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In most cases, slates or tiles are either put onto new buildings or they
are used to re-roof an old roof; either way, all new battens will be
But there are instances where the roof may be fairly
new and repairs need to be undertaken that do not warrant the total
re-battening of the roof, but require the battens to be cut, repaired or
refixed. Where the roof structure is constructed from timber trussed
rafters, the repair needs to be undertaken very carefully to maintain
the integrity of the roof structure.
BS5534 and BS8000 Part 6 state that no batten should be less than 1.2m
long, such that at 600mm centres the batten will rest on at least three
rafters. Battens that only span between two rafters are more likely to
sag than those that go over a central support (hogging moment).
Where the batten goes over a rafter, there is
tension in the top fibres, while there is tension in the bottom fibres
between the rafters. One helps to cancel out the other and keep the
battens reasonably straight. If the end of the batten rests on a rafter
(end bearing) there is no hogging moment, and so the batten is more
likely to sag under load.
If an isolated batten between two rafters has to
be cut out and replaced, it is better to either cut out and replace the
batten over three rafters, or to install an additional batten of the
same size below the short section of batten. The lower batten should be
long enough to span over – and be nail fixed to – four rafters. The
short and long battens should also be nailed to each other.
BS5268 requires that battens
should 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.
If more than one batten has to be replaced,
the batten joints should be staggered. The reason for this is that the
battens provide the lateral restraint for the timber trussed rafters,
and any group of consecutive joints in the battening will affect the
rigidity of the structure.
For interlocking tiles, this means that either
the battens need to span over five rafters and be staggered (meaning
that an area of roof up to 4.2m wide may be affected), or an additional
batten long enough to span over two additional rafters must be installed
below the existing section of batten that has been reinstated, and the
additional batten must be nailed to the rafters, and to the replaced
section of batten.
Verge or side abutment
Where the battens end at a verge
or side abutment, and are either rotten because they have been embedded
in the verge mortar, or need to be lengthened to allow for the correct
installation of a dry verge system or gable wall cladding, the rotten or
affected battens should be cut back and staggered, to make sure only one
in any group of four consecutive battens join on one rafter.
This means that the shortest batten will be
about 1.5m long and the longest approximately 3.3m long where the
rafters are at 600mm centres.
The alternative is to install an additional
batten of the same size (and approximately 1.5m long) directly below the
replaced end section of batten, and twice nail the short end section to
the additional batten, then also nail the additional batten to each
rafter and the existing batten for maximum rigidity.
Mid span support
Where a batten is cut between two
rafters to accommodate a pipe or flue, and the end of the batten is
unsupported, a short length of batten approximately equal to three times
the batten gauge should be slid up under the unsupported end of the
batten and screwed to the unsupported batten and the battens above and
Battens should always be joined
at a rafter. The ends of the battens should be square cut and tightly
butted to the adjacent section of batten and skew nailed into the
rafter, to prevent the batten end from splitting.
With timber trussed rafter, this may result in an
end bearing of less than 17mm. Therefore, it may be better to cut the
batten in line with the side of the rafter and install an additional
38mm x 38mm timber noggin onto the side of the rafter flush with the top
of the rafter, to allow the new section of batten to be nailed to it.
This is easier said than done, as the noggin should be below the
underlay, while the batten is above it. This is normally only possible
where the underlay is also cut through for access.
Where repairs are being undertaken, new battens of the same size should
always be used. Edge fixing into battens thinner than 25mm thick is not
advisable as the nail-to-edge distance will be very small and can split
the batten, taking away any strength that may have existed. Where the
battens are cut out or modified, the resulting repair needs to maintain
– or improve – the integrity of the roof.
- Knotty, rotten or split battens have little or no strength and
should be cut out and replaced.
- Where battens are joined at a
rafter, increase the end bearing by nailing a 38mm x 38mm batten to
the side of the rafter.
- Unsupported ends of battens can be
supported with a vertical batten screwed to the battens above and
by Chris Thomas, The Tiled Roofing Consultancy, 2 Ridlands Grove,
Limpsfield Chart, Oxted, Surrey, RH8 0ST, tel 01883 724774