SOUTH CENTRAL WA PTY LTD and DIPLOMA CONSTRUCTION (WA) PTY LTD
[2015] WASAT 38
•8 APRIL 2015
SOUTH CENTRAL WA PTY LTD and DIPLOMA CONSTRUCTION (WA) PTY LTD [2015] WASAT 38
| STATE ADMINISTRATIVE TRIBUNAL | Citation No: | [2015] WASAT 38 | |
| BUILDING SERVICES (COMPLAINT RESOLUTION and ADMINISTRATION) ACT 2011 (WA) | |||
| Case No: | CC:408/2014 | 20 JANUARY 2015 AND 21 JANUARY 2015 | |
| Coram: | MR D AITKEN (MEMBER) MR R AFFLECK (SENIOR SESSIONAL MEMBER) | 8/04/15 | |
| 19 | Judgment Part: | 1 of 1 | |
| Result: | Application successful | ||
| B | |||
| PDF Version |
| Parties: | SOUTH CENTRAL WA PTY LTD DIPLOMA CONSTRUCTION (WA) PTY LTD |
Catchwords: | Building Services (Complaint Resolution and Administration) Act 2011 (WA) Complaint that building service unsatisfactory Design and construct contract Whether AS/NZS 3500.3 is the design standard for an onsite stormwater detention system |
Legislation: | Building Act 2011 (WA), s 3 Building Code of Australia 2008, Pt F1.1 Building Services (Complaint Resolution and Administration) Act 2011 (WA), s 3, s 5(1), s 11(1)(d), s 36(1), s 38, s 38(1) |
Case References: | Nil |
Orders | On the application heard before Member David Aitken and Senior Sessional Member Richard Affleck, it is on 8 April 2015 ordered that:,1. By no later than 8 July 2015, the respondent must remedy the unsatisfactory building work at Lot 9501 Armadale Road, Jandakot by installing additional below ground stormwater storage to comply with a design certified by a suitably qualified practising engineer prepared in accordance with Australian Rainfall and Runoff 1987 produced by the Institution of Engineers, Australia on the basis of a one in 10 year storm event. |
Summary | The respondent designed and constructed a stormwater drainage system for the carpark of a bulky goods shopping centre in Jandakot as part of the work of constructing the shopping centre under a contract between it and the applicant. The work was completed in late 2008.,There had been flooding in the carpark, although there was disagreement between the parties regarding both the extent of that flooding and when it commenced.,The applicant contended that the stormwater drainage works were unsatisfactory because they had not been designed and constructed to the requirements of the City of Cockburn and was seeking an order that the respondent install additional below ground stormwater storage.,The respondent contended that the cause of the flooding was the failure of the applicant to adequately clean and maintain the soakwells.,One of the conditions of the development approval for the construction of the shopping centre requires that the stormwater drainage system be designed in accordance with Australian Rainfall and Runoff 1987, produced by the Institution of Engineers Australia, on the basis of a one in 10 year storm event and that the design be certified by a suitably qualified practising engineer. One of the conditions of the building licence stated that the respondent must comply with Part F1.1 of the Building Code of Australia 2008 and AS/NZS 3500.3 and the respondent's hydraulic engineer's design.,The respondent contended that the design of the stormwater drainage system met the requirements of the City of Cockburn and that the construction of the stormwater drainage system was in accordance with the design drawings which had been submitted with the application for the building licence and therefore the stormwater drainage works could not be said to be unsatisfactory.,The parties' experts agreed that the stormwater from a one in 10 year rainfall event should be accommodated below ground, but disagreed on the method to be used to calculate the required below ground storage capacity. The expert for the respondent contended that Part 3 of AS/NZS 3500.3 provides the necessary design standard, but the experts for the applicant contended that it does not and that it is necessary to also refer to Australian Rainfall and Runoff 1987.,The Tribunal decided that the issue of flooding was not relevant to the determination of whether or not there is insufficient below ground storage to accommodate a one in 10 year storm event, so the Tribunal did not need to decide whether or not the applicant had adequately maintained the soakwells or consider the extent of the flooding.,The Tribunal decided that a designer cannot design an onsite stormwater detention system on the basis of Part 3 of AS/NZS 3500.3 and, therefore it is necessary to refer to some other source of information. The Tribunal decided that the design of the onsite stormwater detention system was required by the City of Cockburn to be in accordance with the Australian Rainfall and Runoff 1987.,The Tribunal decided that the design prepared on behalf of the respondent did not satisfy that requirement and the stormwater drainage system has less below ground capacity than is required and is, therefore unsatisfactory. The Tribunal also decided that the fact that the City of Cockburn accepted the plans for the stormwater drainage system when they were lodged with the application for the building licence, did not relieve the respondent of the responsibility to construct the stormwater drainage works in a manner which satisfied the conditions of the development approval.,The Tribunal ordered the respondent to remedy the unsatisfactory building work by installing additional below ground stormwater storage to comply with a design certified by a suitably qualified practising engineer prepared in accordance with Australian Rainfall and Runoff 1987 on the basis of a one in 10 year storm event. |
JURISDICTION : STATE ADMINISTRATIVE TRIBUNAL ACT : BUILDING SERVICES (COMPLAINT RESOLUTION and ADMINISTRATION) ACT 2011 (WA) CITATION : SOUTH CENTRAL WA PTY LTD and DIPLOMA CONSTRUCTION (WA) PTY LTD [2015] WASAT 38 MEMBER : MR D AITKEN (MEMBER)
- MR R AFFLECK (SENIOR SESSIONAL MEMBER)
- 21 JANUARY 2015
- CC 416 of 2014
- Applicant
AND
DIPLOMA CONSTRUCTION (WA) PTY LTD
Respondent
Catchwords:
Building Services (Complaint Resolution and Administration) Act 2011 (WA) Complaint that building service unsatisfactory Design and construct contract Whether AS/NZS 3500.3 is the design standard for an onsite stormwater detention system
Legislation:
Building Act 2011 (WA), s 3
Building Code of Australia 2008, Pt F1.1
Building Services (Complaint Resolution and Administration) Act 2011 (WA), s 3, s 5(1), s 11(1)(d), s 36(1), s 38, s 38(1)
Result:
Application successful
Summary of Tribunal's decision:
The respondent designed and constructed a stormwater drainage system for the carpark of a bulky goods shopping centre in Jandakot as part of the work of constructing the shopping centre under a contract between it and the applicant. The work was completed in late 2008.
There had been flooding in the carpark, although there was disagreement between the parties regarding both the extent of that flooding and when it commenced.
The applicant contended that the stormwater drainage works were unsatisfactory because they had not been designed and constructed to the requirements of the City of Cockburn and was seeking an order that the respondent install additional below ground stormwater storage.
The respondent contended that the cause of the flooding was the failure of the applicant to adequately clean and maintain the soakwells.
One of the conditions of the development approval for the construction of the shopping centre requires that the stormwater drainage system be designed in accordance with Australian Rainfall and Runoff 1987, produced by the Institution of Engineers Australia, on the basis of a one in 10 year storm event and that the design be certified by a suitably qualified practising engineer. One of the conditions of the building licence stated that the respondent must comply with Part F1.1 of the Building Code of Australia 2008 and AS/NZS 3500.3 and the respondent's hydraulic engineer's design.
The respondent contended that the design of the stormwater drainage system met the requirements of the City of Cockburn and that the construction of the stormwater drainage system was in accordance with the design drawings which had been submitted with the application for the building licence and therefore the stormwater drainage works could not be said to be unsatisfactory.
The parties' experts agreed that the stormwater from a one in 10 year rainfall event should be accommodated below ground, but disagreed on the method to be used to calculate the required below ground storage capacity. The expert for the respondent contended that Part 3 of AS/NZS 3500.3 provides the necessary design standard, but the experts for the applicant contended that it does not and that it is necessary to also refer to Australian Rainfall and Runoff 1987.
The Tribunal decided that the issue of flooding was not relevant to the determination of whether or not there is insufficient below ground storage to accommodate a one in 10 year storm event, so the Tribunal did not need to decide whether or not the applicant had adequately maintained the soakwells or consider the extent of the flooding.
The Tribunal decided that a designer cannot design an onsite stormwater detention system on the basis of Part 3 of AS/NZS 3500.3 and, therefore it is necessary to refer to some other source of information. The Tribunal decided that the design of the onsite stormwater detention system was required by the City of Cockburn to be in accordance with the Australian Rainfall and Runoff 1987.
The Tribunal decided that the design prepared on behalf of the respondent did not satisfy that requirement and the stormwater drainage system has less below ground capacity than is required and is, therefore unsatisfactory. The Tribunal also decided that the fact that the City of Cockburn accepted the plans for the stormwater drainage system when they were lodged with the application for the building licence, did not relieve the respondent of the responsibility to construct the stormwater drainage works in a manner which satisfied the conditions of the development approval.
The Tribunal ordered the respondent to remedy the unsatisfactory building work by installing additional below ground stormwater storage to comply with a design certified by a suitably qualified practising engineer prepared in accordance with Australian Rainfall and Runoff 1987 on the basis of a one in 10 year storm event.
Category: B
Representation:
Counsel:
Applicant : Mr R Shaw
Respondent : Mr G Cridland
Solicitors:
Applicant : Lavan Legal
Respondent : Jarman McKenna
Case(s) referred to in decision(s):
Nil
Introduction
1 This proceeding concerns two complaints lodged with the Building Commission by South Central WA Pty Ltd (applicant) against Diploma Construction (WA) Pty Ltd (respondent)under the Building Services (Complaint Resolution and Administration) Act 2011 (WA) (BSCRA Act) alleging unsatisfactory building work by the respondent. The Building Commission referred the complaints to the Tribunal under s 11(1)(d) of the BSCRA Act and they have been consolidated into one proceeding.
2 The respondent designed and constructed stage one of a bulky goods shopping centre for the applicant at Lot 9501 Armadale Road, Jandakot (site) pursuant to a design and construct contract, which is undated but was entered into between the parties in or about March 2008 (contract).
3 The work under the contract included the design and construction of the carpark stormwater drainage system for the shopping centre (stormwater drainage system or stormwater drainage works). The work under the contract was completed in or around November 2008.
4 The original development approval for the site was issued by the City of Cockburn (City)on 15 November 2007, but it was replaced by an amended development approval issued by the City on 12 February 2008 (development approval). Condition 39 of the development approval states that all stormwater drainage shall be 'designed in accordance with the document entitled "Australian Rainfall and Runoff" 1987 (where amended) produced by the Institute [sic] of Engineers, Australia' on the basis of a one in 10 year storm event and that the design is to be certified by a suitably qualified practising engineer. The reference to Australian Rainfall and Runoff 1987 is a reference to the publication produced by the Institution of Engineers, Australia in 1987 under the title Australian Rainfall and Runoff - A Guide to Flood Estimation (ARR).
5 The building licence was issued to the respondent on 5 May 2008 (building licence). Condition BC410 of the building licence, under the heading 'Stormwater Drainage', states that the respondent must comply with 'BCA F1.1 and AS/NZS 3500.3 and [the respondent's] hydraulic engineer's design'. The reference to 'BCA F1.1' is a reference to Part F1.1 of the Building Code of Australia2008 (BCA), which was adopted by the Commonwealth and States of Australia on 1 May 2008. The reference to 'AS/NZS 3500.3' is a reference to the 'Australian/New Zealand Standard' published by Standards Australia Limited and Standards New Zealand on 15 December 2003 as AS/NZS 3500.3:2003.
6 The stormwater drainage system was designed by PM White & Partners (Aust) Pty Ltd (PM White & Partners), plumbing and hydraulic design consultants, as part of the performance of the respondent's responsibility under the contract for both the design and the construction of the stormwater drainage works.
7 There has been flooding in the carpark, although there is disagreement between the parties regarding both the extent of that flooding and when it commenced.
Contentions of the parties
8 The first complaint states that the respondent carried out unsatisfactory work, firstly, in respect of awning cleats and secondly, in respect of the southern carpark drainage. The second complaint states that the respondent carried out unsatisfactory work in respect of the drainage in all the other areas of the carpark.
9 The complaint in respect of the awning cleats was resolved between the parties and that part of the proceeding was withdrawn.
10 In the complaints, the applicant states that it is seeking the installation of additional below ground stormwater storage.
11 The applicant contends that the respondent failed to design and construct the stormwater drainage works to the requirements of the City and, in particular, the requirement that the stormwater drainage system be designed in accordance with the ARR.
12 After the complaints were referred to the Tribunal, the applicant further contended that the respondent failed to design and construct the stormwater drainage system to be fit for purpose, as required under clause 2.2 of the contract. That is a contractual issue which is not before the Tribunal, because it was not raised in the complaints. The Tribunal is only able to deal with what has been referred to it by the Building Commission.
13 The respondent denies that the stormwater drainage works are unsatisfactory and contends that the cause of flooding which has occurred in the carpark is due to the failure of the applicant to adequately clean and maintain the soakwells.
14 The respondent contends that the design of the stormwater drainage system met the requirements of the City and that the construction of the stormwater drainage system was in accordance with the design drawings which the respondent had submitted to the City with the application for the building licence and therefore the stormwater drainage works cannot be said to be unsatisfactory.
15 The respondent further contends that even if the Tribunal finds that there is unsatisfactory building work, it should exercise its discretion under s 38(1) of the BSCRA Actnot to make a building remedy order, because there is no evidence of flooding in six of the seven catchment areas and even though there has been flooding in one area, there is no evidence that the flooding is due to an inadequate number of soakwells, rather than being due to a lack of cleaning and maintenance of the soakwells.
Issues to be determined
16 The issues which the Tribunal has to determine are whether the stormwater drainage works are unsatisfactory and, if so, what order should be made.
Legislative scheme
17 Under s 5(1) of the BSCRA Act, a building service complaint is a complaint 'about a regulated building service not being carried out in a proper and proficient manner or being faulty or unsatisfactory'.
18 Under s 3 of the BSCRA Act, a regulated building service includes a building service carried out by a registered building service provider and a building service includes building work, as defined in the Building Act 2011 (WA) (Building Act). The respondent is a registered building service provider. The definition of building work in s 3 of the Building Act includes the construction of a structure incidental to a building and the stormwater drainage works fall within that definition. Although the design of the stormwater drainage system is not building work under that definition, the construction of those works clearly is a regulated building service.
19 Under s 38 of the BSCRA Act, the Tribunal may make a building remedy order if it is satisfied that a regulated building service is unsatisfactory and under s 36(1) of the BSCRA Act, a building remedy order can require that the building service be remedied.
Outline of the evidence
20 During the hearing the Tribunal received into evidence a book of documents (hearing book), some photographs, and the first five pages of Part 3 of AS/NZS 3500.3:2003 and a copy of the instructions to the applicant's experts.
21 Hereafter, for ease of reference, Part 3 of AS/NZS 3500.3:2003 is referred to as AS 3500.
22 The Tribunal heard oral evidence from the development manager of the applicant, Mr Benjamin Lisle and from three experts, who gave their evidence concurrently. Those experts were Mr David Porter of Porter Consulting Engineers and Mr David Wills of David Wills and Associates, who were both called by the applicant and Mr Anthony Serek of PJ Wright and Associates, who was called by the respondent.
23 Each of the experts had prepared reports, which are in the hearing book. Mr Porter's report is dated 22 February 2013. Mr Wills' reports are dated 16 April 2013 and 10 September 2013. Mr Serek's reports are dated 20 August 2014 and 7 January 2015.
Joint expert report
24 The three experts had attended a conferral conducted by Senior Sessional Member John Fisher, following which they produced a joint expert conferral report dated 8 October 2014 (joint expert report), which is in the hearing book.
25 Section 1 of the joint expert report contains a plan which shows the site divided into seven areas and states that area one has incurred recurrent drainage problems to the carpark and other external areas, which has caused flooding of a building.
26 It then gives the following summary of the involvement of the three experts.
27 Porter Consulting Engineers was engaged by the applicant to investigate the drainage in area one and Mr Porter concluded that there is insufficient capacity in the drainage disposal system in that area.
28 David Wills and Associates was also engaged by the applicant to review appropriate design standards and the adequacy of the drainage for the complex. Mr Wills concurred with the Porter Consulting Engineers' report regarding area one and concluded that there is also insufficient capacity in areas two to seven to deal with the critical storm event.
29 PJ Wright and Associates was engaged by the respondent to advise on design compliance of the stormwater drainage with the City'sdesign standards and Mr Serek concluded that the drainage design is in accordance with the deemed to satisfy criteria of the BCA and the building licence issued by the City, except for the southern subcatchment of area one, which has insufficient capacity.
30 Section 2 of the joint expert report states that Mr Porter and Mr Wills are certified practising engineers and members of the Institution of Engineers, Australia and that Mr Serek is a hydraulic services consultant and a member of the Association of Hydraulic Design Consultants of Australia and a member of the Institute of Plumbing Australia. It then states that each of the experts has considerable experience in stormwater drainage design and development of land and building works within the Perth region.
31 Section 3 of the joint expert report states that the development approval and the building licence set out the requirements for the stormwater drainage for the site.
32 Section 4 of the joint expert report states that there are three issues arising in the proceeding which are within the expertise of the three experts. The first issue is whether the stormwater drainage system has adequate capacity. The second issue is whether the design complied with the requirements set by the City. The third issue is whether the construction complied with the design.
33 Section 5 of the joint expert report states that the experts agreed that a one in 10 year rainfall event should be accommodated below ground, that there is insufficient capacity in the southern subcatchment of area one to manage stormwater drainage disposal and that the one in 10 year critical duration storm event for the site has not been used in the calculation of the stormwater capacity. The experts also agreed that it is not possible to confirm whether the construction complies with the design.
34 Section 6 of the joint expert report states that the experts disagreed on the suitability of AS 3500 as the design standard for onsite disposal of stormwater drainage. On the one hand, Mr Serek considered that the deemed to satisfy standard outlined in the BCA that refers to AS 3500 is acceptable and in accordance with the City's requirements. On the other hand, Mr Porter and Mr Wills considered that a first principle engineering approach should have been applied addressing the critical storm event for each catchment area in accordance with the ARR.
Concurrent evidence of the parties
35 At the hearing the three experts gave concurrent evidence and were questioned by counsel for each party and by the Tribunal.
36 The experts agreed that the main point of difference between them was that Mr Serek, on the one hand, said that AS 3500 sets out all of the necessary design requirements for the below ground storage of stormwater, but Mr Porter and Mr Wills, on the other hand, said that AS 3500 does not apply to the design of below ground storage of stormwater and it is necessary to refer to ARR for that design.
37 Mr Serek said that he was not asked by the respondent to address the requirements of the ARR and he conceded that the design of the stormwater drainage system didnot meet the requirements of the ARR.
38 Mr Serek said that the stormwater drainage system complied with the requirements of Part F1.1 of the BCA and AS 3500 and that there was no need to refer to the requirements of the ARR. He referred to section 5 of AS 3500 which he said sets out the necessary design details. Mr Serek stated that section 5 of AS 3500 sets out the formula for calculating design flow in litres per second and that is to be applied for the duration of six minutes to the area of catchment to meet the requirements of the City. Mr Serek said that this six minute duration is taken from the City's Guidelines and Standards for the Design of Subdivision within the Municipality, June 2003 (City's guidelines), which is in the hearing book. Mr Serek said that clause 5.4.4 of AS 3500 only requires a duration of five minutes to be used for a one in 10 year storm.
39 Mr Porter and Mr Wills saidthat the preface to AS 3500 states that it does not cover the criteria for soakers and it cannot be used to design below ground storage requirements for stormwater. They further stated that section 5 of AS 3500 only applies to surface flow, not to the collection and storage of stormwater and clause 5.4.13 of AS 3500 states that a solution is not available in AS 3500 for the design of onsite stormwater detention systems.
40 Mr Porter and Mr Wills saidthat the ARR provides details and design procedures for designing the below ground storage necessary to contain a one in 10 year storm event. They referred to section 1.6.6 in Book 8 of the ARR, which deals with the design of retention storages and the calculation of the volume of storage required.
41 Mr Porter and Mr Wills said that the City'sguidelines referred to by Mr Serek are not relevant to the design of the stormwater drainage works because those guidelines only apply to the subdivision of land and the development of the site in this case was subsequent to the subdivision of the land.
Other evidence
42 Mr Lisle gave evidence on behalf of the applicant about the flooding of the carpark and he was crossexamined by counsel for the respondent.
43 There are witness statements in the hearing book from two employees of the respondent, Mr Andrew Jordan and Mr Anthony Ciprian, regarding the flooding.
44 In the hearing book, there is also a witness statement from Mr Paul White, the managing director of PM White & Partners at the time that it designed the stormwater drainage system and who was the person who prepared the design.
45 Also in the hearing book, is areport dated 14 August 2013 on soil permeability testing in four soakwells by Douglas Partners Pty Ltd and a report dated February 2007 on a geotechnical investigation by Brown Geotechnical & Environmental Pty Ltd.
Consideration of the evidence and the submissions
46 The Tribunal accepts the statement in the joint expert report that Mr Porter, Mr Wills and Mr Serek are all experts in stormwater drainage design.
47 Counsel for the respondent submitted that the opinion of an expert must be based on proven facts and the expert must explain how his opinion has been reached and that a bare 'ipse dixit' or unsupported statement of opinion is not sufficient. The Tribunal accepts that contention.
48 Counsel for the respondent further submitted that the Tribunal either should not accept, or alternatively, should not give any weight to the opinions of Mr Porter and Mr Wills because they did not explain the basis and reasoning for arriving at their opinions that there is an inadequate number of soakwells. Counsel for the respondent saidthat Mr Porter did not set out in his report the facts and reasoning for using a storm duration of three hours in the calculation of the number of soakwells required andthat Mr Wills did not give any explanation in his report of how he arrived at a 2.2 hour storm duration for his calculation.
49 There was a fair amount of time spent during the hearing on the issue of flooding. The applicant contended that flooding had occurred in all areas of the carpark every year since the completion of the work under the contract. The respondent contended that flooding had only occurred since 2011 in area one and that the flooding was due to the failure of the applicant to properly maintain the soakwells. The respondent saidthat the applicant failed to provide evidence regarding maintenance of the soakwells and that the Tribunal should take a dim view of that and make a finding that the lack of maintenance of the soakwells is the cause of the flooding.
50 In the Tribunal's view, the issue of flooding is not relevant to the determination of whether or not the stormwater drainage works are unsatisfactory, because the complaint is that there is insufficient below ground stormwater storage to accommodate a one in 10 year storm event. It may be the case, as contended by the respondent, firstly, that the applicant has not adequately maintained the soakwells and, secondly, that there has not been any flooding in areas two to seven. However, the issue to be decided is whether the stormwater drainage works have been constructed to accommodate a one in 10 year storm event. There has not been any evidence presented as to whether such an event has occurred since the completion of the stormwater drainage works.
51 Condition 39 of the development approval refers to a one in 10 year storm event and that term has also been used by the experts. However, the experts have also used the term average recurrence interval (ARI) and that term is used in both AS 3500 and the ARR. When the term 'a one in 10 year storm event' has been used by the City or the experts, the Tribunal understands that to mean the same as referring to a storm event at the site with an ARI of 10 years.
52 The geotechnical evidence in the reports by Douglas Partners and Brown Geotechnical & Environmental was not challenged by the applicant. Mr Porter and Mr Wills said during the hearing that they accepted the opinions in those reports and that their calculations used a similar assumption regarding the permeability of the soil.
53 The issue raised in those reports and in Mr Wills' reports of possible clogging of the soakwells is not relevant, for the same reason that the issue of flooding is not relevant.
54 It became evident during the hearing that the experts disagreed on the method of determining the design volume to be stored below ground for a one in 10 year storm event. In considering the difference in their views the Tribunal notes the difference between two different terms used. Firstly, there is the time of concentration and secondly, there is the duration of a storm.
55 Time of concentration is used in AS 3500 to calculate the peak design flow of stormwater measured in cubic metres per second which is to be used to determine the size of gutters, rain heads, downpipes and below ground piping for flows from roofs and other surfaces.
56 Duration of a storm is used in the ARR to determine the peak design volume measured in cubic metres which is required to be stored in an onsite stormwater detention system.
57 The question to be decided regarding the expert evidence is not whether the calculations of each expert are to be accepted by the Tribunal, but instead, which of their methods of calculation of the volume of stormwater required to be stored below ground are to be accepted by the Tribunal.
58 The Tribunal does not accept the contention by the respondent that Mr Porter and Mr Wills have not stated the basis and reasoning for their calculations regarding the number of additional soakwells which they say are required. The Tribunal considers that Mr Porter has provided the basis and reasoning for the calculations in his report in the tables which are attached to it. Also, Mr Porter and Mr Wills explained during the hearing how they went about calculating the critical storm duration for a one in 10 year storm event, using data from the Bureau of Meteorology and the ARR. However, the Tribunal does not need to decide the particular number or volume of soakwells which may be required.
59 The Tribunal needs to decide whether there are an adequate number of soakwells in the stormwater drainage works, as constructed, to satisfy the requirements of the City. To decide that question the Tribunal needs to weigh up the opinions of the experts regarding the methods they have chosen to calculate the volume of below ground storage for a one in 10 year storm event which they say is required.
60 The views of the experts may be summarised as follows.
61 The applicant's experts, Mr Porter and Mr Wills said that the designer of the stormwater drainage system was required to comply with both AS 3500 and the ARR. They saidthat AS 3500 is the appropriate standard for the design of drainage systems in which the peak flow rate is the determinant of capacity of the drainage system components, such as gutters, downpipes and below ground piping. They also said that the ARR is the appropriate standard for the design of drainage systems in which the volume of water to be stored is the determinant of capacity of the drainage system components, such as basins, pits and soakwells.
62 The respondent's expert, Mr Serek saidthat the designer of the stormwater drainage system was only required to comply with AS 3500 and had no obligation to comply with the ARR. He said that AS 3500 is the appropriate standard for the design of drainage system components based on both peak flows and storage volumes. Mr Serek relied upon either the time of concentration of six minutes stated in the City's guidelines or, alternatively clause 5.4.4 of AS 3500, to select a time of concentration of five minutes and then used the time of concentration as the storm duration in determining both the design intensity of the storm and the volume of stormwater to be stored below ground during a one in 10 year storm event.
63 Condition BC410 of the building licence required the respondent to comply with Part F1.1 of the BCA and AS 3500 and the respondent's hydraulic engineer's design.
64 Part F1.1 of the BCA simply states that stormwater drainage must comply with AS 3500.
65 There was disagreement between the applicant's experts, Mr Porter and Mr Wills on the one hand and the respondent's expert, Mr Serek on the other hand as to whether AS 3500 contains sufficient details for the design of the stormwater drainage system. Mr Porter and Mr Wills said that it does not, but Mr Serek saidthat it does.
66 A review of AS 3500 shows that it is not intended to be used, in its present form, for the design of what it refers to as soakers, otherwise known as soakwells or onsite stormwater detention systems, which it refers to as OSD systems.
67 The preface to AS 3500 states that this Standard does not cover the criteria for soakers and siphonic systems and that sufficient data was not available in these areas at the time of publication. It goes on to state that these areas will be included in a future edition of the Standard, subject to additional research and investigation being carried out.
68 Clause 3.8 of AS 3500, under the heading of 'Soakers' has a note which states that data for the design of soakers is the subject of research and when available will be considered for adoption in the Standard.
69 Clause 5.4.13 of AS 3500, under the heading of 'Onsite stormwater detention (OSD) system' has a note which states that a solution is not available for design of OSD systems because sufficient data is not available.
70 From these portions of AS 3500 it is clear that a designer cannot design an OSD system on the basis of that Standard and, therefore, it is necessary to refer to some other source of information to design an onsite stormwater drainage system.
71 In section 5 of AS 3500 the term 'time of concentration' is used, but there is no explanation of that term. In section 1.5.4 of ARR, which deals with the design of pipe system drainage, it states that most rainfall runoff models require some estimate of the time to allow for concentration and travel of runoff, which can be expressed as a time of concentration. That section of the ARR also states that for flows from roofs and other surfaces which drain quickly through downpipes and underground drains a single response time can be nominated, which is in the order of five to 15 minutes for commercial and industrial buildings. From that description of 'time of concentration' and the description in clause 5.4.8 in AS 3500 of the determination of design flows, it can be seen that section 5 of AS 3500 is concerned with the design of the capacity of a stormwater drainage system to cope with the maximum flow volume of stormwater in any situation, rather than the design of the stormwater storage required for a one in 10 year storm event.
72 Therefore the Tribunal does not accept Mr Serek's evidence that section 5 of AS 3500 can be used to calculate the stormwater storage requirements for a one in 10 year storm event.
73 Having decided that compliance with Part F1.1 of the BCA and AS 3500 is not determinative of the question of whether the stormwater drainage system is satisfactory, the Tribunal will now consider the third requirement of condition BC410 of the building licence, namely whether the respondent has complied with its hydraulic engineer's design.
74 The Tribunal raised the question during the hearing of whether PM White & Partners were hydraulic engineers for the purpose of condition BC410 of the building licence. In response, the experts agreed that the term 'engineer' is not a description which has a precise meaning and a hydraulic design consultant could be considered to be within the meaning of that term.
75 The Tribunal notes that the applicant is not contending that the respondent has not constructed the stormwater drainage system in accordance with the design prepared by its hydraulic design consultants, PM White & Partners. The Tribunal also notes, however, that the experts stated in the joint expert report that they have not been able to confirm whether that is the case because the 'as constructed' drawings are inaccurate and inadequate to carry out a full detailed analysis of the stormwater drainage system.
76 In the Tribunal's view, the issue of whether or not the stormwater drainage works have been constructed in accordance with the design prepared by PM White & Partners is irrelevant, because that design did not meet the requirements of the City in condition 39 of the development approval, which required the design to be in accordance with the ARR. Mr Serek stated during the hearing that the PM White & Partners design is not in accordance with the ARR.
77 In the Tribunal's view, the designer of the stormwater drainage system, Mr White, failed to recognise the difference between the calculation of the flow of stormwater during a time of concentration of six minutes, with the calculation of the volume of stormwater expected to be generated during a one in 10 year storm and required to be stored below ground.
78 The Tribunal notes that Mr White was not called by the respondent as an expert witness and his witness statement has been put into evidence only as a lay witness, which is rather remarkable since he was the person who designed the stormwater drainage system.
79 The Tribunal notes that the letter dated 2 November 2008 by PM White & Partners, which is in the hearing book, did not specifically state that the design was in accordance with the ARR.
80 The Tribunal also notes that in his witness statement, Mr White referred to the requirement in the development approval to design the stormwater drainage system on the basis of a one in 10 year storm event. Mr White then stated that he contacted the City's Engineering Department requesting more information as to which storm event in the one in 10 year scale he was to design to and says that he was advised it was to be for a six minute storm. The Tribunal finds that part of Mr White's evidence to be extraordinary. The requirement in the development approval to which he referred in his witness statement is condition 39, which specifically states that the design is to be in accordance with the ARR on the basis of a one in 10 year storm. Instead of contacting the City, presumably by telephone because Mr White has not referred to any written communication, Mr White should have referred to the ARR, which would have provided him with the information necessary to prepare the design.
81 The evidence of Mr Porter and Mr Wills is that AS 3500 is the appropriate standard for the design of drainage system components whose sizing is dependent on peak flow rates, but not for drainage system components whose sizing requires the calculation of peak stored volumes. Mr Porter and Mr Wills said that the ARR is the appropriate reference document for the calculation of peak stored volumes and it includes provisions for estimation of volumes of water from storms. Condition 39 of the development approval required that the design of the stormwater drainage system be in accordance with the ARR and condition BC581 in the building licence states that the respondent must comply with the requirements of the development approval.
82 The Tribunal accepts the evidence of Mr Porter and Mr Wills that the City's guidelines are not relevant to the design of the OSD portion of the stormwater drainage system. In any event, the Tribunal notes that if they were relevant then clause 1.1.2 of the City's guidelines states that the stormwater drainage system is to be designed in accordance with the ARR.
Findings and decision
83 The Tribunal makes the following findings:
1. The respondent was responsible for both the design and the construction of the stormwater drainage system. That finding is not disputed by the respondent.
2. The design of the stormwater drainage system was required by the City to be in accordance with the ARR for a one in 10 year storm event. Condition 39 of the development approval states this and condition BC581 of the building licence confirms that requirement.
3. The design prepared by PM White & Partners for the respondent was not in accordance with the ARR. The respondent's expert witness, Mr Serek stated this during the hearing.
4. The stormwater drainage system has less below ground storage capacity than is required under the ARR. The Tribunal accepts the evidence of Mr Porter and Mr Wills in that regard and notes that Mr Serek did not dispute their calculations either in the joint expert report or during the hearing. However, it is not necessary for the Tribunal to decide what additional amount of below ground storage is necessary to meet the requirements of the ARR.
5. The fact that the City accepted plans lodged with the application for the building licence which contained a design which did not satisfy condition 39 of the development approval did not relieve the respondent of the responsibility to construct the stormwater drainage works in a manner which satisfies that condition.
6. The fact that condition BC410 of the building licence required stormwater drainage to comply with Part F1.1 of the BCA and AS 3500 and the respondent's hydraulic engineer's design also did not relieve the respondent of the responsibility to construct the stormwater drainage works in accordance with a design which satisfies condition 39 of the development approval. The reason that the ARR is not referred to in condition BC410 of the building licence is that the condition assumes that the design referred to in it is by a suitably qualified practising engineer in accordance with the requirements of the ARR, which was not the case.
7. The construction of the stormwater drainage works pursuant to a design which does not meet the requirements of the City, because it is not in accordance with the ARR, constitutes unsatisfactory building work.
84 The Tribunal does not accept the contention of the respondent that the Tribunal, having found that there is unsatisfactory building work, should exercise its discretion under s 38(1) of the BSCRA Act to not make a building remedy order. The failure of the respondent to construct the stormwater drainage works in accordance with the requirements of the City is a significant matter which has resulted in there being less below ground stormwater storage capacity than that which is required for a one in 10 year storm event. That failure clearly warrants the making of an order that the respondent remedy the unsatisfactory building work.
85 Condition 39 of the development approval required that the stormwater drainage system be designed in accordance with the ARR on the basis of a one in 10 year storm event and that the design be certified by a suitably qualified practising engineer.
86 The Tribunal considers that a period of three months should be allowed for the respondent to arrange for a design to be prepared to meet those requirements, for a building licence to be obtained for the installation of the additional below ground stormwater storage in accordance with that design and then for the completion of those works.
87 Therefore the Tribunal makes the following order.
Order
It is ordered that:
1. By no later than 8 July 2015, the respondent must remedy the unsatisfactory building work at Lot 9501 Armadale Road, Jandakot by installing additional below ground stormwater storage to comply with a design certified by a suitably qualified practising engineer prepared in accordance with Australian Rainfall and Runoff 1987 produced by the Institution of Engineers, Australia on the basis of a one in 10 year storm event.
I certify that this and the preceding [87] paragraphs comprise the reasons for decision of the State Administrative Tribunal.
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MR D AITKEN, MEMBER
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