Designers Knowledge Base
This includes roof coverings and finishes.
The designer should be aware of, and assess the risks from, the following principal hazards.
Possible hazards and risks
- falls from flat or sloping roofs caused by inadequate edge protection
- falls through openings in roofs such as roof lights caused by inadequate protection
- falls of objects or materials from roofs caused by inadequate edge protection, toe boards etc
- falls whilst gaining access to the roof for roof work and maintenance caused by poor access
- manual handling of materials caused by the size, weight, temperature or chemical nature of materials
- hot or harmful substances during use of hot asphalt or bitumen, welding or burning operations etc
Consideration must be given to safe means of access to and egress from the roof for construction, maintenance cleaning and repair and a means of providing safe working platforms. Influences such as the weather, the size, weight and shape of the roofing materials must be considered.
All of these can be drastically reduced by careful planning, experience and knowledge of safe methods and special equipment. Before any roof work is undertaken a safe system of work must be devised and all workers made aware of its contents. It must be followed throughout the period of the works.
The matter of safe access to roof areas must be described. A check list encompassing barriers, walkways and other necessary safety measures that must be examined must be given.
Designers can be instrumental in reducing the incidence of roof accidents by, for example, specifying non fragile roofing materials. The use of the following precautions universally would make roof work much less hazardous:
Flat roofs include those roofs with a pitch of up to 10º. All edges and roof openings should be fitted with suitable guard rails and toe boards. In the case of roof openings and roof lights an alternative is to provide a substantial cover which cannot be moved by a strong wind or by accident. Such covers should be clearly marked as to their purpose. Safe access on and off the roof must be provided by means of a general access scaffold or tied ladder. Workers should be trained never to walk along the line of roof bolts above the purlins.
Edge protection is necessary for all sloping roofs, that are of more than 10º pitch. It should consist of suitable guard rails and toe boards at the edge or eaves level to stop people or materials from falling off. Purpose made roof ladders or crawling boards must be used to spread weight when moving on the roof. The ridge anchorage of roof ladders should not rely on the ridge capping for support but should bear on the opposite slope of the roof. A safe means of working on the roof must be provided such as guard rails or a safety harness etc.
This involves all of the hazards above and in addition precautions must be taken against falls from the 'leading edge'. These are formed as new roof sheets are laid, or old ones are removed. Falls from these edges should be prevented as well as falls from the roof edges, or through fragile roofing materials. Fragile or lightweight materials, such as liner trays which could buckle and give way under the weight of a person can also be a problem at the leading edge and should also be protected. Careful planning must be done in advance of the work to provide a safe system of work and the following considerations taken into account.
- stagings in advance of the leading edge may be used to provide protection. These can be easily moved if proprietary runners are used and guard rails and toe boards can be used on the stagings
- harnesses attached to a suitable fixing can be used to give added protection together with running lines and inertia reels to give more mobility. Nets may provide a suitable alternative
- how the first sheets are to be laid should be considered as it may be necessary to provide a separate platform
- consideration should be given to the method of lifting roof sheets to the required level. Suitable lifting machinery such as an inclined hoist may provide the answer
- it may be possible to carry out the work using separate access equipment such as mobile elevating work platforms or tower scaffolds. These have the advantage of minimising the need to work on the roof and therefore minimise the risk of falls from the roof
Adverse weather conditions should always be taken into consideration when planning roof work. Roof work in wet slippery conditions or work in a high wind should not be allowed.