NHBC Standards 2006

5.2 Suspended ground floors

SITEWORK STANDARDS

5.2 - S1Sitework standard
5.2 - S2-S3Ventilation and damp-proofing
5.2 - S4Construction of floors
5.2 - S5Thermal insulation
5.2 - S6Floor finishes
5.2 - S7-S8Floor decking: General
5.2 - S9Softwood boarding
5.2 - S10Chipboard flooring
5.2 - S11Oriented strand board flooring
5.2 - S12-S13Other floor decking

5.2 - S1
All sitework shall:
(a) meet the Technical Requirements
(b) take account of the design
(c) follow established good practice and workmanship
 

Sitework that complies with the design and the guidance below will be acceptable for suspended ground floors.

VENTILATION AND DAMP-PROOFING

5.2 - S2
Construction of suspended ground floors shall ensure adequate damp-proofing
 

Masonry supporting suspended ground floors should have been damp-proofed using dpm, dpc or tanking in accordance with the guidance given in the following Chapters:
5.1 'Substructure and ground bearing floors' (each section)
6.1 'External masonry walls' (each section).

Where proprietary floor systems are used, moisture-resistant membranes, etc should be installed in accordance with the manufacturer's recommendations.

5.2 - S3
Construction of suspended ground floors shall ensure adequate ventilation
 

Ventilation should be provided in accordance with the design. This is normally provided by ventilators on at least two opposite external walls.

Air bricks in cavity walls should be properly ducted as detailed in  Chapter 6.1 'External masonry walls' (Design and Sitework).

Sleeper walls should be constructed with sufficient openings to ensure adequate through ventilation. Where underfloor voids adjoin ground bearing floors, ventilation ducts should be installed.

Ventilation should not be obtained through a garage.

CONSTRUCTION OF FLOORS

5.2 - S4
Construction of suspended floors shall ensure that they safely support the intended loads and are reasonably level
 

Items to be taken into account include:

(a) in-situ concrete floors

Concreting should be carried out in accordance with:

(b) precast concrete floors

All sitework for precast concrete floors should be carried out in accordance with the manufacturer's recommendations.

Care should be taken to ensure that dpcs are not damaged or displaced.

(c) timber floors

All sitework for timber floors should be carried out in accordance with the relevant parts of Chapter 6.4 'Timber and concrete upper floors' (Sitework).

THERMAL INSULATION

5.2 - S5
Thermal insulation shall be installed to minimise thermal transmission through the floor
 

The BRE report 'Thermal insulation: avoiding risks' discusses aspects of insulation relevant to suspended ground floors. In England and Wales account should be taken of Robust Details.

Items to be taken into account include:

(a) floor insulation methods

TIMBER FLOORS

Insulation quilts should be supported, eg by draping plastic mesh across the joists and stapling it to joist sides so that the quilt can be laid to the full thickness. Insulation draped over the joists is not acceptable.

Mesh supporting insulation quilt

Rigid insulation boards should be supported on battens or fillets nailed to the sides of joists.

CONCRETE FLOORS

For guidance on insulating concrete floors, reference should be made to Chapter 8.3 'Floor finishes' (each section).

(b) cold bridging

The design should be followed to ensure that any risk of cold bridging is minimised. Pay particular attention to junctions between floor and external walls.

FLOOR FINISHES

5.2 - S6
Finishes to concrete suspended ground floors shall be protected, where necessary, against damp, condensation or spillage
 

For guidance, reference should be made to Chapter 8.3 'Floor finishes' (Design and Sitework).

FLOOR DECKING : GENERAL

5.2 - S7
Flooring shall be fixed only when the dwelling is substantially weathertight
 

For guidance, reference should be made to Chapter 6.4 'Timber and concrete upper floors' (Sitework).

5.2 - S8
Completed floor decking shall not be overloaded and shall be protected against damage
 

For guidance, reference should be made to Chapter 6.4 'Timber and concrete upper floors' (Sitework).

Care should be taken to prevent trapping any water spillage below timber floors.

SOFTWOOD BOARDING

5.2 - S9
Softwood boarding shall be securely fixed
 

For guidance, reference should be made to Chapter 6.4 'Timber and concrete upper floors' (Design and Sitework).

CHIPBOARD FLOORING

5.2 - S10
Chipboard flooring shall be of the type and thickness specified and shall be fixed securely
 

For guidance, reference should be made to Chapter 6.4 'Timber and concrete upper floors' (each section).

ORIENTED STRAND BOARD FLOORING

5.2 - S11
Oriented strand board flooring shall be of the type and thickness specified and shall be fixed securely
 

For guidance, reference should be made to Chapter 6.4 'Timber and concrete upper floors' (each section).

OTHER FLOOR DECKING

5.2 - S12
Plywood decking shall be fixed securely
 

For guidance, reference should be made to Chapter 6.4 'Timber and concrete upper floors' (Design and Sitework).

5.2 - S13
Proprietary materials shall be fixed in accordance with manufacturers' recommendations
 

Other floor decking should have been assessed in accordance with Technical Requirement R3 and should be installed in accordance with manufacturers' recommendations.