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THE
ROOFS OF ENGLAND CAMPAIGN STONE SLATES 1994 TO 1998 TERRY HUGHES |
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In
1993 a conference was held in Derbyshire to discuss the problems of stone
roofing in the region. One outcome of this was research into the status
of stone roofing in the South Pennines, a model area of England. The objectives
of the study were to - |
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1
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produce a database
of historical sources of stone slates in the region including a description
of the slates and a photographic record of slates and roofs; |
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2
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review the state
of the industry, the causes of cessation of production and the potential
for its re-establishment; |
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3
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review the market
for stone slates, the sources of competition, restraints on its development
and sources of support including grant aid; |
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4
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review the mineral
and conservation planning environment to determine how present policies
were assisting with or contributing to the problem; |
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5
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review the training
needs of manufacturers, roofing contractors, architects and planning and
conservation officers in order to support and control the use of new and
reclaimed stone slates |
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6
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develop a methodology
which would be applicable to investigations of similar traditional building
products in other regions. |
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The work was reported in
The Grey Slates of the South Pennines in 1996 and will be published in
English Heritage Transactions during 1998. |
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Concurrently
a DoE funded geological study was carried out with the School of Construction
and Earth Science at Oxford Brookes University. This reviewed the stone
slate geology and attempted to characterise the stone slates of the region.
This work has provided the beginnings of a basis for assessing the suitability
of stones without a known history for use as roofing and an understanding
of factors affecting their durability. There is much more work to be done
in this field and in other regions. The work was reported in Roofing Stones
in the South Pennines in 1995 but is unpublished. It may be possible to
make it available through the Stone
Roofing
Association
website in the future. |
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As a follow up to the South
Pennine work, research into the status of stone roofing throughout England
was carried out in 1997 and will be published later this year or early
1999. |
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This paper presents some
of the outcomes of the work done so far and areas in which further work
is needed. |
| QUARRIES |
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In the South Pennines 190
quarries were examined and ranked on a range of production and impact criteria
to help potential manufacturers select the best opportunities for quarrying.
This is now beginning to show results with a number of mineral planning
applications in the pipeline. |
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In other regions of England
where there are stone slate supply problems and where the history of stone
slate production is not readily accessible there is a need to carry out
similar research. As a first step, in the 1997 study an attempt has been
made to bring together all the historical and geological information in
each of the stone roofing regions. This work will now have to continue
at a local level and areas which stand out for action include Somerset/Dorset,
Horsham and the Welsh Marches. |
| INDUSTRY |
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| Top |
The supply situation is
improving but the industry is still vulnerable and to a large extent dependent
on building conservation grants for its economic viability. The majority
of companies are small some are literally one-man-bands. This is both a
strength and a weakness. Self employed people will work in conditions and
for long hours that would be generally unacceptable. However, illness or
other unforeseen problems can be very disruptive. This happened in 1997
when a quarry owner became ill and re-roofing plans for the region were
thrown into disarray. The outcome was that several buildings were re-roofed
with other products instead of stone. These are probably now lost forever. |
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Where the production of
a particular stone slate is dependent on a single quarry it is important
to co-ordinate supply and demand when establishing conservation schemes.
It is all to easy to overwhelm the supply and to inadvertently promote
the destruction of stone roofs outside the area to make up the deficit.
Good communications between conservation departments, architects and quarries
are essential before large schemes are established. |
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Some structural changes
are taking place within the industry and a number of larger companies are
entering the market. Hopefully this will improve the stability of supply
but it is bringing with it novel manufacturing techniques mainly based
around sawing. If these are not introduced with care they have the potential
to pose both aesthetic and technical problems. |
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Detailing is important to
the appearance of roofs and it is variable and regional. The ways in which
the edges of stone slates are dressed provides one example. They may be
more or less bevelled, or may be square edged and butt up tightly or even
be opposite handed producing an overlap. |
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It is a fundamental fact
that we are loosing stone roofs because they are expensive. The grants
which are available to make up the difference in the cost of a stone roof
are agreed by all concerned to be wholly inadequate to achieve the objectives
of roof conservation. If this is the case (and there is no reason to think
it will get any better in the future) it may be necessary to accept an
element of mechanical manufacture albeit at some detriment to the appearance
of the product in order to achieve lower product costs. The conservation
bodies need to debate the costs and benefits of these initiatives and closer
communication between manufacturers and specifiers is needed to reach agreement
on what is aesthetically acceptable. In the case of new build however,
it may be that the introduction of sawing is simply another step along
the road of technical development and we may be seeing the creation a new
'tradition'. |
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Technically stone slates
sawn to thickness may not be durable if they are made out of unsuitable
stone or because they are sawn off the bed. Because there are no durability
tests for stone roofing it is currently impossible to control this issue.
Some roofs have already failed because of errors in stone selection. Unfortunately
an application to the DETR for funding to research stone slate durability
was unsuccessful and we are left in the doldrums on this fundamental issue. |
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Specifiers and builders
often have great difficulty finding a supply of appropriate stone slates.
To try to overcome this and to help the industry to promote itself the
Stone
Roofing
Association
has been formed for manufacturers. It is too early to say whether this
initiative will be successful. |
| MARKET |
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At present most stone slate
markets are unsophisticated. In a situation where you are lucky to able
to find any new slates you are unlikely to be able to be too discriminating
about how closely they match the subtleties of local slates. But most regions
have used a variety of stones for roofing and ideally all local types should
be available for roof conservation. This is rarely the case and in extreme
instances limestones and sandstones have even been substituted for each
other. This aspect of stone roof conservation was investigated in the South
Pennine study and out of the 34 named stones which have been used for roofing
in the region it was proposed, using only appearance criteria, that seven
generic types might be sufficient for conservation purposes. |
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The criteria for defining
generic stone slates can include - |
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| Geology |
| Grain size |
| Colour |
| Surface features |
| Presence of certain minerals |
| Size range and mix |
| Thickness |
| Worked features such as
tooled surfaces or edge treatments |
| The plant life which they
support affects the ultimate appearance |
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Different stones have different
market sizes. Naturally the size depends on how precisely we define a specific
stone type. However some will inevitably be too small to justify ongoing
production. The magnesian limestone of East Derbyshire is one example where
only a few roofs remain and there are many others. In such situations there
are two options: occasional manufacture or substitution by another stone
slate. The entry of larger companies into the industry increases the likelihood
that stone slates with smaller markets could be manufactured intermittently
and at a reasonable cost. |
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At Harnage in Shropshire
we are in the middle of an attempt to quarry enough stone for one and a
bit roofs; on Pitchford Church and Pitchford Hall. It has been a long hard
road even getting to the point of having planning consent to quarry and
the difficulties are as much to do with people as they are technical. It
remains to be seen how difficult the manufacture and roofing will be for
this most unpromising stone slate. |
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Where a stone slate is simply
unavailable some alternative has to be found. Around Brandsby in East Yorkshire
the traditional limestone slate is often replaced with a sandstone from
the nearby Carboniferous stones of the Pennines. This radically changes
the appearance of the roof as can be seen on these slopes and a limestone
from the Cotswold, for example, would be more appropriate. |
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This points up the need
for better and more readily accessible information to support the decisions
on substitution. |
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Some stone slates are very
distinctive as this example from the New Red Sandstone in the Eden Valley
illustrates and where the same rock is used in Dumfries it has an even
more distinctive, and ancient, roofing method. A debate is required within
the conservation field to decide which stone slates need to be manufactured
because they are important and distinctive and which could be substituted
from other sources. This requires at the least a detailed description,
including pictures, of each of the stone slate types and their localities.
Eventually a protocol and handbook of stone slate types could be produced
to aid decision making. |
| CONSERVATION
PLANNING |
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One of the outcomes of the
South Pennine study was a review of the application of building conservation
grants. English Heritage policy now directs grants towards the use of new
stone slates and away from reclaimed except those from off the same building
or group of buildings. It is hoped that this will support the manufacturing
industry and reduce the deliberate dismantling of roofs simply to sell
the slates. Whilst the recycling of slates claims to be environmentally
sound there is no doubt that the best thing to do with reclaimed stone
slates is to put them back on the roof they came off rather than replacing
them with other products which will have a shorter life and whose production
will probably have a higher environmental impact. To continue to rely on
reclaimed slates for the conservation of roofs is quite simply not sustainable.
It will inevitably undermine the viability of the manufacture of new slates
and without new slates to feed into the re-roofing cycle, it will result
in the disappearance of all stone roofs. |
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| English Heritage policy
now has the following objectives |
| Wherever possible, new stone
slates rather than second-hand should be used. |
| Reclaimed slates should
be used only on the building or group of buildings from which they were
removed. |
| Substitute materials, such
as artificial slates made of fibre resin, concrete tiles, 'reconstituted
stone' and so on, are inappropriate alternatives to real stone slates and
are not suitable for use on historic buildings. |
| New stone slates should
match the existing ones as closely as possible in terms of geological type,
colour, texture, size, and thickness. It is important to recognise the
slates particular to your area. Sandstone and limestone slates should never
be substituted for each other, nor should they be used together. |
| Stone slates which have
been sawn to thickness, rather than split, can be technically and aesthetically
unacceptable and, if they fail to meet these criteria, should not be used
on historic buildings. |
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| MINERALS
PLANNING |
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Minerals planning policy
is supportive of stone slate quarrying. Most local plans recognise the
need for minor products and mineral planning officers are enthusiastic
and helpful. Difficulties do arise however where individuals, inexperienced
in the planning process, make errors in preparing their applications. This
can result in unnecessary extra costs and delays or even rejection. A guide
to preparing an application is badly needed. |
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In most quarries only a
small part of the rock will be suitable for roofing. Whilst the establishment
of a supply or stone slates may be the motivation for the opening of a
quarry it makes neither economic nor environmental sense to restrict production
to roofing alone. The rock which cannot be used for roofing should be permitted
to be used for the full mix of products; flagging, walling etc, which also
contribute to the local distinctiveness and visual harmony of the region. |
| TRAINING |
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This is a problem at all
levels. |
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For professionals some training
is available through architecture or conservation courses but these cannot
provide the practical details which are so much a part of a roofing technique
which relies so heavily on experience, an understanding of how top hung
double lap slating works and keen judgement of how to place every slate
on a roof. Stone roofing evolved in response to the rock and the weather
and techniques vary quite widely across the country. The English Heritage
stone slate technical note tackles the issues but it cannot provide guidance
on the specific, local aspects. This must come from local people and I
hope the conservation departments of each of the stone roofing regions
will now develop their own, specific, guides. |
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Some technical days have
been provided jointly with SPAB and the Technical Advice Note and the Roofs
of England exhibition are useful supports for training events. Lecturers
are available for courses and the stone slate website is a useful source
of information. |
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Roofing continues to evolve
and new problems arise. Insulation and ventilation is one example where
the application of new regulations can be problematical. Much of the development
of roofing design and construction is driven by product manufacturers who
always promise the solution to all your problems but who may not understand
conservation policy or the full implications for stone roofs. Care is needed
when deciding whether, or how best, to adopt modern roof construction techniques.
It may also be that a more precise statement of conservation policy in
this respect needs to be articulated and disseminated. |
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The provision and quality
of craft training is very worrying. The standard of roofing workmanship
in the UK is so low that an initiative, the Roofing Industry Alliance,
has been established to try to improve the situation. However the combination
of misdirected funding for training provision through the colleges, low
uptake of roofing courses and the need to give priority to the simpler
roofing forms such as concrete tiles does not auger well for stone slating. |
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The recently revised NVQ
scheme for roofing includes traditional top hung random slating at level
three but the fact is that most trainees drop out at level two. This means
that most craft training for random slating is carried out within roofing
companies. Sometimes this is excellent, especially where there is a continuity
of knowledge and experience within a family business. Unhappily the opposite
is often the case and where there has been a break in the tradition often
bad practice is adopted and perpetuated. Obviously, in this unstructured
situation there is no way to assess or control the quality of the trainers
or the training given. |
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Much of what is done on
stone roofs today may not be based on genuine knowledge. Stone roofing
is a seriously under-researched field and there is an urgent need for the
construction of older stone roofs to be thoroughly researched before the
disappearance of the remaining examples from the time when the techniques
were well understood. There is also scope for work on the industrial archaeology
of stone slate quarrying. The problem for researching roof construction
is that it can only happen when a roof is being taken apart and what is
needed is a programme to bring in specialists as opportunities present.
Archaeological recording techniques should be used but the people carrying
out the work need to understand what is significant about roof construction
so that they will record the correct details. |
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When I wrote the South Pennine
report I concluded that there were reasons to be optimistic about the future
of stone roofing. Four years on that optimism has been justified and in
some regions the supply problems are being resolved and much useful experience
has been gained which will help further the work. However, one lesson learned
is that success is only achieved with a committed, adequately resourced
and sustained local effort. Help is available through English Heritage
but ultimately success will only be achieved by hard work within the regions. |
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Terry Hughes |
