FALLS & DRAINAGEIt is a requirement of Building Regulation Part H that adequate provision is made for rainwater to be carried from the roof of the building.It is generally considered good practice for flat roofs to be designed to clear surface water as rapidly as possible. According to BS6229 & BS8217, flat roofs should be designed with minimum falls of 1:40 to ensure a finished fall of 1:80 can be achieved, allowing for any inaccuracies in the construction.Water ponding on membrane roofs should be avoided because:1. It encourages the deposition of dirt and leaves which can be unsightly, may obstruct outlets and /or become a slip hazard.2. In the event of damage, the interior may suffer greater water ingress.3. It increases the dead load and may cause progressive deflection of the deck.4. Ice may be a slip or wind hazard during the winter months.5. Roofs with extensive ponding require increased maintenance input.Although all Bauder systems are capable of withstanding ponding water for long periods of time, their ultimate life expectancy will undoubtedly be affected.Falls in the structure can be achieved by adjusting the height of the supporting beams or purlins, by using tapered supports, or by the addition of firring pieces before the deck is laid. In the case of a cast in-situ concrete slab, falls are normally provided by use of a screed.Tapered insulation systems are a lightweight, convenient and cost effective alternative method of providing falls to the roof and can be used with our reinforced bitumen membrane (RBM) and synthetic single ply roof systems. Our Technical Department can design bespoke insulation schemes for individual projects and provide advice on roof fall design.DrainageDrainage needs to be provided via internal rainwater outlets and downpipes or via external guttering systems or hoppers. Even if a roof is very small, it is recommended there are at least two drainage points in case one becomes blocked. Internal gutters linking internal outlet positions should be at least 500 mm wide.BS EN 12056-3 and the Building Regulations Approved Document Part H contain relevant design information to enable rainfall calculations to be undertaken and give design principles for gutters and downpipes. Alternatively, most drainage component manufacturers will make recommendations regarding the type, size and location of their products for any given roof project.204Typical Bauder Tapered Insulation SchemeLOCATING EQUIPMENTLocating Equipment on the RofFrom an integrity point of view, it is far better to site equipment directly onto a finished waterproofing system, as the less interruptions or penetrations to the membranes, the less likely the system is to allow water ingress. Plant is typically supported by paving slabs with a suitable protection layer beneath.Most Bauder warm roof systems (i.e. those using PIR insulation) are capable of supporting permanently sited plant with a weight of up to 2000 kg/m², avoiding the need for penetrations through the waterproofing.If the plant is either too heavy for the waterproofing to support, or requires fixing down to the structure, then it will be necessary to introduce a support system that can be easily waterproofed. For example, hollow section beams should be used in preference to section beams, and the larger the section, the easier it is to waterproof. Additionally, any fixings used should be of the flush head design to allow successful waterproofing.Another satisfactory way to provide support to plant is to cast concrete plinths, which can be waterproofed with Bauder membranes and capped with leadwork. Note the cable tray system employed in this picture, supported by proprietary free-standing adjustable feet with loose laid pieces of capsheet beneath, to provide protection to the waterproofing.Rooftop equipment mounted on a steel framework fixed to an adjacent wall is an excellent solution. It allows any future work required to the roof to be carried out without interfering with the plant.WALKWAYSWhenever there is a requirement for regular foot traffic across a roof, for example to provide maintenance to rooftop plant or a fire escape route, it will be necessary to provide protection to the surface of the waterproofing.It is normally sufficient to provide an extra layer of capping sheet in a contrasting colour to denote the walkway and provide sufficient protection. In cases of extreme traffic, promenade tiles can be bonded to the surface of the capping sheet using hot bitumen or a suitable cold applied adhesive.bauder.ie

205DESIGN FOR SAFE ACCESSAll flat roofs will have a requirement for a certain amount of pedestrian access, whether this is for maintenance of the roof and any rooftop plant or as a fire escape route. It is therefore necessary to design any flat roof to allow for safe access.Careful design can eliminate hazards and make the risks associated with roof access easier to manage. Under the CDM Regulations, designers have a duty to ensure that their designs give adequate regard to health and safety. Foreseeable risks should be avoided. If it is not reasonably practicable to avoid them, they should be combated at source. Priority should be given to design solutions providing general rather than individual protection. For example:1. Eliminate unprotected fragile materials.2. Minimise inspection and maintenance requirements for the completed roof structure.3. Consider carefully the siting of plant which will require maintenance. Are there alternatives to placing it on the roof? If not, is it in the optimum position on the roof where safe access can most easily be provided?4. When incorporating rooflights, always specify "non-fragile" and consider carefully their location.5. Provide clear and unambiguous specifications for safety critical elements of the design.6. Provide information relevant to maintenance for inclusion in the Health and Safety file.ROOFLIGHTSWhere rooflights are used the following should be considered:1. The specification of rooflights that are 'non-fragile'.2. Specifying rooflights that project above the plane of the roof and which cannot be walked on.3. Specifying rooflights with a design life that matches that of the roof.Access to flat roofs is often simple and because they are flat it is easy to walk around on them. Accidents happen not just to roof workers but also to engineers, surveyors, children, and caretakers etc. The first priority is to design out the risk at source; for example, by specifying adequate inbuilt edge protection. Designers should consider the alternatives available in terms of their effectiveness in preventing falls, as well as cost, aesthetics and buildability.Edge protectionThe options for edge protection in order of effectiveness are:1. Designed parapet2. Guard rail at the roof edge3. Permanent protected walkway for access to plant on the roof4. Preformed sockets to support temporary edge protection guard rails5. Running line systems designed, installed and tested to the relevant standards? Edge protection provided by free-standing handrail systemBauder supply rooflights for use in conjunction with our systems that are classified 'non-fragile'. These rooflights are guaranteed for the same duration as the roof system that they accompany. bauder.co.ukSpecification SupportNBS SPECIFICATIONSwww.bauder.co.uk/technical-centreTECHNICAL HELPLINET: +44 (0)1473 257671E: technical@bauder.co.ukFLAT ROOFDESIGN GUIDE