5.1 Substructure and ground bearing floors
MATERIALS STANDARDS
(a) meet the Technical Requirements
(b) take account of the design
Materials that comply with the design and the guidance below will be acceptable for substructure and ground bearing floors.
Materials for substructure and ground bearing floors should comply with all relevant standards, including those listed below. Where no standard exists, Technical Requirement R3 applies (see Chapter 1.1 'Introduction to the Standards and Technical Requirements' ).
References to British Standards and Codes of Practice include those made under the Construction Products Directive (89/106/EEC) and, in particular, appropriate European Technical Specifications approved by a European Committee for Standardisation (CEN).
MASONRY BELOW DPC
Recommendations for the design strength of bricks, masonry blocks and mortars are given in BS 5628.
BRICKWORK
Clay bricks should comply with BS EN 771, which classifies bricks by the durability designations shown below:
F2,S2 (Freeze/thaw resistant, Low active soluble salts)
F2,S1 (Freeze/thaw resistant, Normal active soluble salts)
F1,S2 (Moderately freeze/thaw resistant, Low active soluble salts)
F1,S1 (Moderately freeze/thaw resistant, Normal active soluble salts)
F0,S2 (Not freeze/thaw resistant, Low active soluble salts)
F0,S1 (Not freeze/thaw resistant, Normal active soluble salts)
Fletton or common bricks are usually of durability designations F1,S2 or F1,S1. If in doubt as to their suitability, bricks of F2,S2 or F2,S1 designation should be specified or the manufacturer consulted.
BLOCKWORK
Concrete blocks for use below dpc should comply with BS EN 771 and have:
- a density exceeding 1500kg/m3, or
- a compressive strength not less than 7.3N/mm2, or
- an assessment in accordance with Technical Requirement R3.
Proprietary blocks should comply with Technical Requirement R3.
SITE MIXED MORTAR
Items to be taken into account include:
(a) strength and composition
Mortar should comply with the design and should take account of the strength, type and location of the masonry.
(b) sulfate resistance
Where the ground, ground water or the masonry contains levels of sulfates likely to be harmful, the mortar should be made with sulfate-resisting cement to BS 4027.
PROPRIETARY MORTAR
Proprietary mortars and admixtures should comply with Clause M3 and should only be used strictly in accordance with the manufacturer's recommendations, taking into account the type of masonry unit and its location.
WALL TIES
Wall ties should comply with BS EN 845 or be assessed in accordance with Technical Requirement R3.
WALL INSULATION
Cavity insulation materials, super lightweight blocks, blocks with face bonded insulation and blocks with integral insulation should be either:
- used in accordance with an assessment which complies with Technical Requirement R3 or
- manufactured in accordance with a British Standard and used in accordance with a relevant Code of Practice.
In Northern Ireland and the Isle of Man, it is not permitted to fill cavities with pumped thermal insulants at the time of construction.
In Scotland, it is not permitted to fill the full width of the cavity with any thermal insulants at the time of construction.
Insulants specified and installed in accordance with the following British Standards will be acceptable in England and Wales only:
| BS 6232 | Thermal insulation of cavity walls by filling with blown man-made mineral fibre |
| BS 6676 | Thermal insulation of cavity walls using man-made mineral fibre batts (slabs). |
UF foam when permitted to BS 5617, and installed by a specialist company registered by BSI in accordance with BS 5618, will be acceptable in England and Wales only.
The thickness of materials should be as required by the design.
FILL
(a) be free from hazardous materials unless appropriate precautions are taken, and
(b) provide consistent support to ground bearing slabs
The appropriate precautions to be taken where hazardous materials are present
in fill, are detailed in Appendix 5.1-A.
The test requirements given in Appendix 5.1-A should be followed where necessary.
Fill containing expansive materials or chemicals is not acceptable for the support of ground bearing slabs.
Well graded, inert fill containing no hazardous materials, which passes a 150mm x 150mm screen in all directions, normally will be suitable as support for ground bearing floors.
DAMP-PROOF MEMBRANE
For solid floors, requirements vary with the location of the damp-proof membrane as shown in the following table.
| Selection of damp-proof membrane materials |
| Below the slab |
|
| In a sandwich construction |
|
| On the surface of the slab |
|
CONCRETE
For guidance on the specification and use of concrete, concrete additives and reinforcement, reference should be made to Chapter 2.1 'Concrete and its reinforcement' (each section).
TANKING MATERIALS
Tanking materials should be:
- asphalt to BS 6925 or BS 6577, or
- a proprietary system or product assessed in accordance with Technical Requirement R3.
Polyethylene sheet (such as 'Polythene' or 'Visqueen') is not acceptable for tanking.
FLOOR INSULATION
Thermal insulation materials for use below ground bearing slabs should have:
- appropriate density for the location
- low water absorption.
Insulation to be positioned below both the slab and dpm should be resistant to ground contaminants.
The following materials are acceptable for use as insulation:
- expanded polystyrene boards (grade EPS 70) to BS EN 13163
- a proprietary material assessed in accordance with Technical Requirement R3.
For details of floor insulation materials above ground floor slabs, reference should be made to Chapter 8.3 'Floor finishes' (Materials).
DAMP-PROOF COURSE MATERIALS
Acceptable materials for dpcs are:
- bitumen to BS 6398
- polyethylene to BS 6515 (except below copings and in parapets); polyethylene dpcs should be black and not less than 0.5mm thick
- a proprietary material assessed in accordance with Technical Requirement R3.
Dpcs and flexible cavity trays should be of the correct dimensions to suit the detailed design.
Brick dpcs should consist of two courses of engineering bricks, laid breaking joint and bedded and jointed in a 1 : ¼ : 3, cement : lime : sand, or equivalent, mortar. Brick dpcs are only suitable to resist the upward movement of moisture.
For complicated junctions, preformed cavity trays are recommended. Care may be needed to ensure the correct type and shape is ordered.
