Building on the edge
Designing a building on a slope? You need to be aware of the increased distance now required between the bottom of a building’s foundation and an adjacent bank sloping away from the building.
Clause 3.1.2(b) of NZS 3604:2011 Timber-framed buildings has new requirements for the distance between the bottom of a building’s foundation and an adjacent bank sloping away from the building.
NZS 3604:2011 now considers existing ground conditions and has increased the distance foundations must be away from the edge of the bank to prevent the foundation being exposed by:
- localised slip failures in the bank
- erosion or frittering of the bank.
Minimum distances on banks
The minimum separation requirements from a building to the steeply sloping part of the bank are shown in Figure 1 for three different ground conditions. While the drawings show a foundation wall, the edge distances also apply where the perimeter of the building has an edge-thickened slab or anchor or braced piled foundations.
Other requirements given in NZS 3604:2011 for buildings close to the top of a bank are that:
- dimension H on Figure 1 is not more than 3 m
- the slope of the land away from the bottom of the bank is not more than 5°
- the ratio H/V is greater than or equal to:
• 1 for rock
• 2 for clay or sandy clay
• 3 for other materials. - the ratio L/V is greater than or equal to:
• 2 for rock
• 3 for clay or sandy clay
• 4 for other materials.
Download the PDF
Articles are correct at the time of publication but may have since become outdated.
