DRAINAGE, LAYING OUT THE OPTIONS


PIPES

The Building Code

There are a number of options when it comes to the design of a drainage system, Acceptable Solutions, Verification Methods and Alternative Solutions, as you would expect.  However, it is more complicated than that as there are a number of options and limitations, even within the Acceptable Solutions.

The three areas to be looked at are;

  • Sanitary Systems - Discharge pipe system serving waste water fixtures and soil fixtures, usually within the building, this includes, traps, venting, floor wastes etc.  Up to connection to Foul Water system.
  • Foul Water Systems - Foul water drainage pipes usually beyond the building and underground, this includes, gully traps, grease traps, access/inspection points and chambers, trenching and backfilling, etc.  Up to connection to, main/sewer, treatment or septic tank etc.
  • Surface Water Systems - Includes roof drainage, external surface drainage and subsoil drainage, and may include, spouting, gutters, down pipes, sumps, long or short term storage, filtration, trenching and backfilling, , disposal etc.  Up to connection to, main/stormwater drain, or disposal system (soakage, watercourse etc).

Sanitary Systems

The main Acceptable Solution for this is NZBC G13/AS1 Sanitary Plumbing, it's scope is limited to buildings/systems not more than 3 storeys and does not include specialised systems (ie. hospitals, labs, and some industrial waste, etc).  However there is another Acceptable Solution which does not have these limitations and that is NZBC G13/AS3 Plumbing and Drainage, which allows the use of AS/NZS 3500.2: Plumbing and drainage - Sanitary plumbing and drainage, (modified by clauses in NZBC G13/AS3) as an Acceptable Solution.

NZBC G13/VM1 Sanitary Plumbing, Allows the use of BS EN 12056.2: Gravity drainage systems inside buildings - Sanitary pipework, layout and calculation.  This Standard is strictly a design Standard and does not cover installation.

Beyond these Alternative Solutions and specific design would have to be used.

Masterspec has updated related sections to allow NZBC G13/AS1 or NZBC G13/AS3 (AS/NZS 3500.2) to be easily selected by the Q&A. Related Masterspec sections that have been updated are:

7151 SANITARY FIXTURES TAPWARE

AND ACCESSORIES

(Standard, Basic, Services, Landscapes, Interiors)

 7420 SANITARY FIXTURES

(Basic, Services, Interiors)

 7421 SANITARY FIXTURES 

(Standard, Services, Landscapes)


Foul Water Systems   Sewer_cover

The main Acceptable Solution for this is NZBC G13/AS2 Drainage, it's scope is limited to pipe diameters no more than 150mm and non-pressurised systems (non-gravity flow, pumped etc), it does not include some industrial wastes, etc.  However there is another Acceptable Solution which does not have all these limitations and that is NZBC G13/AS3 Plumbing and Drainage, which allows the use of AS/NZS 3500.2: Plumbing and drainage - Sanitary plumbing and drainage, (modified by clauses in NZBC G13/AS3) as an Acceptable Solution.

There is no Verification Method for Drainage only Alternative Solutions and specific design.

There is  NZBC G13/VM4 Foul Water: On-site Disposal, which allows with some limitations the use of AS/NZS 1547: On-site domestic wastewater management, for the design and construction of the collection, storage, treatment and disposal of foul water on-site.

Masterspec has updated related sections to allow NZBC G13/AS1 or NZBC G13/AS3 (AS/NZS 3500.2) to be easily selected by the Q&A.  Related Masterspec sections that have been updated are:

 7430 DRAINAGE

(Basic)

 7431 DRAINAGE GENERAL

(Standard, Services, Landscapes, Struc & Civil)

 7461 FOUL WATER DRAINAGE

(Standard, Services, Landscapes, Struc & Civil)

 7462 WASTEWATER TREATMENT SYSTEM 

(Standard, Basic, Services, Landscapes, Struc & Civil)

 

Surface Water Systems

The main Acceptable Solution for this is NZBC E1/AS1 which is limited to a catchment area of 2,500m2 maximum.  Up to 100ha NZBC E1/VM1 can be used.  Specific design (Alternative Solution), is necessary beyond this, but can also be used at any time.

NZBC E1/AS1 does not address things like, detention/retention, outflow and on site disposal, NZBC E1/VM1 does a little, 7.0 Outfall Protection and 9.0 Disposal to Soak Pit.  This can make life difficult for the designer as there is not much direction, however most Councils have their own requirements and standard details for these, which may help.

Related Masterspec sections that have been updated:

 7112 RAINWATER STORAGE TANKS

(Standard, Basic, Services, Landscapes)

 7430 DRAINAGE (Basic)

 

 7431 DRAINAGE GENERAL

(Standard, Services, Landscapes, Struc & Civil)

 7441 GROUNDWATER DRAINAGE

(Standard, Services, Landscapes, Struc & Civil)

 7451 SURFACE WATER DRAINAGE

(Standard, Services, Landscapes, Struc & Civil)

 

Warning About NZBC G13/AS3

There is a small warning about NZBC G13/AS3, there seems to be a typo or format problem in AS3 that can be confusing.  The first heading is "1.0 Installation of PVC-U pipe" the following clause 1.0.1 has no heading and is about PVC-U pipe.  But the next clause has a heading and is "1.0.2 AS/NZS 3500.2", which is about the use of the Standard, and the final clause is "1.0.3 Modifications to AS/NZS 3500.2".  The first thing this final clause does is refer to a table with multiple materials for use as pipes.  So what seems to be only PVC-U ends up with a range of pipe material.  It appears as if the first heading was intended for the first (PVC) clause and does not apply or restrict the other two.

Drainage-InstallationBuried Pipes Parallel to Foundations

For Foul Water pipe installation, when the building is to NZS 3604 or NZS 4229, the relationship of parallel pipe trenches to foundations will be to NZBC G13/AS2, fig 8, (even if using AS/NZS 3500.2, refer clause 3.8.2.d.ii), other buildings will be specific design if the drains are below the foundations.

Similarly for Surface Water pipe installation, when the building is to NZS 3604 or NZS 4229, the relationship of parallel pipe trenches to foundations will be to NZBC E1/AS2, fig 14, (which is identical to fig 8 above), NZBC E1/AS1 clause 3.9.8 allows some other options, but beyond these specific design will be required if the drains are below the foundations.

 

Environmental Impact

PVC-U Pipe Environmental Consideration

PVC is allowed under some environmental standards and not under others, but if you are faced with using PVC and wish to use the most minimal environmental impact PVC pipes/conduits, specify Best Environmental Practice PVC (BEP PVC) to AS/NZS 1260: PVC-U pipes and fittings for drain, waste and vent applications and/or AS/NZS 1254: PVC-U pipes and fittings for stormwater and surface water applications.  Compliant pipes should have the words "Best Environmental Practice PVC" or "BEP PVC" printed on them.

This information has been added to most of the Masterspec drainage sections as Guidance Notes.

Link to industry guidance on BEP:

http://www.pipa.com.au/sites/default/files/document/attachment/pop106.pdf

Pipes

Buried PVC-U Pipe

Underground PVC-U pipe to comply with AS/NZS 1254: PVC-U pipes and fittings for stormwater and surface water applications or AS/NZS 1260: PVC-U pipes and fittings for drain, waste and vent applications should be Load Classified as follows:

  Classification

 Use

  SN4 - SN6

  Domestic & light load areas

  SN8 - SN10

  Commercial & Industrial medium load areas

  SN16

  Public roads & high load areas

Note; For critical very high load areas SN20 may be desirable, but check availability.

This information has been added to most of the Masterspec drainage sections.

Civil Engineering Drainage Pipes

The Masterspec sections for Civil Engineering drainage, 8621 STORM WATER DRAINAGE (Struc & Civil) and 8622 SANITARY SEWERS (Struc & Civil), have been updated with further pipe detail added.  Besides the information on PVC-U, further information has been added about concrete pipes, steel pipes and polyethylene pipes.  The increased detail includes, material class, load class, watertight/water pressure class, wall thickness (or dimension ratios SDR), internal pipe linings, and external pipe coatings.


More on Electronic Leak Detection

http://www.icri.org/EVENTS/Spring13Present/05_Weds%20AM%205.pdf

http://www.wbdg.org/resources/roofintegritytesting.php

 

 

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