Ballast
Both washed aggregate and dense concrete paving slabs are suitable as ballast for use with ROOFMATE™ SL insulation.
Aggregate
This gives a good appearance at an economical cost and should be 20 - 40mm nominal diameter, clean, washed and reasonably free from fines.
When boards are overlaid with a suitable separating layer - such as ROOFMATE MK or ROOFMATE R - lapped 300mm, then a 50mm depth of 20/40 aggregate may be sufficient to counter both wind uplift and flotation of the insulation. Additional ballast may, however, be needed in those areas subject to greater wind uplift, such as exposed perimeters and corners.
Aggregate should be replaced by paving slabs:-
-
to form walkways where regular foot traffic is expected.
-
where the kerb at the roof edge is too shallow to retain the aggregate.
-
at perimeters, where calculations indicate aggregate will provide insufficient resistance to wind uplift or will be affected by wind scour - see BRE Digest 311.
Pavers
The pavers should be raised off the insulation on spacers to allow drainage and to avoid rocking. Alternatively, pavers may be set on a 20mm bed of pea gravel or sand spread over a layer of ROOFMATE MK or ROOFSTAT R**. The pea gravel bedding will assist drainage, support low strength pavers, accommodate changes of level and allow the use of thinner slabs: 40mm pavers with a 20mm depth of bedding will impose a total load of 140kg/m2.
** trademark of Terram Limited
