8
BCD Special Report on
Historic Churches
19
th annual edition
Repair and replacement
of slates and tiles
Individual slates can be successfully replaced
but it is not usually quite as simple as repairing
clay tiles, which can often be slotted into
place without too much technical know-how.
By far the best solution is to remove all the
slates above the offending area and re-fix in
same manner as they would have been fixed
originally, usually with two clout nails.
It may not always be practical to remove
large areas of roof just to replace one or two
slates near the eaves, so a little skill can be
required to make a successful replacement.
Unfortunately, many individual slate repairs have
been carried out in the past using inappropriate
methods such as adhesives and tingles, neither
of which can be considered a permanent fix.
Successful, permanent and invisible slate
repairs can be achieved in a number of ways.
For example, copper straps can be threaded
through pre-made slots in the slate and
fashioned to create a wedged spring, which
is flattened while the slate is being pushed
up into place, then springs out behind the
fixing batten when arriving at the correct
position. Because the slate is not secured
into the batten, as with nailing, it wouldn’t be
appropriate to fix a whole roof in this way but
as an individual repair it is effective because the
surrounding nailed slates will prevent uplift.
There are a number of products on the
market that work in a similar way such as
the ‘Jenny-Twin’ fixing, which consists of a
pair of aluminium clips that clasp the sides
of the slate and are secured by a tongue that
passes through a drilled or punched hole in
the slate and a swivel ‘tail’ that rests on the
batten. Installation can be a bit fiddly but
the clips are very effective once in place.
While tingles have had a relatively
useful role in signalling whether a roof needs
replacing, they are only a temporary solution
and need to be replaced by something
more permanent. As long as repairs are
recorded it will still be possible to monitor
the overall condition of the roof and
determine when replacement is necessary.
With double-lap clay tiles, the first indicator
of the end of the roof’s useful life is finding
whole rows of tiles slipping due to corroded
batten nails. These tiles generally have either
‘
nibs’ or oak pegs which allow them to hang
onto the batten even if the tile fixing nail has
corroded. Only a complete re-roof should be
considered when this defect is identified as it
will not otherwise be possible to carry out an
effective, lasting repair. As with slates, it may
well be possible to reuse some proportion of
the existing tiles if the aesthetics and historic
interest of the roof are to be preserved.
However, specifiers and clients should be
realistic when considering reusing roofing
materials and should not expect to save more
than 50 per cent in most instances even if the
material appears to be in good condition.
If renewing a roof completely, it is usually
best to replace materials like-for-like in order
to maintain the authenticity of the building.
Fortunately we are blessed in the UK with
a stable supply of traditional materials such
as Welsh slate and clay tiles and therefore
replacing these can be relatively simple
logistically. However, difficulties may be
encountered finding some stone slates, and
Scottish slate is now rare. In such cases it may
be necessary to use material of similar geology.
Clay tiles can be made by specialist
manufacturers to match almost any profile,
colour or texture. Some may be available from
standard ranges, but specials are often required
to match regional variations, particularly
where pantiles and romans (flat roofing tiles
with one or more rolls) are concerned.
Beneath the slates and tiles themselves
things can be quite different where a roof
covering has been renewed, as modern fixings
and methods have evolved to last far longer
than their predecessors. Also the introduction
of insulation and ventilation systems to comply
with modern regulations can have a major
effect on detailing. It should be remembered
that it is now mandatory to install insulation
to strict current specifications if replacing
25
per cent or more of any roof area.
Modern versus traditional
fixing methods
There is no practical reason to install slates
and tiles using historic fixing methods.
Materials should be fixed according to
current best practice. This shouldn’t mean
that the roof will look any different to the
original, but it will last longer. Laying slates
or tiles using the most appropriate modern
fixings will also allow future generations to
date the work and assess its suitability.
Jonathan Greenough
is a Heritage
Roof Master and a Fellow of the Institute of
Roofing with over 27 years’ experience. His
heritage roofing expertise has been called
upon for projects throughout the UK and
beyond, including at Buckingham Palace.
New polychrome clay tiles made by Dreadnought for the chancel of All Saints’, Nocton near Lincoln (by George Gilbert Scott, 1862). Clay which was naturally the
right colour was sourced to match the originals, rather than dyed, and those original tiles found to be still serviceable were reused on the south face of the nave.
(
Photo: Dreadnought Works, Hinton, Perry Davenhill)
