Guidance document SGD10/11 PROTECTION OF SINGLE PLY MEMBRANE ROOF SYSTEMS DURING CONSTRUCTION AND SERVICE 1.0 Introduction 2.0 Design 2.1 End use considerations 2.1.1 Balcony or roof terrace 2.1.2 Location and access for plant and equipment 2.1.3 Weight provision for located plant and equipment 2.1.4 Access for frequent maintenance 2.1.5 Access for fire escapes 2.2 The choice of construction materials 3.0 Requirements of the construction process 3.1 Access to the roof by 'other trades' 3.1.1 Foot traffic and the construction process 3.2 Use of the roof as a working platform 3.3 Storage of materials 3.4 Green and ballasted roofs 4.0 Temporary protection 4.1 The need for temporary protection of completed roof systems 4.2 Methods of temporary protection 4.3 Areas requiring temporary protection during the construction phase 5.0 Roof management 6.0 Conclusion A Appendix A. Typical insulation compressive strength values B Appendix B. Insulation fitness for use criterion 1.0 Introduction The application of single ply membrane water proofing, to both new build and refurbishment warm flat roof constructions has grown significantly year on year for the past three decades. This growth has been due to the design flexibility of single ply membranes and their ability to provide a high quality, cost effective solution to constantly changing and evolving building regulation requirements. The fast track nature of current construction methods can lead to increased demands upon the roof construction. It is essential now, more than ever, that the necessary design, job planning and project management is applied to ensure that the completed roof provides for a good quality installation. This guide is intended to detail the requirements to provide protection to single ply membrane roof applications and highlight SPRA recommendations to ensure good practice throughout the construction process. 2.0 Design 2.1 End use considerations The design requirements and the functionality of the roof will vary with the building type and occupiers needs. It is important that these requirements together with possible constraints are recognised by the architect at the earliest possible stage in the design and construction process. The design process therefore should include input from the membrane manufacturer, main contractor and roofing contractor, to ensure that the specific design and specification requirements of the client are met and accommodated. This will enable effective review and modification, where required, as the design develops. The proposed use of the completed roof should be considered in the design specification. Roof usage may include any of the following: 2.1.1 Balcony or roof terrace. The design should provide resistance to point loads and dynamic loading caused by regular pedestrian traffic. Typically this would include paving, installed above the membrane layer upon load spreading pedestals. 2.1.2 Location and access for plant and equipment. e&oe Single Ply Roofing Association 2011 1 of 5
Suitable provision should be made for maintenance to plant and any other areas requiring regular maintenance. For plant requiring regular access, design provision should include for the forming permanent walkways, which when provided should follow and protect the obvious direct route, since this is the route that will be taken. The route should be well clear of areas which might be prone to temporary ponding and be finished with a non-slip surface. A handrail or fall arrest system may be an additional requirement. (See SPRA Guidance document - Safety: Design for reduced risk ). SPRA membrane and insulation manufacturers should be consulted for advice on compressive strength of insulation, & supplementary load-spreading sheets below the waterproofing where traffic is frequent. The design of the walkway should be specified in accordance with usage requirements and will be provided by the SPRA membrane manufacturer. 2.1.3 Weight provision for roof located plant and equipment The designer or specifier should consider the installation requirements for any roof located plant or equipment. Wherever possible, any roof mounted plant such as air handling and refrigeration units, PV panels etc should be positioned on independent upstands bearing directly onto the structural deck. The structure should be capable of supporting the weight of any such plant or equipment. In the case where plant or equipment is not to be supported by independent roof mountings but instead applied directly onto the membrane, then the insulation layer beneath the single ply membrane material should provide sufficient resistance to the compression load imposed, including any dynamic loading requirements. Guidance should be sought from the appropriate SPRA insulation manufacturer with respect to the suitability of individual materials to support specific items of plant or equipment and the maximum load bearing capacity of the insulation boards. Comparison of the ability of individual insulation materials to undertake compression strain is achieved using the values of the compressive strength at 10% compression (CS(10)). Appendix A of this guide lists the minimum SPRA compressive strength requirements for typical generic insulation types. Should the weight per square metre to be imposed by the plant or equipment exceed the declared compressive strength (CS(10)) of the insulation material, then the load should be spread over a larger area of the roof using steel plates of appropriate strength. The specification for load spreading of plant and equipment over insulation boards should be provided by the insulation manufacturer and must additionally meet the requirements of the SPRA membrane manufacturer. Should de-mountable feet be used to support roof located plant or equipment then steel plates of appropriate strength should be used to spread the imposed load. Guidance should be sought from the appropriate SPRA membrane and insulation manufacturers. Point loading of insulation and membrane layers may damage the waterproofing layer and should be avoided. 2.1.4 Access for frequent maintenance. All materials developed for single ply roofs are capable of withstanding occasional light foot traffic for inspection purposes. However for reasons of health and safety, the building design should where possible eliminate the necessity for maintenance requiring roof access. Where this is unavoidable, for example for window cleaning or certification checks to equipment, provision must be made in the roof design to accommodate safe access and provide adequate protection of the membrane and insulation from point and cyclical loading associated with it. 2.1.5 Access for fire escape routes. Slip-resistant and secure walkways should be formed delineate the specific fire escape route to be followed. 2.2 The choice of construction materials The flat roof specification should be determined in conjunction with the appropriate SPRA membrane manufacturer. The construction materials chosen for the flat roof specification should reflect the end use requirement. Where frequent access over the roof area is necessary, the roof design should reflect this requirement. Walkways should be formed above the waterproofing membrane, the design of which shall be provided by the SPRA membrane manufacturer. e&oe Single Ply Roofing Association 2011 2 of 5
Should the roof require access for more than annual inspections, then consideration should be made with respect to the suitability of the insulation to accept such regular pedestrian traffic. In this respect, guidance is provided within MOAT No 50:1992 'Technical guidelines for the assessment of thermal insulation systems intended for supporting waterproof coverings on flat and sloping roofs'. See Appendix B which summarised Table 2 of MOAT 50:1992, which details examples of a fitness for use classification for insulation materials. Where frequent maintenance is envisaged, the insulation should be of minimum class C in accordance with MOAT No 50:1992. Note that it is permissible to use a better grade of compressibility than the specified minimum for any application denoted in Table 2. 3.0 Requirements during the construction process 3.1 Access to the roof area by other trades Fundamentally, a single ply roof system must provide protection from all weather conditions likely to be experienced during its design life. Such protection may be required before building completion to facilitate rapid fit-out of the interior. In this event, there may be a requirement from 'other trades' to traffic the installed roof prior to building completion. 3.1.1 Foot traffic and the construction process Consideration should be given to the suitability for roof traffic both during and after construction. Areas that will sustain heavy foot traffic after installation but prior to completion should be adequately protected. During construction, considerations must include the following: The distribution of roof access points and the effect of repeated loads on the system nearby. Load-spreading protection will usually be required. The location of plant and the provision of heavy-duty walkway sheets to protect the waterproof membrane. Even on non-access roofs, the construction process itself places demands upon the resistance of the system to repeated loads; it should be a major consideration in design and product selection. 3.2 Use of the roof as a working platform In general, no building work should be carried out from a completed roof. Paint, cementicious materials, plaster and solvents should not be allowed to come into contact with the completed roof surfacing. Good design and site management should aim to ensure that a completed roof is NOT be used as a working platform. Such practice may cause damage to the roof surface and necessitate repair and or replacement of the membrane and insulation materials. Should 'other trades' be required to access the completed roof area, for example for the installation of roof plant or equipment, the roof surface should be adequately protected to prevent damage. Temporary roof protection must be provided to ensure adequate protection for the completed roof surface from both the expected pedestrian roof traffic and also material transportation and storage across the roof area. (See Temporary Protection, section 4.0). The use of the completed roof area for the construction of scaffolding to access higher roof areas must be discouraged. Good project management should ensure that higher roof areas are completed in advance of the lower roof areas (see Roof management, section 5). Where this is not possible, the roof surface should be adequately protected to spread the anticipated point loading. It is important to seek advice from both the membrane and insulation manufacturers should this be undertaken in order to ensure that the required loading provision can be met without damage to the completed roof construction. 3.3 Storage of materials Where construction materials are stored on the completed roof construction, point loading on the surface of the waterproofing layer should be avoided by means of load spreading using adequate temporary roof protection. No sharp objects should be in contact with the roof surface. Waste skips must never be located on completed roof areas. The temporary storage of large H & V equipment on the completed roof construction, prior to installation should be avoided. It is preferable that this equipment is craned onto the roof area and located at the time of installation. e&oe Single Ply Roofing Association 2011 3 of 5
3.4 Green and ballasted roofs During the construction phase of green and ballasted roofs, there will be a requirement for the loading of heavy duty ballasting materials upon the completed roof surface, prior to its usage installation. Suitable load spreading measures are required in this instance and advice should be sought from the appropriate insulation and membrane manufacturers with respect to the maximum permissible loading. Where possible, ballast should be applied adjacent to the area of application. Where this is not feasible and transport across the completed roof area is necessary, then additional temporary load spreading will be required to protect the completed roof area (see section 4.0 below). 4.0 Temporary protection To avoid damage to a completed roof construction it is recommended that temporary roof protection is always installed. 4.1 Temporary protection of completed roof systems Full temporary protection of the roofing is essential if following trades are to use the finished roof as a working platform or access walkway. The responsibility for ensuring this must be agreed between relevant parties during the course of the building operations. 4.2 Methods of temporary protection The most effective protection is timber panels such as plywood or oriented strand board with taped or linked joints, laid on a geotextile fleece. Re-usable, rolled reinforced mats are becoming available and are recommended since they reduce waste and cost but their suitability/compatibility should be checked with the membrane manufacturer. Where load spreading of heavy duty materials are required, it is essential that the load spreading medium rests fully upon the roof surface. The use of 'raft' constructions whereby the load is distributed directly to timber bearers, thereby applying a point load onto the completed roof surface must be avoided. 4.3 Areas requiring temporary protection during the construction phase These include the following: All areas of the completed roof where frequent pedestrian traffic is anticipated 'by other trades'. All roof access points, particularly for 'step down' access areas onto the roof area. For all completed roof areas being used as 'working platforms' (see 3.2). Below all roof areas being used for the storage of roofing materials (see 3.3). NB In all cases it is essential that any protection layer is in itself adequately ballasted to resist wind uplift. 5.0 Roof management Good project management will always ensure that the risk of damage to the completed roof area by other trades is reduced. Cooperation between the main contractor, the roofing contractor and other trades is essential to provide a co-ordinated approach to the demands of individual trades. In this way it is possible to ensure that good practice is followed and provide for a high quality product. The use of handover certificates to record that completed sections of roof have been inspected prior to access from following trades is recommended. The use of electronic testing to roof areas prior to access from following trades, when appropriate, is also recommended to verify integrity. SPRA recommends that the main contractor or the roofing contractor (whichever is appropriate) operates a permit to work system for any follow on trades in areas where the roof installation is complete. It is essential that accurate records are kept, along with photographic evidence, when roof areas are being accessed. e&oe Single Ply Roofing Association 2011 4 of 5
6.0 Summary The application of good working practice during all stages of the flat roof construction process will ensure that the completed waterproofing system meets the client s needs and requirements. Addressing the client's requirements at an early stage in the design process will ensure that the most suitable system specification including the most appropriate products and installation sequences are employed. The most important of all of these provisions is the need to protect the membrane surface from damage caused due to excess loading and trafficking without the use of either temporary or permanent (where required) load spreading protection. Success will be achieved every time by using best practice in the form of good site management, good design provision and correct installation of all components. 7.0 References [1] SPRA Design Guide 2016 [2] SPRA/BRUFMA Component quality standard for PIR insulation [3] SPRA/MIMA Component quality standard for mineral wool insulation [4] SPRA/BPF Component quality standard for expanded polystyrene [5] MOAT No 50:1992 ' Technical guidelines for the assessment of thermal insulation systems intended for supporting waterproof coverings on flat and sloping roofs' 8.0 Appendix A Typical insulation compressive strength values Product Type Minimum compressive strength Comments at 10% deformation CS(10) PUR / PIR 150 kpa See SPRA/BRUFMA Component quality standard Mineral wool 60 kpa See SPRA/MIMA Component quality standard Expanded Polystyrene 150 kpa See SPRA/BPF Quality Component Standard Note: the compressive strength value of individual insulation materials may vary. Consult the appropriate SPRA insulation member to obtain the correct value and additional guidance with respect to load spreading requirements. 9.0 Appendix B Insulation fitness for use criterion Table 2 of MOAT No 50:1992 ' Technical guidelines for the assessment of thermal insulation systems intended for supporting waterproof coverings on flat and sloping roofs' Fitness for use of class of insulation A B C D Roof only accessible for Roof only accessible for Roof accessible to pedestrian Roof accessible to lightweight purpose of maintenance. purpose of maintenance. May traffic. May be used where vehicles. Only to be used Only to be used with be used without any frequent maintenance of where the waterproof special assessment of the restrictions equipment is envisaged. covering is protected by Institute concrete paving or similar e&oe Single Ply Roofing Association 2011 5 of 5