Bottom line: A roof isn't just shingles or metal panels — underlayment, flashing, and the right fasteners are what actually keep water out and hold the system together over time. Southern Utah's sun exposure, wind, and occasional heavy snow at higher elevations make these supporting materials just as important as the roof covering itself, and they're the items most often left off a first material order.
What Goes Under the Shingles or Metal Panels?
Underlayment is the water-resistant layer installed directly on the roof deck before shingles or metal panels go down, and skipping it or under-ordering it is one of the most common callback causes on a roofing job. Southern Utah roofs typically use one of three underlayment types, and picking the wrong one for the application causes problems later.
| Underlayment type | Best for | Notes |
|---|---|---|
| Synthetic underlayment | Most asphalt shingle and metal roofs | Lighter, more tear-resistant than felt, holds up better if exposed briefly during install |
| Traditional felt (15# or 30#) | Budget asphalt shingle jobs | Heavier, absorbs moisture more readily, still specified on some projects |
| Ice-and-water shield | Eaves, valleys, and roof penetrations | Self-adhering membrane for the areas most prone to water backup |
Most jobs actually use a combination — synthetic across the field of the roof, with ice-and-water shield reinforcing eaves and valleys. Our complete guide to roofing materials in Southern Utah walks through how these layer together with the roof covering itself.
Why Does Flashing Matter as Much as the Roof Covering?
Flashing is the metal material installed at roof transitions — chimneys, vent pipes, valleys, skylights, and where a roof meets a wall — and it's where most roof leaks actually start, not in the middle of a shingle or panel field. Flashing needs to match the roofing material and the specific transition it's covering:
- Valley flashing — open metal valleys are common on both asphalt and metal roofs in this region
- Step flashing — for roof-to-wall transitions, installed shingle-by-shingle or panel-by-panel
- Pipe boot flashing — around vent penetrations, a frequent source of leaks as the boot material ages
- Drip edge — along eaves and rakes, directs water away from the fascia
Undersizing a flashing order because it seems like a small line item is a common way jobs end up back on the schedule for a return trip.
Which Fasteners Are Right for Metal Roofing vs. Asphalt Shingles?
Fasteners aren't interchangeable between roofing systems, and the wrong choice affects both how well the roof holds up to wind and how it looks once installed.
- Metal roofing — needs gasketed screws sized and spaced to the panel profile, matched to the substrate (wood deck vs. metal purlins)
- Asphalt shingles — roofing nails sized to penetrate the deck properly, with placement that follows the shingle manufacturer's nailing pattern
- Coating — exposed fasteners on metal roofs should be corrosion-resistant, since they're visible and weather-exposed for the life of the roof
If you're still deciding between roofing systems for a project, our comparison of metal roofing vs. asphalt shingles covers how the fastener and flashing requirements differ between the two.
Order Separately or as a Package?
For contractors, ordering underlayment, flashing, and fasteners alongside the primary roofing material in one order is usually simpler than sourcing them piecemeal — it avoids a second trip or a delivery delay because one component didn't get ordered with the rest. Homeowners managing their own project should ask specifically whether a quote includes these supporting materials or only the shingles or panels, since a quote that looks low may just be missing them. Current material pricing is listed on our pricing page.
Where to Get These Materials in Cedar City and Southern Utah
Southern Utah Roofing Supply stocks underlayment, flashing, and fastener options alongside our roofing, siding, and drywall materials at our Cedar City location on UT-56, serving contractors and homeowners across Southern Utah. If you're finalizing a roofing material list for a job, our Covered With Care page outlines how we handle orders, and our Cedar City location page has directions and details for picking up or arranging delivery of a full material package in one order.