Key numbers
45 verified hail storms with stones of 1.75 inches or larger reached Denver County from 1984 to 2026 in the storm records we keep; the largest measured 4.5 inches (softball size) on July 13, 2011 (NOAA NCEI).
| Hail storms by decade, 1984 to 2026 | 1980s: 1, 1990s: 4, 2000s: 12, 2010s: 17, 2020s: 11 Source: Storm library: Denver metro hail history |
|---|---|
| Largest hail | 4.5 in. (softball), July 13, 2011 Source: NOAA NCEI |
| Costliest hail storm | $2.3 billion insured losses (2017 dollars), May 8, 2017 Source: RMIIA |
A storm counts when the library lists Denver County among the areas it hit. Each hail size is the storm's largest report, which may have fallen in a neighboring county, and insured losses cover every area the storm hit.
Commercial roofing in Denver usually means a low-slope membrane (TPO, PVC, EPDM or modified bitumen), a metal system, or shingles on a sloped commercial building, installed under a Denver permit by a contractor with the right license class. The rules change with building size: once a building reaches 25,000 square feet, Denver’s repair permit threshold tightens from 10% of the roof to 5%, quick permits are no longer available, and the city’s Green Buildings Ordinance applies to the roof permit. Getting the system and the permit path right at the start saves time and change orders later.
Which commercial roof system fits
| System | Good fit | Notes |
|---|---|---|
| TPO | Warehouses, retail, offices | Heat-welded single-ply, light colored and reflective. |
| PVC | Restaurants and buildings with rooftop grease or chemical exposure | Heat-welded single-ply that resists oils and chemicals. |
| EPDM | Simple low-slope roofs | Synthetic rubber membrane; seams are adhered or taped. |
| Modified bitumen | Smaller low-slope roofs, roofs with foot traffic | Multi-ply torch-down or peel-and-stick sheets. |
| Metal | Sloped commercial and industrial buildings | Long service life; panels sized to the slope. |
| Coatings | Sound roofs that need more years | A fluid-applied restoration; Denver does not require a permit for coatings. |
| Asphalt shingles | Sloped offices, churches and multifamily | Same wind-zone rules as homes. See asphalt shingle roofing. |
Denver rules that shape a commercial bid
- Minimum slope for membranes. New modified bitumen, EPDM, TPO and PVC roofs need a design slope of at least 1/4 inch per foot. Re-roofs are exempt when the existing roof already drains.
- Drainage. Where parapets trap water, secondary (overflow) drains or scuppers are required, installed 2 inches above the main drain, and scuppers need at least a 4-inch opening. A re-roof on a roof that drains does not have to add them.
- Rooftop equipment. Units must sit on 8-inch legs or an 8-inch curb bearing on the deck. Setting equipment on pads or slip sheets is not allowed.
- New penetrations. Every new skylight, rooftop unit, pipe or solar array needs a permit.
- Inspections. Low-slope roofs and commercial shingle roofs get a pre-inspection before work and a final at the end.
- License class. Membrane roofs need a D-Roof Covering/Waterproofing licensed contractor.
Suburbs add their own steps. Lakewood requires a mid-roof inspection on commercial membrane roofs and the manufacturer’s installation certification before the city final, and Littleton wants the warranty certificate attached to the permit before a commercial membrane roof can pass final. Broomfield asks for the roof deck type and fire rating on its permit application.
Repairs and maintenance
Most commercial leaks start at seams, flashings, drains and rooftop equipment. Our article on commercial roof repair covers the common failures. For storm damage, see Denver storm damage repair; for small leaks on homes and small buildings, see Denver roof repair. To keep small problems small, see our commercial roof maintenance program guide, the property manager roofing guide, low-slope roof systems compared, and the commercial and HOA roofing hub.
Request an on-site evaluation
We are veteran-owned, family-run since 1990, an Owens Corning Platinum Preferred contractor, and have 650+ Google reviews. Our Denver-area office is in Centennial and we reply the same business day. Call (303) 209-0152 or request an inspection, and we will walk the roof with you and give you a written scope.
Sources: City and County of Denver, Roofing Guide and Checklist (updated 4/11/2024); City and County of Denver, Green Buildings Ordinance; City of Lakewood, Roofing and Re-roofing handout; City of Littleton, Policy 24-001; City and County of Broomfield, Re-roofing Permit Application (March 2026).
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