A soffit is the underside of the eaves of a roof: the board or panel, usually horizontal, that closes the gap between the fascia and the external wall. Soffits are often ventilated to let air into the roof space and help prevent condensation.
The word is also used more widely in construction for the underside of any building element, such as a beam, slab, arch, stair or opening. For quantity surveyors this wider meaning matters in measurement. For example, formwork to the soffit of a suspended slab is measured separately from formwork to vertical faces, because it needs propping and costs more to erect and strike. On roofs, typical points to note include:
- soffits are usually measured as a linear item, stating the width and material
- uPVC soffit boards are now common in place of painted timber
- ventilation is often provided by vents in the soffit board or by over-fascia vents
Related terms: fascia, eaves, formwork.
