Does a New Roof Need New Battens?

What battens do

Every pitched tile or slate roof has the same build-up. Rafters run from the ridge to the eaves, a waterproof layer called underlay lies over them, and battens are nailed through it into the rafters. The tiles hook over the battens and are held by gravity, clips and nails. If a batten fails, the tiles it carries slip or lift. Wind loads on the roof pass through the battens into the rafters, so they are structural, not decorative.

Battens are cut from treated softwood to a stated grade and size, set by the covering and the rafter spacing. The standard that sets out how roof coverings should be fixed, BS 5534, also governs how battens are specified and fixed. A tile or slate maker will state the batten size and the gauge, which is the distance between battens measured up the slope.

How old battens fail

After decades under tiles, battens suffer in several ways. Water that has run under slipped tiles soaks them and starts a rot, particularly around valleys, chimneys and eaves. Timber dries and becomes brittle in the roof's heat. Nails rust and the timber around each nail hole splits, a condition called nail sickness. Nail heads that once pulled through the underlay now hold nothing. A batten can look sound from the top and crumble in the hand when lifted.

Old battens often carry the marks of earlier work too: patched sections, mismatched thicknesses, and nail holes from a previous covering. Each hole is a place where a new nail has less to bite into. Put new tiles on that, and the first storm tests it.

The gauge changes with the covering

A change of covering means a change of gauge. Plain tiles, interlocking concrete tiles and slates are all laid to different spacings, and even two kinds of concrete tile can differ. Old battens are fixed where the old covering needed them, so they will almost never line up for the new one. Counter battens, which are battens laid up the slope over the rafters to create a ventilated gap above a breathable membrane, are another case where new timber is needed. Our page on choosing materials for a new roof explains how the covering sets the rest.

Even a like-for-like swap of the same tile is affected, because a new batten gives a fresh surface for the nails and lets the roofer check the gauge and set the roof out from a straight line. A roof laid on tired battens gets uneven courses, and the dips show from the street.

When old battens might stay

There are rare exceptions. If a roof was re-battened recently and is being re-covered because the tiles failed, and the batten is the correct size and gauge for the replacement, the battens may be sound enough to keep. That is a judgment made on the roof, after the strip, when the timber can be inspected closely. We would not quote on that basis without seeing it.

Conservation work is another exception. On a listed building, traditional riven oak laths and pegged slates may be part of the character, and repairs follow the existing fabric. Anything you plan to alter on a listed roof should be run past the council's conservation officer first. The exact fixings differ there, and the work is more specialised.

Fixing and nailing

How the batten is fixed matters as much as the timber. Each batten is nailed to every rafter it crosses with corrosion-resistant nails of the right length, so that it bites into the rafter well beyond the underlay. Where the roof is exposed, the specification calls for more fixings, and the end joints in the battens are staggered and made over a rafter so that no run of joints lines up. These details are unglamorous and invisible once the tiles are on, which is why a roofer who explains them is worth listening to.

What you pay for

Battens are one of the cheaper parts of the job in materials. The labour of fixing them is more than the timber costs, and the risk of skipping them is greater than the saving. When comparing quotes, check whether each one states new battens and new underlay, since a quote that does not say may be assuming a reuse. Our page on comparing roof replacement quotes covers other items to look for.

If you are reusing your old tiles, the battens are still replaced, because the tiles can be lifted and relaid without the timber. Our page on reusing old roof tiles explains the details.

At the survey we photograph the battens from the loft side where we can, and you can see for yourself whether they are rotten or sound. The quote names the timber, and the workmanship is guaranteed for ten years in writing. The whole service sits on our roof replacement page.