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Project Summary
History
This large Italianate mansion, completed in 1848, has a grade II* listed building status due to its exceptional architectural interest. It was designed by Anthony Salvin, a renowned architect well known for his restorations of Windsor Castle and the Tower of London, for Col. J.L.V. Watkins whose family had married into the Pennoyre family of Herefordshire.
The current building occupies the site of a former country house of 1779 and is actually said to be a recasing of this original home.
The property was used as a special school from 1947-67, a nursing home from 1968-2003 and has remained unoccupied since.
In 2005, the building was acquired by Bluewater Homes of Tredegar who began a total renovation and conversion to luxury apartments, which command spectacular views across the Brecon Beacons. M. Camilleri & Sons Roofing Ltd was appointed as a specialist roofing contractor to undertake the re-roofing of this historic building and its coach-houses. This work was successfully completed in September 2006.
The Project
On 13 January 2005, we visited site to carry out our initial survey in order to produce a budget quotation for the re-roofing works of the house and the coach-house.
The existing roofs appeared to be finished with a combination of 3 or 4 different slate types in various sizes. Initial overviews suggested a large roof of fairly complex design:
However, further investigations revealed that the project also carried further complexities and challenges once the “internal elevations were surveyed:
As a final revelation, the rear and side roof areas which appeared to be of bitumen covered lead cladding were in fact finished with an interesting “slate slab and roll” finish:
Research confirmed that the roof was originally entirely finished with this slab and roll detail, which was mostly removed around 1890 along with the very impressive conservatory dome (see above picture).
The Slate "Slab and Roll" System
Upon initial inspection, the existing slab and roll detail appeared to be a fairly simplistic combination of butt-jointed slate slabs (4, 5, and 6 feet long, 30 inches wide and 1 inch thick) with rounded slate rolls (about 3 inches wide and 3 inches high) located over the perpendicular joints of the slabs. Weatherproofing appeared to be achieved by the 7 inch laps of the slabs which spanned the timber purlins and by the slate rolls which appeared to have been required due to the straight bond pattern of the slabs.
 However, further investigation revealed a much more involved and ingenious design. The slab rolls were actually found to consist of a lower square edged section and an upper curved section which were rebated in order to provide a strong interlock. Furthermore, the lower roll sections were actually tapered to provide a uniform line down the roof and to avoid the steps which would have been created by the slab laps. The lowest roll section was laid on top of the first course of slabs from the eaves up and, once fixed, actually provided further mechanical resistance against the sliding load of the slabs above it (each slab was fixed at the head with 2 Nr. 1.5 inch screws). 
It seemed that water ingress was occurring as the putty and paint filler used in the fixing holes was failing due to thermal expansion and contraction. Furthermore, the side joints between the slate slabs and rolls were also permitting the passage of moisture.
A direction originating from Cadw meant that an element of the slab and roll system was to be retained and it was agreed to relay the system to the rear elevation of the main house, facing the Coach-house - an area which originally housed a majority of the remaining slabs.
Our research also revealed that a similar slate “slab and roll” system had also been used on the Reform Club in London, which has also suffered with roof leaks.
As the slabs were coated with a bitumastic compound, it was deduced that water ingress had previously been a problem. Our problem now was how to re-install the system to current standards, providing a guaranteed watertight finish without affecting the aesthetics of the roof.
The Solution
The major issues which were to be considered in designing a new fixing method were:
· Where are the weak points which are likely to permit water ingress?· How can the slabs and rolls be adequately secured? · Does the existing structure provide sufficient support for the slabs? Initial ideas revolved around a similar fixing method, with added measures to combat the known water ingress weaknesses. The biggest problem appeared to be the integrity of the filler used in the fixing holes of the slate rolls as the existing putty filler appeared to be breaking down and permitting water entry through the fixing point. A secondary water access point appeared to be via the joint of the roll to the slabs, as water tracks across to the slab joints. In order to combat the first point, it was proposed to use a linseed putty or molten lead filler with an oil paint finish as well as providing a mastic seal around the fixings. It was acknowledged that such measures would have a finite lifespan, however the easy access to surface based fixings means that remedial works every 5-10 years would be relatively easy. Consideration of the latter point brought about a secret gutter arrangement to facilitate the safe discharge of any side penetrating moisture. Lead welded weirs were included behind each fixing to prevent any water entering through the fixing points. 
Whilst this design was an improvement on the existing arrangement, concerns remained about:
· The ability of the slate slabs to span the proposed 25 inch distance between the 25 x 25 counterbattens.· The absence of any underlay. · The remaining potential for water entry through the side roll/slab joints. · The fact that upon further investigation, there was actually no close-boarding beneath the slab system. The design therefore evolved to include additional timber supports for the slabs, underlay and underlay supports, sealed roll/slab joints, noggins and layboards for the secret gutters. 6mm timber runners were introduced to aid airflow around the secret gutters, similarly 6mm counterbattens were used to ensure that the horizontal slab supports would not cause moisture traps. Mastic beads were included about the gutter tilting fillets as a further cautionary measure. The lead weirs were retained from the original secret gutter design to divert discharging moisture around fixing points. 
This final design was accepted by the client. (All design work, research and investigation was carried out free of charge).
Having completed this system re-design, further problems lay ahead in the logistics of actually removing and replacing the slab and roll system.
Site Work
As the slab system had been in place for around 100 years, the putty fillings in all of the fixing holes had solidified to such an extent that our only option for removal was to drill around each fixing and lift the slabs off. This applies to all roll fixings as well as the two head fixings per slab. A specialist water-cooled drill bit was procured for this purpose.
As the slabs were arranged on the roof in 4', 5' and 6' lengths (plus cut lengths at hips, valleys, chimney stacks, etc.) and the rolls rebated and tapered to suit this particular roof, it was obvious that the best results would be achieved by re-fixing the slabs and rolls in the same configuration. This required a very careful removal and indexing process for all components. Furthermore, it was vital that the system was removed with absolute minimal damage as replacement items carried a very high cost – this high level of care was also required to extend to the temporary storage of these elements.
The drilling element of the removal process resulted in enlarged fixing holes, unsuitable for countersunk fixings. These were therefore amended to suit:
Roof section with underlay, lead secret gutters and timberwork: Completed slab area: 
This was the first section of the main roof to be completed. When the entire roof was completed some 8 months later, no leaks had been reported.
The Traditional Slate Roofs
The refurbishment scheme also involved the removal and renewal of over 1,450m2 of pitched and vertical traditional slate coverings as well as over 720m2 of sheet lead coverings (box gutters, flat roofs, pitched roofs and vertical cladding).
The slated roofs included standard details such as open lead valleys, lead ridge and hip rolls as well as bespoke lead cappings to ornamental bathstone parapets. As the ornate Georgian ceilings and columns were to be retained, it was imperative that any water ingress suffered during the roof renewal work was kept to an absolute minimum.
However, as the central core of the main roof was to re-designed on a continuous, piece-meal basis this was not as straightforward to achieve as anticipated. As the client's budget could not accommodate an over-roof, we were required to work very closely with the main contractor and the carpentry team in order to achieve completion with minimal water entry. This was achieved with only two minor leaks suffered in a very extensive re-design.
N.H.I.C. Award
Our efforts in completing this project to the highest possible standard were recognised by the National Home Improvement Council as it secured their "Excellence in Roofing" award for 2007. The judges commented that this was a "complex project requiring utmost skills and attention to detail, it was completed on time and to budget. The new owners' succinct comments are probably the ultimate accolade when they concluded 'there are only a few roofing companies in this country who could have tackled a project of this complexity in such a successful and efficient manner." This is our second success in as many entries in this category as it repeats our 2002 award.
Gallery
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