directionincludingany end laps, expansionioints or steps that may be
oresentin the roof.
Note:See Chapters11 & 12 for gutterand downpipecapacities.
11. Gutter Gapacity
The gutter ctoss sectionalareas given in Table 11.1.are providedlor Guftersand downpipesshouldbe madelrom coatedsteelcontorming
guidanceonlWhere moredesigndetailis required,tfrefollowingreports to AS 2179.
shouldbe mnsulted:CSIRODivisionof BuildingReseardtReport02'2.30 Rainwaterrun-ofi from inert roofing materialssuch as ZINCALUME,
"The influenceof SlopeUponthe DischargeCapacityof RoofChannels", COLORBOND,aluminiumor glazedtile surfacesshouldnot be drained
The lnstitutionof Engineers,Australia,"First Reportof the Stormwater into a Pl-AlN galvanizedgutter. ZINCALUMEor COLORBONDsteel
StandardsCommittee,AustralianRainfalland Run-Off"and the Bureau guttersand downpipesare recommendedfor these rootirg materials.
of Meteorology,Bull.etin51 August 1984, "The Estimationof Probable
MaximumPrecipitationin Australiafor ShortDurationsand SmallAreas." GUTTER SIZES FOR YARIOUS RAINFALL
TABLE 1I.I
Table 11.1 listsa selectionof roof catchmentareasthat are drainedby IT{TENSITIESAND ROOF CATCHMEXT
one dornpipe and shows the cross sectionalarea of gutter requiredfor a AREAS PER DOWI{PIPE
rangeof raintallintensities.The roofcatchmentareafor eachdownpipeis
-roof
the lengrthof rqn (ridge to gutter) muhipliedby the spacing between
dorvnpipos. Roof
A turther safety margin of 25 mm freeboardon the deph of internalbox Catc'hmnl
fuea 10 flf 20ttf 50l'f lm'tf 200m'z
guttersshouldbe addedto the crosssectionalareasgivenin TaUe 11 1.
AuslralianStandard218G1978statesthat eavesguttorsshouldhavea
j,-tall tci,vardsthe outleb of 1 in 500 and internalbox guttersa tall of t in 200'
'f Cross Sectional Area of Gutter (mm2)
tf for somedesignor otherconsUerationguttersare installedwithoutfall, Rainlall
,F ponOlngwill result and this could reducethe life of the gutter. In sucft Intensity required to drain above roof catchment
situationsthe guttershouldbe cleanedout regularly. (mm/hr) area into one downpipe
Wilh high fronted eaves fasciautters, care should be taken to prevent
overllow from tre back of the gutter into the building, in the event of a 80 1300 / 2200 4600 8000 14000
bbcked downpipe.This can be done by poviding drainageslots along 90 142o 2M 5100 8750 15220
the tronl of the gutter, at a lower'bvel than the back of the gutter' or by 100 1540 2600 5500 9450 16430
prwiding s)dra downFtps. 10150 17630
110 1630 2800 5890
Intemalbox gutters ol more lhan 15 000 mmzcross-section,should be 120 1740 2990 6280 10850 18820
a minimumof 300 mm wide and fully supportedto allow workmento walk 1850 3180 6670 11530 20000
130
along ttre botbm of the gutter. Sheetingsuch as Span&k Hi'Ten can be
1/tO 1950 sri,70 7050 12210 21't70
used under a wide box gutter to povide full support between the gutter
hangers. 150.. 2050 3560 743r) 12890 22330
160 2150 3750 7810 13570 23490
'175 2300 4030 8370 14570 25210
200 2550 44W 9290 16220 28060
225 2800 4920 10200 17820 30860
275 3300 5760 12000 20,920 34|00
325 3780 6560 13750 23920 4170o
425 4650 8060 16800 29250 51000
Guter harqerwith Note:Forintemalboxguttersadd25 mmof freeboarddepthto cross
adjustmentfor fall sectionalareasgivenin Table 11.1
12. Downpipe Capacity
Thecross-section of a dornpipelromdn eavesgutlershouldbe 65 mrn-
for eachsquare-metre of roofareadririningintothe downpipe.
Thecross-sec.tion of a dovnpipetroman intemalboxguttershouldbe
95 mm2tor eachsquaremere of roofareadrainingintothedownpip'
However, lhe minimum cross-cectionof anydownflpeshouldbe at
leasihalfthatof theguttertromwhichit drains.
It is goodpracticeto providedrainagesumpsat dwnpipe connections
b guttersord leasthavefunnelsattheheadof eacfidovmftpe'parliculady
tor intemalboxgutters.
Wherepossible downPipes shouldbe spacedat no morethan18 m
centres.
22
. ( I\STRUCTION AND COMPLETION OF THE PROPOSED NEW FACADE,
. \\OPY (LEVEL 2), INTERNAL ALTERATION WORKS TO KUCHING PLAZA
,\ I-OT 16,SECTION30,KTLD KUCHING
TABLE OF CONTENTS
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:- TO TENDERERS
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