Plumbing Connection 4-2015

6 4

PLUMBING CONNECTION

SUMMER 2015

NOTE:

Methods of preventing this backflow are as follows:

(A) PROVISION OF SLOTS IN THE FRONT OF THE GUTTERING.

This clause was superseded by: AS/NZS 3500.3.1 – 1998;

however the fact that it had been deleted and replaced with AS/

NZS 3500.3.2003 Cl3.5.3 was never passed on to the industry.

This Standard directs you to Appendix G (See below).

Take particular notice of Diagram C which shows a 10mm

gap off the fascia. We have argued with the VBA at length

about this gap, it allows for 10,000mm

of overflow for every

metre. To put that into perspective, it is the same as two

100 x 50mm downpipe pops – the most common downpipe

pop used in domestic gutter installations – for every metre

of gutter.

I met with members from the VBA and members of the

Association of Hydraulic Services Consultants Australia

(AHSCA) to discuss this regulation. They both agreed that

the 10mm gap will in principal not only look bad but the

allowance for overflow in a large number of cases will be

excessive. The VBA have given BlueScope Lysaght the okay

to use a 2mm spacer clip which we believe will provide

sufficient provision for overflow, but in my meetings with

VBA members, it was agreed that a circumstance could

arise when the 2mm or 2000mm

per metre might not be

adequate.

I also discussed this with Mark Alexander from (AHSCA)

and he didn’t feel comfortable with a clip that only spaced

the gutter 2mm off the fascia unless the job had been

hydraulically estimated and proven 2mm was sufficient. He

also believed it was leaving the roofing contractor open to

litigation.

I told them I was developing a new clipping system for my

customers and wanted them to sign off on it before putting

it into production. They told me that for my business to be

assured it had the best solution for our customers and our

business, they would like it to be a minimum of 4mm. That

would mean 5000mm

or one 100 x 50mm downpipe pop per

1.25m of gutter. Both groups thought that this would offer a

more broad solution and would provide enough overflow on

all domestic dwellings.

I had the pleasure of meeting with Matt Jansen from

Stratco where he showed a video of their testing. They set

up a rig that used the 1 in 100 year rainfall from Bundaberg:

Highest 1 in 100 year rainfall according to them. It saw

340mm per hour over a 5 minute period on a roof that was

16m long by 1m wide (16m

Their testing showed that even at the highest rainfall

reading in Australia, a 2mm gap will work, but it has no

room for error. They recommend a 100% buffer which is a

5mm spacer). This was disputed by AHSCA who stated that

the way it was tested in a calm environment and making

calculations for the water pressure over a 16m sheet,

without actually using a 16m sheet, was a factor.

This test proves in theory that we are working toward a

solution. Neil Creek from the Australian Steel Institute and the

other rollformers in the meeting asked the question, “If we

have this testing done in the correct conditions and ratified by

a known expert, will it be accepted?” The VBA agreed. Some

of the people in the room were also on the NCC committee and

said that this would make its way straight into the code.

BOX GUTTERS

I also took time to look back at an article I wrote about

the correct sizing of box gutters and started to look at some

of the other problems that contractors are facing such as

box gutter compliance.

Plumbers and roofing contractors have been working

with builders and supervisors to design effective box gutters

while on site but some of the issues that are stated in both

Australian Standards and HB39 are things that need to be

addressed at the design stage of the production process.

I will outline all of the points that are important in

properly designing box gutters to ensure they are installed

correctly across the industry.

Extracts taken from

SA HB 39:2015 and AS/NZS

3500.3:2015.

SA HB 39:2015 – 5.1 BOX GUTTERS UP TO 600MM

1.1.1 OVERFLOWPROVISION AND SIZE

To protect buildings from a total or partial blockage of

outlets, downpipes or stormwater drains, it is essential that

box gutters discharge all roof water clear of the building via

overflows. To ensure that adequate overflow provisions are

made and any surcharge is accommodated, the overflow

weir of any rainhead is to be 25 mm below the sole of the

gutter discharging to the rainhead or alternatively rainheads

are to have appropriately sized and positioned overflow

provision [see Figure 5.3.1(a)].

Particular attention is to be paid to the following (see

Figure 5.3.1):

(a) The size of overflows are to be calculated in accordance

with AS/NZS 3500.3.

(b) Overflows are to be terminated in such a way as to

prevent damage to buildings and property.

not less than the design flow for the associated gutter

outlets, and discharge to atmosphere.

NOTE:

For the design of appropriate overflow devices

such as rainhead, sump/side overflow and sump/high

capacity overflow devices, see AS/NZS 3500.3.

This basically says that you have to allow for sufficient

provision for overflow, assuming that

all outlets are

blocked.

Plumbers must ensure that no water can backflow

into the house if this happens.

METAL ROOFING 101

PETER COLL