BCD Special Report on
Historic Churches
19
th annual edition
7
process of cleaving the rock from the face
were used, eliminating unnecessary wastage.
Roofs were fixed with the largest slate at the
eaves diminishing to the smallest slate at
the ridge. This ensured that the area of the
roof that carried the most water made use
of the slates that provided the most lap.
Once the quarries were furnished with
machines and linked by rail, it became far
more efficient to transport slate in standard
sizes, despite the fact that this produced
much more waste (evidenced by the huge
slate tips we see today). Fixing standardised
slate also saved many man-hours on site and
didn’t require the same level of expertise.
The vast majority of slate produced
around the world today is sized
slate, but it is still possible to source
random slate from UK quarries.
Stone-slates have been used in many
areas across the UK for centuries and were
generally laid in a similar fashion to random
slate. However, these tend to be formed in much
thicker and heavier pieces than true slate to
allow for their relative weakness and porosity.
Tile
Double-lap clay tiles
were the main alternative
to slate in most areas of the UK. Produced in
the Midlands and the South East in particular,
these tiles were laid in much the same way
as slate, being double lapped. In other words,
because plain tiles do not overlap their
neighbours on either side, there needs to be a
double thickness of tile over every part of the
roof to keep it water-tight. The tiles therefore
overlap not only those in the course below
but also those in the course below that.
Many tiles were produced with ‘nibs’
at the top in order to hook them onto the
fixing battens. This lessened the need for
additional fixings such as nails, and made them
relatively quick to install given their small
size, which was generally around 10" x 6".
Clay tiles are still produced and used on
a large scale throughout the UK, and a few
roof failure on historic buildings. Usually of
lead but sometimes of other materials such
as copper, these flashings were designed with
prolonged exposure in mind, and well-detailed
leadwork can last for centuries. The most
common reasons for failure are not defects
in the material itself but poor design, bad
installation and inadequate maintenance.
Roof failure will normally make itself known
where the rainwater is most concentrated such
as the lower portions of valleys, parapet gutters
and outlets. Internally, problems will generally
become evident on the outer walls. It is vital to
investigate the source of these problems at the
earliest opportunity if outbreaks of dry rot and
extensive structural damage are to be avoided.
Repair or replace?
In many instances it
will be quite possible to carry out localised
repairs in order to prolong the life of
an entire roof. However, if nail failure is
advanced then a complete re-roof may be
the only answer. If water ingress has gone
undetected or ignored for long periods then
structural work may also be necessary.
Simple maintenance
Whether there is
internal evidence of water ingress or not, it
is always prudent to carry out regular visual
inspections of all roof areas and attend to
any minor defects such as the odd slipped
slate or tile, damaged flashing or blocked
rainwater channel. Parapet gutters, valleys
and rainwater channels must be regularly
cleared of leaves, plant growth and even dead
pigeons. Keeping up with simple regular
maintenance in this way can prolong the life
not just of the roof, but the entire building.
specialist firms can still produce tiles by hand,
using clays and firing techniques to match
the less regular appearance of older tiles.
Single-lap clay pantiles
were traditionally
seen all down the eastern coast of the UK.
This is because they were originally produced
in countries such as Holland and Belgium
and were imported across the Channel
and North Sea, tiles being an ideal ballast
material for ships returning from exporting
British goods to the continent. Bridgwater,
Somerset was another centre of production.
Because they overlap neighbouring
tiles in the same course, single-lap pantiles
only need to overlap a single course below
them to keep the roof water-tight.
My church roof is failing:
what are the likely causes
and is it repairable?
Slate, stone and fired clay are all extremely
long-lasting materials, and fixed to modern
standards can last for centuries. However,
one weakness is common to all types of
traditional pitched roofing: fixing failure.
Metal fixing nails are particularly
vulnerable. Once exposed to atmospheric
conditions, corrosion causes ferrous fixings to
fail far more rapidly than the roofing material
itself. This is why slipped slates and ‘tingles’ are
a common sight on old slate roof slopes. Tingles
are narrow strips of lead, copper or other metal
which are nailed to the batten at one end and
hook under the lower edge of the slate at the
other to form a simple, if unsightly, temporary
fix. However, It isn’t just the slate nails that
can fail prematurely, batten nail failure can
lead to whole courses of slate or tiles slipping
down the roof as gravity slowly takes over.
Clay nibs and riven oak pegs, although
more durable than galvanised steel nails,
also present a weak point. Clay nibs can
fracture due to thermal stresses in the roof
covering, and oak will eventually decay.
However, after nails it is the failure of metal
flashings that is the most common reason for
Tingles (metal clips) pepper the roof of a church at Llangollen in North Wales,
indicating widespread failure of the nails fixing the slates.
New handmade nibbed clay tiles (above) being laid across new battens on breathable
felt and (below) two samples of tiles being compared with the weathered originals to
ensure the most suitable match (Both photos: Jamie Moore, Recclesia)
