What is a roll batten?
A roll batten is the timber batten that, on a batten roll roof, runs down the fall over the decking and forms the joint between two metal bays. The bays are turned up against it on both sides; the metal roll cap goes over the top. The batten is therefore not a decorative moulding but a working component: it sets the height of the joint, the position of the fixings, and with that, how well the roof keeps water out. In Dutch it is called a roeflat.
Shape and size
Roll battens come in two basic sections:
- Rectangular — the simplest form, with a straight upstand on each side.
- Trapezoidal — slightly wider at the top. This is the classic form: the undercut flanks let the roll cap grip over it, so the joint holds itself closed.
The height determines how deep water can stand before it creeps over the joint; the shallower the roof, the more important a sufficiently tall batten. The centres between battens set the bay width of the metal and are usually around 500 to 600 mm.
Timber choice and fixing
- Use dry, durable timber. A roll batten sits sealed under metal for decades; wet or shrinkage-prone timber leads to a loose cap later.
- Mind the preservative. Some wood preservatives, and the natural extractives of oak and larch, are acidic and attack zinc. Use timber and treatments approved by the metal supplier, or separate timber and metal with a suitable interlayer.
- Set the battens straight and true. Every bump in the batten will telegraph through the metal; the roof is only as flat as its substrate.
- Fix into the decking, not only the rafters. The clips that hold the bays are screwed into the decking beside the batten.
- Plan the ventilation. A continuous ventilated void belongs under the decking, or the metal corrodes from underneath.
Related terms
- Roll cap
- Batten roll roof
- Zinc
- Roof boarding
- Batten
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