Advice & Reviews
December 4, 2018

The importance of roofing batten selection

Whether you’re building a new house or refurbishing an old one, installing the roof battens is an important step. Battens may be hidden by the roof covering, but their purpose is to provide a reliable anchor that tiles or slates can be fixed securely to.

Battens also play an important part in ensuring that a roof is installed to BS 5534 the British Standard that sets out the requirements for roofing battens, and it covers everything from the type and size of timber required, to spacing and fixings.

Simple guide explaining how to install roofing battens to BS 5534

 

Choose your battens:

Selecting the right batten for roofing is essential not only for compliance with BS 5534 but for overall safety on the roof.

JB Red from Marley is a high-quality roofing batten that is pre-graded and meets the performance requirements of BS 5534. JB Red battens are suitable for all roofing applications and are ideal for situations in which the batten may also be used as a foothold.

What the battens are made of is also important. The quality of the timber is essential for the overall strength of the batten. JB Red is made from FSC or PEFC-certified timber and manufactured to provide a consistent thickness of 25mm.

To comply with BS 5534, battens intended for roofing must be graded to the requirements set out by the standard. JB Red is made from kiln dried sideboards which helps ensure the overall quality and consistency of the roofing batten.

 

What to look for in graded battens

 

When checking the grade of other battens areas to check are:

  • Defects – should be cut out and any batten less than 1.2m long (or sufficient to span at least 3 supports) should be discarded)
  • Knot sizes – knots are allowed but they must not exceed certain sizes.
  • Knot position – a knot appearing on both sides of the batten, which does not appear on the face, is not deemed to be a permissible defect, if the knot on the other side is greater than 1/5 of the depth. A knot appearing on both sides of the batten and on the face is not deemed a permissible defect.
  • Distortion – battens need to be straight and there is now a tolerance on distortion. Battens cut from side boards are unlikely to distort, bow, spring or twist should each not be greater that 5mm, measured over a length of 1.2m at a reference moisture content of 20%.
  • Slope of grain – the deviation of the slope of grain from the longitudial axis should not exceed 1 in 6 on either axis.
  • Wane – wane which is found along the whole length of the batten is permissible (in these instances it is recommended the roofer turns the batten over and fixes the tile on the full face).
  • Rate of growth – there should be an average of not less than four annual growth rings per 25mm measured at each end.
  • Splits and fissures – end splits (through the pieces) that occur before fixing should be trimmed off. End splits or splits at intermediate supports that occur due to nailing should not be greater that 150mm long. Fissures (not through the piece should not exceed half the batten thickness or 300mm in length)

 

Dimension Tolerances Battens should meet the following tolerances: Width +/- 3mm Thickness +3mm/-0mm when measured at a reference moisture content of 20%.

Decay and Insect Attack Battens and counter-battens should be free from rot and live insect attack.

Sap stain Sap stain such as ‘blue stain’ is not deemed to be a structural defect and is therefore permitted.

Resin Pockets Resin pockets on either face of the batten are permitted provided that no resin pocket exceeds 70mm in length, or 6mm in width, or one-third of the batten thickness. Resin pockets on either side of a batten are permitted provided that no resin pocket exceeds 70mm I length, or 6mm in width, or 12mm in depth.

 

Installation guide to roofing battens

 

Check size and spacing of battens

Before installing the battens, be sure to check you have the size and spacing right, as these can have a direct influence on the weather tightness of the roof, as well the finished appearance.

The correct batten spacing is necessary because it corresponds to the gauge and head lap of the roof covering being installed. This is important because the correct gauge and head lap has a direct influence on a tiles resistance to withstand the ingress of rainwater through capillary – ensuring that the roof remains watertight. It is also important aesthetically, so that the tiles on the finished roof are equally spaced.

Battens should be fixed to rafters set at centres not more than 600 mm apart and should span at least 3 rafters. To ensure this, the battens should be at least 1.2 m long.

Not more than one in four battens should be joined over one truss for gauges over 200mm. Below 200mm there can be 3 consecutive joins in any twelve battens.

The best way to meet this is to use a spread of lengths so that joints can be staggered.

Battens should be nailed to the centre of the rafter and any joints should be directly over a rafter with the batten square cut, tightly butted and skewed nailed.

When set in mortar a cut batten end should be treated or the batten turned so that the treated end is in the mortar. With dry fix systems the batten cut end is deemed to be within the roof and does not require treating.. Relevant standards

  • BS 5534,The Code of Practice for Slating and Tiling
  • BS 8000-6, Workmanship on Building Sites, Code of Practice for slating and tiling of roofs and claddings
  • NFRC Technical Bulletin 33 Graded battens for slating and tiling

 

Fix battens into place

To secure the battens to the rafters, it is important that you choose the right nail.

According to BS 5534, the nails used to fix battens to rafters should usually have a diameter of at least 3.35mm. The nails should provide a minimum of 40mm penetration into the rafter, so a nail length of 65mm is generally recommended..

Start at the lower edge of the roof, nailing the batten into place at the centre of the rafter. Joints should be directly over rafters, with the batten square cut, tightly butted and skewed nails.

If a batten end is to be set in mortar, be sure an appropriate treatment has been applied; this is not required for dry-fix systems.

Find your local MKM stockist of roofing Battens here.