Installing roof battens for tiled roofs

A tiled roof is not one continuous surface. Each tile hangs on a batten by the nibs on its back and overlaps the tiles around it. That is why the distance between battens, known in the trade as the gauge, is not a matter of taste. The tile manufacturer sets it for each tile type and roof pitch. If the battens are too close together, the tiles overlap more than they should and the top course does not sit properly. If they are too far apart, the overlap becomes too small, and driving rain or blown snow gets under the tiles.

Battens also carry loads: the weight of the tiles, snow, people walking on the roof for maintenance, and wind suction, which tries to lift the tiles off. On modern roofs, battens sit on counter battens. These are vertical strips fixed along the rafters over the breathable roofing membrane. They create a ventilated gap between membrane and tiles. Moisture escapes through this gap, and any water that gets past the tiles runs down the membrane into the gutter.

Why not fix battens straight onto the membrane? Because they would press the membrane against the rafters, and water would collect above every batten. That is why counter battens have become practically standard, and the tiling battens go on top of them.

This price-list item assumes the base underneath is finished. The roofer should arrive at a roof where:

• The roof structure has been checked by a carpenter, with no rotten or cracked rafters
• The breathable membrane is laid, with laps and joints overlapped and taped as the manufacturer specifies
• The counter battens are fixed, straight and in one plane
• The eaves flashing is installed, or at least it is clear how the eaves detail will be built
• The exact roof covering has been chosen, including its ridge and verge system

The last point is the one people underestimate most. Without the tile manufacturer's technical data sheet, nobody can set out the battens. The data sheet gives the range within which the gauge can vary, the position of the first batten at the eaves and of the last batten at the ridge. Metal tile sheets have a fixed module, so the gauge is set exactly and cannot be adjusted at all. If the covering is chosen only after the battens are on, the roofer may have to take them off and fix them again.

If only the battens and the covering are replaced during a renovation, the condition of the counter battens and membrane can only be judged once the old tiles are off. On an older roof without a membrane, where battens sat directly on the rafters, the usual solution is to add a membrane and counter battens. That is a different, combined job.

Before replacing a roof covering or altering a roof, check with your local building authority whether the work needs approval or notification under local building regulations. Rules differ by country and region, and listed buildings or conservation areas often have stricter requirements. In a block of flats, the roof is a shared part of the building, so the building management or owners' association decides on the work.

Work at height must be organised before anyone climbs up: scaffolding or edge protection at the eaves and fall protection for the crew. Battens act as footholds during the job, but they are not safety equipment.

Size depends on the spacing of supports

A batten is a small beam spanning from one counter batten to the next. The further apart the counter battens (and therefore the rafters), the thicker the batten needs to be. Batten sizes vary by country and building tradition. At the usual rafter spacing of a family house, battens of roughly 25 × 50 mm to 30 × 50 mm are common. With wider rafter spacing, heavier tiles or higher snow loads, roofers use larger sections of roughly 40 × 60 mm. The decision should come from the design or the tile manufacturer's recommendation, not from habit.

Timber quality and moisture

Battens are usually made from spruce, fir or similar softwood that has been strength graded. A good batten has no large knots through the whole section, no splits and no bow. The timber should be reasonably dry, roughly 20 % moisture content or less as a guide. Wet battens twist and shrink after fixing, the tile courses start to wave and the nails loosen. In practice, battens often lie on site uncovered for weeks. Before fixing, they should be sorted and any twisted pieces rejected.

Preservative treatment

Battens should be treated against wood-boring insects and fungal decay, ideally industrially by dipping or pressure treatment. Ends cut on the roof get an extra coat of the preservative recommended by the treatment manufacturer. Untreated cut ends are where rot appears first.

Fixings

Battens are fixed with galvanised or stainless nails, often ring-shank nails, which resist pulling out better. As a rule, the nail should be at least two and a half times as long as the batten is thick, so that it passes through the batten and counter batten and anchors in the rafter. Some roofers use screws, especially in exposed windy locations or where a more precise fixing is needed. Plain bright steel nails corrode on a roof and shorten the life of the fixing.

Setting out the gauge

The roofer first measures the length of the roof slope at both verges and in the middle. From that length, he deducts the zones at the eaves and at the ridge that the manufacturer specifies. The remainder is divided into equal gauges that fall within the permitted range. The aim is for every tile course to have the same overlap, so there is no need to cut tiles under the ridge. With metal tile sheets, the process works the other way round: the gauge is fixed, and the position of the top batten at the ridge is adjusted to suit.

Eaves batten and ridge batten

The first batten at the eaves is raised, usually by the thickness of one batten or as the tile system requires. The bottom course has no course beneath it to rest on, and without this lift it would sit flatter than the rest. At the ridge, the roofer fixes the top batten and the ridge batten in its brackets, which carries the ridge tiles. Its height is set to suit the ridge system.

Fixing the battens

1. Mark the batten positions on the outer counter battens and stretch a line between them, or use a laser.
2. Fix the raised eaves batten.
3. Work up towards the ridge, checking the gauge at every batten with a gauge rod or template.
4. Nail the batten at every crossing with a counter batten.
5. Make batten joints only over a counter batten and stagger them so they do not all fall on the same rafter.
6. Check regularly with a line that the battens run parallel to the eaves.
7. Fix the top batten and the ridge batten brackets to suit the tile system.
8. Add battens around details and treat all cut ends.

Each batten should span at least three supports. Short offcuts that cross only one or two counter battens are weak points in the roof slope.

Details that belong to battening

• Extra battens around chimneys, roof windows and dormers, following the installation instructions for the window or flashing
• Battens or boards for valleys, which carry the valley flashing or valley liner
• Hip battens on hipped roofs
• Verge battens for verge tiles or verge trims
• Extra battens for snow guards, walkways and solar panel roof hooks, where their manufacturer requires them
• Eaves ventilation grille or bird comb, as agreed

In quotes, these details are sometimes charged separately and sometimes included in the rate per m². Clarify before work starts what exactly the item covers.

The price list contains three related items. They differ in scope and in the state the roof is in before work begins.

• Installing roof battens for tiled roofs (this page): only the horizontal battens on counter battens that are already in place. This suits jobs where the carpenter fitted the counter battens together with the roof structure and membrane, or where the original counter battens and membrane stay in good condition during a re-roof. The work depends mainly on accurate setting out and equal gauges.
• Installing counter battens: only the vertical strips along the rafters over the membrane. Their job is to create the ventilated gap, hold the membrane in place and even out the plane of the roof. This work deals with packing, flatness and sealing the nail penetrations through the membrane.
• Battening and counter battening (combined): one crew installs both layers in one sequence. This is common on new builds and on renovations where a membrane is being added. The advantage is that one contractor is responsible for both the flatness of the roof and the gauges.

You order battening on its own when someone else is responsible for the counter battens. Keep in mind that the roofer is then only responsible for his own layer. If the counter battens are crooked, the battens will not straighten them. A batten follows whatever is under it, and the wave carries through into the tiles. A good roofer therefore inspects the counter battens before starting and reports any defects before the first nail goes in.

The simplest case is a gable roof with two flat slopes, no penetrations and good access from scaffolding. Battens run from verge to verge, one setting out covers the whole slope and the work moves quickly.

The job becomes longer and more complicated mainly with:

• Hipped and pyramid roofs, where every batten has to be cut at an angle at the hip
• Valleys, dormers, several roof windows and chimneys
• Different rafter lengths within one slope, for example on mansard roofs, where several setting outs are needed
• Coverings with a small gauge, such as plain tiles or beaver tail tiles laid double, where there are many more battens per m²
• Wider rafter spacing, which calls for thicker and heavier battens
• A steep pitch, a tall building and limited access for a materials hoist
• Renovations where old battens must be stripped and leftover nails pulled out
• Wind, rain or frost, when it is not safe to work on the roof

On a simple family house roof, an experienced crew of two or three usually finishes battening in one to two days. A complex roof with many details can take several times as long. Battening has no drying or curing time. Still, the membrane under the battens should not stay uncovered for long. Most membranes tolerate sunlight only for a limited period, according to the manufacturer, and battens without tiles do not keep the rain out.

Battening is a short intermediate step, but many trades depend on it. Most problems arise when something that should have been done under the battens is done afterwards.

• Carpenter: hands over the roof structure, membrane and counter battens, and the roofer checks flatness and spacing
• Sheet metal worker: the eaves flashing, gutter brackets and some flashings go on before or together with the battens, so the sequence must be agreed
• Roof window installer: the window is set into the battening with extra battens according to the window manufacturer's instructions
• Solar installer: roof hooks are fixed to the rafters, so their positions are sorted out during battening, not on the finished roof
• Lightning protection: conductor supports and fittings are installed by a qualified electrician or lightning protection specialist, and the roofer leaves the positions ready
• Loft insulation: done from inside after the roof is covered, and battening nails must not damage the vapour control layer if it is already fitted

If a vent terminal, aerial or roof access hatch is planned, mark its position before battening. The roofer can then add the extra battens around it straight away.

Battening mistakes often appear only when the tiles go on, and some only after years.

• Uneven gauge: tile courses cannot hang properly, gaps or tension appear, and tiles under the ridge have to be cut
• Eaves batten not raised: the bottom course sits flatter, water can blow back under the tiles and the course looks sunken
• Battens not parallel to the eaves: tile courses run at a slant or in waves, and the fault is visible from the ground
• Batten joints all over one rafter: a weak line forms that can sag under snow
• Missing nails at some crossings: the batten flexes in wind or underfoot and works loose
• Untreated or wet timber: battens twist, and later rot appears at the eaves and around the chimney
• Battens fixed straight onto the membrane without counter battens: water stands above the battens, the membrane is pressed down and damp patches appear in the loft
• Missing extra battens at the chimney and windows: the flashing has no support and the tiles around the detail do not sit firmly
• Ventilation gap blocked at the ridge or eaves: moisture stays under the tiles and frost forms on the membrane in winter

Most of these faults show up with one simple step: hang two or three trial courses of tiles on one slope before the whole delivery goes up on the roof.

Check the battens before tiling starts, while everything is still easy to fix. Measure the gauge in several places, at both verges and in the middle. Check that the battens are parallel with a line stretched along them. Also look at the details that cannot be inspected once the tiles are on.

• The batten gauge matches the technical data sheet of the chosen tiles and is the same across the whole slope
• The eaves batten is raised as the tile system requires
• The ridge batten and its brackets are set at the correct height
• The battens run parallel to the eaves and lie in one plane with no visible waves
• Each batten is nailed at every crossing with a counter batten
• Batten joints sit on counter battens and are staggered
• Each batten spans at least three supports
• The timber is treated and cut ends have been coated
• Extra battens at chimneys, windows, valleys, hips and verges are in place
• Positions for snow guards, solar hooks and lightning protection are prepared
• The membrane is undamaged and the ventilation gap at eaves and ridge is clear
• Trial courses of tiles hang without gaps and without tension