Mesh, spacers, chairs and tying
Mesh sheets for an area, with end and side laps, and weight (BS 4483)
- where
- sheets along the length
- length of area (m)
- end lap (mm)
- sheet length (m)
- sheets across the width
- width of area (m)
- side lap (mm)
- sheet width (m)
- total sheets
- total mass of mesh (kg)
- mesh mass per m² (kg/m²)
Explain this equation
Works out how many mesh sheets cover a rectangular area with laps at the end and side joints, and their weight. Use it for ordering mesh and planning the lift.
L and W are the length and width to be covered. SL and SW are the sheet sizes and le and ls the end and side laps. na and nb are the sheets needed along and across, N the total, q the mesh weight per m² and M the total mass.
After the first sheet, each extra sheet only adds its length less one lap, so the number of sheets is the area length less a lap divided by the sheet length less a lap, rounded up. The divisions by 1000 convert laps from mm to m. Weight is whole sheets bought times sheet area times q.
Sense check: a 10 × 5 m slab in A193 with 350 mm laps takes 9 sheets, about 313 kg. A standard 4.8 × 2.4 m A142 sheet weighs about 25.6 kg.
Watch out: lap lengths for structural slabs come from the designer, not a site rule.
Works out how many mesh sheets cover a rectangular slab or base with laps at the end and side joints, and the weight to order and lift.
Enter your values to see the result.
Good to know
BS 4483 A-meshes are square at 200 mm centres: A142 (6 mm wire) 2.22 kg/m², A193 (7 mm) 3.02, A252 (8 mm) 3.95, A393 (10 mm) 6.16 kg/m². B-meshes have main wires at 100 mm (B385 4.53, B503 5.93 kg/m²). The standard sheet is 4.8 × 2.4 m. Enter the area the mesh has to cover (the slab less the edge cover). Laps come from the designer; a common site rule for A-mesh is two wire spacings plus 50 mm, which is 450 mm. Flying-end meshes reduce lap build-up.
Common mistake
Dividing the slab area by 11.52 m², which ignores the laps and part sheets and leaves you short.
Limits
Rectangular areas with all sheets laid the same way. The mass counts whole sheets bought, including offcuts. Structural laps must follow the design (Eurocode 2 8.7.5).
Sources
- BS 4483:2005 Steel fabric for the reinforcement of concrete. Specification
- CR Steel, Steel calculator sheet (bar mass per metre, metres per tonne, 12 m bars per tonne; BS 4483 mesh masses: A142 2.22, A193 3.02, A252 3.95, A393 6.16 kg/m²)
- LABC Warranty, How to get it right: using reinforcement in your foundations (spacers at no more than 1 m centres; mesh lap rule of thumb two wire spacings + 50 mm; minimum covers)
- BS EN 1992-1-1:2004 Eurocode 2 (Table 3.1 fctm, fctk,0.05; 3.1.6 fctd; 4.4.1 cover; 8.4 anchorage, Eq. 8.2–8.6; 8.7 laps, Eq. 8.10–8.11)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Always work to the engineer’s drawings and bending schedules, BS 8666, BS EN 1992, BS EN 1090-2, BS 5531/the BCSA National Structural Steelwork Specification and manufacturers’ data. Lifting must be planned under LOLER by a competent person.