Sub structure work to a conservatory can be restricted to a single brick foundation in some circumstances, according to Surveyor Don Wentworth of the Installer magazine, the official journal of Top 100 Trades Windows, Doors and Conservatories.
Don points out that exempt conservatories can benefit a simplified foundation design conditional on the ground conditions being acceptable and the foundation strip being proportioned to ensure acceptable load spread. With a foundation depth in excess of 700mm (to avoid frost heave) a simplified approach permits conservatory contractors to reduce both time and cost in arriving at conservatory base level.
The important aspect according to Don is that the arrangement incorporates a ground level cavitray that also functions as the wall dpc. The slab membrane extends partly into the brickwork bedding course onto which the cavitray is bedded. The cavitray rises within the cavity created by the inner skin and then returns into the block work.
Water arrested within the cavity by the tray is discharged out of the structure via caviweeps incorporated within perp joints at 900mm centres. With profiled lengths and preformed angles, the conservatory installation can benefit a consistent and instantly formed build detail. The Conservatory Base Cavitray is manufactured by Cavity trays of Yeovil and in the words of Don makes this design approach perform 100%.
This cost-effective simplified approach should be considered for lightly loaded conservatories only. Alternative approaches are recommended where the conservatory structure departs from the points outlined above or where the conservatory is being used as an extension of the living space. And if protection against radon gas is required or thermal breaks might be beneficial, Cavity Trays of Yeovil has a whole range of compliant protective solutions.