29 As the Senior Sessional Member recognised, each party found support for its submission in a part of the explanatory text of element 8. This was because there is an unfortunate, direct conflict in the explanatory text. On the one hand, at page 77, the explanatory text describes the cone of vision for privacy design in terms of both a horizontal component and a vertical component. Mr Adam correctly submitted that, at page 77 at least, the R-Codes contemplate that a space would not be relevantly "overlooked" if a person carrying out ordinary activities there did not fall within the congruence of the horizontal and vertical components of the cone of vision taken from a particular window.
30 However, under the heading "Privacy separation distances", at page 79, the R-Codes expressly state that, because it is not possible to easily predict "how a neighbouring site may be developed in the future", privacy separation distances are to be determined on the basis of the diagram entitled "Measuring setbacks using the cone of vision". As noted earlier, this diagram is concerned only with the horizontal component of the cone of vision. The limitation to the horizontal component is consistent with the apparent intention of the privacy separation distances, as explained at page 79, to provide a desirable degree of privacy not only in relation to existing adjoining development, but also in relation to potential redevelopment of adjoining properties. As adjoining properties may be undeveloped, and as buildings may be altered, added to or replaced over time, the determination of appropriate minimum setbacks by reference only to the horizontal component is more likely to facilitate a desirable degree of privacy in both the short and long term.
31 As noted earlier in these reasons, the first note to the acceptable development provision states that "line of sight setback distances shall be measured by application of the cone of vision set out in the explanatory text". The note does not indicate whether the "explanatory text" is that at page 77 or at page 79. Similarly, the words "in direct line of sight within the cone of vision" in par A1(i) of the acceptable development provision do not identify whether the cone referred to is that at page 77 or at page 79.
32 The Senior Sessional Member was correct in construing the acceptable development provision such that the words "explanatory text" and "cone of vision" referred to the text and diagram at page 79 of the R-Codes, for two reasons.
33 First, the explanatory text and diagram at page 79 specifically concern privacy separation distances, which is the subject of par A1(i) of the acceptable development provision. The extract from page 79, set out at [17] above, states that the acceptable development provision contains a set of privacy setbacks "based on [the] considerations" in the first paragraph of the extract. That paragraph states that "privacy separation distances can most realistically be applied between the proposed development and the property boundary, that is as line of sight setbacks". It also states that the way in which setbacks should be determined is illustrated in the diagram on that page. Clearly, therefore, note (i) to the acceptable development provision, which states that "line of sight setback distances shall be measured by application of the cone of vision set out in the explanatory text", is a reference to the explanatory text (and diagram) at page 79.
34 Second, this interpretation promotes the objective of Element 8, namely "to ensure a reasonable level of visual ... privacy for ... adjoining residents". Section 18 of the Interpretation Act 1984 (WA) provides that, in the interpretation of a "written law", a construction that would promote the purpose or object underlying the written law shall be preferred to a construction that would not promote that purpose or object. The term "written law" is defined in s 5 of that Act as including "subsidiary legislation", which is defined as including a town planning scheme. Although the R-Codes do not form part of a town planning scheme, conformity with their terms is required by TPS2. It is appropriate that the R-Codes are, therefore, construed in a manner which promotes the relevant purpose. As noted earlier, it was common ground that the windows in question would permit overviewing of the adjoining property. The interpretation adopted by the Senior Sessional Member would avoid that overviewing (unless it conformed to the performance criteria), and, therefore, promotes the objective of the Element.
35 Having correctly construed the acceptable development provision, it was for the Senior Sessional Member to determine whether the windows in question conformed to the performance criteria, without the imposition of the conditions in question. At [49], he stated that he was not convinced, from the evidence presented, that the cones of vision from the west-facing window of the large bedroom and the north-facing window of the small bedroom were sufficiently elevated above the adjoining property such that those windows could be accepted without condition. This conclusion did not involve a question of law, and was entirely within the province of the Senior Sessional Member as the tribunal of fact. As the Tribunal stated in Williams and Western Australian Planning Commission [2005] WASAT 10 at [17]: