Roof Tile Association (RTA) members strive to offer the best quality roofing products, in terms of technical performance and long-term durability. The RTA endorses BS 8612 Dry fix products which have been used in the UK now for almost 50 years, though their use has hugely increased in recent years, particularly with the requirements for mechanically fixed ridge and hip tiles, introduced in the last 2014 revision of BS 5534.
There are many advantages to dry fix products, such as being maintenance-free. Unlike mortar bedding, dry fix systems can cope with settlement by allowing a degree of flexibility in the movement in the surrounding materials. RTA dry fix systems are designed to mechanically fix the roof components to withstand the highest wind loads a roof is ever likely to encounter and can also provide the required amount of high-level roof space ventilation.
BS 8612 provides material specifications and durability criteria, as well as performance criteria for rain resistance and mechanical resistance against wind loads. The Standard then goes on to give performance criteria for dry ridge, hip and verge systems, as follows: –
Dry Ridge Systems
A dry ridge system must perform four major functions; 1) withstand wind loads to prevent the system and associated ridge and hip tiles from being dislodged, 2) prevent the ingress of driving rain and snow, 3) where applicable, provide the required high-level roof space ventilation in accordance with BS 5250 and 4) remain durable.
BS 8612 provides test procedures to determine the resistance of a dry ridge/hip system to vertical and horizontal wind loads. The Standard also provides the methodology to determine the predicted wind load for any given situation.
For ridge and hip rolls; i.e. the types that dress and bond to the shape of tiles, there are test methods to determine the strength of the material after aging, the bond strength of the adhesive and the extent of elongation. There are two classes to define whether a ridge/hip roll is suitable for a) flat and low-profile tiles, or b) for high profile tiles; eg. deep-dish bold roll tiles and pantiles.
Dry Verge Systems
A dry verge system must remain durable and perform the following technical functions; 1) resist predicted wind loads, 2) close the gap between the tiles/slates and wall or bargeboard top, 3) drain any water from the roof away from the gable wall and 4) act as one of the fixings for the roof tiles or slates.
BS 8612 sets out test methods to determine the resistance of a dry verge system to horizontal and vertical wind loads. It also provides information, based on BS 5534, to determine the predicted wind loads on verges. The vertical uplift resistance data can be used to check that the dry verge system is suitable to resistance wind loads on the roof tiles at verges when used in conjunction with their primary fixings.
The verge system must prevent water from running down the gable wall in concentrated streams, which can lead to staining and mould growth on the wall. In this regard, BS 8612 gives a test method to determine if water running through a verge system will run away from the wall. The same test can be carried out on continuous dry verge systems and in particular the joints in continuous systems.
So, what does this all mean for the designer, client and roofing contractor? Actually, it is quite simple; you can be sure that by choosing products from RTA members, your dry fix systems are in full compliance with BS 8612 and will offer reliable technical performance and long-term durability.