How to apply a ballasted roof?
A ballasted (gravel/paved) roof will generally require a stronger supporting structure than that for the exposed membrane one, but will allow the roof to be used as a trafficked or leisure use area.
In the case of ballasted roofs, ballast will consist of rounded gravel 20–40 mm diameter at a minimum rate of 80 kg per square metre and 50 mm thickness, or pre-cast hydraulically pressed concrete pavers of 50 mm minimum thickness and approximately 120kg/m2. Gravel ballast of 20–40 mm diameter is required in order to provide resistance to the effects of wind scour, BRE Digest 311 (July 1988) refers, which can easily remove smaller units from the roof.
The use of timber decking can also be considered as a ballasted application but due to its general lack of sufficient actual dead weight to resist the wind forces, special measures would need to be considered.
Sika-Trocal Ballasted Roof Systems
Sika-Trocal SGmA is a multi-layer, synthetic roof waterproofing sheet based on premium quality polyvinyl chloride (PVC) with an inlay of non-woven glass fibres.
A homogenous sheet, with the addition of a layer of random glass fibres in the middle of its thickness which is designed to virtually eliminate shrinkage and provide the necessary dimensional stability. Intended to be used solely as a covered roof membrane restrained against wind uplift forces by the dead weight of ballast. In certain applications, such as with timber decking for instance, it can also require the use of additional restraint in the form of mechanical fasteners as used with the S types.
Containing biocides, Type SGmA is highly resistant to ageing and industrial pollutants and the bacteria that flourish in the moist layer of dirt present at membrane level in all ballasted roofs for long periods of time. Like Type S the Type SGmA will not require any maintenance throughout its service life. Additionally, the membrane and its joints are root proof, which makes the material suitable for incorporation, if required, into a garden roof.
Type SGmA membranes are not intended to be exposed, as they are not formulated to resist the effects that arise in that very different environment. We manufacture specific products for that application, the Type S membranes.