9.4 Metal Roof Systems, Tile, Slate & Wood Shingles and Shakes
Key Takeaways
Minimum slopes for metal panels are 3:12 for lapped, nonsoldered seams without sealant, 1/2:12 with applied lap sealant, and 1/4:12 for standing-seam systems, and metal shingles need at least 3:12.
Without manufacturer instructions, steel roofs use galvanized fasteners, copper roofs use copper, brass, bronze, copper alloy, or 300-series stainless fasteners, and stainless fasteners are acceptable for metal roofs (R905.10.4).
Clay and concrete tile need at least 2 1/2:12, with double underlayment up to 4:12, and in areas subject to snow each tile needs at least two fasteners.
Slate requires at least 4:12, a solid deck, two fasteners per slate, and headlaps of 4 inches below 8:12, 3 inches from 8:12 to below 20:12, and 2 inches at steeper slopes.
Wood shingles and shakes need at least 3:12. Shakes are interlaid with 18-inch strips of No. 30 felt, and solid sheathing is required under the ice barrier area in cold climates.
Metal Roof Panels (R905.10)
| Item | Rule |
|---|---|
| Deck | Solid or spaced sheathing, unless the covering is designed for spaced supports (R905.10.1) |
| Minimum slope (R905.10.2) | 3:12 for lapped, nonsoldered-seam roofs without applied lap sealant. 1/2:12 with lap sealant applied per the manufacturer. 1/4:12 for standing-seam systems |
| Materials (Table R905.10.3(1)) | Galvanized steel ASTM A653 G90. Stainless steel ASTM A240 300 series. Aluminum ASTM B209, 0.024 inch minimum for roll-formed panels. Cold-rolled copper 16 oz per square foot (12 oz high-yield). Zinc 0.027 inch |
| Corrosion resistance (Table R905.10.3(2)) | 55% aluminum-zinc coated steel AZ50. Galvanized G-90. Prepainted steel over one of the listed metallic coatings |
| Structural panels | Systems with supporting structural members must be designed to the building code |
| Fasteners (R905.10.4) | Follow the manufacturer. If there are no instructions: galvanized fasteners for steel roofs; copper, brass, bronze, copper alloy, or 300-series stainless for copper roofs. Stainless fasteners are acceptable for metal roofs generally |
| Underlayment (R905.10.5) | Per R905.1.1. For metal panels at design wind speeds below 140 mph, apply per the manufacturer's instructions |
Standing Seam vs. Exposed Fastener
- Standing-seam panels join at raised seams and are held by concealed clips. Many clips let panels expand and contract with temperature. Mechanically seamed profiles suit the lowest slopes, down to 1/4:12, if the manufacturer rates them for it.
- Exposed-fastener panels, such as ribbed or corrugated panels, are screwed through the face with sealing washers. They need the steeper slopes above unless the laps are sealed, and the washers age, so they need periodic inspection.
Thermal Movement, Dissimilar Metals, and Snow
- Long panels move with temperature. Use the manufacturer's clips, expansion details, and trim so panels are not pinned at both ends.
- Avoid galvanic corrosion: keep copper away from galvanized steel and aluminum, including copper runoff onto them. Use compatible fasteners, and separate dissimilar metals. The code requires compatible materials (R904.2).
- Snow slides off metal roofs suddenly. Snow guards, placed where the manufacturer and site conditions call for them, protect walkways, decks, gutters, and lower roofs.
Metal Roof Shingles (R905.4)
- Applied to a solid or closely fitted deck, unless designed for spaced sheathing.
- Minimum slope 3:12. Underlayment per R905.1.1, and ice barrier where required, which means every Michigan home (R905.4.3.1).
- Materials per Table R905.10.3(1), with corrosion resistance per Table R905.10.3(2). Aluminum press-formed shingles are at least 0.019 inch.
- Valley flashing at least 8 inches each side of center, with a 3/4-inch diverter rib (Section 9.3).
Clay and Concrete Tile (R905.3)
| Item | Rule |
|---|---|
| Deck | Solid sheathing or spaced structural sheathing boards |
| Slope | At least 2 1/2:12. Double underlayment from 2 1/2:12 to 4:12 |
| Standards | Clay tile ASTM C1167. Concrete tile ASTM C1492 |
| Nails | Corrosion-resistant, at least 11 gauge, 5/16-inch head, penetrating the deck at least 3/4 inch or through it. Tile wire at least 0.083 inch |
| Fastening | Per the manufacturer and R905.3.7. Perimeter tiles get at least one fastener each. In areas subject to snow, at least two fasteners per tile |
| Weight | Tile is heavy. The framing and deck must be designed for the load (R908.2; Section 7.1) |
Slate (R905.6)
| Item | Rule |
|---|---|
| Deck | Solidly sheathed |
| Slope | At least 4:12 |
| Standard | ASTM C406 |
| Fastening | Two fasteners per slate |
| Headlap (Table R905.6.5) | 4 inches for 4:12 to below 8:12. 3 inches for 8:12 to below 20:12. 2 inches at 20:12 and steeper |
| Valleys and flashing | Sheet metal flashing and counterflashing. Valley flashing at least 15 inches wide, at least 0.0179-inch G90 |
| Fire | Slate over underlayment on a combustible deck counts as Class A (Michigan R902.1) |
Exposure for slate is calculated from length and headlap:
An 18-inch slate on a 10:12 roof, which takes a 3-inch headlap, has an exposure of (18 − 3) ÷ 2 = 7.5 inches.
Existing slate may be reinstalled, but damaged, cracked, or broken slate may not (R908.5). Slate repairs typically use copper or stainless nails and slate hooks or bibs as trade practice directs.
Wood Shingles (R905.7) and Wood Shakes (R905.8)
| Item | Wood shingles | Wood shakes |
|---|---|---|
| Deck | Solid, or spaced boards at least 1×4 spaced on centers equal to the exposure | Same, with extra boards where 1×4s are spaced at 10 inches |
| Cold climate | Solid sheathing where the ice barrier is required, in areas with an average January temperature of 25°F or less | Same |
| Minimum slope | 3:12 | 3:12 |
| Grades | No. 1, 2, or 3 (Cedar Shake and Shingle Bureau) | No. 1 for naturally durable shakes. Tapersawn No. 1 or 2 |
| Spacing between pieces | 1/4 to 3/8 inch | 3/8 to 5/8 inch |
| Side lap | At least 1 1/2 inches, and no two joints aligned in any three adjacent courses | At least 1 1/2 inches |
| Fasteners | Stainless 304 or 316, or hot-dip galvanized ASTM A153 Class D. Two per piece, penetrating 3/4 inch or through the sheathing. Stainless 316 within 15 miles of salt water | Same |
| Interlayment | None specified | 18-inch-wide strips of at least No. 30 felt between courses. The bottom edge of each strip sits above the shake butt by twice the weather exposure (R905.8.7). The starter course at the eave is doubled |
| Exposure | Table R905.7.5(1) by length, grade, and slope. Example: 16-inch No. 1 at 5 inches on 4:12 and steeper | Table R905.8.6. Example: 18-inch No. 1 at 7 1/2 inches |
A recover with metal or tile over existing shakes must cover the old surface where it creates a combustible concealed space (R908.4; Section 8.2).
What is the minimum slope for a standing-seam metal panel roof under the 2015 MRC?
1/4:12
1/2:12
3:12
4:12
What headlap does Table R905.6.5 require for slate on a 10:12 roof, and what is the exposure for 20-inch slates?
3 inches of headlap and an 8 1/2-inch exposure
4 inches of headlap and an 8-inch exposure
2 inches of headlap and a 9-inch exposure
3 inches of headlap and a 10-inch exposure
How many fasteners per tile does R905.3.7 require for clay or concrete roof tile in areas subject to snow?
At least two per tile
One per tile on perimeter tiles only
None when battens are used
One per tile on every other row
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