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  • Fixing battens in accordance with BS5534

    by | Dec 11, 2018

    In the second of a series of articles that examine how to comply with the revised BS5534 code of practice, we focus on the second task – fixing the battens.

    BS5534 is the code of practice for installing slates and tiles to new-build pitched roofs and vertical cladding. Although it’s not a legal requirement, a roof specified to the code of practice can be upheld by law, so you should refer to the complete BS 5534 document or seek advice from the manufacturer.

    All battens and counterbattens must conform to BS 5534:2014+A2:2018, which prescribes minimum sizes and tolerances, as shown in the table below. Using ungraded battens, which are not prescribed in the code of practice, pose a serious safety hazard as they may not be able to support the weight of the fully slated/tiled roof.

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    Table 3 – Minimum timber batten sizes (roofing and vertical work)

    Application

    Basic minimum size of battenA), B), C)

    Up to450mm spanD)

    451mm to600mm spanD)

    Width

    Depth

    Width

    Depth

    mm

    mm

    mm

    mm

    Slates (double-lap):

     

     

     

     

    natural: sized or random

    50

    25

    50

    25

    fibre-cement or concrete

    38

    25

    50

    25

    Clay and concrete tiles:

     

     

     

     

    double-lap

    38

    25

    38

    25

    single-lap

    38

    25

    50

    25

    A) Tolerances on the basic sizes of timber batten should be: width±3mm, depth mm, based on measurement at a reference moisture content of20% (seeAnnexD).

    B) These minimum sizes do not apply to battens used to support ridges, hips and valleys.

    C) Batten sizes for other slates, tiles and shingles such as timber shingles and shakes and metal tiles, or other proprietary roofing products, should be in accordance with the manufacturer’s recommendations.

    D) Span is defined as the distance between centres of supports, or the clear distance between the face of supports plus half the bearing length at each end support, whichever is the lesser. The end-bearing length should be not less than17.5mm.

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    Grading

    BS 5534 describes the allowable characteristics and defects such as knots and splits. For example:

    • Knots or knot holes of less than 5mm may be ignored, however other visible defects should be considered in conjunction with BS 5534 Fig D.1, and where K1 + K2 should not exceed the batten width.

    Only source factory-graded battens that have the appropriate markings, as follows:

    • Supplier identification
    • Origin (imported or British-grown, and/or species code)
    • ‘Graded BS5534’
    • Size

    This information should also be included in the documentation accompanying the delivery of battens to site.

    Fixing, cutting and jointing the battens

    Fixing

    Batten nails should always be of the approved type for the material used and sized to suit the application, with a diameter generally not less than 3.35mm. Battens should be continuous over no less than three supports and never be cantilevered or spliced between supports.

    Cutting

    Battens should not be cut at penetrations and terminations such as valleys without the provision of suitable support to the ends.

    Jointing

    Butt joints over intermediate supports should be staggered. When cut and joined on the rafter, the battens should have no more than:

    • one joint in four courses on the same rafter for gauges over 200mm
    • three joints in 12 courses for gauges below 200mm

    Battens at the verge

    Only expose the pre-treated ends of the batten at the verge or if cut, they must be treated with a suitable preservative, which should be dry before the timber is used. However, always check the preservative manufacturer’s guidance as the performance and durability of different types of underlay and insulation can be affected:

    • Solvent-based preservatives can cause bitumen-based and polymer-based underlays and polymer-based insulation materials to soften and swell
    • Water-based preservatives can reduce the resistance of some underlays to water penetration. This can also occur if dried timber treated with water-based preservatives is significantly re-wetted.

    Next month: Slates and Tiles

    This this series of articles, which cover underlay, battens; slates and tiles, mortar and fixings, will form the basis of a complete guidance document for NFRC members.

     

     

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