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Review of Gutter Systems

and Fixing Methods

This document contains the findings from two earlier reports:

1. ADDENDUM to Review of Gutter Systems and Fixing Methods: 29 May 2008

2. Review of Gutter Systems and Fixing Methods: 10 April 2008

These documents should be read in conjunction.

Chief Investigator: Dr Shaun Manning (PhD, B.Engineering)

24 June 2008

ADDENDUM Review of Gutter Systems and Fixing Methods pdf Dr S. Manning 10 April 08

DATE: 29 May 2008

2

ADDENDUM to

Review of Gutter Systems

and

Fixing Methods Chief Investigator: Dr Shaun A. Manning (PhD, B.Engineering)

Newcastle Innovation Limited –

Industry Development Centre

University Drive

Callaghan NSW 2308

Australia

Date prepared: 10 April 2008

Addendum prepared: 29 May 2008


DATE: 29 May 2008

3

Executive Summary

After circulation of the report entitled - Review of Gutter Systems and Fixing Methods - dated 10 April the Author was alerted to two Planning Circulars:

1. P&D Circular Number 1/2008 ( 7 March 2008) published by the Committee on

Uniformity and Plumbing and Drainage Regulations in NSW (CUDPR) entitled:

“Requirements for the installation of eaves gutters”

2. Planning Circular no. BS 08-001 (10 April 2008) published by the NSW

Department of Planning entitled – “High Front Gutters”.

P&D Circular Number 1/2008 reminds plumbers and roofing plumbers that “the

requirements for Roof Drainage Systems – Design and Installation, which are contained

in AS/NZS 3500.3 (2003) Section 3 and 4 …must be complied with.”

One of the important requirements set out in AS/NZS 3500.3 (2003) is stated in Clause

3.5.1:

“Eaves gutter systems, including downpipes, shall be designed and installed in

accordance with Clause 3.2 so that water will not flow back into the building”

The P&D Circular also directs the reader to examples of overflow provisions set out in

AS/NZS 3500.3 (2003) Appendix G. As explained in the original report - Review of Gutter Systems and Fixing Methods - dated 10 April - examples given in Appendix

G show how compliance with overflow provisions can be met with all examples

involving full-length (continuous) overflow measures. Non-continuous overflows are

not recognised in the Standard because non-continuous overflows such as slotted

gutters may not be adequate, as the BCA 2007 advises that:

“in heavy downpours a slotted gutter may be inadequate.”

Planning Circular no. BS 08-001 was published to “raise awareness and remind

practitioners of the regulatory provisions applying to the design and installation of

gutters”. This circular was released because “issues have been raised in relation to

water penetration in certain houses that have been fitted with high front gutters”


DATE: 29 May 2008

4

This Planning Circular directs the target reader (all building practitioners and certifying

authorities) to requirements set out in the BCA 2007 Vol.2 part 3.5.2. Notably, the reader

is reminded of the BCA 2007 Compliance and Performance Requirements (Part 3.5.2)

and Deemed to Satisfy Provisions with direct reference to AS/NZS 3500.3 (or AS/NZS

3500.5 2000). These were the provisions assessed for high front gutters in the original

report - Review of Gutter Systems and Fixing Methods date 10 April-. It was

concluded in the original report that:

“results indicate that during heavy rainfall events or if a blockage occurs, slotted gutters

cannot be relied upon to prevent water overflowing the gutter. In the case of high fronted

gutters, without appropriate continuous overflow provisions, the water would be directed

back into the building in breach of the BCA 2007”.

Concerns with current gutter design and installation practices have been raised

concurrently in the two circulars and in the original report. Each if these publications

were issued to remind manufacturers, installers and authorising bodies of their

obligations to adhere to the legislative requirements stated in the BCA 2007 and in

AS/NZS3500.3. The risks to property resulting from the use of high front gutters,

particularly when attached to fascia with spring clips, can only be addressed when

designers, manufactures and installers discontinue current practices and begin

conforming to the legislative requirements of the BCA 2007.

Review of Gutter Systems and

Fixing Methods Chief Investigator: Dr Shaun A. Manning (PhD, B.Engineering)



University Drive

Callaghan NSW 2308

Australia

Date: 10 April 2008

Review of Gutter Systems and Fixing Methods pdf Dr S. Manning 10 April 08 5

Review of Gutter Systems and Fixing Methods Executive Summary Current eaves gutter systems were assessed against requirements for overflow

measures and fixing methods as set out in the Building Code of Australia (BCA) 2007

and The NSW Code of Practice for Plumbing and Drainage, 3rd Edition 2006. Provisions

given in Australian/New Zealand Standards referred to in these Codes were also

reviewed. Two additional reports were drawn on for insight, one that reviewed the

efficacy of installing slots into the front face of high fronted gutters, and another that

reviewed the corrosion potential of zinc coated spring clips (which are commonly used to

attach high fronted gutters to metal fascia). The major findings can be summarised as:

(a) Gutter systems must be designed with appropriate overflow measures to ensure

water does no pool against, damage or enter a building when a gutter overflows,

whether by excessive rainfall or from a blockage.

(b) Examples given in the Standards of possible designs for overflow measures all

involve full length (continuous) overflow.

(c) Slotted gutters are not recognized in the Australia Standards due to reservations in

their ability to adequately divert overflowing water. This inadequacy has also been

confirmed by fluid mechanics modeling

(d) An assessment of common methods of fixing high fronted gutters to fascia revealed

that gutters attached with spring clips are unable to direct overflowing water away from

the building when a blockage occurs. This method of gutter attachment does cannot

comply with BCA requirements for providing overflow measures when required.

(e) Departure from the requirements established in the BCA 2007 (which includes

compliance with relevant Standards) is not permitted without appropriate verifications.

(f) The practice of electroplating spring clips does not meet the Standard’s requirement

and is unlikely to ensure satisfactory service for the design lifetime of the drainage

installation.


Background Guttering

Eaves gutters come in many proprietary designs. Recent trends have leaned toward the

manufacture and supply of “high front” gutters. High front gutters are popular as they are

seen to improve the street appeal of the gutter systems. High front gutters are available

in many styles and are manufactured in slotted and unslotted forms.

Fascia

Fascia is available in timber and pre-painted metal. Metal fascia has become

increasingly popular in domestic installations due to its ease of installation, neat

appearance and because it needs no priming or painting. These considerations have led

to metal fascia becoming more common than timber fascia in modern domestic

dwellings.

Fixing methods for guttering to fascia

Manufacturer’s supply accessories and generally recommend fixing methods of

attaching guttering to fascia. The accessories available for timber fascia are external or

internal brackets to suit each gutter type. The accessories for metal fascia are spring

clips used in conjunction with over-straps. The design of the spring clip requires the clips

to be attached over the top of the fascia, when the guttering is installed, it is held tight

and high on the fascia. These fixing methods are common to all manufacturers.

Overflow Measure

“Measure to divert water from flowing back into a building from a blockage anywhere

along or at the outlet of an eaves gutter” AS/NZS 3500.3.2003.

Average recurrence interval (ARI)

“The expected or average interval between events of a rainfall intensity of a given

magnitude being exceeded.” AS/NZS 3500.5.2000.

References

AS/NZS 3500.3.2003 Storm water drainage

AS/NZS 3500.5.2000 Domestic installations

AS/NZS 2179.1.1994 Specification for rainwater goods, accessories and fasteners


BCA 2007 requirements –Overflow Measures The BCA Part 3.5.2 describes the required design methods for the design and

installation of eaves gutters. A number of quotes taken directly from the BCA give insight

into design requirements and the intent of the Code.

Part 3.5.2.0

“Performance Requirement P2.2.1 is satisfied for gutters and downpipes if they are

designed and constructed in accordance with AS/NZS 3500.3. – Stormwater drainage,

or AS/NZS 3500.5 – Domestic installations, Part 5 – Stormwater drainage.”

By invoking this requirement, the design and construction of eaves gutters must comply

with the specified standards. However, if an alternative solution is proposed that does

not follow the design requirements of Part 3.5.2 then it still must comply with the

performance requirement P2.2.1 and the relevant performance requirements set out in

accordance with P1.0.10.

PART 3.5.2.3

“The size of guttering must –

(a) be in accordance with Table 3.5.2.2; and

(b) be suitable to remove rainwater falling at the appropriate rainfall intensity listed in

Table 3.5.2.1 as follows-

(i) for eaves gutters – 20 year average recurrence interval ..”(ARI)

This part of the BCA describes how to design the size of guttering to cope with the

expected 1 in 20 year high rainfall event. Further guidance is given in AS/NZS

3500.3:2000 which states:

“Note: For Australia Table 3.1 should be used in conjunction with the BCA, which

has requirements to prevent rain and stormwater from roof drainage from entering

certain buildings” and “The ARI’s for eaves gutters given in Table 3.1 assume the

provision of appropriate overflow measures.”

As described in the Explanatory information in the BCA 2007, this design method does

not protect the guttering from overflowing if rainfall intensity is sufficient. The explanatory

information states:


“Stormwater drainage systems specified in the Housing Provisions are not designed to

remove all the water during exceptionally heavy rain, especially in tropical areas.

Accordingly, it is necessary to design and install the system so that when

overflowing occurs any water is directed away in a manner which ensures it does

not pond against, or enter into, the building.”

This part of the BCA 2007 clearly indicates that specified design methods for gutter

systems are not intended to prevent overflowing during extreme weather. Furthermore,

when overflowing does occur, the water must be directed away from the building to

prevent damage to the dwelling.

The explanatory notes go on to state:

“This (directing water away from the building) may be achieved by using slotted gutters,

oversized gutters and downpipes, locating the gutter so that it is below the top of the

fascia or the installation of rainwater heads with overflow slots”………………”There are

many options available to designers using the requirements of the Housing Provisions.

The designer will need to choose an overflow system that will cope with the expected

rain intensity, ie in heavy downpours a slotted gutter may be inadequate.”

Two comments can be drawn from this quotation:

1. the design of the spring clip prevents high fronted gutters from “locating the gutter so

that it is below the top of the fascia”

2. In this part, the BCA 2007 acknowledges a common practice of installing slots in to

the front face of high front gutters but casts doubt on this design’s effectiveness of

meeting the requirement that “ when overflowing occurs any water is directed away

in a manner which ensures it does not pond against, or enter into, the building.”

See Performance of gutter slots (Appendix A)

The BCA 2007 relies on further detail to be provided in the referenced Australian/New

Zealand Standards. However, before reviewing the Standards, it is important to note that

the BCA at clause AO.5 ‘Meeting the Performance Requirements’, requires that


compliance with the Performance Requirements can only be achieved by complying with

the Deemed-to-Satisfy provisions or formulating an Alternative Solution which complies

with the Performance Requirements or is shown to be at least equivalent to the Deemed-

to-Satisfy provisions or a combination of both aspects.

The BCA states that Assessment Methods must be followed in developing any

Alternative Solution to determine that a Building Solution complies with the Performance

Requirements.

These include:

1. Evidence to support that the use of a material, form of construction or design

meets a Performance Requirement or a Deemed-to-Satisfy Provision; and/or

2. Verification Methods such as the Verification Methods in the BCA or others that

the local government accepts; and/or

3. Comparison with the Deemed-to-Satisfy Provisions; and/or

4. Expert Judgment.

In order to comply with all sections of the BCA it is necessary to adhere to the following

method when determining whether an Alternative Solution meets all the relevant BCA

Performance Requirements by:

1. Identifying the relevant Deemed-to-Satisfy provisions of each Section or Part that

is to be the subject of the Alternative Solution; and

2. Identifying the Performance Requirements from the same Sections or Parts that

are relevant to the identified Deemed-to-Satisfy provisions; and

3. Identifying Performance Requirements from other Sections and Parts that are

relevant to any aspects of the Alternative Solution proposed or that are the

application of the Deemed-to-Satisfy provisions that are subject of the Alternative

Solution

Part 1.1.2 of the BCA 2007 states that:

“Where a Deemed-to-Satisfy Provision adopts a Standard, rule, specification or provision

included in any document issued by Standards Australia or other body, that adoption

does not include a provision –


(e) Permitting departure from the code, rule, specification or provision at the sole

discretion of the manufacturer or purchaser, or by any arrangement or agreement

between the manufacturer and purchaser.”

Alternative solutions to those specifically mentioned in the Housing Provisions outlines in

the BCA 2007 are permitted, but only if the following is satisfied (Part 3.3):

“Alternative solutions may we used provided they comply with the Performance

requirements listed in Part 2 (for further explanation see part 1.0).”

Part 1.0.8 states:

(a) “An Alternative Solution must be assessed according to one or more of

the Assessment Methods.

(b) An Alternative Solution will only comply with the BCA if the Assessment

Methods used to determine compliance with the Performance Requirements

have been satisfied.

(c) The Performance Requirements relevant to an Alternative Solution must

be determined in accordance with 1.0.10.”

Part 1.0.9 states:

“The following Assessment Methods, or any combination of them, can be

used to determine that a Building Solution complies with the Performance

Requirements:

(a) Evidence to support the use of the material, form of construction

or design meets a Performance requirement or a Deemed to

Satisfy Provision as described in 1.2.2.

(b) Verification methods such as:

(i) the Verification Methods in the BCA; or

(ii) such other Verification Methods as the appropriate

authority accepts for determining compliance with the

performance Requirements

(c) Comparison with the Deemed-to-Satisfy Provisions.

(d) Expert Judgment.”


The BCA 2007 clearly indicates that deviation from performance requirements must be

demonstrated to satisfy the verification rules outlined in Part 1.0.9.

Summary As established in the BCA 2007, when gutters overflow the water must be directed away

from the building to prevent damage to the building. Part 1.1.2 reiterates the need for

compliance with AS/NZS 3500.3:2003 and AS/NZS 3500.5:2000 in order to satisfy the

performance standards required by BCA 2007. Departure from the requirements

established in the BCA 2007 (which includes compliance with relevant Standards) is not

permitted without appropriate verifications.

The NSW Code of Practice for Plumbing and Drainage, 3rd Edition 2006 The code was prepared by the Committee on Uniformity of Plumbing and Drainage in

New South Wales (CUPDR) to provide uniform administrative and technical

requirements for the installation of plumbing and drainage in NSW.

This Code replaces the New South Wales Code of Practice; Plumbing and Drainage,

Edition No 2 July 1999.

This Code adopts the National Plumbing and Drainage Code AS/NZS 3500:2003 and

amendments and Part 5:2000, with New South Wales variations and additional

provisions as set out in this Code.

Requirements of AS/NZS 3500.5:2000 (DOMESTIC INSTALLATIONS)

The gutter and downpipe design methods given in BCA 2007 are also included in

AS/NZS 3500.5:2000, with additional detail. In Clause 5.5.1 the Standard states:

“Roof drainage systems are designed in respect to the risk of monetary loss, property

damage (including contents of buildings) and injury to persons due to overtopping. A

frequent cause of such overtopping is inadequate inspection and cleaning and not the

intensity of rainfall.”


Clause 5.5.1 -

“Roof Drainage systems shall comply with the following:

(C) Be designed in accordance with-

“(i) eaves gutter systems (eaves gutters and associated downpipes with

appropriate over flow devices) method of Clause 5.5.4.”

In this section, the Standard has acknowledged the potential risks of overtopping.

Furthermore, it is noted that even during modest rainfall events, conditions exist that can

produce overtopping. Examples of such conditions are given as:

Clause 5.5.1-

“Notes-2 The design methods do not include an allowance for the following:

(b) Blockages of roof drainage systems, e.g. by snow, hail and debris”

Clause 5.5.4.1-

” Eaves gutters shall be designed so that they will not overflow with flows resulting from

a storm burst with an average recurrence interval (ARI) of not less than 20 years in

Australia” and “Appropriate measures shall be taken, if necessary, to ensure that

overflowing water will not flow into the building but will fall to the ground”

Clause 5.5.4.2-

“Method for design of eaves gutters and downpipes with appropriate overflow measure

shall be as follows:

“STEP 1 Determine 5min/20 year ARI”

Note that the ARIs for eaves gutters given in Table 3.1 assume the provision of

appropriate overflow measures - AS/NZS 3500.3.2003.

STEP 3 Select eaves gutter and the gutter slope

Note that Clause 5.5.4.4 states:

“The selection of eaves profiles shall suit the type of eaves construction. Where

stormwater from overflowing eaves gutters can flow over the eaves lining and back into

the building, overflow measures shall be required.”


STEP 9 Select an overflow measure if required-

Note that Clause 5.5.4.3(f) explains Step 9 as:

“Blockages may occur anywhere along an eaves gutter causing overtopping which

would not be prevented by an overflow device at the outlet of an eaves gutter. An

overflow method may be selected to suit building design or gutter shape. See Figure 5.3

for examples of overflow measures for eaves gutters for use where overflows may cause

significant damage. “

Figure 5.3 provides examples of overflow measures suitable to a variety of gutter styles.

All of the overflow measures suggested in Figure 5.3 provide for full length (continuous)

overflow in order to provide sufficient overflow capacity to remove water away from the

building during heavy storms or blockages.


Summary AS/NZS 3500.5:2000 The standard, consistent with the BCA 2007, requires that” the

roof drainage system is designed so that any overflow during heavy rain periods is

prevented from flowing back into the building”. The design guidelines above incorporate

appropriate overflow measures as part of the design criteria. The method of overflow

required is dependant on the gutter type selected.

Requirements of AS/NZS 3500.3:2003 (Stormwater Drainage) This standard further qualifies the requirements for overflow measures in the design and

installation of gutters. Clause 3.2 states:

“The general method assumes regular inspection and cleaning (see Clause 4.6) and is

applicable to-

(a) eaves gutters and associated vertical downpipes with appropriate

overflow measures (see Clause 3.5)

NOTES: 1 The general method does not include allowance for any of the following:

(b) Blockages of roof drainage systems, e.g., by snow, hail and debris.”

Clause 3.3.1

“Roof drainage systems are designed in respect to potential monetary loss, property

damage (including contents of buildings) and injury to persons due to overtopping.

NOTES:. 1. A frequent cause of such overtopping is inadequate inspection and cleaning

(see Clause 4.6) and not to the intensity of rainfall.”

Clause 3.3.4

“The ARI (Average Recurrence Interval) shall be given in Table 3.1

NOTE: For Australia Table 3.1 should be used in conjunction with the BCA, which has

requirements to prevent rain and stormwater from roof drainage from entering certain

buildings.”

Clause 3.5.1

–“ Eaves gutter systems, including downpipes, shall be designed and installed in

accordance with Clause 3.2 so that water will not flow back into the building”


Cause 3.5.2 –

“ The design procedure shall follow the general method for design of eaves gutters

systems flow chart, in Figure 3.4 (l) Select over flow measures in accordance with

Clause 3.5.

NOTE: An example of the application of the design procedure is given in Appendix H.”

Clause 3.5.3 –“NOTE: Examples of overflow measures for eaves gutters are given in

Appendix G.”

Appendix G provides examples of overflow measures suitable to a variety of gutter

styles. All of the overflow measures suggested in Appendix G provide for full length

(continuous) overflow in order to provide sufficient overflow capacity to remove water

away from the building during heavy storms or blockages. The examples in Appendix G

are consistent with the examples given in AS/NZS 3500.5:2000 Figure 5.3.

Summary AS/NZS 3500.32003, consistent with AS/NZS 3500.5:2000, provides further guidance on

how to comply with the BCA performance requirements. Examples given in Appendix G

on how compliance with overflow provisions can be met all involve full length

(continuous) overflow measures.

OBSERVATIONS

The design methods for gutters and downpipes given in the BCA 2007 and the

Standards are designed to prevent water flowing back into a building and causing

damage to the building. The design method assumes that the gutters are regularly

cleaned to prevent blockages. In this way, the gutters are designed to collect and convey

rainwater except in exceptional rainfall events. However, the Standards recognize that

blockages do occur, and exceptional rainfall events also occur. The BCA 2007 states

that stormwater drainage systems are not designed to remove all of the water during

exceptionally heavy rain. The BCA states that:


“it is necessary to design and install the system so that when overflowing occurs any

water is directed away in a manner which ensures it does not pond against, or enter into,

the building.“

AS/NZS 3500.5:2000 states the “Where stormwater from overflowing eaves gutters can

flow over the eaves lining and back into the building, overflow measures shall be

required.”

The design methods outlined in the Standards include the provision of overflow

measures to ensure that in extreme rainfall events and when blockages occur, the intent

of the BCA 2007 is satisfied.

Further clarification is found in AS/NZS 3500.5.2000 Figure 5.3 and AS/NZS

3500.3:2003 Appendix G which provide examples of acceptable overflow measures. All

of these measures provide full-length (continuous) overflows. This is to ensure that water

can escape at a sufficiently high rate and to ensure anywhere overtopping occurs, water

will not enter the building.

It is noted in Appendix G that:

“Blockages can and do occur anywhere along an eaves gutter causing overtopping that

would be affected by an overflow device located at the outlet of an eaves gutter

e.g.rainhead (see Figure 3.7(a)). The overflow devices given in Paragraph G2 are

located along an eaves gutter so that any overtopping is unlikely to cause monetary loss

of property damage including damage to contents of buildings. The ARIs for eaves

gutters given in Table 3.1 assume the provision of appropriate overflow measures.”

As stated in Appendix G, it is assumed that the general design method based on ARIs

(average recurrence intervals) includes appropriate overflow measures to ensure that

when blockages occur, the water is directed away from the building.

It is clear from the assessment of the BCA 2007 and the referenced AS/NZS Standards

that overflow protection is needed to protect buildings from water damage in all cases

where there is a risk of property damage. This is confirmed as the Standards and the

BCA design methods for gutters use the ARI values including allowance for appropriate

overflow measures.


Summary of BCA 2007 Requirements for Overflow Measures The preceding assessment has identified a number of requirements for eaves-gutters

which can be summarised as:

1. Gutter systems must be designed and installed using appropriate overflow

measures to ensure water cannot pond against or flow into a building.

2. Overflow measures designed in accordance with AS/NZS 3500.5.2000 and

AS/NZS 3500.3:2003 involve continuous overflows, since blockages can occur

at any point on the gutter. In all examples given in the Standards, overflowing

water is directed away from the building.

Additional requirements for gutter fixing components

3. Roof drainage system components made from aluminium alloys,

aluminium/zinc alloy-coated steel, copper, copper alloys, zinc-coated steel and

zinc shall comply with AS/NZS 2179.1.

4. 3500.5 Clause 5.3.1 “The selection and use of materials and products shall

ensure satisfactory service for the design lifetime of the Stormwater drainage

installation”.


Assessment of common eaves-gutter designs for compliance with BCA

2007

In order to assess compliance of an eaves-gutter system with the BCA 2007

requirements, the following tests can be applied:

1. Does the system have an overflow measure designed such that whenever

overflowing of a gutter occurs for any reason, is all the water directed away

from the building in a manner compliant with AS/NZS 3500.5.2000 Figure 5.3

and AS/NZS 3500.3:2003 Appendix G.

2. Are roof drainage components designed in accordance with ASA/NZS

2179.1:1004 and be compatible, and ensure satisfactory service for the design

lifetime of the drainage installation

There are many gutter designs on the market, but the most common design are high

fronted quad style gutters also referred to as D gutters which are installed by either

external brackets, internal brackets or spring clips with over-straps. These systems

will be assessed in turn.

1. Overflow measures:

High Fronted Gutters attached to fascia with external or internal brackets Due to the front of the gutter being higher than the back, overflowing water will be

directed into the building unless an appropriate overflow measure is adopted. With

reference to AS/NZS 3500.5.2000 Figure 5.3 or AS/NZS 3500.3:2003 Appendix G,

the three methods for high fronted gutters attached with brackets are to:

(a) Pack the brackets away from the fascia to provide 10 mm continuous weir

at the back off the gutter.

(b) Attach the brackets low on the fascia so that the front of the gutter is a

minimum 20mm freeboard (figure 5.3 domestic installations) lower than the

top of the fascia at all points. Or calculate the amount of freeboard

required to comply with details in Appendix G.

(c) Provide continuous flashing to the rear of the gutter with the top edge of

the flashing not less than the required freeboard in accordance with the

standards (20mm domestic installations).


High Fronted Gutters attached to metal fascia with spring clips and over-straps As stated, due to the front of the gutter being higher than the back, overflowing water

will be directed toward the building unless an overflow measure is adopted. Unlike

brackets, spring clips are designed to hold the gutter tightly against and at the top of

the fascia. This fixing method cannot be installed with any of the three continuous

overflow measures listed above for high front gutter. With spring clips the option of:

(a) Packing the gutter to provide a 10 mm weir gap is impossible as the spring

clip design requires the gutter to be held tight against the fascia.

(b) Installing the gutter lower so that the front bead of the gutter will be below

the top of the fascia is impossible. The spring clip is fixed over the top

edge of the fascia, the short length of the spring clip does not allow for

fixing the gutter with the required freeboard (20 mm domestic installations)

and fall.

(c) Providing a continuous flashing to the rear of the gutter is impossible as

the spring clip is attached over the top of the fascia making it impossible

for flashing to be installed.

Without providing an appropriate overflow measure, high front gutters attached with

spring clips cannot satisfy the requirements of the BCA 2007.

High front gutters with slots Gutter manufactures recognize the need for overflows and offer the option of slots in

the front face of high front gutters to act as the overflow measure to remove excess

water. The BCA 2007 makes note of this method but advises that:

“in heavy downpours a slotted gutter may be inadequate.”

The Standards do not recognize slotted gutters as a suitable overflow method. However,

tests were conducted to assess the effectiveness of slotted gutter systems. Newcastle

Innovation conducted an assessment on a number of slotted gutter profiles obtained

from NSW manufacturers. The assessment involved applying hydrodynamic principles of


fluid flow using the Bernoulli equation. Results from this report are given in Table 1, with

the full report attached.

Table 1 Measured properties of tested gutter

Gutter Brand Slot Length (mm)

Slot Width (mm)

Gap between neighbour slots (mm)

Slot Area (mm2) per hole

ACE 17 1.5 120 25.5

STRATCO 22 2 80 44

LYSAGHTS 45 3 110 135

STRAMIT 50 2 90 100

Table 2 Flowing rates (L/s) for various gutter brands

Gutter Brand Flowing Rate (L/s)

For slots every 1 metre gutter

Flowing Rate (L/s) For 10 mm gap

every 1 metre gutter

Flow through slots compared to flow over required 10 mm gap


ACE 0.078 6.264 1.24%

STRATCO 0.181 6.264 2.89%

LYSAGHTS 0.366 6.264 5.83%

STRAMIT 0.300 6.264 4.79%

It can be seen from Table 2 that the calculated flowrates of overflow water through the

slots in the front face of proprietary slotted gutter systems is between 1.24% to 5.83% of

the flowrate capable of being removed by other recommended overflow measures. The

assessment was made assuming a 20 mm head of water above the slots. The

recommended system used in the comparison in Table 1 is shown in Figure 1. Note that

if the 10 mm gap were not provided, the water would overflow the fascia toward the

building.


Figure 1: Example of 10 mm gap to provide continuous over flow as described in AS3500

The relatively poor overflow capacity of slotted gutter systems (all tested gutters were

high front) explains the comments in the BCA 2007 ie “in heavy downpours a slotted

gutter may be inadequate.” The results given in Table 2 confirm that slotted gutters are

unlikely to satisfy the BCA requirement that “when overflowing occurs any water is

directed away in a manner which ensures it does not pond against, or enter into,

the building.”

Standards Australia does not recognize slotted gutters as an acceptable overflow

measure. These results indicate that during heavy rainfall events or if a blockage occurs,

slotted gutters cannot be relied upon to prevent water overflowing the gutter. In the case

of high fronted gutters, without appropriate continuous overflow provisions, the water

would be directed back into the building in breach of the BCA 2007.

Fixing accessories: Compliance AS/NZS 2179.1.1994 The Standards require that roof drainage components are designed in accordance

with ASA/NZS 2179.1:1004 and be compatible, and ensure satisfactory service for

the design lifetime of the drainage installation.

The common practice of using aluminium/zinc alloy-coated steel plain or pre-painted

steel shall comply with AS1397 with a minimum Class AZ150. Zinc-coated steel shall


comply with AS1397 with a minimum coating of Class Z275. Brackets must be

manufactured to these specifications in order to be compliant with AS/NZS

2179.1:1994.

Internal and External Brackets

External and internal brackets have been used for many years with success the

method of manufacture appear to satisfy the appropriate standards. Brackets are

manufactured using aluminium/zinc alloy-coated steel or zinc-coated steel.

Spring Clip with Overstrap

Spring clips with overstraps are a relative recent method of fixing gutters to fascia,

and has grown in popularity with the increasing use of metal fascia.

The common practice of using aluminium/zinc alloy-coated steel for overstraps

complies with AS1397 with a minimum Class AZ150 and satisfies AS/NZS

2179.1:1994.

Spring clips are manufactured using spring steel with zinc electroplating. An

assessment was made on whether spring clips satisfy requirements set out in

AS/NZS 2179.1:1944. The common practice of zinc electroplating spring clips does

not comply with AS1397 which requires a minimum coating of Class Z275. In this

way, the manufacturing process for spring clips does not comply with AS/NZS

2179.1.1994 (see Evaluation of Gutter Fixtures).

Zinc electroplating is not recognized in AS/NZS 2179.1.1994 as a suitable coating for

rainwater goods and accessories. Therefore this method of coating spring clips fails to

meet the requirements of the standards and the Codes.


SUMMARY

The use of the spring clip as a fixing method does not meet the requirements of the

following Standards: AS/NZS 3500.5.2000, AS/NZS 3500.3.2003, AS/NZS 2179.1.1994

and AS 1397. The failure to meet the requirements of the Standards prevents the spring

clip fixing method from complying with the NSW Code of Practice for Plumbing and

Drainage, 3rd Edition 2006. The spring clip fixing method does not meet the Performance

Requirements or comply with the Deemed-to-Satisfy Provisions of the BCA 2007. The

practice of electroplating the spring clip does not meet the Standards requirement and is

unlikely to ensure satisfactory service for the design lifetime of the drainage installation

(see Evaluation of Gutter Fixtures). These factors demonstrate that the spring clip is

not fit for purpose and therefore should not be used as a method of installing gutters..


APPENDIX A

PERFORMANCE OF GUTTER SLOTS COMPARED TO AS/NZS REQUIREMENTS

Chief Investigator: Dr Shaun A. Manning (PhD, B.Engineering)



University Drive

Callaghan NSW 2308

Australia

Date: 10 April 2008

Client: Jason Higgins

Jason Higgins Plumbing

55 Cumberland St Cessnock

NSW 2325

Date: 3 March 2008


Performance of Gutter slots compared to AS/NZS Requirements & NSW Plumbing and Drainage Code of Practice & Building Code of Australia Four gutter profiles, containing slots in the front face, were assessed for ability to

discharge rainwater. The gutters under test were manufactured by:

1. Ace Gutters

2. Stratco

3. Lysaghts

4. Stramit

Performance was based on the ability of the gutter systems to discharge rain

water through the provided slots, compared to the ability of the gutter to

discharge rain water via a 10 mm gap at the rear of the gutter. Examples of gap

requirements for continuous overflows are given in AS/NZS 3500.3 2003 and

AS/NZS 3500.5 2000 (Figure 1).

The basis of calculation assumed a water level in the gutter 20 mm above the

slots, reflecting conditions where the fascia extends 20 mm higher than the back

of the gutter. Such water depths in the gutter could arise if the downpipes were

blocked (leaf debris, hail etc.).

The calculation procedure involved application of the Bernoulli fluid mechanics

equation. A correction factor of 0.67 was applied to the slot calculations to allow

for flow effects at the edges of the slots. A factor of 1 was applied for the 10 mm

gap calculations. Slots were treated as being rectangular due to the relatively

large length to height ratios. All predicted rainfall discharge calculations are

reported as litres/second (L/s).

Data used in the calculations and final results are given in Table 1. It can be seen

from Table 1 that the flowrates through the slots in each gutter system are


significantly lower than (well less than 10%) the predicted flowrate of water flow

over a 10 mm gap as required by the Standards. For the conditions simulated in

this study, the slots in the front face of the gutters are shown to be ineffective in

discharging rainfall overflow when compared to the 10 mm gap at the rear of the

gutter specified in the Standards.

Table 3 Measured properties of tested gutter

Gutter Brand Slot Length (mm)

Slot Width (mm)

Gap between neighbour slots (mm)

Slot Area (mm2) per hole

ACE 17 1.5 120 25.5

STRATCO 22 2 80 44

LYSAGHTS 45 3 110 135

STRAMIT 50 2 90 100

Table 4 Flowing rates (L/s) for various gutter brands

Gutter Brand Flowing Rate (L/s)

For slots every 1 metre gutter

Flowing Rate (L/s) For 10 mm gap


Flow through slots compared to flow over required 10 mm gap


ACE 0.078 6.264 1.24%

STRATCO 0.181 6.264 2.89%

LYSAGHTS 0.366 6.264 5.83%

STRAMIT 0.300 6.264 4.79%


Figure 1: Example of 10 mm gap to provide continuous over flow as

described in AS3500 Required Design Method for Eaves-Gutters

The 2007 and associated Standards indicate intentions and mandate design and

installation procedures for gutters to ensure rainfall does not enter and damage

buildings. It is stated in Part 3.5.2 of the BCA 2007:

“when overflowing occurs any water is directed away in a manner

which ensures it does not pond against, or enter into, the

building.”

The BCA 2007 gives no detail on how to comply with this intent and relies on

guidance given in AS/NZS3500.3:2003 and AS/NZS3500.5:2000.

The design procedure for Eaves-Gutter systems is given in AS/NZS 3500.3:2003

Clause 3.5.3 (Figure 4) where the gutter system is designed to prevent

overtopping based on an expected 1:20 year rainfall event. That is, assuming a


gutter is free of blockages it should not overtop more frequently than once each

20 years. Recalling that the BCA 2007 states that whenever overtopping occurs,

the system should direct water away from the building, the design method in

Figure 4 requires overflow measures to be added to in all cases where

overtopping occurs because:

AS/NZS3500.5:2000 Clause 5.5.4.1 states:

“Appropriate measures shall be taken, if necessary, to ensure that

overflowing water will not flow into the building but will fall to the

ground”

By following the design flow chart given in AS/NZS 3500.3:2003 Clause 3.5.3

(Figure 4) the designer is required to:

“Select over flow measures in accordance with clause 3.5”

Clause 3.5.1 states:

“Eaves gutter systems, including downpipes, shall be designed

and installed in accordance with Clause 3.2 so that water will not

flow back into the building.

Clause 3.2 states:

“The general method assumes regular inspection and cleaning

(see Clause 4.6) and is applicable to-

eaves gutters and associated vertical downpipes with appropriate overflow

measures (see Clause 3.5)”


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