10.6 Roof Covering Materials: Asphalt, Rolled Roofing & Wood Shingles/Shakes
Key Takeaways
- Asphalt shingles require a minimum 4:12 slope for single-layer underlayment, or 2:12 with double-layer underlayment; slopes under 2:12 prohibit asphalt shingles entirely.
- Standard asphalt shingle fastening is four nails per shingle, increasing to a six-nail pattern in Minnesota's higher wind-exposure areas per manufacturer instructions.
- Rolled roofing has a minimum 1:12 slope and is limited in practice to low-slope accessory roofs, not primary dwelling roof coverings.
- Wood shingles and shakes require a minimum 3:12 slope, offset course joints, felt interlayment for shakes, and open valley construction with metal flashing.
- Minnesota's 24-inch ice barrier membrane requirement at eaves applies to asphalt shingle and wood shingle/shake roofs alike, independent of the covering material chosen.
Roof Covering Materials: Asphalt, Rolled Roofing & Wood Shingles/Shakes
Beyond underlayment and flashing (covered in Section 10.1), the exam separately tests the roof covering material itself — the slope limits, fastening schedules, and application details specific to asphalt shingles, rolled roofing, and wood shingles/shakes under the Minnesota Residential Code (MN Rules Chapter 1309 / IRC Chapter 9).
1. Asphalt Shingles (IRC R905.2)
Asphalt shingles remain the dominant residential roof covering in Minnesota, but their use is governed by strict slope thresholds:
| Roof Slope | Asphalt Shingle Status |
|---|---|
| Less than 2:12 | Prohibited — requires a low-slope membrane system (TPO, EPDM, modified bitumen) |
| 2:12 up to less than 4:12 | Permitted, but requires double-layer underlayment (see Section 10.1) |
| 4:12 or greater | Permitted with standard single-layer underlayment |
Fastening: Each shingle requires a minimum of four nails, driven flush and positioned per the manufacturer's nailing pattern (typically just above the cutout slots). In Minnesota's higher wind-exposure areas, or wherever the manufacturer's listing calls for it, the schedule increases to a six-nail pattern per shingle. Nails must penetrate through the shingle and underlayment and at least 3/4 inch into the roof sheathing, or completely through sheathing thinner than 3/4 inch.
Starter course and ridge: A starter strip — either a factory starter product or field-cut shingles with tabs removed — is installed at the eave with sealant strip facing up and out, so the first full course bonds to it and its own tabs are shielded from wind uplift. Hip and ridge caps use manufacturer-specified ridge shingles fastened with two nails each, lapped so no fastener is exposed.
Ice barrier recall: Because Minnesota has a documented history of ice damming statewide, an ice barrier membrane is required at eaves on steep-slope roof coverings (asphalt shingles, wood shingles/shakes), extending from the eave edge to a point at least 24 inches inside the interior line of the exterior wall — this is the same rule covered in Section 10.1 and it applies regardless of which shingle material is used above it.
2. Rolled Roofing (IRC R905.4)
Rolled roofing is a mineral-surfaced asphalt roll product used mainly on low-slope accessory structures — porch roofs, shed roofs, and other secondary roof areas — rather than as a primary dwelling roof covering.
- Minimum slope: 1:12, applied with exposed-nail or concealed-nail construction depending on the specific product and manufacturer instructions.
- Application limitations: Because rolled roofing has a shorter service life and lower wind and hail resistance than shingles, its use is generally limited to low-visibility, low-slope accessory areas rather than the main roof plane of a dwelling. It is not an acceptable substitute for asphalt shingles on slopes suited to shingle installation.
- Double-coverage option: Where a slightly longer service life is needed on a qualifying low-slope area, rolled roofing can be installed with double coverage (each course overlapping more than half its width), which improves water-shedding performance compared with single-coverage exposed-nail application, though it still does not extend rolled roofing's use onto primary steep-slope roof planes.
3. Wood Shingles and Shakes (IRC R905.7 / R905.8)
Wood shingles and shakes are a traditional, higher-maintenance roof covering still specified on some Minnesota homes for appearance, and the exam tests their distinct slope and spacing rules separately from asphalt shingles.
| Requirement | Wood Shingles | Wood Shakes |
|---|---|---|
| Minimum slope | 3:12 | 3:12 |
| Underlayment | Breather-type or felt per manufacturer | Felt interlayment (typically 18-inch-wide strip) woven between courses |
| Exposure/spacing | Side lap joints offset a minimum of 1-1/2 inches from the course below | Same offset principle; shakes are thicker and split, requiring wider joints for expansion |
| Ice barrier | Required at eaves per the statewide ice-dam rule | Required at eaves per the statewide ice-dam rule |
Spacing for expansion: Wood shingles and shakes must be installed with a small gap between adjacent pieces in the same course (typically 1/4 to 3/8 inch depending on the wood's moisture content at installation) to allow for seasonal swelling; joints between courses must be offset so no two consecutive courses share a common joint line, which prevents a direct water path through the assembly.
Valleys: Wood shingle and shake roofs require open valley construction with a metal valley flashing (minimum 26-gauge corrosion-resistant metal), because the closed/woven valley techniques used with flexible asphalt shingles do not work with rigid wood pieces. The flashing must extend a minimum distance up each side of the valley centerline, and shingles/shakes are trimmed to the valley line rather than woven across it.
Cross-reference to ice barrier and underlayment: Both the eave ice barrier membrane and the general underlayment requirements are detailed fully in Section 10.1 (Roofing Underlayment, Ice Dam Protection & Flashing Details); this section focuses on the covering material itself, but a contractor should remember the two topics are inspected together — a correctly slotted wood shake roof with no ice barrier underneath still fails inspection in Minnesota's climate.
4. Quick Comparison for the Exam
| Material | Min. Slope | Key Fastening/Application Note |
|---|---|---|
| Asphalt shingles | 4:12 (single layer); 2:12 (double layer) | 4 nails/shingle standard, 6 nails in high-wind areas |
| Rolled roofing | 1:12 | Low-slope accessory roofs only, not a primary dwelling covering |
| Wood shingles/shakes | 3:12 | Offset joints, felt interlayment for shakes, open valley metal flashing |
Which statement correctly describes Minnesota's mandatory ice barrier requirement at eaves for a steep-slope shingle roof covering?
Under the Minnesota Residential Code, what fastening pattern applies to asphalt shingles installed in the state's higher wind-exposure areas, in place of the standard four-nail pattern?
What is the minimum roof slope permitted for wood shingle and wood shake roof coverings under the Minnesota Residential Code (IRC R905.7/R905.8)?