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 |
| 15% | Tempered glass reportedly adds 15% or more to the cost of a window, per DOE's Building America Solution Center. Source: U.S. DOE Building America Solution Center (PNNL) |
| 6 to 10 | CAPE Analytics found the highest hail loss ratios on homes with roofs just 6 to 10 years old, not the oldest roofs. Source: CAPE Analytics, 2021 |
| Up to 10% | ENERGY STAR says sealing air leaks and adding insulation can save up to 10% on annual energy bills. Source: ENERGY STAR (U.S. EPA) |
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.
A replacement window stays dry when water that gets past the window has a planned way back out. That means a sloped sill pan under the window, flashing at the jambs and head lapped shingle-fashion so each upper layer covers the one below, and a weather barrier that laps over the head flashing, not under it. Caulk helps with air, but it is not the water barrier. Integrity Roofing and Painting replaces windows in existing Denver-area homes, most often with Simonton units or a brand you choose, and this page explains how we flash them. We do not supply windows for new construction.
What the code and standards say
- IRC R703.4 requires corrosion-resistant flashing at window and door openings, installed to keep water out of the wall.
- IRC R703.4.1 says windows are flashed per the window maker’s instructions; when there are none, a pan flashing at the sill plus head and jamb protection.
- ASTM E2112 is the consensus practice for installing windows in new and existing homes. It sets minimums, and the window maker’s instructions win where they differ.
- AAMA 2400 covers flanged windows in wood-frame walls with exterior barrier methods. Its publisher points to a separate drainage practice, FMA/AAMA 100, for wetter exposures, which suits walls facing wind-driven rain and snow.
Insert or full-frame: two different water strategies
Insert replacement keeps the old frame and its existing flashing. We check the old frame for rot and stains first. If it is dry and sound, the new unit is set in a bead of sealant against the old stops, the exterior gap is sealed, and the sill is left free to drain.
Full-frame replacement removes the window to the rough opening, which is the only way to fix flashing that failed. It is what we recommend when there is any sign of water in the wall, and it is the natural choice during a siding replacement.
Our full-frame flashing sequence
- Open up and inspect. Remove the old window, trim and enough siding to reach the weather barrier. Replace soft sheathing or framing.
- Slope the sill. A slight outward slope, or a beveled sill piece, so water runs out, not in.
- Install the sill pan. Formable or liquid membrane, turned up at the back and at least several inches up each jamb, lapped over the barrier below.
- Set the window. Level, plumb and square on shims, fastened per the maker, with no continuous sealant along the bottom flange so the pan can drain.
- Flash the jambs, then the head. Jamb flashing laps over the pan; head flashing laps over the jambs.
- Lap the wall barrier. The upper course of barrier tucks over the head flashing, shingle-fashion. A cut barrier flap above the head is taped down over it.
- Air seal from inside. Low-expansion foam or backer rod and sealant in the gap between the frame and the rough opening.
- Trim and drip cap. Head trim gets a drip cap tucked under the barrier above.
This order follows the shingle-lapped sequence in Building Science Corporation’s RR-0407 installation detail and the principle in its BSI-085 article: the window’s water control layer has to connect to the wall’s.
Brick, stucco and siding walls
| Wall | How the window ties in |
|---|---|
| Lap siding (fiber cement, wood, vinyl) | Full flashing sequence; siding and trim go back over the barrier |
| Brick veneer | Unit set in the masonry opening over a sloped pan; sealed head and jambs; metal or trim wrap |
| Stucco | Inserts where the frame is sound; otherwise a cut-back and patch tied to the existing barrier |
Stucco and brick walls often need inserts to avoid tearing up the wall. Brick bungalows in older Denver neighborhoods and stucco homes in Aurora, Highlands Ranch and Littleton each get the detail that fits their wall, and permit rules differ by city; see Denver building code data. If stucco around windows is cracking or stained, read stucco cracking first.
Signs the old flashing failed
Stains or soft drywall under the sill, peeling paint below the window outside, rotted sill trim and swollen siding below a corner all point to failed flashing. Diagnosis is covered in window leaks at the flashing and water behind siding. For choosing between new windows and repairs, see repair or replace.
Get a Denver window estimate
Integrity Roofing and Painting is veteran-owned and family-run since 1990, an Owens Corning Platinum Preferred roofing contractor with 650+ Google reviews. Read more on Denver window replacement, call (303) 209-0152 or book a free inspection; we respond the same business day.
Sources: 2021 IRC sections R703.4 and R703.4.1 (UpCodes); ASTM E2112-23, Installation of Exterior Windows, Doors and Skylights; FGIA, AAMA 2400-20; Building Science Corporation, RR-0407; Building Science Corporation, BSI-085 Windows Can Be a Pain.
