ABCB Housing Provisions
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7.4

Part 7.4 Gutters and downpipes

Part 7.4 Gutters and downpipes

(1) Part 7.4 applies subject to H2D6(2) and the limitations set out in H2D6(3).

(2) Part 7.4 need not be complied with if H2D6(1)(a) is complied with.

Explanatory information

  • The requirement to install drainage systems from roofs and sub-soil drains should be confirmed with the appropriate authority. These provisions need only be applied when drainage systems are necessary.
  • Information on drainage requirements outside the allotment can be obtained from the appropriate authority.
  • Where box gutters are proposed to be installed, AS/NZS 3500.3 may be used to calculate minimum sizes, falls and overflow requirements.
  • For Class 10 buildings, it may not be necessary to comply with the requirements for removing surface water where the Class 10 building is not connected to or does not impact a Class 1 building. For example, where a Class 10 garage is attached to a Class 1 dwelling, the run-off from the garage would most likely directly impact the dwelling and therefore be required to be removed. However, a garage that is separated by a reasonable distance from the dwelling so as to not have an impact would not necessarily have to comply with the requirements for removal of surface water.
  • The following are a number of other Clauses and Parts of the ABCB Housing Provisions that contain requirements related to drainage and roofing in addition to the provisions of this Part:

Explanatory information: Design of stormwater drainage systems

Stormwater drainage systems specified in the NCC Volume Two and the ABCB Housing Provisions are not designed to remove all water to an appropriate outfall during exceptionally heavy rain, particularly in tropical areas. Specifically, eaves gutter systems are designed to remove water arising from rainfall events with an annual exceedance probability of 5% provided they are not blocked.

Accordingly, it is necessary to design and install the system to incorporate overflow measures so that when overflowing occurs, during a rainfall event with an annual exceedance probability of up to 1%, any water is directed away in a manner which ensures it does not pond against, enter or damage the building, even if the stormwater drainage system is blocked.

Insufficient and poorly located downpipes are a frequent cause of poor roof drainage system performance. The installation of downpipes, especially near valley gutters, is designed to ensure rainwater from areas on the roof that have concentrated water flows is adequately removed.

Particular consideration needs to be given to box gutters, valley gutters etc. located above the internal areas of a building. There are several options available to designers using the requirements of NCC Volume Two and the ABCB Housing Provisions. The designer will need to choose an overflow system that will cope with the rainfall intensity for the particular location. Consideration needs to be given to the total capacity of overflow measures on lower level roofs where overflow measures adopted for a higher roof catchment will result in overflow to a lower one. Overflow discharge onto lower roofs may also require consideration of sarking, flashing and other weatherproofing precautions to the lower roof area.

The acceptable overflow measures in Table 7.4.4a and Table 7.4.4b were calculated using the following formulas:

  • For continuous slots or rainhead:
    Q=CdA2ghMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyuaiabg2 da9iaadoeadaWgaaWcbaGaamizaaqabaGccaWGbbWaaOaaaeaacaaI YaGaam4zaiaadIgaaSqabaaaaa@3D2D@

where—

AMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyqaaaa@36BA@
= Area (m2)

CdMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4qamaaBa aaleaacaWGKbaabeaaaaa@37D1@
= Discharge coefficient = 0.61

gMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4zaaaa@36E0@
= Gravity = 9.81 m/s2

hMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiAaaaa@36E1@
= Effective head (m)

QMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyuaaaa@36CA@
= Flow rate (m3/s)

  • For front face weir, end stop weir, inverted nozzle, front bead or controlled gap:
    Q=0.67Cdb2gh1.5MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyuaiabg2 da9iaaicdacaGGUaGaaGOnaiaaiEdacaWGdbWaaSbaaSqaaiaadsga aeqaaOGaamOyamaakaaabaGaaGOmaiaadEgaaSqabaGccaWGObWaaW baaSqabeaacaaIXaGaaiOlaiaaiwdaaaaaaa@429E@

where—

bMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOyaaaa@36DB@
= Width (m)

CdMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4qamaaBa aaleaacaWGKbaabeaaaaa@37D1@
= Discharge coefficient = 0.63

gMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4zaaaa@36E0@
= Gravity = 9.81 m/s2

hMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiAaaaa@36E1@
= Effective head (m)

QMathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyuaaaa@36CA@
= Flow rate (m3/s)

Gutters, downpipes and flashings must—

  1. be manufactured in accordance with AS/NZS 2179.1 for metal components; and
  2. be manufactured in accordance with AS 1273 for UPVC components; and
  3. be compatible with all upstream roofing materials in accordance with 7.2.2(2); and
  4. not contain any lead if used on a roof forming part of a drinking water catchment area.

The size of guttering must—

  1. for eaves gutters, be in accordance with Table 7.4.3a, Table 7.4.3b and Table 7.4.3c; and
  2. be suitable to remove rainwater falling at the appropriate 5 minute duration rainfall intensity listed in Table 7.4.3d as follows—
    1. for eaves gutters — 5% annual exceedance probability; and
    2. for eaves gutter overflow measures — 1% annual exceedance probability.
Table 7.4.3a Size of gutter required to drain roof catchment area into one (1) downpipe for various rainfall intensities and roof catchment areas (A, B, C, D, E and F defined in Table 7.4.3b)
Design rainfall intensity (mm/h) (as per Table 7.4.3d) Roof catchment area per downpipe — 30 m2 Roof catchment area per downpipe — 40 m2 Roof catchment area per downpipe — 50 m2 Roof catchment area per downpipe — 60 m2 Roof catchment area per downpipe — 70 m2
90 mm/h A or C A or C A or C A or C A or C
120 mm/h A or C A or C A or C A or C A or D
140 mm/h A or C A or C A or C A or D B or E
160 mm/h A or C A or C A or C A or E B or E
175 mm/h A or C A or C A or D B or E E
200 mm/h A or C A or C A or D B or E F
225 mm/h A or C A or C A or B E F
255 mm/h A or C A or D B or E E F
275 mm/h A or C A or D B or E F F
325 mm/h A or C B or E F F F
425 mm/h A or C E F F F
Table 7.4.3b Gutter sizes for various rainfall intensities
Gutter type Gutter description Minimum cross-sectional area (mm2)
A Medium rectangular gutter 6500
B Large rectangular gutter 7900
C 115 mm D gutter 5200
D 125 mm D gutter 6300
E 150 mm D gutter 9000
F Gutter must be designed in accordance with AS/NZS 3500.3 N/A
Table 7.4.3c Downpipe selection for gutter types (A, B, C, D, E and F defined in Table 7.4.3b)
Downpipe section Gutter type A Gutter type B Gutter type C Gutter type D Gutter type E
75 mm dia. Yes Yes Yes Yes No
100 mm x 50 mm Yes Yes Yes Yes Yes
90 mm dia. Yes Yes Yes Yes Yes
100 mm x 75 mm Yes Yes Yes Yes Yes
Table Notes
  1. Yes — downpipe is suitable for the eaves gutter selection.
  2. No — downpipe is not suitable for the eaves gutter selection.
Table 7.4.3d 5 minute duration rainfall intensities
State Locality Annual exceedance probability, 5% (mm/h) Annual exceedance probability, 1% (mm/h)
ACT Canberra 143 192
ACT Gungahlin 137 179
ACT Tuggeranong 148 210
NSW Albury 139 180
NSW Broken Hill 142 217
NSW Goulburn 120 154
NSW Kiama 225 320
NSW Newcastle 225 316
NSW Orange 141 186
NSW Sydney 201 262
NSW Avalon, Sydney 210 287
NSW Campbelltown, Sydney 166 223
NSW Penrith, Sydney 178 240
NSW Windsor, Sydney 175 234
NSW Tweed Heads 252 332
NSW Wollongong 218 311
NT Alice Springs 165 239
NT Darwin 233 274
NT Katherine 216 250
QLD Bamaga 252 298
QLD Brisbane 236 306
QLD Ipswich, Brisbane 211 278
QLD Victoria Point, Brisbane 245 320
QLD Bundaberg 266 339
QLD Cairns 230 279
QLD Cloncurry 219 278
QLD Innisfail 248 302
QLD Mackay 250 315
QLD Mt Isa 201 262
QLD Noosa Heads 258 332
QLD Rockhampton 229 300
QLD Toowoomba 203 268
QLD Townsville 235 300
QLD Weipa 238 281
SA Adelaide 120 174
SA Gawler, Adelaide 111 158
SA Mt Gambier 103 144
SA Murray Bridge 120 177
SA Port Augusta 133 199
SA Port Pirie 123 183
SA Yorketown 155 166
TAS Burnie 128 178
TAS Flinders Island 124 167
TAS Hobart 86 120
TAS Launceston 91 123
TAS Queenstown 94 120
TAS St. Marys 150 207
VIC Ballarat 134 192
VIC Benalla 146 194
VIC Geelong 103 143
VIC Horsham 121 173
VIC Lakes Entrance 145 199
VIC Melbourne 132 187
VIC Hastings, Melbourne 112 145
VIC Sorrento, Melbourne 106 140
VIC Mildura 142 219
VIC Stawell 130 187
WA Albany 127 179
WA Broome 232 287
WA Bunbury 147 198
WA Derby 211 256
WA Geraldton 138 194
WA Kalgoorlie 136 204
WA Perth 129 172
WA Joondalup, Perth 133 180
WA Midland, Perth 122 164
WA Port Hedland 168 232
WA Tom Price 138 182
Table Notes

Locations used in this table are based on the nearest Bureau of Meteorology grid cell latitude and longitude to the central Post Office of each city or town.

Explanatory information

The cross sectional area referred to in Table 7.4.3b is measured up to the lowest part of the relevant overflow facility including the lower edge of a slot, gutter back, end-stop weir, inverted nozzle, front-face weir or overflow opening in a rainhead.

Explanatory information: Worked example — determining appropriate overflow measures

The location of a proposed building is in Wollongong, NSW. Using Table 7.4.3d the 5 minute duration rainfall intensity for a 1% annual exceedance probability is 311 mm/h. The 5 minute duration rainfall intensities in Table 7.4.4a and Table 7.4.4b are provided in 25 mm/h increments, therefore for the purpose of the worked example 325 mm/h will be used.

Table 7.4.4a and Table 7.4.4b provide required overflow volumes in both litres per second for dedicated overflow measures and litres per second per metre for continuous overflow measures. Extrapolation of the values in these tables can be used to inform a Performance Solution complying with the Governing Requirements of the NCC. Where both dedicated and continuous measures are proposed, Table 7.4.4b can be used to determine the required overflow volume.

  1. Multiple overflow measures are proposed to be used with a roof catchment area of 60 m2, incorporating a 10 m eaves gutter.
  2. Using Table 7.4.4b for a 325 mm/h 5 minute duration rainfall intensity, the overflow volume in litres per second (L/s) for a roof catchment area of 60 m2 is 5.4 L/s.
  3. Select an acceptable dedicated overflow measure from 7.4.7.
    1. The selected dedicated overflow measure is an end-stop weir which provides 0.5 L/s.
    2. One end-stop weir does not achieve the required overflow volume of 5.4 L/s, and additional overflow measures are required to remove the overflow volume.
  4. To achieve the required overflow volume a continuous overflow measure is also selected from 7.4.6.
    1. A front face slotted gutter is the selected overflow measure as it provides 0.5 L/s/m.
    2. Taking account of the eaves gutter length (10 m), the combined overflow measures (0.5 L/s for the end-stop weir and 0.5 L/s/m × 10 m) will remove up to 5.5 L/s.
  5. The 5.5 L/s capacity provided by the selected overflow measures exceeds the required 5.4 L/s overflow volume.

(1) Eaves gutters must be—

  1. installed with a fall of not less than 1:500; and
  2. supported by brackets securely fixed at stop ends, corners and at not more than 1.2 m centres; and
  3. fitted with overflow measures capable of removing the overflow volume specified in Table 7.4.4a and Table 7.4.4b.

(2) Overflow measures in accordance with 7.4.6 and 7.4.7 are deemed to be capable of removing the overflow volume specified in those provisions.

(3) Where the overflow volume values for ridge-to-gutter lengths in Table 7.4.4a and roof catchment areas in Table 7.4.4b are not stated, interpolation may be used to determine the applicable overflow values.

(4) Valley gutters must—

  1. be installed on a roof with a pitch more than 12.5 degrees; and
  2. have dimensions in accordance with Table 7.4.4c for the relevant rainfall intensity; and
  3. have minimum freeboard of not less than 15 mm; and
  4. have a side angle of not less than 12.5 degrees.

(5) The requirement of (1)(c) does not apply to eaves gutters fixed to a verandah or an eave that is greater than 450 mm in width, which—

  1. has no lining; or
  2. is a raked verandah or a raked eave with a lining sloping away from the building.
Table 7.4.4a Overflow volume for continuous measure (L/s/m)
Design 5 minute duration rainfall intensity (mm/h) (from Table 7.4.3d) Ridge to gutter length — 2 m Ridge to gutter length — 4 m Ridge to gutter length — 6 m Ridge to gutter length — 8 m Ridge to gutter length — 10 m Ridge to gutter length — 12 m Ridge to gutter length — 14 m Ridge to gutter length — 16 m
150 mm/h 0.08 L/s/m 0.17 L/s/m 0.25 L/s/m 0.33 L/s/m 0.42 L/s/m 0.50 L/s/m 0.58 L/s/m 0.67 L/s/m
175 mm/h 0.10 L/s/m 0.19 L/s/m 0.29 L/s/m 0.39 L/s/m 0.49 L/s/m 0.58 L/s/m 0.68 L/s/m 0.78 L/s/m
200 mm/h 0.11 L/s/m 0.22 L/s/m 0.33 L/s/m 0.44 L/s/m 0.56 L/s/m 0.67 L/s/m 0.78 L/s/m 0.89 L/s/m
225 mm/h 0.13 L/s/m 0.25 L/s/m 0.38 L/s/m 0.50 L/s/m 0.63 L/s/m 0.75 L/s/m 0.88 L/s/m 1.0 L/s/m
250 mm/h 0.14 L/s/m 0.28 L/s/m 0.42 L/s/m 0.56 L/s/m 0.69 L/s/m 0.83 L/s/m 0.97 L/s/m 1.1 L/s/m
275 mm/h 0.15 L/s/m 0.31 L/s/m 0.46 L/s/m 0.61 L/s/m 0.76 L/s/m 0.92 L/s/m 1.1 L/s/m 1.2 L/s/m
300 mm/h 0.17 L/s/m 0.33 L/s/m 0.50 L/s/m 0.67 L/s/m 0.83 L/s/m 1.0 L/s/m 1.2 L/s/m 1.3 L/s/m
325 mm/h 0.18 L/s/m 0.36 L/s/m 0.54 L/s/m 0.72 L/s/m 0.90 L/s/m 1.1 L/s/m 1.3 L/s/m 1.4 L/s/m
350 mm/h 0.19 L/s/m 0.39 L/s/m 0.58 L/s/m 0.78 L/s/m 0.97 L/s/m 1.2 L/s/m 1.4 L/s/m 1.6 L/s/m
375 mm/h 0.21 L/s/m 0.42 L/s/m 0.63 L/s/m 0.83 L/s/m 1.0 L/s/m 1.3 L/s/m 1.5 L/s/m 1.7 L/s/m
400 mm/h 0.22 L/s/m 0.44 L/s/m 0.67 L/s/m 0.89 L/s/m 1.1 L/s/m 1.3 L/s/m 1.6 L/s/m 1.8 L/s/m
Table 7.4.4b Overflow volume for dedicated measure (L/s)
Design 5 minute duration rainfall intensity (mm/h) (from Table 7.4.3d) Roof catchment area — 30 m2 Roof catchment area — 40 m2 Roof catchment area — 50 m2 Roof catchment area — 60 m2 Roof catchment area — 70 m2
150 mm/h 1.3 L/s 1.7 L/s 2.1 L/s 2.5 L/s 2.9 L/s
175 mm/h 1.5 L/s 1.9 L/s 2.4 L/s 2.9 L/s 3.4 L/s
200 mm/h 1.7 L/s 2.2 L/s 2.8 L/s 3.3 L/s 3.9 L/s
225 mm/h 1.9 L/s 2.5 L/s 3.1 L/s 3.8 L/s 4.4 L/s
250 mm/h 2.1 L/s 2.8 L/s 3.5 L/s 4.2 L/s 4.9 L/s
275 mm/h 2.3 L/s 3.1 L/s 3.8 L/s 4.6 L/s 5.3 L/s
300 mm/h 2.5 L/s 3.3 L/s 4.2 L/s 5.0 L/s 5.8 L/s
325 mm/h 2.7 L/s 3.6 L/s 4.5 L/s 5.4 L/s 6.3 L/s
350 mm/h 2.9 L/s 3.9 L/s 4.9 L/s 5.8 L/s 6.8 L/s
365 mm/h 3.1 L/s 4.2 L/s 5.2 L/s 6.3 L/s 7.3 L/s
400 mm/h 3.3 L/s 4.4 L/s 5.6 L/s 6.7 L/s 7.8 L/s
Table 7.4.4c Valley gutters — Dimensions
Design rainfall intensity mm/h Sheet width (minimum, mm) Effective depth (he), (minimum, mm) Effective width (we), (minimum, mm)
≤200 355 32 215
>200 to ≤ 250 375 35 234
>250 to ≤300 395 38 254
>300 to ≤350 415 40 273
>350 to ≤400 435 43 292

Explanatory information: Valley gutters

Figure 7.4.4 (explanatory) Valley gutter profile
image-7-4-4-explanatory-valley-gutter-profile.svg

Downpipes must—

  1. not serve more than 12 m of gutter length for each downpipe; and
  2. be located as close as possible to valley gutters; and
  3. be selected in accordance with the appropriate eaves gutter section as shown in Table 7.4.3a, Table 7.4.3b and Table 7.4.3c.

Explanatory information

A maximum 12 m gutter length served by each downpipe is to ensure effective fall and adequate capacity to discharge all water anticipated during a storm having an annual exceedance probability of 5%.

Where a rainhead overflow device is incorporated in the top of the downpipe, its overflow discharge should be directed away from the building.

(1) For a front face slotted gutter with—

  1. a minimum slot opening area of 1200 mm2 per metre of gutter; and
  2. the lower edge of the slots installed a minimum of 25 mm below the top of the fascia,

the acceptable overflow capacity must be 0.5 L/s/m, constructed in accordance with Figure 7.4.6a.

(2) For a controlled back gap with—

  1. a permanent minimum 10 mm spacer installed between the gutter back and the fascia; and
  2. one spacer per bracket, with the spacer not more than 50 mm wide; and
  3. the back of the gutter installed a minimum of 10 mm below the top of the fascia,

the acceptable overflow capacity must be 1.5 L/s/m, constructed in accordance with Figure 7.4.6b.

(3) For the controlled back gap option, the spacer can be a proprietary clip or bracket that provides the required offset of the gutter from the fascia.

(4) For controlled front bead height with the front bead of the gutter installed a minimum of 10 mm below the top of the fascia, the acceptable overflow capacity is 1.5 L/s/m constructed in accordance with Figure 7.4.6c.

Figure 7.4.6a Construction of front face slotted gutter
image-7-4-6a-construction-of-front-face-slotted-gutter.svg
Figure 7.4.6b Construction of controlled back gap
image-7-4-6b-construction-of-controlled-back-gap.svg
Figure 7.4.6c Construction of controlled front bead height
image-7-4-6c-construction-of-controlled-front-bead-height.svg
Figure Notes

Front bead of gutter to be a minimum of 10 mm below the top of the fascia.

(1) For an end-stop weir with—

  1. a minimum clear width of 100 mm; and
  2. the weir edge installed a minimum 25 mm below the top of the fascia,

the acceptable overflow is 0.5 L/s constructed in accordance with Figure 7.4.7a.

(2) An end-stop weir is not suitable where the end-stop abuts a wall.

(3) For an inverted nozzle installed within 500 mm of a gutter high point with—

  1. a minimum nozzle size of 100 mm × 50 mm positioned lengthways in the gutter; and
  2. the top of the nozzle installed a minimum of 25 mm below the top of the fascia,

the acceptable overflow is 1.2 L/s constructed in accordance with Figure 7.4.7b.

(4) For a front face weir with—

  1. a minimum clear width of 200 mm; and
  2. a minimum clear height of 20 mm; and
  3. the weir edge installed a minimum of 25 mm below the top of the fascia,

the acceptable overflow capacity is 1.0 L/s constructed in accordance with Figure 7.4.7c.

(5) For a rainhead with—

  1. a 75 mm diameter hole in the outward face of the rainhead; and
  2. the centreline of the hole positioned 100 mm below the top of the fascia,

the acceptable overflow capacity is 3.5 L/s constructed in accordance with Figure 7.4.7d.

(6) The rainhead should be detailed to avoid nuisance discharge from the overflow at rainfall intensities below the normal design level.

Figure 7.4.7a Construction of end-stop weir
image-7-4-7a-construction-of-end-stop-weir.svg
Figure 7.4.7b Construction of inverted nozzle
image-7-4-7b-construction-of-inverted-nozzle.svg
Figure 7.4.7c Construction of front face weir
image-7-4-7c-construction-of-front-face-weir.svg
Figure 7.4.7d Construction of rainhead
image-7-4-7d-construction-of-rainhead.svg