Short answer: the panel maker’s installation manual and your local building code control every metal roof. This guide lays out the usual order of work and the reason for each step. It does not replace the manual, the engineering for the job or the permit.
Before you start: manual, code and engineering
Get the installation manual and details for the exact panel you are installing. Clips are a good example of why. The Metal Construction Association (MCA) says clips are made for a specific panel profile, and often for one manufacturer. Swapping clips between systems needs an engineering review or testing.
Clip spacing is engineered too. MCA calls for a clip analysis that sets spacing for the field, edges and corners of the roof. Where local code requires it, a registered design professional does that analysis.
Then check slope. New Jersey’s one- and two-family code sets minimum slopes for metal roof panels. Many panels list a higher minimum than the code, and the higher number wins.
| Roof type | NJ code minimum | Example panel minimum |
|---|---|---|
| Lapped, non-soldered seams, no sealant | 3:12 | Check the panel maker’s manual |
| Lapped, non-soldered seams with lap sealant | 1/2:12 | Check the panel maker’s manual |
| Standing seam, snap-lock | 1/4:12 | 3/12 for the 1″ FF and 1.5″ SnapLock 450+; 2/12 for the 1.5″ SnapLock 550 |
| Standing seam, mechanical lock | 1/4:12 | 2/12 for the 1.5″ and 2″ mechanical seams |
Store the material dry
Water trapped between nested panels or coil wraps causes wet storage stain. Galvalume warranties from Sheffield Metals, Drexel Metals and Metal Sales all exclude it. Keep bundles and coils covered, off the ground and sloped so water drains. If a bundle gets wet, separate and dry it before it stains.
On zinc, RHEINZINK says to remove the protective film right after installation. For other metals, follow the panel maker’s note on film.
The order of work
1. Deck
The code calls for solid or spaced sheathing under metal roof panels. The exception is a panel designed to span spaced supports, such as purlins. Check that the deck is sound, dry and flat before anything goes on it. Flat pans show every hump underneath.
2. Underlayment
For metal panels where wind design is not required, the code points to the manufacturer’s instructions. Where wind design is required, it lists ASTM D226 Type II felt or ASTM D4869 Type III or IV. Synthetic sheets are common. DuPont lists Tyvek Protec 120 as ideal for slopes of 2:12 or higher. Self-adhered membranes for hot roofs are sold as high-temperature grades, such as SOPREMA’s Lastobond Shield HT under ASTM D1970. Lap every layer so water runs over the course below it. Browse roof underlayment, including Tyvek Protec 120 and Lastobond Pro HT-N.
3. Eave trim
Set the eave trim before the first panel, because panels hem or lock onto it. Follow the manual’s detail for how the underlayment laps the trim.
4. First panel, square
Start square to the eave. A small error at the first panel grows across the whole roof. Check it again every few panels.
5. Panels and clips
Standing seam panels need one fixed point and room to move everywhere else. MCA notes that panel temperatures can swing more than 150°F in a single day. One-piece clips allow some movement. Two-piece sliding clips are common on longer panels. Either way, each panel must be fixed at a single location so it cannot creep downslope.
PAC-CLAD adds that aluminum moves almost twice as much as steel. Never pin both ends of a long panel.
On mechanical seams, many systems call for hand seaming at each clip before the power seamer runs the full length. MCA warns that skipping this step can cut the roof’s wind uplift capacity. See standing seam clips, fixed clips, floating clips and power seamers.
Exposed fastener panels go down with screws through the face. The code says to fasten panels per the manufacturer’s instructions. Use the screws, spacing and sealing washers in the manual. See roofing fasteners and exposed fastener panels.
6. Rake, ridge and hips
The manual says whether rake trim goes on before or after the panels. Ridge and hip details use closures and sealant where the manual shows them. Butyl tape and other sealants must suit the panel finish.
7. Flashing at walls and penetrations
Walls, chimneys, skylights and pipes need the most care. Flash them so water always laps downhill. Let panels slide under trim and counterflashing instead of fastening through both. Check pipe flashing options when you order.
8. Snow retention
Snow guards need a layout, not a guess. Stortz says rafter length, pitch, snow load and panel type all change it. A qualified engineer, an architect or the guard maker should confirm it. Stortz cites Alpine Snow Guards’ rule of one row for every 5 feet of rafter length. It also sets the first row at least 24 inches back from the eave. Use clamps rated for your seam. Browse snow guards, including ML seam clamps.
9. Clean up as you go
Sweep metal shavings off the roof the same day. MBCI warns that left-behind swarf can stain a roof for good, and enough of it can rust through a panel.
Common mistakes
- Cutting with an abrasive blade or grinder. MBCI says to cut with nibblers, snips or shears so edges do not rust. Cut on the ground, never over other panels.
- Marking with a graphite pencil. MCA calls graphite extremely corrosive to aluminum and aluminum-zinc coatings. Metal Sales excludes graphite contact from its Galvalume warranty.
- Treated lumber or wood blocking on the roof. MCA says treated lumber carries copper salts, and any wood traps moisture.
- Copper or condensate draining onto the panels. MCA says to plumb rooftop AC condensate to a drain.
- The wrong fasteners. A galvanized fastener in an aluminum roof is MCA’s classic failure.
- Mixing parts from different systems. MCA says swapping clips between panel systems needs an engineering review first.
- Skipping hand seaming at clips. Do it before the power seamer runs.
- Bending trim too tight. Sheffield, Drexel and Metal Sales Galvalume warranties exclude bends tighter than 2T on sheet .030 inch and thinner, and 4T on sheet .031 inch and thicker.
On the coast, read aluminum vs. steel roofing near the coast first. To estimate material, see coil width and panel coverage.
Quick answers
Does New Jersey code require an ice barrier under metal panels?
The ice barrier rule in the NJ one- and two-family code lists metal roof shingles, not metal roof panels. Your panel maker’s manual may still call for a membrane at eaves and valleys, so follow it.
Can standing seam go over spaced sheathing?
The code allows solid or spaced sheathing, and panels designed for spaced supports can span them. Sheffield lists plywood as the substrate for its 1.5-inch SnapLock 450+, for example, so check the manual.
Sources
Figures in this guide come from the documents below or are calculated from them. Specs and warranty terms change, so check the current version before you order.
- New Jersey UCC One- and Two-Family Dwelling Subcode 2021 (IRC 2021, NJ edition), Chapter 9 Roof Assemblies, via UpCodes
- Metal Construction Association, White Paper: Standing Seam Roof Clips Best Practices Guide
- Metal Construction Association, Technical Bulletin: Dissimilar Metal Corrosion in Roofing Installations (06/22)
- MBCI, Proper Cutting and Cleaning of Metal Building Panels
- Sheffield Metals, SMI 1.5″ SnapLock 450+ cut sheet
- Sheffield Metals, SMI 1.5″ Mechanical Seam cut sheet
- DuPont, Tyvek Protec 120 Roof Underlayment
- SOPREMA, LASTOBOND SHIELD HT underlayment
- PAC-CLAD (Petersen), Thermal Expansion and Contraction in Metal Roof Systems
- Stortz, Seam-Mounted Snow Guard Best Practices
- Metal Sales Manufacturing Corp., 25 Year Galvalume AZ55 Warranty (effective 2/13)
- Sheffield Metals, 50-Year Painted AZ50 Galvalume Limited Metal Warranty, sample
- Drexel Metals, 25-Year DREXLUME Warranty, sample (revised June 2020)
- Sheffield Metals, SMI 1.0″ FF SnapLock cut sheet
- Sheffield Metals, SMI 1.5″ SnapLock 550 cut sheet
- Sheffield Metals, SMI 2.0″ Mechanical Seam cut sheet
- RHEINZINK, Material Data Sheet RHEINZINK-CLASSIC
Order the job as a system: clips, fasteners, underlayment, sealants and snow guards that match your panel. Send your takeoff and we will quote it.