Soffit formwork

The support to the underside of in situ concrete, either a flat or an inclined slab, requires formwork to contain and mould the concrete to the desired shape. Often supported on foundations by means of falsework, the soffit formwork is an important part of temporary works. The supports can only be removed when the concrete has gained sufficient strength, so the assessment of concrete strength and the procedure and sequence for striking needs to be understood and approved before concreting.

The forming of the underside of concrete structures while the concrete gains strength utilises soffit formwork, either inclined or nominally level. Unlike vertical formwork (discussed in Chapter 23), the concrete has to have gained sufficient strength before the structure can support itself, allowing the formwork to be removed. Generally, in situ concreting on soffit formwork will have supporting falsework (see Chapter 22) to transfer the load to suitable foundations. In certain cases, such as permanent formwork or in the case of cantilever soffit formwork, supporting falsework may not be required and the loads are transferred directly to the permanent works.