Roof Battening and Counter Battening Installation

This page covers two jobs that always go together on a roof, even though each one does a different task.

Counter battening means fixing battens that run down the slope, from the eaves to the ridge, exactly along the centre line of each rafter. They press the membrane against the rafters and lift the tile battens above it. This creates a ventilated gap. Air moves through it from the eaves to the ridge and carries away moisture and condensation. If wind-driven rain or snow gets under the tiles, the water can run down the membrane into the gutter. The height of this gap depends on how thick the counter battens are, not on the load.

Battening for tiles on a timber roof means fixing horizontal battens across the counter battens. Each row of tiles hooks onto one batten, so the spacing has to be exact. Between the counter battens each batten works like a small beam. Its size therefore depends on the rafter spacing and on the weight of the tiles and snow.

Why can you not have one without the other? Without counter battens the battens would sit directly on the membrane. Water would stop at every batten, and the roof would have no way to breathe.

The order of the layers is fixed. The membrane goes onto the rafters before the counter battens, never the other way round.

1. The carpenter checks the roof structure. Are the rafters in one plane, dry, and free of rot or insect damage? A string line stretched across the roof shows whether they are level. Low rafters are packed up and high ones are trimmed.
2. The carpenter measures the actual rafter lengths from eaves to ridge. These often differ from the drawings by a few centimetres.
3. The membrane is laid parallel to the eaves, working upwards from the eaves. Each run overlaps the one below by the amount the manufacturer gives, usually around 10 cm and more on shallow pitches. At the eaves it is led into the gutter or onto the eaves flashing.
4. Nail sealing tape goes on the rafters or on the underside of the counter battens. It seals the holes the nails make in the membrane.
5. The counter battens are fixed along the rafter centre lines with galvanised nails or screws long enough to bite firmly into the rafter. At the ridge and in valleys a path is left open for the air.
6. The first batten at the eaves and the last at the ridge are set as the tile installation guide says. The space between them is divided into equal gauges, and the marks are transferred to both end counter battens.
7. The remaining battens are fixed to a string line, with each batten fixed into every counter batten. Joints always land over a counter batten and are staggered between neighbouring rows.

Common batten sizes are 30 × 50, 40 × 50 and 40 × 60 mm. The rule of thumb is simple: the wider the rafter spacing and the heavier the tiles, the stronger the batten needs to be. A typical tiled family house often uses 40 × 50 mm. Wider rafter spacing or a snowier area may call for 40 × 60 mm. An undersized batten does not show at first. It shows the first time heavy snow sits on the roof and a whole row of tiles sags.

The counter batten size depends on how big a ventilated gap the roof needs. A plain pitched roof usually manages with a lower profile. Shallow pitches, long rafters and areas around dormers and valleys, where air moves less freely, need taller counter battens.

The batten gauge, meaning the spacing between battens, comes from the covering length of the specific tile and from the roof pitch. On a shallower roof the battens sit closer together so the rows overlap more. The binding figures are in the manufacturer's installation guide, and following it is often a condition of the tile warranty. So the gauge should never be copied from another job or guessed. Metal roofing follows its own rules based on the sheet profile, so battening set out for tiles cannot simply be reused for it.

Look at the timber when it is delivered. Battens should be dried (moisture content roughly up to 20 %), strength graded, free of large knots running through, and treated against insects and fungi. Before fixing, stack them on site with spacers and keep them covered for a few days. Do not wrap them airtight.

A simple pitched roof on a new, straight roof structure goes fastest. These factors mainly add effort, and so cost:

• A complex roof with dormers, valleys, hips, chimneys and roof windows, which means more measuring and cutting
• Renovation work, where the old battens have to come off first, old nails pulled and bent or damaged rafters repaired
• A shallow pitch, which needs closer battens, a better membrane and sealing tape
• Poor access to the roof and the need for scaffolding

This is work at height. It should be done by a carpenter or roofer with proper fall protection and scaffolding. Before you replace the roof covering or alter the roof structure, ask your local building authority what your building regulations require. Do not assume nothing needs to be approved. In a block of flats, decisions about the roof belong to the building management or the owners' association.

• Counter battens left out or a gap that is too small, so condensation cannot escape and slowly damages the timber and the loft insulation
• Membrane laid over the counter battens instead of directly on the rafters
• No sealing tape, so every nail becomes a possible leak
• Batten gauge set "by eye", which only shows at the ridge when the last row of tiles does not fit
• Damp or untreated timber that twists once it is fixed
• Batten joints between supports and unprotected nails that rust over time
• A ventilated gap blocked at the ridge, in a valley or around a roof window

In practice these mistakes often show only after a few seasons. By then a repair means taking off a finished roof.

Correcting the gauge now takes minutes. Once the first rows of tiles are on, it means stripping them off again. Before you sign off the work, check:

• Seen from the eaves, the battens are straight, with no waves or kinks
• The number of rows is the same on both sides of the roof
• The batten gauge and the position of the first and last battens match the tile manufacturer's guide
• Battens and counter battens do not move or spring when you press on them
• Counter battens sit on the rafter centre lines with sealing tape underneath
• Batten joints are over counter battens and staggered between rows
• The ventilated gap is open from eaves to ridge, including around chimneys and windows
• The membrane is not torn and runs into the gutter at the eaves
• The build-up is photographed before it is covered, in case of a later complaint