Drawing standards: dimensioning of ceiling heights (Nat)

Problems can arise in the way dimensioning is shown on building plans.

The standard practice when dimensioning floor plans is to show room size dimensions between the structural components of the walls and not include internal wall linings, for example plasterboard or wall tiling.

However for ceiling heights, there is some difference of opinion within the building industry as to whether the dimension includes floor and ceiling linings or finishes.

To avoid any misunderstanding between the designer, builder, carpenter and client it should be clearly noted on the working drawings as to whether the height shown is the finished floor/ceiling dimension or the height between the structural members.

This will avoid the possibility of builders constructing walls at the heights shown on plans and not allowing ceiling and floor linings and plaster battens if used. It removes the responsibility from the carpenter to have to ‘guess’ what the finished floor to ceiling dimension will be when constructing his walls.

A good practice when preparing building plans is to indicate whether the ceiling height dimension is taken from the finished floor level (F.F.L) and the finished ceiling level (F.C.L), or the height is taken from the structural floor, if installed before the wall framing, and the bottom chord of roof truss or ceiling joist/ upper storey floor joist, whatever the case may be.

These abbreviations should be included on the dimension floor and ceiling lines, with an explanation of the abbreviations, or noted if the dimension is between structural members. It should be up to the designers to establish the floor to ceiling height at design stage.

It is also important to consult the project specifications, as they may nominate where the ceiling height dimension is to be measured from and this will take precedence over the working drawings.

Another issue can be that of width of wall linings to accommodate standard ceiling heights. For example, plasterboard lining is manufactured in two standard widths, 1200mm and 1350mm. These are designed to fit in with 2400mm and 2700mm ceiling heights and allowance must be made for ceiling linings, flooring (if fitted after wall framing) and clearance for settlement and shrinkage. This should be taken into consideration when establishing a finished ceiling height.

Also maintaining a certain overall height of buildings can be important in two storey construction where the building is approaching maximum allowable heights.

If an accurate overall height is not established during the design stage and builders have to ‘add on’ height for clearances then they may breach this requirement. 

For further information HIA members can contact HIA’s Building Services staff on 1300 650 620 or hia_technical@hia.com.au .

To find out how to become an HIA member call 1300 650 620 or click here to join online

Ref No. NAT MAT 08-15

The above is intended to provide general information in summary form. The contents do not constitute specific advice and should not be relied upon as such. Formal specific advice should be sought by members with respect to particular matters before taking action.  ABN 99 004 631 752