Glance west on the M1 between junctions 13 and 14 and you will see something almost surreal. As if a vast blue spacecraft has landed in the fields, the new 60,000m² John Lewis MP2 building shimmers on the horizon. It is part of the huge Magna Park development by McLaren Construction for IDI Gazeley/Brookfield Logistics Properties, on which there are already eight buildings of over 23,000m², let to big names such as River Island and A G Barr – makers of ‘Irn Bru’. But even these will be dwarfed by the 65,000m2 Waitrose national distribution centre, known as Project Barley, which may have achieved a world first for McLaren by completion in 22 weeks from first pour.
The vast composite panel roof by FK Construction using Kingspan Panels, Brett Martin Rooflights and SFS Intec fasteners was completed in just nine weeks. This involved careful planning and collaborative working on such potential conflicts as safety netting required for roof cladding, but elevated work platform access required for installation of drainage pipework.
This plot lies near the highest design loading for drainage in the UK. As anyone familiar with the rainfall maps in BS EN12056 Part 3 ‘Gravity drainage systems inside buildings – Part 3: Roof drainage, layout and calculation’ will know, drainage capacity is related to how hard it rains, not how often. The prevalence of big thunder events in this region provides design intensities almost twice what might be experienced where it rains frequently, such as the North-West or Scottish West Highlands. The numbers are truly staggering. The siphonic drainage designed and installed by SRDA member West Siphonics was also completed in nine-weeks. It has two-level operation, with three hundred outlets and over 8Km of high density Polyethylene (HDPE) pipework. The primary will drain 100.8mm/hour/m²; the secondary will drain 136mm/hr/m². The combined siphonic systems will drain a combined 7037 litres per second in peak storm conditions – enough to fill an Olympic sized swimming pool within six minutes. The main warehouse has two areas; the Low Bay, at 18.9m high by 302m long has six primary drainage systems and twelve secondary systems (twin secondary systems were required in the valley gutters given the huge volumes of water).
The High Bay is 21.9m high and 116m long, with six primary and six secondary systems. In the highly unlikely event of rainwater intensity exceeding the design levels, overflows are incorporated at the end of each gutter, which direct water to ground via separate downpipes, thus avoiding overflow from high level. As West Siphonics’ design manager Michael Barraclough put it: “On a project of this scale, and with such a short site programme, coordination with all parties was key. From design stage through to completion of our works all parties worked handin- hand to ensure the works, were completed within programme and to the highest standards.” This care over design is not just theory. Those in the midlands and south will remember nature’s revenge over the weekend of August 8 and 9, when rainfall intensity nudged fifty-year values in parts of the south-east and leading to the evacuation of several supermarkets. This new system had just been completed and it had to cope and it did. Siphonic systems cannot be tested live for the obvious reason that the volumes of water required would be prohibitive. Instead, they are jointly inspected by the roofing contractor and siphonic specialist and air-pressure tested. So the water is successfully transferred to ground, but what then? At Project Barley, the primary systems have siphonic underground drainage which discharges direct to SUDS lagoons on the site. The office areas transfer to three rainwater harvesting tanks for grey water re-use.
The building is aiming for a BREEAM ‘Excellent’ rating, partly through its retention and re-use of rainwater. SRDA sets standards for the UK siphonic industry and provides a helpline to designers, contractors and clients, but its influence is wider, with around 10% of enquiries coming from the Project Barley at Magna Park, the vast new logistics centre for Waitrose follows other huge projects at the site. Jim Hooker of the Siphonic Roof Drainage Association explains more about this vast project The record breaker Gulf States and Far East. In particular, its Criteria for Membership makes specific reference to HDPE pipework systems as follows:
2. Pipes, fittings and joints (without brackets) should be suitable to withstand the positive pressures applied during pressure testing. The pipes, fittings and joints (without brackets) should also be suitable to withstand the magnitude and duration of the negative pressures that might be generated during siphonic operation taking account, if necessary, of possible ovality of pipe. 3. The pipe clamp system must be capable of restraining pipework against lateral movement by providing support around the entire circumference of the pipe. Pipe supports may be fixed to a rail to prevent lateral movement or directly to the structure. 4. In the event of a dispute, calculations shall be presented to the Secretary of the Association to prove the adequacy of a pipe support system.
And… D.2 Full Member Installation
1. Members must publish full installation instructions covering: – Detailed drawings which demonstrate the method of attachment of the outlet to the waterproof membrane for which the outlet is designed. – Compliance with BS8490 regarding system design and jointing. – System maintenance. 2. HDPE pipework: factory-control conditions must be achieved in all fusion welding: – Butt fusion jointing must be by use of hydraulically-controlled machinery. – Electrofusion sleeves must be used for all other welding. – The installation must be in compliance with BS 8490 regarding jointing. SRDA was also instrumental in the development of BS 8490:2007 ‘Guide to Siphonic Roof Drainage Systems’ the key parts of which are contained in the freely downloadable ‘SRDA Guide to Siphonic Drainage’ available from www.siphonic-roof-drainage.co.uk . Members must demonstrate compliance of their software against this standard both at application and by triennial audit, with includes a site inspection by an independent consultant.