NHBC Standards 2006

7.1 Flat roofs and balconies


7.1 - M1Materials standards

7.1 - M1
All materials shall:
(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 flat roofs and balconies.

Materials for flat roofs and balconies 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).

Appendix 7.1-A lists the materials suitable for:

  • weatherproofing, including flashings
  • structure and decking
  • thermal insulation
  • vapour control layers
  • preservative treatment.

Roofing felts to BS 747 are colour coded for identification. The codes are as follows:

  • felt Type 3 - red.
  • felt Type 5 - blue.

Appendix 7.1-B gives suitable surface treatments to the weatherproofing.

See the tables published by TRADA for sizes and spacings of structural timbers.

Structural softwood for internal use should be dry graded to BS 4978 and marked 'DRY' or 'KD'.

Joist hangers should be the correct size for the timber joists being supported and meet with BS EN 845.

Pre-drilled vertical holding down straps should be:

  • at least one metre long, and
  • 30mm x 2.5mm in cross section.

Restraint straps should have a minimum cross section of 30mm x 5mm. Straps which do not meet with this specification should be assessed in accordance with Technical Requirement R3.

All mild steel straps and fixings should be protected against corrosion in accordance with Tables 1 and 14 of BS 5628 : Part 3.

Materials should be in accordance with the following:

BS EN 501Specifications for fully supported roofing products of zinc sheet.
BS EN 504Specification for fully supported roofing products of copper sheet
BS EN 506Specification for self supporting products of copper or zinc sheet
BS 6915Design and construction of fully supported lead sheet roof and wall coverings

Proprietary roofing systems which do not meet with the specifications in Appendix 7.1-A should be assessed in accordance with Technical Requirement R3.