The choice of ground floor system affects programme, insulation strategy, cost and long-term durability. Three options dominate UK domestic construction: beam and block (B&B), ground-bearing concrete slab, and suspended timber. Each has a distinct set of applications and constraints. Getting the choice right at design stage saves significant remedial cost later.
What Each System Is
Beam and block (B&B): prestressed concrete T-beams at 225 mm centres (standard module) span between the foundation walls. Standard infill blocks (typically 100 mm dense concrete or lightweight aggregate) drop between the beams. A 50–65 mm structural screed (or 60 mm structural floor-grade concrete) is poured over the top to create a composite floor slab. The whole system is suspended above ground level — so it is tolerant of variable ground conditions, tree roots and poor fill.
Ground-bearing concrete slab (solid slab): a reinforced or unreinforced slab cast directly on a compacted hardcore bed (well-graded crushed stone or MOT Type 1), DPM (damp-proof membrane), and insulation. The slab bears on the ground beneath it, so it requires ground that is competent, not subject to tree root heave, and free of made ground or significant fill. A standard domestic slab is typically 100–150 mm concrete (C25/P design mix), often with A142 mesh reinforcement.
Suspended timber: traditionally used in pre-1919 housing, suspended timber involves floor joists (47 × 100 mm to 47 × 175 mm) spanning between sleeper walls built off the strip foundation. Still used in heritage-sensitive projects and where site levels make a solid floor impractical.
Beam and Block: How It Works
Standard B&B uses T-beams at 225 mm (standard) centres, giving a clear infill space of approximately 160–175 mm depending on beam flange width. Infill blocks are available in:
- Dense aggregate (7.3 N/mm²): standard option, suitable for most loads
- Lightweight aggregate (Lytag-type): reduces weight and improves acoustic performance
- Insulated infill block (EPS core): reduces cold bridging through the floor system
The screed topping ties the system together and provides the working floor surface. In many new builds, underfloor heating (UFH) pipes are clipped into the screed layer.
Beam and block is delivered to site as flat panels (beams) and loose infill blocks. The crew lifts beams by hand or with a telehandler (for long spans), drops in blocks, then screeds. Weather protection is not critical — the system is inherently robust to rain during installation.
Ground-Bearing Slab: How It Works
A ground-bearing slab is simpler in concept but demands good ground preparation:
- Strip topsoil to undisturbed ground or engineered fill
- Lay 150–300 mm well-compacted hardcore (Type 1 MOT or clean crushed stone)
- Lay DPM (1200 gauge polythene minimum, lapped and taped at joints) to BS 8102:2022
- Lay rigid insulation (EPS 150, XPS, or PIR) — see below
- Pour and level the concrete slab (C25 minimum, typically 100–150 mm)
- Cure and then lay floor finish as required
For tree-affected sites, a ground-bearing slab over engineered fill must account for heave — the slab may need to be thickened and reinforced, or replaced with a suspended system entirely.
Cost per m²
| Floor system | Supply & install (exc. screeds, finishes) | Notes |
|---|---|---|
| Ground-bearing concrete slab | £30–£50/m² | Includes hardcore, DPM, insulation, 150 mm C25 slab |
| Beam and block | £35–£55/m² | Includes beams, infill blocks, edge details; excludes screed |
| Screed (if separate) | £12–£22/m² | Sand:cement screed 65–75 mm; liquid screed similar |
| Suspended timber | £40–£65/m² | Includes sleeper walls, DPC, joists, decking |
| Beam and block + screed (total) | £47–£77/m² | Most common new-build ground floor package |
Prices are 2026 UK averages, ex-VAT. London and South East rates typically sit at the upper end; Scotland and Wales at the lower end.
Insulation Requirements
Under Building Regulations Part L 2021 (England), ground floors must achieve a U-value of ≤0.25 W/m²K. In practice, most specifications target 0.13–0.18 W/m²K to meet the full Building Emissions Rate (BER) for new dwellings, and to achieve SAP compliance.
| Floor type | Common insulation approach | Thickness for ≤0.18 W/m²K |
|---|---|---|
| Ground-bearing slab | PIR board under slab, or EPS 200 over slab | 80–100 mm PIR (λ 0.022); 150 mm EPS (λ 0.036) |
| Beam and block | Insulated infill block + PIR over | 75 mm insulated infill + 50 mm PIR over |
| Beam and block (alternative) | Full PIR/EPS board over screed | 100–120 mm PIR or 150 mm EPS |
| Suspended timber | Mineral wool or rigid board between joists | 150 mm mineral wool (λ 0.033–0.035) |
Insulation continuity at floor perimeter is critical. Cold bridging at the edge of a ground-bearing slab (where the slab meets the cavity wall foundation) is a common compliance failure. Perimeter upstand insulation (50–75 mm EPS or PIR) should be installed to prevent edge losses.
Where Each System Suits
| Condition | Recommended system |
|---|---|
| Competent ground, no trees nearby, level site | Ground-bearing slab (cost-effective, simple) |
| Made ground, fill, trees nearby, variable subsoil | Beam and block (suspended, tolerant) |
| Ground heave risk (clay, trees) | Beam and block or structural slab on piles |
| Split-level or sloping sites | Beam and block (accommodates level change) |
| Heritage/conservation project (pre-1919) | Suspended timber (reversible, breathable) |
| UFH as primary heat source | Ground-bearing slab or B&B + screed (high thermal mass) |
| Quick programme (fewer wet trades) | Beam and block (no large pour; screeded later) |
| Radon-affected areas | Ground-bearing slab + radon membrane + sump (or B&B with ventilated void) |
Radon and Damp
All ground floor systems must incorporate a DPM continuous with the wall DPC to satisfy Building Regulations Part C (site preparation and resistance to contaminants and moisture).
In high-radon areas (Parts of Cornwall, Devon, Northamptonshire, Derbyshire and others), Part C and Public Health England guidance require:
- A radon-resistant DPM (typically 1500 gauge polythene or purpose-made radon barrier)
- Radon sump provision (sealed sump with upstand for future fan connection)
- Beam and block floors have a natural advantage here: the void beneath can be mechanically ventilated
Check the UKHSA radon map (ukhsa.gov.uk) at design stage for any new-build site.
Building Regulations
Ground floor systems are governed primarily by:
- Part A (Structure): beam sizing, slab reinforcement and bearing design
- Part C (Resilience): DPM, radon barriers, subsoil drainage
- Part L (Conservation of fuel and power): U-value targets and SAP compliance
The beam and block system is typically confirmed by the beam manufacturer’s standard span tables (certified per BS EN 15037-1). Ground-bearing slabs are designed to BS 8500-1 (specifying concrete) and Eurocode 2 (BS EN 1992-1-1) for reinforced slabs, though most domestic slabs rely on standard recipes from NHBC Standards Chapter 4.2.
Always confirm the ground floor specification with your structural engineer before tendering — the difference in total floor thickness between systems has knock-on effects on finished floor levels, door thresholds, external steps and drainage connection heights.
