The basic system height without packing should be able to fit between the high point in the subfloor and the desired Finished Floor Level (FFL). Packers and, where necessary, elevating blocks are then used to level out areas below the high point.
To calculate the basic system height determine the size of the void needed beneath the floor boarding by considering the height of services which will run in the void. Remember that service pipes may need space to cross over each other and that in the worst case this could occur at the high point of the tolerance in the subfloor. Add the thickness of the preferred floor boarding to give the basic system height. (N.B. If the floor is to comply
with Robust Details the void allowed must be at least 50mm.)
Double check that the basic system height at the high point will marry in with other fixed points in the building such as stairs, corridor screed levels or the thresholds of patio doors.
From the table below select the basic system height and floor boarding closest to (but not more than) your needs. Packing will make up any difference.
The above table is based on a Uniformly distributed load of 1.5kN/m2 and Concentrated load of 1.4kN as specified for self contained, single family dwelling units in BS6399-1:1996. Exceptional loads (such as storage heaters) may require support direct from the subfloor. It is also recommended that in high load areas such as kitchens and bathrooms support bearer centres are reduced to 300mm. Communal areas in blocks of flats such as corridors and vestibules will require special consideration. CMS Danskin can provide centres for other floor boarding and types of use.