An H20 beam is a timber I-beam 200 mm high with 80 mm flanges, weighing about 5 kg per metre. Typical H20 beams to EN 13377 have a permitted bending moment of about 5 kNm and shear of about 11 kN. In slab formwork, secondary beams are commonly set around 0.5 m apart under 18–21 mm plywood, but spacing must come from the formwork design.
What is an H20 beam?
An H20 beam is a lightweight timber I-beam used as the horizontal member in formwork. Two solid timber flanges are glued to a web (solid timber or board), giving a stiff beam that one or two people can carry. "H20" means it is 200 mm high.
Dimensions and weight
| Property | Typical value |
|---|---|
| Height | 200 mm |
| Flange width × thickness | 80 × 40 mm |
| Weight | about 5 kg per metre |
| Permitted bending moment | about 5 kNm |
| Permitted shear force | about 11 kN |
| Standard | EN 13377 (prefabricated timber formwork beams) |
Typical published values. Always use the datasheet of the actual beam for design.
How H20 beams are used in slab formwork
- Props (shoring) stand on the floor below.
- Primary beams sit in the prop heads.
- Secondary beams sit across the primaries, closer together.
- Film faced plywood is laid on the secondaries as the formwork face.
Typical spacing
Secondary beams are commonly set around 0.5 m apart under 18–21 mm plywood for normal slab thicknesses. Primary beam and prop spacing depend on slab thickness and the formwork system, and are taken from the system supplier’s tables or the temporary works design. Thicker slabs need closer spacing.
Ordering tips
- Choose lengths that suit your bays: see H20 beam sizes and lengths.
- Order 5–10% spare for damage and odd bays.
- Order the film faced plywood in the same delivery.