Balcony drainage for a multi-level apartment building at 5 O Reily Avenue, Wellington

Transcription

1 Balcny drainage fr a multi-level apartment building at 5 O Reily Avenue, Wellingtn 1 The matter t be determined 1.1 This is a determinatin under Part 3 Subpart 1 f the Building Act ( the Act ) made under due authrisatin by me, Jhn Gardiner, Determinatins Manager, Department f Building and Husing( the Department ), fr and n behalf f the Chief Executive f that Department. The applicant is the wner, Bulctt Village Prperties Ltd acting thrugh a management cmpany ( the applicant ), and the ther party is the Wellingtn City Cuncil ( the territrial authrity ). 1.2 The matter fr determinatin is whether the use f spillver strmwater discharge (unifrm discharge) frm the balcnies n the building, Levels 2 t 8 inclusive, cmplies with the Building Cde (First Schedule, Building Regulatins 1992). 1.3 In making my decisin, I have cnsidered the submissins f the parties, the reprt f the independent expert cmmissined by the Department t advise n this dispute ( the expert ), and the ther evidence in this matter. 1.4 In this determinatin, unless therwise stated, references t sectins are t sectins f the Act and references t clauses are t clauses f the Building Cde. 2 The building wrk 2.1 The building wrk has been planned and built in tw stages. Stage Tw cnsists f seven flrs (Levels 2 t 8) (currently partially cmpleted) cnstructed n the existing Stage One tw-strey building (Levels G and 1). The matter in dispute is abut the strmwater discharge frm the balcnies t the Stage Tw wrk, being the balcnies frm Levels 2 t 8 inclusive. 2.2 Levels 2 t 8 each cntains three apartments, being 24 apartments in ttal. It is prpsed t cnstruct a cantilevered balcny t each f the 24 apartments cnstructed n the nrth elevatin f the building. Each balcny will extend t the bundary f the prperty. The verall size f each balcny is 3480mm x 1025mm (3.567m2) n plan. The balcnies are timber-framed and are supprted n structural 1 The Building Cde and the Building Act 2004 are available frm the Department s website at Department f Building and Husing 1 1 December 2006

2 steel frames. The decks t the prpsed balcnies cnsist f 19mm thick Kwila clse barding cvered with a 1.5mm thick butyl-rubber membrane. Each balcny is t be prtected by a balustrade frmed frm perfrated aluminium panels. The strmwater drainage discharge frm the decks is a spill-ver system at the deck perimeters. 2.3 At Grund flr there is a cntinuus verandah canpy, at Level One there is a cntinuus balcny. Bth features have a cntrlled strmwater dispsal system cnsisting f gutters and dwnpipes. Figure 1: Sectin thrugh the building. 3 Sequence f events 3.1 Prir t the issuing f a building cnsent, varius s passed between the applicant s architect ( the architect ) and the territrial authrity frm 26 Octber 2005 t 21 Nvember These basically discussed the strmwater drainage f the balcnies if they were t be f a slid surface cnstructin. In particular, the crrespndence frm the architect nted that: Department f Building and Husing 2 1 December 2006

3 ther multi-level prjects cnsented t by the territrial authrity had nt required cntrlled dispsal systems fr slid flr balcnies similar t the nes in questin the applicant was f the pinin that the principles f Apprved Dcument E2/AS1f the Building Cde culd nt apply t the building unless that dcument s scpe was amended the balcnies did nt have an enclsed deck in terms f E2/AS1 the applicant cnsidered aspects f Determinatin 2003/4 supprted its arguments. 3.2 The territrial authrity s psitin as set ut in the crrespndence can be summarised as saying: perfrated decks d nt require drainage decks with a membrane r rf cladding have t cmply with sectin 17 f the Act and the relevant clauses f E1and E2. This wuld require the installatin f a cntrlled strmwater dispsal system at each balcny. 3.3 In the final f 21 Nvember 2005, the applicant stated that the deck design wuld be changed frm a slid surface t a perfrated metal surface. 3.4 Subsequent t this amendment, the territrial authrity issued a building cnsent n 29 March 2006, and wrk then cmmenced n the prject. 3.5 The applicant requested a determinatin as t whether the use f spill-ver decks n the prperty wuld cmply with the Building Cde. The determinatin applicatin was received by the Department n 9 August At present all the units are under a single wnership, but they are likely t be sld under separate titles nce the building is cmpleted. 4 The submissins 4.1 In a lengthy submissin t the Department dated 31 July 2006, the architect set ut the backgrund t the dispute. He als nted that ther prjects already apprved by the territrial authrity had spillver decks. The applicant had assessed the prpsed amended balcnies in terms f the Act, clauses E1 and E2 f the Building Cde and Determinatin 2003/4. The cnclusins reached by the architect were that: the catchment area f each deck is slightly ver 3m 2. The cumulative affect f water cascading dwn a set f seven balcnies wuld nly be nminal as the ttal vlume f surface water wuld nt increase because f the balcnies the cntinuus gutter and assciated dwnpipes at Level 1 wuld absrb the effect n peple at street level f any rainwater cascading ff the balcnies it is unlikely that ccupants f the building will be ut n their balcnies if it is raining there wuld be n adverse effects t any adjining prperty. Department f Building and Husing 3 1 December 2006

4 as it is unlikely that adjining prperty will be affected, the requirements f clause E1 will nt be breached as the balcnies d nt have enclsed balustrades, the principles f paragraph 7.4 f E2/AS1 d nt apply the building in questin is utside the scpe f paragraph 1.2 f E2/VM1 (I nte here that the submissin errneusly refers t E2/AS1 in this respect) the findings set ut in Determinatin 2003/4, particularly paragraphs 5.2 and 6, supprt the applicant s psitin. 4.2 The applicant als frwarded cpies f: the crrespndence between the parties phtgraphs f varius Wellingtn high-rise buildings with spill-ver balcny decks relevant legislative dcuments. 4.3 In a letter t the Department dated 7 September 2006, the territrial authrity als set ut sme f the backgrund t the dispute. The territrial authrity als said: if the serviced apartments were t be sld ff as separate titles, the questin f lss f amenity t the lwer balcnies wuld have t be cnsidered. The use f spillver balcny decks wuld cnstitute such an amenity lss it cnsidered that the principles f clauses E1.2 and E1.3.1 applied and cnsideratin needs t be given t paragraphs and f E2/AS1 strmwater frm slid-surface decks must be cntrlled withut causing nuisance r damage t ther prperty. This can be achieved either by the use f sputings at the deck edges r an internal gutter that wuld discharge int dwnpipes cnnected t the strmwater system. 4.4 I then prepared a draft determinatin, which was frwarded t the parties n 9 Nvember The applicant ntified the Department n 13 Nvember 2006 that the draft determinatin was accepted. 4.5 The territrial authrity respnded in a letter dated 17 Nvember 2006, stating that fr varius reasns it did nt accept the draft. The territrial authrity s main area f cncern was the effect that any discharge f water frm the balcny decks wuld have n the adjacent public spaces. 5 The expert s reprt 5.1 The expert reviewed the issues relating t the surface water discharge frm the balcnies and furnished a reprt that was dated 6 Octber The expert stated that, in rder t judge the degree f ptential nuisance t the flrs belw a given balcny, it was necessary t calculate the quantity f surface water likely t cllect n the balcny. The expert cnsidered that the apprach adpted in Determinatin 2003/4 t calculate surface discharge frm the face f a building was verly cnservative. The expert was f the pinin that the research undertaken by CSIRO and described in its publicatin NSB 177A was mre relevant t the current situatin. Department f Building and Husing 4 1 December 2006

5 5.2 The main pints raised by the expert in the cntext f the CSIRO research can be summarised as fllws: The distributin f wind and wind-driven rain is cncentrated at the upper flrs and at the edges f buildings and is quite lw in the centre and lwer stries f buildings. During wind gusts in strm cnditins, surface water accumulates n the face f buildings within a time-span f less than a minute t a pint where it is trn ff and is re-distributed alng, arund r ver the building. As rain strikes a building in waves, wind deflectin gives rise t perids during which the face f a building is free frm rain. It is apprpriate t calculate and take int accunt the likely vlume f water expected t discharge ver a balcny when cnsidering hw such water might behave when intercepted by a balcny and whether the cmbined flw might cause a nuisance t the flrs belw. Cnservatively, n a multi-strey building the catchment area wuld span up t 2 streys and ignring whether a balcny wuld interrupt the water flw, the flw shuld be calculated n this area. In the Wellingtn area this wuld equate t apprximately 0.12 l/s in a 10% AEP (annual event prbability) event. The rain cllected n the 3.5m2 hrizntal tp surface f the tp balcny wuld be n mre than 0.07 l/s in a 10% AEP event. It is incrrect t cumulatively add the flw frm the upper balcnies as rain either falls n an upper balcny r is blwn nt the face f the building within any 2 strey catchment area. Based n these calculatins, the estimated flw rate f discharge frm ne f the higher balcnies wuld be 0.19 l/s in a 10%AEP event. 5.3 The expert s cnclusins can be summarised as: The 0.19 l/s run-ff calculatin equates t the discharge frm a rf with an area apprximating 7m2. As the face f the balcny is 3.4m lng, the discharge flw ver its face apprximately 0.06 l/ s in a 10% AEP event, which might be nticeable and can be cmpared t the 0.02 l/s in a 10% AEP event f the surrunding rainfall falling n a 1m2 hrizntal area. It is nt cnsidered that the 0.04 l/s increase in misture in the air wuld be a nuisance in the cntext f the amunts f wind and rain required t prduce such an increase. In the event f lesser events, the flw frm a single balcny wuld reduce t as little as 0.02 l/s per metre f balcny face. 5.4 The expert stated that if the cnclusin reached was t ptimistic, the ptential nuisance culd be mitigated by slping the deck f the balcnies twards the face f the building. This wuld ensure that the water flw wuld run dwn the sides f building until it was re-distributed by the wind. Department f Building and Husing 5 1 December 2006

6 5.5 Cpies f the reprt were frwarded t the parties. In an t the Department n 25 Octber 2006, the architect nted that the reprt cncluded that the water discharge wuld be insignificant and therefre justified the design. 5.6 The territrial authrity als replied by n 26 Octber 2006, stating that it still believed that the cntrl f the strmwater was an issue. It als cnsidered that any free-falling water wuld d s ver the bundary and pssibly cause damage t the adjining territrial authrity legal rad. 6 The legislatin 6.1 The relevant perfrmance f the building cde is: Perfrmance E1.3.1 Except as therwise required under the Resurce Management Act 1991 fr the prtectin f ther prperty, surface water resulting frm a event having a 10% prbability f ccurring annually and which is cllected r cncentrated by buildings r sitewrks, shall be dispsed f in such a way that avids the likelihd f damage r nuisance t ther prperty. 7 Discussin 7.1 As nted in paragraph 3.6, the apartments are likely t be sld under separate titles. If this is nt the case, then the questin f ther prperty des nt arise with regard t the individual units. Hwever, assuming that the building will eventually be unittitled, I have cnsidered that each unit will be ther prperty in relatin t the ther units in terms f clause E The territrial authrity als has cncerns abut damage t its legal rad, which I als accept is ther prperty. Althugh the Cmpliance Dcument E2/AS1 describes apprpriate guttering details if required, I d nt believe that clause E2 is relevant in this case. 7.2 Befre addressing the effect that prjecting balcnies n high-rise buildings have n wind-driven rain, I nte that blank external walls f high-rise buildings withut such balcnies will als cncentrate water and discharge it nt ther prperties. Hwever, as this situatin has nt been raised in this determinatin, I am nt required t decide n this issue. 7.3 Reference has als been made by the parties t Determinatin 2003/4, which in effect decided that balcnies n multi-strey buildings cncentrated surface water and discharged it nt the balcnies belw ( ther prperty ), with cumulative effects fr lwer balcnies. Hwever, this determinatin did nt address the necessary issue f hw t calculate the resultant flw frm the 10% AEP nr whether the calculated flw wuld cause damage r nuisance t ther prperties. In additin, I d nt accept that Determinatin 2003/4 endrsed the CSIRO statement that balcnies with areas less than 10m2 d nt require their water runff t be calculated as this can be cnsidered nminal nly. 7.4 Neither f the parties has prvided calculatins relating t the balcny discharge flw resulting frm a 10% AEP event. The expert has prvided such calculatins in line with the CSIRO publicatin NSB 177A, and has cncluded that the increase in misture in the air caused by the balcnies in a 10% AEP event wuld nt cnstitute a nuisance t the wners f lwer-level balcnies. In the absence f any cnflicting Department f Building and Husing 6 1 December 2006

7 evidence frm the parties, I accept this pinin. In additin, I nte there is a fulllength cantilevered deck with a cntrlled strmwater dispsal system at a level belw all the balcnies. Accrdingly, I cnsider that the effect n the territrial authrity s legal rad f free-falling water resulting frm a 10% AEP event wuld be negligible, and as such, nt cnstitute a nuisance in terms f clause E I cnsider that the basic cncern raised in the territrial authrity s respnse t the draft determinatin was in regard t the effect the balcny water discharge had n the adjining prperty. I nte that the expert has calculated that the discharge frm the balcnies in a 10% AEP event is quite negligible. If there is n wind then any rain wuld nly fall n the tp balcnies. I am f the pinin that, even if the balcnies were nt there, in a 10% AEP event the strength f the wind wuld be such as t drive rain utside the bundaries f the building. Accrdingly, I am nt cnvinced that the balcnies exacerbate this scenari. 7.6 The territrial authrity is prepared t accept that if the balcnies have perfrated decks they wuld nt require cntrlled strmwater drainage. I am f the pinin that in many instances, the slid deck balcnies withut cntrlled drainage wuld affrd better prtectin t lwer balcny users than wuld the perfrated alternative. 8 The decisin 8.1 In accrdance with sectin 188 f the Act I determine that the prpsed amended design f the spillver slid decked balcnies cmplies with the prvisins f E1 f the Building Cde. Signed fr and n behalf f the Chief Executive f the Department f Building and Husing n 1 December Jhn Gardiner Determinatins Manager Department f Building and Husing 7 1 December 2006