — worth doing in hail country on its merits, and often worth a carrier credit, but not something an inspector will require. In the Texas hail belt specifically, we have now read the adopted code amendments of most of the permitting authorities we cover there and found no residential Class 4 mandate in any of them; the driver there is insurer pricing, not code.

For which products actually carry the rating and how to verify one before you buy, see Class 4 Impact-Resistant Shingles: A Buyer’s Guide. For the jurisdiction-by-jurisdiction list in directory form, see the Class 4 requirement facet. And note that impact resistance is a separate test from fire and wind ratings — a “Class A” roof is a fire rating and tells you nothing about hail; Wind & Fire Ratings Explained untangles the three.