Suspended Ground Floors: Which System Is Right for Your Project?

A suspended ground floor sits above the ground on supports rather than directly bearing on a prepared sub-base. It is typically used when foundation depths are too great for a ground-bearing slab to be practical, or when underfloor heating requires a void beneath the floor for services.

Three systems are used in domestic construction. The choice between them is generally made by the builder and architect, not the structural engineer.

Option 1: Beam and Block

Beam and block is the most common suspended ground floor system in UK residential construction. Prestressed concrete beams span between the internal walls and external foundation walls, and concrete blocks are laid between them to form the floor surface. The void beneath is provided by the beam depth.

Who designs it? The beam and block manufacturer designs the layout, including the beam spans, spacings and any sleeper walls needed for intermediate support. You donot need your structural engineer to design this — you supply the plan to the manufacturer and they provide a layout drawing and a structural certificate.

Option 2: Proprietary Deck System

Various manufacturers (Jackodeck, Omnidec and others) offer proprietary permanent formwork or composite deck systems that perform a similar function to beam and block but in different formats. Some suit longer spans or unusual column arrangements.

Who designs it? Again, the supplier carries the design responsibility. You provide the plan and loading information; they provide a layout and technical approval. Your structural engineer does not need to specify or check this — their role ends at the supporting structure.

Option 3: Timber Joists

Timber joist suspended floors are an option, particularly in older building styles or where the builder has a preference. They require more detail design than beam and block because joist sizing depends on span, spacing, imposed loads and deflection limits.

Who designs it? If you want PorthouseDean to size the timber joists, this must be specifically requested as part of the brief — it is not included in a standard structural package. Where timber joists are specified, PorthouseDean provides span tables and member sizes. If no timber joist design is requested, the builder chooses their own floor system.

Important: Unusual Loads Need Engineer Input

Regardless of which floor system is used, the builder should contact their structural engineer before the floor system is finalised if:

– Significant point loads from posts or columns are coming down into the floor zone
– An unusual support arrangement is required (e.g. the floor must cantilever)
– The standard system does not work for the site geometry

In those cases, the structural engineer needs to check that the supporting structure can carry the loads from the chosen floor system.

Ready to Get Your Extension Designed?

PorthouseDean produces structural packages for domestic extensions including foundation and wall design. Get a quote to start your project.