Section 4 Roof covering

Roof covering

  1. Materials
    1. Re-covering of roofs

      Materials

      4.1 All materials used to cover roofs, excluding windows of glass in residential buildings with roof pitches of not less than 15°, shall be capable of safely withstanding the concentrated imposed loads upon roofs specified in BS EN 1991-1- 1:2002 with its UK National Annex. Transparent or translucent covering materials for roofs not accessible except for normal maintenance and repair are excluded from the requirement to carry the concentrated imposed load upon roofs if they are non-fragile or are otherwise suitably protected against collapse.

      Re-covering of roofs

      4.2 The re-covering of roofs is commonly undertaken to extend the useful life of buildings. Roof structures may be required to carry underdrawing or insulation provided at a time later than their initial construction. This section provides guidance on determining whether such work to a roof constitutes a material alteration under the Building Regulations. 4.3 Where the work involves a significant change in the applied loading the structural integrity of the roof structure and the supporting structure should be checked to ensure that upon completion of the work the building is not less compliant with Requirement A1 than the original building. 4.4 A significant change in roof loading is when the loading upon the roof is increased by more than 15%. 4.5 Where such checking of the existing roof structure indicates that the construction is unable to sustain any proposed increase in loading (e.g. due to overstressed members or unacceptable deflection leading to ponding), appropriate strengthening work or replacement of roofing members should be undertaken. This is classified as a material alteration. 4.6 In carrying out the checks mentioned in paragraph 4.3 an increase of stress in a structural member arising from increased loading does not necessarily indicate that the roof structure is less compliant than the original roof provided an adequate factor of safety is maintained. 4.7 Where work will significantly decrease the roof dead loading, the roof structure and its anchorage to the supporting structure should be checked to ensure that an adequate factor of safety is maintained against uplift of the roof under imposed wind loading.

      • 1 Size and proportion of residential buildings of not more than three storeys Diagram 1 Size and proportion of residential buildings of not more than three storeys
      • 2 Size and proportion of non-residential buildings and annexes Diagram 2 Size and proportion of non-residential buildings and annexes
      • 3 Determination of wall thickness Diagram 3 Determination of wall thickness
      • 4 Parapet walls - height Diagram 4 Parapet walls - height
      • 5 Maximum floor area enclosed by structural walls Diagram 5 Maximum floor area enclosed by structural walls
      • 6 Fig 1-2 - Map showing wind speeds in m per s for maximum height of buildings Diagram 6 Fig 1-2 - Map showing wind speeds in m per s for maximum height of buildings
      • 6 Fig 3 - Map showing wind speeds in m per s for maximum height of buildings Diagram 6 Fig 3 - Map showing wind speeds in m per s for maximum height of buildings
      • 7 Max height of buildings Diagram 7 Max height of buildings
      • 8 Measuring storey and wall heights Diagram 8 Measuring storey and wall heights
      • 9 Declared compressive strenght of masonry units Diagram 9 Declared compressive strength of masonry units
      • 10 Maximum span of floors Diagram 10 Maximum span of floors
      • 11 Differences in ground levels Diagram 11 Differences in ground levels
      • 12 Openings in a buttressing wall Diagram 12 Openings in a buttressing wall
      • 13 Buttressing Diagram 13 Buttressing
      • 14 Sizes of openings and recesses Diagram 14 Sizes of openings and recesses
      • 15 Lateral support by floors Diagram 15 Lateral support by floors
      • 16 Lateral support at roof level Diagram 16 Lateral support at roof level
      • 17 Size and location of openings Diagram 17 Size and location of openings
      • 18 Wall thinckness Diagram 18 Wall thinckness
      • 19 Lateral restraint at roof level Diagram 19 Lateral restraint at roof level
      • 20 Proportions for masonty chimneys Diagram 20 Proportions for masonry chimneys
      • 21 Elevation of stepped foundation Diagram 21 Elevation of stepped foundation
      • 22 Piers and chimneys Diagram 22 Piers and chimneys
      • 23 Foundation dimensions Diagram 23 Foundation dimensions
      • 24 Area at risk of collapse in the event of an accident Diagram 24 Area at risk of collapse in the event of an accident
      • Table 1 Areas at risk from house longhorn beetle Table 1 Areas at risk from house longhorn beetle
      • Table 2 Wall types considered in this section Table 2 Wall types considered in this section
      • Table 3 Minimum thickness of certain external walls, compartment Table 3 Minimum thickness of certain external walls, compartment
      • Table 4 Imposed loads Table 4 Imposed loads
      • Table 5 Cavity wall ties Table 5 Cavity wall ties
      • Table 6 Declared compressive strength of masonry units complying with BS EN 771-1 TO -5 [N PER nn SQ] Table 6 Declared compressive strength of masonry units complying with BS EN 771-1 TO -5 (N/mm SQ)
      • Table 7 Normalised compressive strength of masonry units of clay and calcium silicate blocks complying with BS EN 771-1 and 2 [Nn/mm SQ] Table 7 Normalised compressive strength of masonry units of clay and calcium silicate blocks complying with BS EN 771-1 and 2 (N/mm SQ)
      • Table 8 Value of Factor X - see Dia 14 Table 8 Value of Factor 'X' (see Dia 14)
      • Table 9 Lateral support for walls Table 9 Lateral support for walls
      • Table 10 Minimum width of strip footings Table 10 Minimum width of strip footings
      • Table 11 Building consequence Table 11 Building consequence