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Slating and tiling battens have
developed from the thin coppice saplings that were used to support and
fix the reeds in thatching. For early peg tiling the timber was split
with an axe or lathing hammer to give it a square top edge for the oak
pegs to rest on. Being split, the battens were never straight, so were
kept as narrow as possible to allow the tiler to bend them and achieve
the straightest line possible when nailing them to the rafters.
The rafters were often a quarter of a tree trunk,
and tapered from eaves to ridge, so the spacing of the rafters were at
close centres of 300mm-400mm. The size of the batten was, therefore,
sometimes as small as 25mm x 12mm.
With the introduction of mechanised saws it
became possible to cut rafters to a regular size, allowing the rafter
centres to increase. The offcuts were sawn down to make the battens;
this practice is still used today. With split timbers it was essential
to have the longest knotfree length you could achieve, as the grain was
impossible to keep straight, close to a knot.
With sawn timbers, knots have become more common
in battens. With the introduction of trussed rafters, the rafter spacing
has expanded out to 600mm, requiring battens to be larger to span
between the rafters at wider centres.
Because timber is a natural
material that comes from many species of coniferous trees, the
characteristics of the material will be different. This will have an
effect on the splitting and bending properties of the finished batten.
To reflect this, battens should be sourced from
either European and home-grown Redwoods, Whitewoods, Sitka Spruce, Scots
Pine, Canadian Spruce Pine and Fir, Douglas Fir- Larch and Hemfir.
Timbers that do not fit into these classifications should not be used
Prior to the introduction of European competition
rules, timber for battens came from different climatic zones, and the
density and spacing of the growth rings could vary. Generally, timber
that grows quickly in a warm wet climate will have wider and softer
growth rings than timber grown in a cold dry climate.
The spacing and density of the growth rings
affects the grip of the timber to a nail fixing.; the harder it is to
drive a nail into timber, the harder it will be to pull it out.
There is no specific British
Standard for timber slating or tiling battens, but there is a definitive
list of species and permissible characteristics that all battens for
slating and tiling should comply with, contained in BS5523: The code of
practice for slating and tiling: 2003, which contains a table of minimum
batten sizes for the common roof coverings of natural and FC slate, and
single and double-lap clay and concrete tiles. For rafter centres up to
450mm centres, all tile roof coverings and FC slate should use 38mm x
25mm battens, while natural slates should use 50mm x 25mm. For rafter
centres up to 600mm centres, 50mm x 25mm battens should be used for
natural and FC slate, and interlocking clay and concrete tiles. Plain
tiles should use 38mm x 25mm battens.
It may be possible by calculation to prove that for a
specific situation, 38mm x 19mm battens are appropriate, but without
valid calculations the recommendation contained in the table should be
used. For rafter centres in excess of 600mm the batten size needs to be
calculated. There is also a maximum and minimum tolerance: +/- 3mm wide,
The main reason for using 50mm x 25mm battens, particularly with natural
slates, is to reduce the amount of batten bounce at midspan when driving
in nail fixings.
There comes a point, with small
sections of timber, where the force required to push the nail into the
timber is more than the force to bend the timber. Therefore, the batten
bends before the nail goes into the batten. With head-nailed tiles it is
possible to hold the batten while you nail, to stop the batten bending.
But with centre-nailed slates this is almost impossible.
The reason why all the battens are 25mm deep,
regardless of the rafter centres, is to ensure the maximum nail-grip for
the nails specified for the tiles or slates. With a 19mm-thick batten
there is the risk that the nail will pass through the batten and stick
6mm out of the back of the batten, and may puncture the underlay.
Battens that are 50mm wide should not be used with plain tiles as the
position of the eaves tile relative to the first whole tile is critical.
If a 50mm wide batten was used, the eaves tiles would not align
It is always better to use rectangular sections of timber on
the roof as they are less likely to roll if stood on. All battens
generally come treated with preservative. While there are some locations
where it is mandatory (Surrey), it is a wise precaution to use treated
timbers, but will add a slightly higher risk of pollution entering the
environment when the building is demolished. No batten should be less
than 1.2m long, so that at 600mm centres the batten will rest on at
least three rafters. Battens should always be joined on the centre line
of a rafter and with trussed rafters; no more than one in any group of
four consecutive battens should be joined on the same rafter.
For tiles and slates where the batten gauge is less
than 200mm, no more than four in 12 consecutive battens should be joined
on the same rafter. Knots that affect two edges, up to a certain size,
may remain in a batten, but where the knot affects three edges, or is
over a certain size, the knot should be cut out and the batten joined on
a rafter, as knots can severely weaken the performance of a batten and
make fixing nails into, or through it, very difficult. Battens should
always be set out to a calculated gauge which is measured for tiles from
top of batten to top of batten. While slates are laid to the centre of
the batten, the position of the eaves slates should be set out so that
all gauges above that point are to the top edge of the batten.
In Scotland it is traditional with natural slates to lay ply or OSB
board directly onto the rafters, and cover with underlay to keep it dry
until the slates can be nailed directly through the underlay into the
boarding. This method allows the roof to be constructed quickly without
knowing what will cover it, as the batten gauge is irrelevant. The lack
of slate battens means that where there are inclined valleys there is no
natural space to form the tilt or the welt of the valley construction,
without kicking up the edge slates.
- All slate or tile battens should
comply with the recommendations of BS5534, for timber species,
markings and sizes.
- Battens less than 1.2m long should
not be used on a tiled or slated roof, except as a noggin.
- Undersized battens will sag between
the rafters and appear as a series of waves in the roof covering,
after a few years.
- The same thickness of batten should
be used throughout the roof to ensure the roof covering lays in the
by Chris Thomas, The Tiled Roofing Consultancy, 2 Ridlands Grove,
Limpsfield Chart, Oxted, Surrey, RH8 0ST, tel 01883 724774