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Structure and support

Floor Structure and Build-Up Systems

A floor is rarely one thing. There is an element that spans, whatever fills between the spanning members, and a topping or finish zone laid over both — and the useful difference between two floors is usually which of those three is doing the work. A ground-bearing slab has no span at all; a beam-and-block floor separates spanning from infill; a floating screed is a topping deliberately isolated from everything beneath it.

Floor coverings, their adhesives, underlays and thresholds are not described here, and neither is the frame the deck is carried on. Where a floor exists to separate one dwelling or tenancy from another rather than one room from the next, it is discussed under acoustic separation. Spans, imposed loading, deflection and screed specification are design matters for qualified professionals working on the real building.

7 system entries · educational assemblies reference · how a system performs always depends on the whole building and qualified professional design

Scope

What this category covers

Where the boundary of this part of the encyclopedia sits, including what it deliberately leaves to qualified professionals.

  • Ground floors bearing directly on prepared ground or suspended over a ventilated void
  • Spanning upper-floor decks in timber, steel and concrete, with their infill elements
  • Toppings, screeds and isolated build-ups laid over a completed structural deck
  • Not covered: spans, imposed loading, deflection limits, or screed and heating layout

All entries

Every floor structures entry

The complete set for this category. Frequently referenced entries come first — a starting point, not a ranking.

Ground-Bearing Slab →A ground floor built directly off prepared ground, combining sub-base, barrier, thermal and slab layers in an order the design settles, with the slab carrying only floor loading.Timber Joisted Upper Floor →An intermediate floor of timber or engineered joists spanning between walls or beams, decked above and lined below, with services routed in the depth between.Beam and Block Floor →A suspended floor of precast concrete beams with blocks infilled between them, completed with a grout or topping so beams, infill and topping act as one deck.Suspended Timber Ground Floor →A ground floor of timber joists carried on perimeter and sleeper supports over a cross-ventilated void, so the deck is separated from the ground rather than resting on it.Composite Metal Deck Floor →A floor where profiled steel decking spans between beams and then works together with the concrete cast onto it, so sheet and topping behave as one element.Precast Plank Floor →A floor of factory-made concrete units laid side by side between supports, their joints grouted and tied so the units act together as one structural plate.Floating Screed Build-Up →A screed laid on a resilient or insulating layer instead of bonded to the base, isolated at its edges so it moves independently of the structure and the walls.

Elsewhere on Build Design Hub

Planning guidance for this subject

This encyclopedia explains how these assemblies are organised. These sections help with choosing between them and preparing for the conversation.

Joist and floor loading questions →Preparation before a conversation about floor loading.Subfloor condition questions →What to establish about the base before a floor is specified.Floor insulation planning →How insulation within a floor build-up is planned.

Materials Library

What these assemblies are built from

A systems entry explains how an assembly is organised. These materials sections describe the substances themselves — what they are, how they behave and what governs their use.

Concrete & Cement →Reference entries for cement-based materials — ready-mixed and precast concrete, screeds, levelling compounds, renders of the cementitious family and the admixtures that modify them.Timber & Wood →Reference entries for solid timber and wood-based panels and engineered products — from structural softwood and plywood to cross-laminated timber, OSB, MDF and veneers.Flooring Materials →Reference entries for floor coverings and floor surface systems — wood and engineered wood, laminate, vinyl and LVT, linoleum, rubber, cork, bamboo, carpet, terrazzo and resin.

Building Systems Encyclopedia

Reference entries for building assemblies — how each is organised, what role every component plays, how the parts interact and which junctions matter.

Browse all building systems →