072 RCI 0717

RCI July 2017

New SPRA guidance on We can’t turn the clock back. Construction is getting more complex; work operations more specialised. Programmes are being squeezed and just-in-time roof protection procurement adds to the pressure. One of the consequences for membrane roofing is the intensification of activities at roof level during or after installation of the roof system. In recent years these pressures have resulted in some main contractors adopting a strategic policy of inverted roofing in the often misguided belief that they afford more inherent resistance to abuse. Since the waterproofing and insulation / ballast follow chronologically, the waterproofing can still be vulnerable to damage until covered. Sometimes this selection is appropriate, for example in areas with complex plant, terraces and podium decks. Sometimes this is the inappropriate choice, for example on large open areas or where there is complex detailing. In all circumstances, there is no excuse for an illinformed or casual attitude to protection of roofs. All roofing systems must be suitably protected during construction and during service. Risks A new SPRA publication ‘Protection of single ply membrane roofs – guidance and checklists’ was 072 JULY 2017 RCIMAG.COM By Jim Hooker, SPRA technical director drafted by representatives of membrane and insulation manufacturers with a vital contribution from the people who matter at site – specialist roofing contractors. It highlights the risks of failure to consider protection of the roof during construction and service. These include: • Compromised safety: a poorly protected and managed roof is often a less safe one, more prone to slip and trip hazards. • Water ingress and patch repair: in warm roofs, water ingress will pass to the insulation, where depending on type it may pass downwards to the vapour control layer where it can spread to other areas. With inverted roofs or uninsulated roofs, water ingress will pass directly to the deck. Tracing the source of ingress may be difficult, remedial work highly disruptive and concrete decks may be slow to dry out. • Delay to programme: water ingress or damage requiring repair will delay following trades and could have high consequential cost if insulation has to be dried out or replaced. The client will be unsettled and may legitimately ask why they are expected to be handed a new roof that has been repaired. Cost and delay will also be caused if it is necessary to undertake additional testing for integrity. • Reduced resistance to wind load: the attachment may be affected by repeated loading, especially if the single ply membrane is adhered. • Inverted and green roofs: a damaged membrane may go unnoticed before the insulation and ballast are applied. Investigation and repair will then be very difficult. Success starts with design The Guide recommends thorough consultation with the client as to how the roof will be used, with allowance for intensification of that use – or new uses – during its service life. Live loads, access routes and frequency, possible contaminants and likely additional self-loaded plant are just some of the considerations. Roof access points require special consideration and designated routes across the roof must match the ‘desire lines’ of users (visit your typical motorway services to see how not to design these). In warm roofs, the insulation should then be selected based on design static loading well within its compressive stress at 2% deflection (a table of suggested values is included). Where point and cyclical loads may be high, load-spreading using fleece-wrapped sheet steel beneath the membrane is recommended. Checklists The Guide includes a series of checklists for use by designers, main contractors and roofing contractors: • Performance parameters: for design and product selection. • Options: for temporary and permanent protection. • Pre-start agenda: standard items relating to protection and storage. • Site management: temporary protection, storage, sequencing, permit-to-work, testing. • Contractual arrangements: allows a quick SPRA MATTERS An unprotected roof as a working platform; never acceptable Patches are generally avoidable and they undermine confidence


RCI July 2017
To see the actual publication please follow the link above