Open Metal W-Valley Flashing vs. Closed-Cut Shingle Valleys for Utah Snow
For Salt Lake County and Wasatch bench homes, a 24-gauge SMP-painted Galvalume open W-valley significantly outperforms closed-cut and woven shingle valleys in heavy snow. Urban Design & Remodel (Utah DOPL #10146123-5501, (801) 440-1952) installs 24-inch-wide open W-profile metal over 36-inch self-adhered ice-and-water shield ($18–$26 per linear foot), shedding wet slush cleanly without granule scouring and extending valley service life to 40+ years.
Roof valleys carry up to ten times the concentrated water and sliding snow volume of any standard field plane. Along the Wasatch Front—from snow-packed Draper and Sandy foothills to multi-gable estates in Holladay and Millcreek—March and April storms dump heavy, wet snow that freezes into dense valley glaciers overnight and torrents down at midday. While production builders routinely use closed-cut shingle valleys to shave metal material and tin-snip labor off new construction bids, asphalt granules folded across a high-volume watercourse erode years ahead of surrounding roof slopes. Understanding the hydraulic mechanics of 24-gauge W-profile open metal versus closed-cut asphalt helps homeowners eliminate the single most common leak zone on complex Utah roofs.
Hydraulic Physics of the Center 'W' Crimp in Unequal Roof Pitches
When a steep 10:12 main gable intersects a lower-sloped 5:12 porch or dormer roof, snowmelt rushing down the steeper slope hits the valley centerline with high lateral momentum. On flat pan metal or closed-cut shingles, that fast-moving water shoots sideways up underneath the opposing lower-pitch shingle courses—a failure roofers call valley wash-over. Open W-valley flashing solves this with a factory-formed 5/8-inch to 3/4-inch inverted center rib running down the entire trough. That raised 'W' baffle splits opposing water streams, forces meltwater straight down toward the eave gutter, and adds longitudinal structural rigidity so heavy ice packs cannot crush oroil-can the 24-inch-wide metal pan.
- Center 3/4-inch inverted W-rib stops water wash-over from steep intersecting dormers
- Dual hemmed outer water-return edges trap capillary creep before it reaches OSB decking
- Smooth SMP-coated steel sheds sticky spring slush 3x faster than coarse asphalt granules
Why Closed-Cut & Woven Shingle Valleys Fail Prematurely in Utah
In a closed-cut valley, roofers run one slope's architectural shingles 12 inches past the valley centerline, press them into the trough crease, and trim the overlapping slope's shingles 2 inches back from the center with a hook blade. Although visually seamless from the driveway, two winter realities punish closed-cut valleys in Utah. First, sliding crusted snow acts like 60-grit sandpaper, scouring protective ceramic granules off the exposed asphalt crease until UV rays crack the fiberglass mat by year 12 to 16. Second, thick laminated architectural or Class 4 SBS shingles bridge slightly over tight valley angles—especially woven valleys, which manufacturers explicitly prohibit on heavy laminate shingles because hollow voids crack underfoot during cold repairs.
- Woven valleys are barred by shingle manufacturers on heavy multi-layer architectural shingles
- Closed-cut valley creases suffer accelerated granule loss from sliding Wasatch ice sheets
- Accidental hook-blade scoring during closed-cut trimming frequently slices underlying shingles
IRC R905.2.8.2 Fastening, Cleats & 36-Inch Ice-Barrier Layering
Per Utah Residential Code IRC R905.2.8.2, open metal valleys must be at least 24 inches wide and lined underneath with self-adhered polymer-modified bitumen complying with ASTM D1970. We first center a full 36-inch roll of high-temp ice-and-water shield directly into the clean OSB valley deck, then set 24-gauge (0.024-inch thick) Galvalume W-metal—never flimsy 28-gauge hardware-store tin that dents in hail. Crucially, no roofing nail ever penetrates within 6 inches of the valley centerline: our installers secure the outer hemmed flanges using metal valley cleats or wide-head nails along the extreme 1-inch outer edge, chalk straight diverging cut lines (widening 1/8 inch per foot downward), and clip every upper shingle corner at 45 degrees to deflect debris.
- Zero nails within 6 inches of valley center prevents thermal expansion slot leaks
- Tapered chalk cut (4 inches wide at top, widening 1/8"/ft toward eave) prevents ice jams
- 45-degree dubbed top shingle corners stop pine needles and meltwater from wicking sideways
Aesthetic Color Matching & Cost Comparison Across Salt Lake County
Homeowners sometimes hesitate over open valleys remembering shiny unpainted galvanized tin from 1980s ranch homes. Today's 24-gauge architectural W-valley stock comes factory baked in Kynar 500 PVDF or Silicone-Modified Polyester (SMP) matte finishes—Charcoal, Weathered Wood, Dark Bronze, Matte Black, and Slate Gray—that blend crisply into shadow lines on modern farmhouse and craftsman homes. While a closed-cut shingle valley uses $6 to $9 per linear foot in extra starter and crossover shingles, a true 24-gauge painted open W-valley over high-temp ice shield runs $18 to $26 per linear foot installed. On a typical home with 75 linear feet of valleys, that $900–$1,250 upgrade eliminates mid-life valley tear-outs costing $2,800+.
- Matte Kynar/SMP finishes in Black, Charcoal, Bronze & Weathered Bronze match shingle tones
- 24-gauge steel resists 1.5-inch hailstones without denting, matching Class 4 shingle lifespans
- Typical 75 LF valley package upgrade: ~$900–$1,250 during full roof replacement
Utah Roof Valley Systems Compared: Open W-Metal vs. Closed-Cut vs. Woven
| Valley Attribute | 24-Gauge Open W-Metal | Closed-Cut Shingle Valley | Woven Shingle Valley |
|---|---|---|---|
| Snow & Slush Shedding Speed | Excellent (slick metal + center rib) | Moderate (granule friction holds snow) | Poor (lumpy hump traps ice) |
| Expected Utah Lifespan | 35–50 years (matches Class 4 roof) | 14–20 years before crease erosion | 10–15 years (void bridging cracks) |
| Unequal Pitch Wash-Over Protection | High (3/4" W-baffle blocks crossflow) | Low unless double starter bleed-strip used | Low; not rated for laminate shingles |
| Installed Cost per Linear Foot | $18–$26/LF (with 36" high-temp ice shield) | $8–$13/LF (ice shield + crossover cut) | Not recommended on modern roofs |
Grant Helmer's Utah Field Pro-Tip (DOPL #10146123-5501)
In my field inspections across Sandy and Cottonwood Heights (Utah DOPL #10146123-5501), 70% of 'mysterious' valley leaks come from roofers shooting pneumatic shingle nails 3 inches from the valley center or forgetting to clip the top corners of cut valley shingles. Always insist on 24-gauge W-valley widened 1/8 inch per foot toward the gutter so sliding ice never wedges stuck.
Frequently Asked Questions: Open Metal Valley Vs Closed Cut Valley Snow
Why does an open W-valley widen slightly from the ridge down to the gutter?
Tapering the exposed shingle cut lines outward by 1/8 inch per linear foot—starting around 4 inches wide at the top and reaching 6 to 7 inches at the eave—accommodates increasing meltwater volume downslope and allows frozen ice wedges to slide freely into the gutter without jamming.
Should roofers caulk or tar the cut shingle edges along an open metal valley?
Never smear continuous roof cement sealing the bottom edge of shingles tight to valley metal, because water that gets behind the upper shingle course becomes trapped and backs up past nails. Instead, we use hemmed water-return flanges on 24-gauge W-metal and clip upper shingle corners at 45 degrees.
What gauge metal is required for open roof valleys in Salt Lake County?
While minimum IRC code permits thin 26- or 28-gauge galvanized steel, thin valleys dent easily during Wasatch hailstorms and oil-can under thermal swings. We specify 24-gauge G90 galvanized or AZ50 Galvalume steel with SMP or Kynar matte paint over high-temperature self-adhered underlayment.
Can I keep closed-cut valleys if my HOA prefers no visible valley metal?
Yes, provided the valley is reinforced properly: we line the deck with 36-inch self-adhered ice barrier, add a centered 18-inch flat metal coil liner underneath as hidden insurance, install a vertical shingle bleed-strip along the cut line, and prohibit any nails within 6 inches of the trough.
Related Utah Roofing, Bathroom & Remodeling Resources
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