Battens, furring and strapping

Frequently asked questions

Is a roofing batten the same as a furring strip?

No, and the difference is that one is graded structure and the other is packing. A British roofing batten carries the whole weight of the tiles or slates plus anybody walking on the roof, spans between rafters, and resists the uplift trying to pull the covering off — so it has a specified size, a strength grade, a knot and wane limit, and a preservative treatment, and substituting an ungraded strip of the same dimensions is a real reduction in the roof. A furring strip is normally doing none of that: it levels an uneven surface, holds a covering off the wall to create a drained cavity, or gives a fixing line. Both are thin strips of timber, and only one of them is a structural member.

What does the batten gauge mean, and why is it not simply the tile length?

The gauge is the distance from one batten to the next, and it is the tile length MINUS the lap, divided by however many courses cover a given tile. Each course has to overlap the one below by enough to keep water out, so the exposed part of a tile is always shorter than the tile — which is why a 265 mm tile at a 65 mm lap gives a gauge around 100 mm on a double-lap covering rather than anything resembling 265 mm. The lap itself depends on the roof pitch and on the exposure of the site, so the same tile on a shallower roof needs a bigger lap, a tighter gauge, more battens and more tiles. Taking the gauge from a table without checking the pitch it was written for is one of the ways a tile order comes out short.

Why would a roof have battens running in both directions?

Because the second set creates a drainage and ventilation path that the first set blocks. Where an underlay is laid over the rafters and the tile battens go straight onto it, each batten sits tight against the underlay and acts as a small dam: water running down the underlay is held at every batten line, and air cannot move up the slope. Counter-battens fixed along the rafters first, with the tile battens across them, lift the whole grid clear so water runs to the eaves and air passes behind the covering. It matters most on low pitches, on long slopes, and wherever the underlay is vapour-permeable and depends on that air movement to work. It also adds a full extra set of timber and a longer fixing to the material list, which is why it should be identified before pricing rather than discovered on site.