4/12 Roof Pitch
A 4/12 roof rises 4 inches for every 12 inches of horizontal run. That is a 18.43° angle, a grade of 33.3% and a roof area multiplier of 1.054, so every square foot of plan area becomes 1.054 square feet of roof surface.
Rafter length for a 4/12 pitch
Multiply the horizontal run by 1.054. Every foot of run needs 12.65 inches of common rafter. Add the overhang (horizontal overhang × 1.054) and deduct half the ridge board thickness.
| Building span | Run (½ span) | Common rafter | Ridge rise |
|---|---|---|---|
| 12 ft | 6 ft | 6 ft 4 in | 2 ft 0 in |
| 16 ft | 8 ft | 8 ft 5¼ in | 2 ft 8 in |
| 20 ft | 10 ft | 10 ft 6½ in | 3 ft 4 in |
| 24 ft | 12 ft | 12 ft 7¾ in | 4 ft 0 in |
| 28 ft | 14 ft | 14 ft 9 in | 4 ft 8 in |
| 32 ft | 16 ft | 16 ft 10½ in | 5 ft 4 in |
| 36 ft | 18 ft | 18 ft 11¾ in | 6 ft 0 in |
| 40 ft | 20 ft | 21 ft 1 in | 6 ft 8 in |
Gable roof, imperial. Rafter length is measured along the slope from wall plate to ridge centre line, before eave overhang and ridge board deduction.
| Building span | Run (½ span) | Common rafter | Ridge rise |
|---|---|---|---|
| 4 m | 2 m | 2.11 m | 0.67 m |
| 6 m | 3 m | 3.16 m | 1.00 m |
| 8 m | 4 m | 4.22 m | 1.33 m |
| 10 m | 5 m | 5.27 m | 1.67 m |
| 12 m | 6 m | 6.32 m | 2.00 m |
Gable roof, metric. Rafter length is measured along the slope from wall plate to ridge centre line, before eave overhang and ridge board deduction.
Roof area at 4/12
Roof surface area = plan area × 1.054. Use the roof calculator for multi-section roofs, waste and material costs.
| Plan area | Roof surface | Squares (+10%) | Shingle bundles |
|---|---|---|---|
| 1,000 sq ft | 1,054 sq ft | 11.6 | 35 |
| 1,500 sq ft | 1,581 sq ft | 17.4 | 53 |
| 2,000 sq ft | 2,108 sq ft | 23.2 | 70 |
| 2,500 sq ft | 2,635 sq ft | 29.0 | 87 |
| 3,000 sq ft | 3,162 sq ft | 34.8 | 105 |
Plan area includes eave overhangs. Bundles assume 3 bundles per square (100 sq ft) with 10% waste; hips, valleys and dormers need more.
| Plan area | Roof surface | With 10% waste |
|---|---|---|
| 80 m² | 84.3 m² | 92.8 m² |
| 100 m² | 105.4 m² | 116.0 m² |
| 150 m² | 158.1 m² | 173.9 m² |
| 200 m² | 210.8 m² | 231.9 m² |
| 250 m² | 263.5 m² | 289.9 m² |
Plan area is the footprint measured to the outside of the eaves. Multiply by 1.054 for the sloped surface.
Roofing materials for a 4/12 pitch (US & Canada)
Minimum slopes from the 2021 International Residential Code. Canadian codes and manufacturers use similar limits for shingles and metal. Minimum pitch by material →
| Roofing system | At this pitch | Code section |
|---|---|---|
| Asphalt shingles | Meets the 2/12 minimum | IRC R905.2.2 |
| Clay & concrete tile | Meets the 2½/12 minimum | IRC R905.3.2 |
| Metal roof shingles | Meets the 3/12 minimum | IRC R905.4.2 |
| Slate & slate-type shingles | Meets the 4/12 minimum | IRC R905.6.2 |
| Wood shingles & shakes | Meets the 3/12 minimum | IRC R905.7.2 / R905.8.2 |
| Standing-seam metal panels | Meets the ¼/12 minimum | IRC R905.10.2 |
| Lapped (exposed-fastener) metal panels | Meets the ½/12 minimum | IRC R905.10.2 |
| Mineral-surfaced roll roofing | Meets the 1/12 minimum | IRC R905.5.2 |
| Membranes (TPO, EPDM, modified bitumen, built-up) | Allowed, but normally used on low-slope roofs | IRC R905.9–R905.13 |
Roofing materials for a 4/12 pitch (Australia & UK)
Typical manufacturer minimums. Check the specific product, sheet thickness, rafter length and exposure before ordering.
| Roofing system | At this pitch | Notes |
|---|---|---|
| Concealed-fix steel deck (e.g. Lysaght Klip-Lok 700) | Meets the typical 1° minimum | 1° applies to thicker sheet; 0.42 BMT is generally 2°. |
| Trapezoidal steel sheet (e.g. Lysaght Trimdek) | Meets the typical 2° minimum | — |
| Corrugated steel sheet (e.g. Lysaght Custom Orb) | Meets the typical 5° minimum | — |
| Interlocking concrete or terracotta tiles | Meets the typical 15° minimum | Profile dependent; many UK interlocking tiles need 17.5°–22.5°. |
| Natural slate | Below the typical 20° minimum | Typical for larger slates; smaller slates and exposed sites need steeper pitches. |
| Plain tiles (clay or concrete) | Below the typical 35° minimum | Some products allow 30°. |
| Flat-roof membranes (EPDM, single-ply, felt) | Usually reserved for flat and low-slope roofs | Designed for a finished fall of about 1:80 (0.7°) or more. |
Is a 4/12 roof steep?
Moderate pitches suit nearly every residential roofing material, shed water and snow well, and keep labour costs low because the roof is still workable.
A 4/12 roof is walkable for experienced roofers, but footing gets less forgiving on dew, dust or loose granules. Plan fall protection before going up.
4/12 roof pitch FAQ
What is a 4/12 roof pitch in degrees?
A 4/12 pitch is 18.43°. It rises 4 inches per 12 inches of run, so the angle is arctan(4 ÷ 12). As a percentage that is a slope of 33.3%, and in metric it rises 333 mm per metre.
What is the roof pitch multiplier for 4/12?
The 4/12 multiplier is 1.054. Multiply the roof's plan (footprint) area by 1.054 to get the sloped surface area. A 2,000 sq ft plan area, for example, is 2,108 sq ft of roof before waste.
How do I calculate rafter length for a 4/12 pitch?
Multiply the horizontal run by 1.054. Each foot of run needs 12.65 inches of rafter, so a 24 ft wide gable (12 ft run) needs a common rafter of about 12 ft 7¾ in before adding the overhang and deducting half the ridge board. Hip and valley rafters on a regular hip roof need 17.44 inches per foot of common run.
Can you walk on a 4/12 roof?
A 4/12 roof is walkable for experienced roofers, but footing gets less forgiving on dew, dust or loose granules. Plan fall protection before going up. OSHA (29 CFR 1926.500) treats any roof steeper than 4/12 as a steep roof for fall protection purposes.
What roofing materials can go on a 4/12 pitch?
Under the US International Residential Code a 4/12 pitch meets the minimum slope for asphalt shingles, clay & concrete tile, metal roof shingles, slate & slate-type shingles, wood shingles & shakes, standing-seam metal panels, lapped (exposed-fastener) metal panels and mineral-surfaced roll roofing. Always check the manufacturer's installation instructions and your local code.