Shingle file at primary school
Since the mid-1980s Hampshire County Council's (HCC) Winchester-based practice has undertaken a large and varied programme of work involving new build, rationalisation and refurbishment of the county's built estate. It has also established an international reputation for its innovative, quality buildings with costeffective solutions.But it is the remarkable series of primary schools produced during the past 25 years for which the practice is best known.
Senior architect Neville Churcher, who has been with HCC for more than 20 years, says: 'We try to design and produce buildings in a 'green'way, and hope to promote the culture of responsible and sustainable development to all the building's users, particularly the children.'
Churcher is the project architect for Whiteley Primary School, which is constructed on an environmentally significant site and comprises two phases, the first of which was completed last year.
The second phase, now under way and due for completion this year, will extend the school of 420 pupils in 14 classes to one catering for 630 children in 21 classes. The contract values of the two phases were respectively £2 million and £1 million, and the building has become a popular point of focus for the new and growing community.
Whiteley Primary School's building, playing fields and play courts are set within a heavily wooded landscape with a natural stream harnessed to make ponds.
Landscape features have been created to enhance the teaching facilities, and daylight and natural ventilation are key components of the design. Materials such as brickwork, laminated timber and cedar shingles help the building blend with its beautiful woodland setting.
John Brash and Company of Gainsborough supplied 1500m 2of shingles, in 420 and 230 bundles, for phase one and two respectively at Whiteley Primary School. It was also commissioned to supply the Childsplay Nursery at Hayling Island. Like Whiteley, this timber-framed nursery is a low-energy, fully day-lit building. Its design format may be used as a prototype for other nursery schools built by HCC over the next few years.
This 50-place nursery for children up to the age of four has clearly defined teaching, storage and service zones, with no wasted space or corridors. All of the areas open off the entrance hall or main teaching spaces, with the staff room on one side of the entrance and the head's room on the other. Such a design gives 360degrees vision for security and supervision.
Natural light and ventilation is achieved by a double-glazed roof with electricallyoperated vent panels. Approximately 300m 2of cedar shingles were specified for the nursery's large monopitch roofs.
Cedar shingles have a projected lifespan of 50 years if properly maintained and weather well in green settings, the aging process giving them a silver-grey appearance. Their lightness compared with tiles also reduces the costs of the support structure.
Depending on their size, shingles can be laid up to an angle of 14degrees although it is recommended that they be laid at 21degrees.
At Wh ite ley, the roof has been la id at 22.5degrees. The 400 x 75 cedar shingles are laid in four layers over standard roofing battens.Because it is a natural material, which needs to breathe, no sarking felt has been incorporated. Instead, the air flow from the ventilated space circulates around the underside of the roof covering. In wet or humid conditions, the shingles swell and careful fixing detailing is needed, with expansion gaps between adjacent shingles.
In general, without sarking, staining might be visible on the underside of the cedar roofs and, if necessary, a breathable sarking membrane may be incorporated.
However, the bonding of the overlayers of cedar shingles, as shown by traditional construction techniques, is sufficient to eliminate detrimental water ingress in suitably ventilated cold roof conditions.
The architect reports that at Whiteley, where there is no sarking, there have been no leaks associated with the roof, which was completed 16 months ago and has gone through a tough winter.
The shingles for both projects were chosen by the council because of their lowmaintenance and their obvious aesthetic qualities. They are equally suited to traditional and modern buildings and, in the particular case of Whiteley Primary School, were perfect for its rich woodland setting. The cedar shingles were also viewed as a sound long-term investment.
'Natural materials such as timber, cedar shingles and shakes, are part of a 'green' policy for Hampshire County Council which has proved very successful, ' says Churcher. 'The use of natural light in buildings occupied mainly during daylight hours has the dual benefit of a healthier environment for the users, and a near nil energy requirement.'
He adds: 'We talk about the cost of bad buildings and the value of good buildings.
Cedar shingles are relatively expensive but represent good value over the lifecycle of the material.'
The most thumbed portion of the Building Regulations Approved Documents must be Part A. It is one of those reassuring documents for the hard-pressed architect who wants a no fuss, no bother guide to easy structural integrity. The tables throughout Appendix A are designed for those architects specifying timber joists, beams, rafters etc and provide quick and easy checklists sufficient to abrogate the need for a structural engineer's input into the basics of roof and floor construction.
The tables are arranged in easyto-read columns and primarily differentiate between two Strength Classes (SC) - SC3 and SC4. The former has slightly less structural integrity than the latter, predominantly determined by the number of knots, etc. It is the grade stresses, which are the primary determining feature in terms of structural integrity, and the value of that particular grade stress determines the strength class of a timber.
BS 5268: Part 2:1996, Structural Use of Timber, based on European Committee for Standardisation (CEN) standards, contains an update to the established practices within the Building Regulations Approved Document. It is now legislation that the strength classes be determined by BS EN 338 strength classes (C16 - C30 for softwoods and D30 - D70 for hardwoods). In essence, the old standard SC3 and SC4 are replaced by the minimum equivalent strength class standards of C16 and C24 respectively.
In TRADA's Introduction and supply of timber to BS5268: Part 2:1996, it states that, 'specifications for structural timber prepared after August 1996 should refer to the BS EN 338 strength classes . . . however, specifications based on designs to the old strength class system may be encountered for some time'. After four years, maybe it is time that architects learned the new classification, and that the Building Regulations were updated to comply with the current legislation.