Single tile vs double tile
Single tile is one layer of Mangalore tiles only — the tile underside and rafters are what you see from below, the simple traditional finish for patios, terraces and open sitouts. Double tile adds a second layer: a small designer (ceiling) tile fixed below the Mangalore tile, so the ceiling seen from inside is finished and decorative, and internal temperature is also reduced. Double tile is not two layers of Mangalore tile — the lower layer is a different, smaller tile.
How the count works
Roof area = roof width × slope length × faces. Tiles = roof area × tiles per m², then waste % added and rounded up. Top and ceiling tiles are counted separately in a double roof, because they are different tiles.
Worked example
Roof 10 m wide × 5 m slope, 1 face = 50 m², waste 5%. Single, 16 × 10 inch Mangalore at 14 / m²: 50 × 14 = 700, × 1.05 = 735 tiles. Double, same top tile plus 12 × 8 inch ceiling tile at 15.5 / m²: 50 × 15.5 = 775, × 1.05 = 814 ceiling tiles, total 735 + 814 = 1,549 tiles.
Tile sizes and rates
Top Mangalore tile rates (Affa Tiles catalogue, per sq ft, converted to per m²): 16 × 10 inch — 1.3 / sq ft (14.0 / m²); 12 × 8 — 2.0 (21.5); 11 × 7 — 2.4 (25.8); 9 × 6 — 4.0 (43.1); 8 × 5 — 5.0 (53.8). Ceiling tiles for a double-tiled roof: 12 × 8 — 1.44 / sq ft (15.5 / m²); 9 × 6 — 4.0 (43.1). Older Mangalore effective sizes 410 × 235, 420 × 250 and 425 × 260 mm are quoted at about 15 tiles / m² — if your tile differs, use the Custom rate.