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Disclaimer

Although the information contained in this Code has been obtained from sources believed to be reliable, New Zealand Metal Roofing Manufacturers Inc. makes no warranties or representations of any kind (express or implied) regarding the accuracy, adequacy, currency or completeness of the information, or that it is suitable for the intended use.

Compliance with this Code does not guarantee immunity from breach of any statutory requirements, the New Zealand Building Code or relevant Standards. The final responsibility for the correct design and specification rests with the designer and for its satisfactory execution with the contractor.

While most data have been compiled from case histories, trade experience and testing, small changes in the environment can produce marked differences in performance. The decision to use a particular material, and in what manner, is made at your own risk. The use of a particular material and method may, therefore, need to be modified to its intended end use and environment.

New Zealand Metal Roofing Manufacturers Inc., its directors, officers or employees shall not be responsible for any direct, indirect or special loss or damage arising from, as a consequence of, use of or reliance upon any information contained in this Code.

New Zealand Metal Roofing Manufacturers Inc. expressly disclaims any liability which is based on or arises out of the information or any errors, omissions or misstatements.

If reprinted, reproduced or used in any form, the New Zealand Metal Roofing Manufacturers Inc. (NZMRM) should be acknowledged as the source of information.

You should always refer to the current online Code of Practicefor the most recent updates on information contained in this Code.

Scope

This Code of Practice provides requirements, information and guidelines, to the Building Consent Authorities, the Building Certifier, Specifier, Designer, Licensed Building Practitioner, Trade Trainee, Installer and the end user on the design, installation, performance, and transportation of all metal roof and wall cladding used in New Zealand.

The calculations and the details contained in this Code of Practice provide a means of complying with the performance provisions of the NZBC and the requirements of the Health and Safety at Work Act 2015.

The scope of this document includes all buildings covered by NZS 3604, AS/NZS 1170 and those designed and built under specific engineering design.

It has been written and compiled from proven performance and cites a standard of acceptable practice agreed between manufacturers and roofing contractors.

The drawings and requirements contained in this Code illustrate acceptable trade practice, but recommended or better trade practice is also quoted as being a preferred alternative.

Because the environment and wind categories vary throughout New Zealand, acceptable trade practice must be altered accordingly; in severe environments and high wind design load categories, the requirements of the NZBC will only be met by using specific detailing as described in this Code.

The purpose of this Code of Practice is to present both Acceptable Trade Practice and Recommended Trade Practice, in a user-friendly format to ensure that the roof and wall cladding, flashings, drainage accessories, and fastenings will:

comply with the requirements of B1, B2, E1 E2 and E3 of the NZBC;
comply with the design loading requirements of AS/NZS 1170 and NZS 3604 and with AS/NZS 1562;
have and optimised lifespan; and
be weathertight.

COP v23.09:Roof-Drainage; Valleys

Valleys

5.5 Valleys

A valley is a gutter at the internal intersection of two sloping panes of roof cladding.

Valley Fixing

5.5.1 Valley Fixing

Valleys should not be positively fixed, except at the head, because that would inhibit expansion and can produce noise.

Alternative means of securing the valley gutter to the substrate include:

A clip system allows for thermal movement and security.
A compatible washered nail or screw or a galvanised nail, provided they do not penetrate the sole of the gutter.

5.5.1A Valley Clip System

Valley clip system

Valley Design

5.5.2 Valley Design

Valley gutters must discharge into a rainwater head, sump, or an eaves gutter. The discharge point must be within 2 m of a downpipe if the catchment area exceeds 50 m².

When the roof pitch is less than 12°, the valley should be made in one piece or the joints must be sealed. To ensure snug fitting, the valley angle should be matched to the pitch of the valley support. Having the valley too open will result in a diminished capacity, and too sharp an angle will make installation difficult.

5.5.2A Common Valley Shapes

RD06 Tray depth

5.5.2B Internal Valley Angle

Roof Pitch	Internal Angle
3°	176°
5°	173°
10°	166°
15°	159°
20°	152°
25°	145°
30°	139°
35°	132°
40°	126°
45°	120°
50°	114°
60°	104°

5.5.2C Maximum Valley Catchment in m² for Areas Having a 50-year Rainfall Intensity <150 mm/h

Roof Pitch	3°	5°	8°	10°	12.5°	15	20°	25°	30°
A 3-fold			12	18	29	41	70	106	146
B standard			25	34	47	63	99	140	184
C Deep	60	86	152	180	215	251	321	389	452
D Tile					17	22	33	45	57

Free Board: 15 mm for pitches 8° and above
20 mm for pitches below 8°

For other pitches, rainfall intensity, and valley shapes refer to the 5.5.7 Valley Capacity Calculator tool.

For information about internal corners, refer to 5.4.3 Internal Corners.

Bifurcated Valleys

5.5.3 Bifurcated Valleys

The maximum recommended catchment area for a bifurcated valley is 10 m².

5.5.3A Ridge Meets a Valley in line with the Valley

Bifurcated Valley

Intersecting Valleys

5.5.4 Intersecting Valleys

5.5.4A Correct Valley Intersection

Correct Valley Intersection

Centre line of intersecting valleys to meet 50 mm past the fascia line.

5.5.4B Incorrect Valley Intersection

Incorrect Valley Intersection

Changing Angles in Valleys

5.5.5 Changing Angles in Valleys

A change of roof pitch in a valley run will usually result in the change of angle in plan view. The change is acceptable, but the freeboard of the lower valley must be at least 20 mm to allow for turbulence.

Asymmetrical Valleys

5.5.6 Asymmetrical Valleys

Where opposing roofs of different pitches discharge into a valley‚ an asymmetrical valley is required. As these have reduced cross-section area compared to a symmetrical valley at the same (lower) pitch, it is often necessary to increase the valley dimensions. Increasing the depth has the biggest effect on capacity. Greater depth can be gained by using 10 mm ply valley boards, standing purlins on edge, or fitting valley boards flush with the rafter. The consequences that a deeper valley will have on the capacity of the gutter it discharges into must also be considered.

A valley baffle is recommended where the difference in roof pitches exceeds 10°. Valley baffles are also helpful in wooded locations to minimise lodging of debris under the roof overhang.