Finished Levels are Critical
…to you and your client
The rotting or wetness of the bottom area of external cladding is a regular topic on client call-backs or leaky building investigations.
One common reason is the absorption of moisture from landscaped ground cover such as bark and mulch which touches the cladding. The technical term for this is wicking and the action is similar to the edge of blotting paper touching and absorbing wet ink.
This occurs when landscaping and extra high ground cover is added by the client well after the building has been completed. Hopefully you have photos of the elevations of completed buildings that show compliance with the regulations, however it is important and necessary for builders to inform new home owners of the building regulation minimum heights and the consequences of not adhering to these.
These critical levels are the house floor level must be:
1. A minimum of 225mm above ground level
2. Or 150mm above paved surfaces
It's a timely reminder that your drawings must show specific levels and the relationship between them to comply with these regulations. Without these, you, the builder, are accepting liability for setting levels, which is an extra risk that you do not need to be taking on.
A range of levels are necessary for all projects and it is best that levels are set from a datum.
A datum is a clearly defined survey reference marker, from which ground and building levels are measured. This level is referenced to the distance above zero, being mean sea level.
Use of and links to an official datum level is required where BCA rules the building’s floor level is critical, such as in a flood plain or where there are height restrictions.
Such levels must be established by a Registered Surveyor and should be completed at the same time as boundary lines defined, again a BCA requirement, particularly when houses are located close to fence lines.
Some BCAs also require surveyor certification confirming the as-built location and building envelope compliance. Be aware of all these legal requirements and ensure the client meets such payments as required.
If there is no official datum or legal requirement to be linked to it, then the top of a suitable metal pin or timber stake is set in position to become the datum, with a level of 0 or 100 from which the levels are measured. GPS instruments can be used to determine heights but the experts warn that bogus results can occur from ignorance of this new technology.
In addition to floor levels, the other levels that should be shown on drawings for accurate construction include:
existing and future site(ground)levels. Showing ground levels on drawings varies from contour lines of the same level, grid lines containing levels, or simply random spot levels.
• Existing site or ground levels are identified as GL (Ground Level) or numbers (levels) on a site plan, relative to a datum and its location.
• Final levels are shown as RL (Reduced Level) or FGL (Finished Ground Level) because these often vary from the original site levels.
• Building floor levels are presented as BFL (Basement Floor Level), GFL (Ground Floor Level), FFL (First floor Level) and so on.