Services Trenches Next to Buildings

Tuesday 16 June 2015

The Council has been asked to clarify the minimum requirements for the location of trenches in close proximity to existing or proposed buildings that are to receive foul water or surface water drains. This page explains the requirements.

Proximity of Trenches to Buildings to Receive Foul or Surface Water Drains

The specific requirements for trenches in close proximity to buildings are addressed in a number of compliance documents and standards. 

For the purposes of this article Council has decided to focus exclusively on New Zealand Building Code (NZBC) compliance documents E1/AS1 (acceptable solution for surface water drains), and G13/AS2 (acceptable solution for foul water drainage), plus standard AS/NZS 3500.5.2012 (Plumbing and drainage, part 5: housing installations).

When submitting a Building Consent application, the building Owner, or nominated Agent, or Designer, should indicate on the appropriate application form which means of compliance is being used (i.e. E1/AS1 and G13/2, or, AS/NZS 3500.5.2012).

Surface Water Drains

E1/AS1 – item 3.9.7 and Figure 14

Item 3.9.7: For light timber frame and concrete masonry buildings constructed to NZS 3604 or NZS 4229 in accordance with B1/AS1 (Structure), pipe trenches which are open for no longer than 48 hours shall be located no closer than distance “V” (see Figure 14 copied below) to the underside of any building foundation. Where the trench is to remain open for periods longer than 48 hours, the minimum horizontal separation shall increase to 3V in all ground except rock.

fig 14 pipe trench to building400px

[Note: AS/NZS 2032 (Installation of PVC pipe systems), AS/NZS 2566.1 (Buried flexible pipelines, part 1: structural design), and AS/NZS 2566.2 (Buried flexible pipelines, part 2, installation) also provide other acceptable solutions].

Foul Water Drains

G13/AS2 – Item 5.6.1 and Figure 8:

Item 5.6.1:  For light timber frame and concrete masonry buildings constructed to NZS 3604 or NZS 4229 in accordance with B1/AS1 (Structure), pipe trenches which are open for no longer than 48 hours shall be located no closer than “V” to the underside of any building foundation as shown in Figure 8 (copied below).  Where the trench is to remain open for periods longer than 48 hours, the minimum horizontal separation shall increase to 3V in all ground except rock.

fig 8 pipe trench to building 400px

 

Excavation Near Footings

AS/NZS 3500.5.2012 – Item 4.15.2 and Figure 4.15.2 ()

For reasons of copyright Council is unable to copy the information contained in AS/NZS 3500.5.2012 into this article.

However, AS/NZS 3500.5.2012 can be purchased from at www.standards.co.nz, or they can be contacted on freephone 0800 782 632, or by e-mail on enquiries@standards.co.nz.

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