7.5° Roof Pitch
A 7.5° roof rises 132 mm for every metre of horizontal run, which is 1.58 in 12 in imperial terms (closest standard pitch 1.5/12). Its roof area multiplier is 1.009, so every square metre of plan area becomes 1.009 m² of roof surface.
Rafter length for a 7.5° pitch
Multiply the horizontal run by 1.009. Add the overhang (horizontal overhang × 1.009) and deduct half the ridge board thickness.
| Building span | Run (½ span) | Common rafter | Ridge rise |
|---|---|---|---|
| 4 m | 2 m | 2.02 m | 0.26 m |
| 6 m | 3 m | 3.03 m | 0.39 m |
| 8 m | 4 m | 4.03 m | 0.53 m |
| 10 m | 5 m | 5.04 m | 0.66 m |
| 12 m | 6 m | 6.05 m | 0.79 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.
| Building span | Run (½ span) | Common rafter | Ridge rise |
|---|---|---|---|
| 12 ft | 6 ft | 6 ft 0½ in | 0 ft 9½ in |
| 16 ft | 8 ft | 8 ft 0¾ in | 1 ft 0¾ in |
| 20 ft | 10 ft | 10 ft 1 in | 1 ft 3¾ in |
| 24 ft | 12 ft | 12 ft 1¼ in | 1 ft 7 in |
| 28 ft | 14 ft | 14 ft 1½ in | 1 ft 10 in |
| 32 ft | 16 ft | 16 ft 1¾ in | 2 ft 1¼ in |
| 36 ft | 18 ft | 18 ft 1¾ in | 2 ft 4½ in |
| 40 ft | 20 ft | 20 ft 2 in | 2 ft 7½ 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.
Roof area at 7.5°
Roof surface area = plan area × 1.009. Use the roof calculator for multi-section roofs, waste and material costs.
| Plan area | Roof surface | With 10% waste |
|---|---|---|
| 80 m² | 80.7 m² | 88.8 m² |
| 100 m² | 100.9 m² | 110.9 m² |
| 150 m² | 151.3 m² | 166.4 m² |
| 200 m² | 201.7 m² | 221.9 m² |
| 250 m² | 252.2 m² | 277.4 m² |
Plan area is the footprint measured to the outside of the eaves. Multiply by 1.009 for the sloped surface.
| Plan area | Roof surface | Squares (+10%) | Shingle bundles |
|---|---|---|---|
| 1,000 sq ft | 1,009 sq ft | 11.1 | 34 |
| 1,500 sq ft | 1,513 sq ft | 16.6 | 50 |
| 2,000 sq ft | 2,017 sq ft | 22.2 | 67 |
| 2,500 sq ft | 2,522 sq ft | 27.7 | 84 |
| 3,000 sq ft | 3,026 sq ft | 33.3 | 100 |
Plan area includes eave overhangs. Bundles assume 3 bundles per square (100 sq ft) with 10% waste; hips, valleys and dormers need more.
Roofing materials for a 7.5° 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 | Below 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) | Meets the typical 0.7° minimum | Designed for a finished fall of about 1:80 (0.7°) or more. |
Roofing materials for a 7.5° 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 | Below the 2/12 minimum | IRC R905.2.2 |
| Clay & concrete tile | Below the 2½/12 minimum | IRC R905.3.2 |
| Metal roof shingles | Below the 3/12 minimum | IRC R905.4.2 |
| Slate & slate-type shingles | Below the 4/12 minimum | IRC R905.6.2 |
| Wood shingles & shakes | Below 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 | Allowed — only with applied lap sealant below 3/12 | IRC R905.10.2 |
| Mineral-surfaced roll roofing | Meets the 1/12 minimum | IRC R905.5.2 |
| Membranes (TPO, EPDM, modified bitumen, built-up) | Meets the ¼/12 minimum | IRC R905.9–R905.13 |
Is a 7.5° roof steep?
Low-slope roofs drain slowly, so most shingles and tiles are excluded or need extra underlayment. Membranes, standing-seam metal and roll roofing are the usual choices.
A 7.5° roof is walkable for most people in dry conditions with soft-soled footwear.
7.5° roof pitch FAQ
What is a 7.5 degree roof pitch as a ratio?
7.5° is a rise of 1.58 in 12, closest to a standard 1.5/12 pitch. In metric that is 132 mm of rise per metre of run, or a slope of 13.2%.
How long is a rafter on a 7.5° roof?
Divide the horizontal run by cos 7.5°, which is the same as multiplying it by 1.009. On an 8 m wide building with a gable roof (4 m run), the rafter is 4.03 m before the eaves overhang.
How high is the ridge on a 7.5° roof?
Ridge height above the wall plate is the run × tan 7.5° (0.132). For an 8 m span (4 m run) that is 0.53 m.
Which roofing materials suit a 7.5° pitch?
7.5° meets the typical minimum for concealed-fix steel deck, trapezoidal steel sheet, corrugated steel sheet and flat-roof membranes. It is below the usual minimum for interlocking concrete or terracotta tiles, natural slate and plain tiles. Minimums vary by product, sheet thickness, rafter length and exposure, so confirm with the manufacturer and local regulations.
Can you walk on a 7.5° roof?
A 7.5° roof is walkable for most people in dry conditions with soft-soled footwear.