"As an interface, Lifespan SBEM should have no limitation on the number of zone which can be entered, however the SBEM calculation engine (provided by the BRE on behalf of the CLG), to which Lifespan SBEM interfaces may encounter problems with a high number of zones. We have been advised by the BRE that users should avoid creating more than 100 - 150 zones as creating a project with a very large number of objects may cause the calculation engine to slow down or crash. In order to reduce the number of objects handled by SBEM, any contiguous areas (vertically and horizontally) which are served by the same HVAC and lighting systems, and which have the same Activity within them may be merged. Small unconditioned spaces like store cupboards, riser ducts, etc., can be absorbed into the adjacent conditioned spaces similar envelopes may be combined. Within zones, any similar envelopes which have identical properties other than area may be merged. Where zones are absolutely identical the zone multiplier field may be used. The zone multiplier field will duplicate the zone, AND IT'S ASSOCIATED ENVLEOPES, WINDOWS AND DOORS, by the order specified in the multiplier field within the calculation. The duplicates will not be editable or displayed to the user and the building navigation reporting facility will report discrepancies in the floor/ ceiling areas when compared to the zonal area accordingly. The zone multiplier field can be found in the field after the Zone Name for each individual zone. Please note, these issues are inherent to the SBEM calculation engine (provided by the BRE on behalf of the CLG) and are not isolated to Lifespan SBEM.