Guide
Standing seam vs exposed fastener metal roofing
Standing seam panels hide their fasteners under raised seams. Exposed fastener panels are screwed through the face. Standing seam costs more and needs less upkeep; exposed fastener costs less and suits barns, shops and simple roofs. Here is how to choose, and how roofers measure your roof.
How standing seam works
Standing seam panels run from the ridge to the eave with raised seams where neighboring panels meet, often 1 to 2 inches tall. The panels are held down by clips or by a fastening strip that sits under the seam, so no screw goes through the face of the panel where water runs.
- Snap-lock panels click together by hand. They are quicker to install.
- Mechanical seam panels are folded together with a seaming tool, in a single or double fold. They hold up better on low slopes and in high wind.
Metal grows and shrinks as it heats and cools. Many standing seam systems use clips that let each panel slide a little, so that movement does not work at the fasteners. Panels are often made to length on a roll former, sometimes right at the job site.
How exposed fastener panels work
Exposed fastener panels (also called screw-down or through-fastened) are the ribbed or corrugated sheets you see on barns, shops and many homes. Each sheet overlaps the next, and screws with rubber washers go straight through the panel into wood strips or the roof deck below. The washer is what keeps each hole dry.
The panels are simple to install, which keeps labor lower and makes them a common choice for do-it-yourself outbuildings. The tradeoff is hundreds or thousands of holes, each one relying on a washer that ages in sun and heat, and screws that can slowly loosen as the metal moves.
Side by side
| Factor | Standing seam | Exposed fastener |
|---|---|---|
| Fasteners | Hidden under the seams | Screws through the face |
| Up-front cost | Higher | Lower |
| Install | Specialist crew and tools | Simpler; common on outbuildings |
| Low slopes | Systems are made for low slopes; check the panel's rated minimum | Most panels need more slope; check the manufacturer's minimum |
| Upkeep | Low | Screws and washers need checking |
| Movement with heat | Clips let panels slide | Screws pin the panel, which can enlarge holes over time |
| Look | Clean, flat panels with crisp lines | Ribbed, farm or industrial look |
| Waviness (oil canning) | Can show on wide flat panels; ribs or stiffening lines reduce it | Ribs hide it well |
Lifespan and upkeep
Metal roofing lasts a long time when it is installed well. Standing seam is generally expected to last for decades with little care, since there are no exposed screws to wear out. Exposed fastener panels can last decades too, but the screws and washers usually need attention long before the metal itself wears out.
A simple routine for either type:
- Look it over every year or two and after big storms. Binoculars from the ground are enough for a first look.
- Check screws on exposed fastener roofs: backed-out screws, cracked or flattened washers, and rust stains around holes. Loose or stripped screws are often replaced with a slightly larger size.
- Check flashing and sealant around chimneys, vents and skylights on both types. Most leaks start there.
- Clear debris from valleys and gutters, and keep branches off the roof.
- Keep other metals off. Copper and some other metals touching or draining onto steel panels can speed up corrosion.
- Touch up scratches with the manufacturer's matching paint.
Gauge and finish
Steel thickness is given as a gauge: the lower the number, the thicker the steel. Residential standing seam is often 24 or 26 gauge, and exposed fastener panels are often 26 or 29 gauge. Finishes matter as much as thickness. PVDF paint systems (often sold under the Kynar 500 name) hold their color longer than SMP paints, which cost less. Ask which you are getting and what the paint warranty covers.
Is a metal roof noisy?
Over solid roof decking with underlayment and an insulated attic, rain on a metal roof is not much louder than on other roofs, and most people notice little difference indoors. The loud metal roof people remember is usually on a barn or porch, where the panels sit on open framing with nothing underneath. If noise worries you, ask about solid decking and the underlayment.
How roofing squares work
Roofers price by the square. One square is 100 square feet of roof. Your roof is bigger than your home's footprint, because it slopes. To estimate it, take the footprint (including overhangs) and multiply by the factor for your roof pitch:
| Pitch | Multiply footprint by |
|---|---|
| 3 in 12 | 1.03 |
| 4 in 12 | 1.05 |
| 6 in 12 | 1.12 |
| 8 in 12 | 1.20 |
| 10 in 12 | 1.30 |
| 12 in 12 | 1.41 |
For example, a 1,800 square foot footprint with a 6 in 12 pitch is about 1,800 x 1.12 = 2,016 square feet of roof, or about 20 squares. Roofers then add material for waste, trim and cuts, more on roofs with many valleys and dormers. The metal roof calculator works out squares from your footprint and slope.
Which one to choose
Choose standing seam for a home you plan to keep, for low-slope roofs, in high-wind areas, or when you want the clean look and the least upkeep.
Choose exposed fastener for barns, sheds, shops and carports, for simple roofs on a tighter budget, or for a do-it-yourself project. It is also a fine choice for a home if you accept the screw checks.
Either way, ask for the panel profile, gauge, paint system, underlayment and whether the old roof comes off, all in writing. Some cities and homeowner associations also have rules on metal roofs and colors, so check before you sign.
Sources
- Metal Construction Association (MCA) guidance on metal roofing systems