Masterspec
08 Dec 2020
MASTERSPEC BEGINS A NEW INDUSTRY PARTNERSHIP WITH STEEL CONSTRUCTION NEW ZEALAND (SCNZ)
Masterspec and SCNZ are delighted to announce a new industry partnership to support the structural steel design, fabrication and erection in the New...
26 Nov 2020
STORMWATER DRAINAGE DESIGN – NEW OPPORTUNITIES IN NZBC E1 NOVEMBER 2020 UPDATE
November 2020 brought a number of updates to the Building Code, including a new Acceptable Solution in the form of E1/AS2 in its newest version,...
26 Nov 2020
GREEN STAR UPDATE TO VERSION 1.0
The Green Star Technical Manual v3.2 has been superseded by Green Star Design and As Built NZ v1.0. Also Green Star Office Interiors v3 has been...
24 Nov 2020
GUTTER & DOWNPIPE DESIGN MADE EASY
It is not often that changes to the NZBC Acceptable Solutions and Verification Methods provide a windfall that makes life a whole lot easier for a...
29 Oct 2020
LATEST BUILDING CODE 2020 UPDATES
Earlier this year MBIE ran public consultation on proposed changes to a number of Acceptable Solutions and Verification Methods. Despite a number of...
06 Oct 2020
THE STATE OF CONSTRUCTION – BY THE NUMBERS
At Masterspec the amount of specifications live on the platform at any one time has always given us an indication of the health of the industry. In...
29 Sep 2020
UPDATES TO MASTERSPEC SUSTAINABLE & GREEN BUILDING GENERAL SECTIONS
A number of the formal sustainable systems, Living Building Challenge and Green Star, have recently made significant changes to their systems....
01 Sep 2020
AMENDMENTS TO STRUCTURAL STEEL STANDARD AS/NZS 5131
AS/NZS 5131: 2016, Structural Steelwork - Fabrication and Erection is cited in NZBC B1/VM1, 5.0 Steel. This new Amendment A1, which has just been...
04 Aug 2020
WHAT ON EARTH IS EQUIPOTENTIAL BONDING
This month Masterspec has added more clauses to the electrical sections about earthing and equipotential bonding of conductive elements of the...
02 Jul 2020
NEW GENERIC WORK SECTION 7765 - ELECTRIC VEHICLE (EV) CHARGING STATIONS
Masterspec's new generic section, 7765 Electric Vehicle (EV) Charging Stations, responds to increasing EV ownership and NZTA's coordination of NZ's...
30 Jun 2020
REPLACEMENT STANDARDS FOR CEILINGS & SPRINKLERS
There have been quite a few new and amended Standards since the beginning of lockdown. Two major replacement Standards you should know about...
30 Apr 2020
STRUCTURAL INSULATED PANEL SYSTEMS (SIPS) - AN ALTERNATIVE BUILDING SYSTEM
Masterspec introduces a new generic section 3876 STRUCTURAL INSULATED PANEL SYSTEMS (SIPS) (available in Standard, Basic,
23 Apr 2020
COVID-19 GUIDANCE FOR THE SPECIFIER
Masterspec's Managing Editor Alex Shaw suggests how using the information at this link can help ensure your project fulfils its obligations to provide...
31 Mar 2020
SCHEDULING FUNCTIONALITY INCREASED TO INCLUDE SLIP RESISTANCE
To help reduce repetitive content and streamline the user experience, a new schedule section 1278SR SCHEDULE OF SLIP RESISTANCE TESTING has been...
31 Mar 2020
PROPOSED BUILDING CODE UPDATES - CONSULTATION REPORT APRIL 2020
MBIE are proposing changes to a number of Acceptable Solutions and Verification Methods which can be viewed in their consultation document....
17 Mar 2020
MASTERSPEC TOOLS FOR REMOTE WORKING
With the challenges facing everyone in the coming months it’s likely to be busier than ever for many Masterspec users. Here are some of the Masterspec...
17 Dec 2019
BUILDING CODE NOV 2019 UPDATES - INTERIM CHRISTMAS REPORT
On 28 November 2019, the transition period started for updates to six Acceptable Solutions and Verification Methods. Masterspec has almost completed...
17 Dec 2019
NEW GENERIC SECTION 7455 STORMWATER SOAKAGE SYSTEMS
The section relates to the design, supply and installation of stormwater soakage systems for residential and non-residential applications. Stormwater...
16 Aug 2019
UPGRADED EDITOR ON NEXTGEN2
We have been working on improvements to the editor function on NextGen2, and the new upgrade will go live from the weekend of the 17th of August. You...
02 Aug 2019
BUILDING CODE UPDATES 2019 - INTERIM REPORT
Masterspec has almost completed its review of the updates to the approximately sixteen Acceptable Solutions and Verification Methods. Although one or...

GUTTER & DOWNPIPE DESIGN MADE EASY

24 Nov 2020

From the 5th November 2020 the new changes to the NZBC Acceptable Solutions and Verification Methods have been able to be used for compliance.  In this case with Surface Water, the changes to NZBC E1/AS1 and the addition of NZBC E1/AS2, unusually provide a windfall that makes life a whole lot easier for a designer.  This windfall relates to the NZ Metal Roofing Manufacturers Association Inc. (NZMRM), Code of Practice (CoP), roof drainage design 5.7 Capacity Calculator.

Changes to E1/AS1 and the addition of E1/AS2

E1/AS1 Appendix A has had the Rainfall Intensity maps deleted and very extensive Rainfall Intensity tables added providing locations all over New Zealand and their Annual Exceedance Probability (AEP). These tables have been based on National Institute of Water and Atmospheric Research (NIWA) rainfall data. This rainfall data forms the bases of calculations for roof and rainwater goods design for a particular site.

The new E1/AS2 allows AS/NZS 3500.3: 2018 Stormwater Drainage to be used as an Acceptable Solution (with some modifications). AS/NZS 3500.3, among other things, allows more complex and accurate calculations for roof and rainwater goods design, also using NIWA rainfall data. The calculation can get a little complex, however an easier solution already exists.

NZMRM Capacity Calculator

The Capacity Calculator has existed for some time, it was developed by NZMRM in response to what they believed was an Acceptable Solution that severally under-rated requirements for roof and rainwater goods design. NZMRM developed the Calculator to be consistent with AS/NZS 3500.3 not the old Acceptable Solution.

The new changes adding NIWA rainfall data to E1/AS1 and the addition of E1/AS2 means there is a close alignment with AS/NZS 3500.3. This means the NZMRM Calculator can produce an outcome that corresponds with or exceeds the Acceptable Solutions.

The calculator allows you to easily calculate or test:
  • gutter sizes for residential and commercial projects, both internal and external gutters (& spouting) and the resulting maximum roof area, etc.
  • downpipe sizes for residential and commercial projects, for both internal and external gutters (& spouting), round or rectangular downpipes and the resulting maximum roof area, etc.
  • valley gutter sizes for various roof pitches and the resulting maximum roof area, etc.
Note; for all the above elements the calculator applies various "short term multiplication factors". This allows for 1or 2 minute rainfall intensities which can be as much as 4.3 times the intensity over a 10-minute period used by the NIWA rainfall data. This is important as the velocity of water on a steep smooth metal roof can compound high rainfall intensity at the gutter very quickly.

Check it out

If in the past you have registered on the NZMRM website then the links below to the Calculator and other documents will work. If you have not registered before, click here on the NZMRM Capacity Calculator do the register and agree to terms and it will then open for you.

The NZMRM Capacity Calculator is a very handy tool which allows you to run a number of scenarios very quickly. The scenarios can range from sizing gutters to reduce cost to testing extreme rainfall events to reduce risk.

The NZMRM CoP provides details on roof drainage design and what drives the Calculator in the CoP section 5.6 Roof Drainage.

For more background, NZMRM have an old article on the Calculator called "Gutter and Downpipe Design". However, it pre-dates the new changes to NZBC E1/AS1 and the addition of NZBC E1/AS2, so ignore the references to NZBC E1/AS1 in their article as they may not reflect the current situation.


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