Page 5 - roofing

PITCHED ROOF

ROOFING BATTENS

UNDERLAYS Roofing battens must meet the recommendations
stated in BS 5534 in terms of their species,
permissible characteristics and defects
(knots, fissures and splits, wane, slope of
grain, rate of growth, distortion, decay
and insect attack, sap stain, resin pockets
and moisture content), including minimum
dimensions and grading requirements.
All documentation with a roofing
batten delivery must include:
• Name of supplier (the company that

graded the roofing battens NOT
the company that cut them)
• Origin
• Graded in accordance with BS 5534
• Basic size
• Type of preservative (if applicable) Counter
battens need not be marked or graded
where they are fully supported by the
rafters, but this should be considered if
counter battens are being used to create
a ventilation gap for moisture purposes.

A new test method in BS 5534 establishes the RECOMMENDED MINIMUM TIMBER BATTEN
resistance to wind uplift of the underlay. Stricter SIZES (ROOFING AND VERTICAL WORK)
recommendations for the securement of the laps
of the underlay and a new labelling system has Basic Minimum up Size of Battens 451
been introduced, to assist with the specification to 450mm Span* to 600mm Span*
of underlays in five UK geographical wind zones
for single-lap and double-lap tiles, and doublelap Application
slates. Only underlays suitably labelled and
meeting the new standard should be installed and Width Depth Width Depth
laps should be covered by a batten or secured (mm) (mm) (mm) (mm)
by a proprietary sealant tape and laid with a
nominal 10mm drape to allow a drainage path Natural: Slates (Double-Lap) 25
for moisture and prevent excessive deflection sized or 50 25 50
under wind load. A batten tape or sealant should random
be used where the underlay is not self-sealing
to prevent water ingress at fixing points. Fibrecement 38 25 50 25
or concrete
MORTAR
Clay and Concrete Tiles
Mortar is now deemed to have no tensile strength,
so any tensile bond strength offered by the Double-Lap 38 25 38 25
mortar bedding of concrete or clay ridge and
ridged hip tiles, verge and valley tiles should be Single-Lap 38 25 50 25
supplemented by mechanical fixings to secure
them to the roof structure where the wind uplift
load exceeds the dead load resistance. Heritage
solutions where lime mortar is often used is
excluded from the scope of the standard.

ROOFING – ISSUE 1 5