This programme, supported by Construction Skills and the National Federation of Roofing Contractors, is designed for roofers with experience in slating or tiling and provides training tailored to the candidate’s needs.  It enables them to understand the historical development and related theory and technology of the various materials, tools and equipment, as well as the craft techniques employed, in order to understand roof conservation in relation to repair and restoration.

The courses comprise from two to thirteen days off-the-job and employer supervised on-the job training leading to assessment in NVQ level 3 Heritage Skills.

The courses are flexible and can cover any type of traditional slating or tiling.  Candidates will also be given an understanding of the wider range of roofing types beyond their own regions and the technical principles which underly each.

In 2012 a two week course was run on the granary at Trehilyn Farm Pembrokeshire.  It covered -

  1. 1. Understanding and recording the original roof construction

  2. 2. The need for and reasoning behind necessary changes to the original construction

  3. 3. Slate making

  4. 4. Gauging the roof and lath fixing

  5. 5. Slate laying

  6. 6. Use of lime mortar

  7. 7. Field trips to other historic roofs in the region


All historic roof repair or restoration should be based on a clear understanding of the existing roof.  This will involve inspecting the way in which the slates were set out on the main areas of the roof, especially the head and side laps, and the detailing of the eaves, ridge, valleys, hips and abutments.


On Trehilyn granary the inspection was complicated by the mortar grouting which completely covered the roof.

What was found was that the main areas had been re-slated at some time with sawn battens but that the valley was earlier and still included riven laths.  The slating was set out in thirds so that the lath / batten gauges were one third of the slates’ lengths.  This would probably have been determined by using a compass.

There was a triple eaves. Normally eaves slating has one course of short slates underneath the first full length slates.  here there are two short courses.  The reason is not known but there could be a number of reasons.

  1. - The extra course provides lift (or tilt) which ensures the slates above sit tightly onto each other.  But on other roofs this is more often provided by the wall plate or by setting the rafters back from the walls outer face.

  2. -It provides extra protection against leaks where there is most water but in principle there is no need for this. 

  3. -Triple eaves have been described for triple lap scantle slating and although this roof was slated in thirds it had been renewed as the sawn laths show so maybe the eaves is a left over of the earlier roof.

  4. -Three layers of slate would be heavier and therefore more resistant to wind uplift.  Trehilyn is a very windy place.

The valley was a collar and tie type and there was a wrestler ridge topped with mortar, a Pembrokeshire detail, a close mitred hip and an abutment with slate listings with an open channel below.

Courses can cover any type of

historic slating or tiling


Slate making involves, splitting (or riving) the block successively into thinner pieces; dressing the edges with a sax and break iron and shouldering the tops; making a peg/nail hole with a holing machine and then sorting the slates into sets of equal length.  When this is done the total width of each length is measured with a string line and the number of courses which can be slated calculated in relation to the roofs width.


Once the number of courses has been worked out for each length the gauging of the laths can be worked out by calculation or using a traditional gauging stick.  It is very important that the gauge (the lath spacing) is adjusted at a change of slate length so that the margins (the height of the exposed part of the slates) diminishes continuously up the slope and to ensure there is adequate head lap.  You can see this where the lath spacing get narrower and then wider going up the slope.

Because this roof was originally slated in thirds this was reproduced.


One of the most important steps when renewing a roof is to decide if modern techniques or materials should be used.  This can be very difficult and often involves balancing off better technical preformance and durability against loss of historic detail and character.

On this roof the decision was taken to top hang the slates on copper nails (used as pegs).  Top hanging reproduces the historic detail but copper lasts longer and metal pegs are more reliable than the original wooden pegs.  Usually this choice is based on whether the underside of the roof is going to be visible.  If not then copper nails or pegs are selected. 

Decisions also have to be made on whether to instal an underlay  (here a vapour permeable membrane is used) or whether to use riven lath or sawn batten.  Riven laths are not straight and so the tails of the slates undulate slightly adding character to the roof.

The slates are lime mortar bedded across the tail and up the perpendicular joints (which are later scrapped out to allow free drainage).  This is an important detail which affects the roof’s appearance especially as it encourages the growth of lichens etc and for this reason the excess mortar was not cleaned off the slates’ surfaces.  Cement mortar supports completely different plants which radically changes the roofs ultimate appearance.



The mortar abutment on this roof is another example like the valley of weathering and intersection, in this case between the slating and a wall, without using lead soakers.  It was very common to seal the joint with a mortar flaunch with lengths of slate known in some regions as listings set into it to improve extra water shedding and to protect the mortar.  What seems to be special on this roof is that there was a void behind the slates rather than the listings being pressed into a solid mortar bed.


Traditional valleys are very important features of slate roofs and need not and should not be replaced with open lead valleys.  This is an instance where presumed better technical performance is cited for change but is not warranted and more likely is just an excuse for lack of skill.

The collar and tie valley reinstated here is known from Pembrokeshire and the West Country. 



The ridge was completely buried under the mortar slurry but when cleared it was found to be a wrestler.  These are made by notching slates or stones and interlocking them over the the top slating.  In Pembrokeshire the light-weight slates are mortared along the open top to lock the two halves together.