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New Home Plumbing Tauranga

plumbing planWe undertake many new homes each year. We treat them like a blank canvas and try to paint each one perfectly, how perfectly is often influenced by other sub trades... so it is really important for all trades to be all on the same page. This is where the client enters, or the project manager; a full set of correct  plans is vital.

The following information is to assist the people trying to project manage there own build, builders or architect/designers.

In recent times it is clear there is confusion that stems from the designer or architect trying to draw a drainage plan, a knowledge of the plumbing code is required here. If you require help we offer a free service to get this correct at the beginning.


There are two plumbing systems available to use commonly in New Zealand,  NZS G13 and NZS/AS 3500  designers are getting these systems confused; drawing lines that the plumber has to try decypher. The designers are without knowledge or training and unknowingly forming a hybrid system that does not comply with the building code.

Building inspectors are blaming the plumber for having to design a compliant system onsite and deviating from what is drawn on the plan (it is obvious the design needs to be correct on plan at beginning). Unfortunately the plan is also passing through council approval stage and only being sorted out once the home begins construction.

I will attempt to outline the key point differences in a nutshell below:

NZS G13 is characterised by not being very flexible in its design. The waste pipes in 32mm, 40mm or 50mm must not exceed 3.6 meters in length, if they exceed this length they must be fixture vented through roof, they must also be vented if two or more fixtures  are connected to one pipe.

These pipes must run to a gully trap and dish. If any of these points are varied from the system is not a NZSG13 system at prefloor.

The head of the drain must have a 80mm terminal vent usually by a toilet, all toilets must have a 50mm vent through roof. Because the terminal vent is 80mm it is difficult to have vent inside the building as  holes larger than 40mm go through the top plate or studs require plate stiffeners (these are engineered and premade) the plate stiffener has a hole size of 50mm and pipe is 80mm in diameter, the terminal vent needs to boxed into a void or run up outside wall so as to not disturb the structural integrity of building. If any of these points are varyed from the system is not a actual NZSG13 system at prefloor.

NZS/AS 3500 is a much more flexible system in design but often confused with G13. Wastepipes are in 40mm, 50mm, they must not exceed 4 meters in length without back venting or a air admitance trap being fitted, if the waste pipe can be run in  65mm the length can extend out to 10 meters with requiring a back vent, multiple fixtures can be connected to the 65mm waste pipe or 100mm pipe with out back venting, technically these pipe sizes are now called drainage.

The venting requirements are also much more forgiving with possibly only one 50mm diameter back vent to serve a whole house  as long as its at head of drain. Because the vent diameter is only 50mm this can be run easily internally without affecting any structural integrity by installing the premade engineered plate stiffeners.

We recomend more than one terminal vent for this system as we have noticed that the shower traps get pulled through and bathrooms get smelly. The description I have written has over simplified a very complex system and there is a lot more to understand and consider on a job by job basis to get thigs correct

The NZS/AS3500 system is obviously an easier system to work with however the designers have been mislabelling the plans in a effort to fool councils into skipping a extra inspection at prefloor stage, to save on the minor cost and calling it g13. Things come unstuck though when the plumber is required to do the pipework legally and in a compliant manner, We have to redesign the system and the sometimes under trained building inspector in plumbing systems often does not understand why it has been done, only that it is different to what is shown incorrectly on the plan. What follows is sometimes a heated arguement and a paperwork nightmare with amendments to council file.

There is often a lot of confusion for people trying to project manage and sometimes results in wasted effort. We would try to encourage people to organise a nice timeline of when work is to be done with some allowance for poor weather.


There are three distinct phases to a project for plumbing:

1 Before we begin prefloor pipework, we like to have the confirmed kitchen plan layout, a list of all plumbing fixtures or at least the toilet, shower and bath detail before the prefloor stage. These are vital to ensure the pipework is in correct place at the beginning, otherwise there is costly breaking up concrete and altering pipework, a definite smear on our perfect canvass of work. The pipework is filled with water and tested for leaks and inspected, insulation placed around pipework to stop damage and rubbing from cured concrete.

2 At the preline stage, this is where all information absolutly needs to be known, This is when home moisture barriers are on outside and the ceiling battens are in place, Any pipework alterations to prefloor pipework is done now if required. We install hot and cold pipework, pressure test pipework  to over 1500kpa as required by the building code (we surpass this and test to 1900kpa).

After a plumbing inspector has sited the test pressure guage we then install the bath and shower mixers and repressurise the pipework to 500 kpa again to check for any leaks on unions (most plumbing companies don't bother to do this). Then fit the bath and showers trays, these we flood test and check for any leaks on waste pipes or traps connected to the trays (many plumbers don't bother to do this) then the home is ready for gib linings.

3 Nearing the home's completion we are called to fit off the fixtures. This is after the tiling is completed, the shower linings are completed, the kitchen is installed fully with bench tops. Any flooring or vinyl in the kitchen is installed under the dishwasher. Then the plumber can begin his fit off, preferably before any carpet is laid. If there is any under-sink filtration or fridges or any extra items now is the time to have it onsite so it can be installed with efficiency.

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