The intermediate floor, and the strongest quantified argument the system makes for mid-rise. At 159 kg/m² against a traditional equivalent of 513 kg/m², it removes roughly 350 kg from every square metre of floor plate. On a 5,000 m² four-storey building that is about 1,750 tonnes of dead load that the foundations never have to carry.
D.07
Intermediate floor
Forjado intermedio
528 mm
Total thickness · Revision 01 · 2026-08
D.07
Intermediate floor
SCALE 1:10
Dashed layers sit inside the joist depth, not in addition to it. Keyboard navigable with the arrow keys; the same data is published as a table in the layer schedule below.
Photographs
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Layer schedule
| Layer | Material | Thickness | λ | Function |
|---|---|---|---|---|
| 1 Ceramic floor tiling | Ceramic floor tile | 15 mm | — | Floor finish |
| 2 Tile adhesive | Cement-based tile adhesive | 5 mm | — | Bonds the floor finish |
| 3 Lightweight concrete | Lightweight concrete | 145 mm | — | Floor diaphragm and mass Measured over the steel deck, layer 4: its 50 mm ribs are cast into this 145 mm rather than adding to it. |
| 4 Trapezoidal steel deck within layer 3 | Trapezoidal profiled steel sheet | 1 mm | — | Composite deck and permanent formwork for the concrete, resting on the OSB Trapezoidal ribs 50 mm high with 70 mm between them, from the section sketch supplied by the client on 2026-09-15; 1 mm is the sheet. The width of each rib is drawn as that sketch shows it, not dimensioned. |
| 5 OSB board | Oriented strand board | 15 mm | — | Structural decking |
| 6 Void within the joist depth within joist depth | Air | 200 mm | — | Services zone Approximately 200 mm: the 300 mm joist depth less the 100 mm of glass wool. |
| 7 Glass wool within joist depth | Glass mineral wool | 100 mm | — | Acoustic absorption |
| 8 Steel lattice joist | Prefabricated cold-formed steel lattice joist | 300 mm | — | Structure — the joist depth contains layers 6 and 7 |
| 9 Ceiling void | Air | 20 mm | — | Ceiling void Drawn as 20 to 30 mm. The 528 mm total is taken at 20 mm. |
| 10 Knauf ceiling channel | Steel ceiling suspension channel | 15 mm | — | Carries the ceiling |
| 11 Pladur plasterboard ceiling | Gypsum board | 13 mm | — | Ceiling finish |
| Total | 528 mm |
An em dash means the source document does not state that value; it is not a zero. Layers within the joist depth are indented — they sit inside the joist, so the column does not sum to the total.
Calculated performance
| Property | Value | Basis |
|---|---|---|
| U-value, bridging corrected | 0.26 W/m²K | EN ISO 6946, one-dimensional steady state, with a +15% bridging correction for horizontal elements, applied as an engineering estimate. |
| Self-weight | 159 kg/m² | Mass estimate from the layers and dimensions in the source document. |
| Traditional equivalent | 513 kg/m² | Derived from the published self-weight and reduction percentage. |
| Weight reduction | −69% | Self-weight against the traditional equivalent build-up. |
| Fire resistance (EI) | Test programme in progress — contact technical department | Awaiting laboratory test report |
| Airborne sound reduction (R_A) | Test programme in progress — contact technical department | Awaiting laboratory test report |
| Impact sound (L_nw) | Test programme in progress — contact technical department | Awaiting laboratory test report |
| Structural span | Test programme in progress — contact technical departmentSpan selection tables in preparation | Awaiting laboratory test report |
U-values are one-dimensional steady-state calculations to EN ISO 6946. Bridging correction is applied as an engineering estimate: +20% for walls, +15% for horizontal elements. 2D numerical analysis to EN ISO 10211 is in progress; values will be updated on completion.
Not yet stated
- EIFire resistance · in test
- R_AAirborne sound reduction · in test
- L_nwImpact sound · in test
- spanStructural span · in test
Test programme in progress — contact technical department
Weight against traditional
| Element | Solid System | Traditional | Reduction |
|---|---|---|---|
| D.07 Intermediate floor | 159 kg/m² | 513 kg/m² | −69% |
Where to use it
- Intermediate floors in residential and hotel buildings
- Mid-rise floor plates where foundation load governs
Design notes
- Cold-formed steel joists are available in 250, 300, 350 and 400 mm depths.
- The external INSULTERM 600 of the façade must be continuous across the floor junction. A break here forfeits most of the thermal advantage of D.02.
- Span selection tables are in preparation. Joist depth must not be selected from the depth range alone.