Attachment B Green Roof Plan

3            Proposed Drainage, Irrigation and Substrate (Soil)




                                                                                                                           Drainage

                                                                                                                           Green roofs are capable of storing rainwater and slowing water run off however sufficient drainage is important to eliminate standing water / water-
                                                                                                                           logging which presents long term risks to the integrity and success of the green roof.. Roof drainage will consist of the following:

                                                                                                                           •    A drainage layer, located beneath substrate, consisting of moisture retention cells to help achieve a balance between storage and drainage of
                                                                                                                                stormwater.
                                                                                                                           •    A grid of intercept drains or rock gabions to assist with surface runoff and provide linear holding points to support drainage and substrate layers.
                                                                                                                           •    Drainage / downpipes are proposed behind off form concrete facade areas to assist with drainage at steeper sections of the roof where substrate
                                                                                                                                moisture content levels will be higher.
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                                                                                                                           Irrigation Considerations

                                                            5                                                              Irrigation will need to be controlled and respond to plant growth, substrate moisture content and climatic conditions.

                                                                        3                                 4
                                                                                                                       5   Drip and tube irrigation, buried in the substrate, is proposed for the following reasons:
                                                                                                                           • water is directed only to plant roots;
                                                                                                                           • less water is lost by drift and evaporation;
                                                                                                                           • buried pipework is not visible and more efficient than surface pipes; and
                                                                                                                           • weeds are less likely to germinate if substrate surface is kept dry.
                                                                                                                           (Dunnett N and Kingsbury N. 2008. p. 98.)
                                                                                                                   7       Irrigation is required during the first few years until planting has established. Following establishment irrigation requirements will be reduced and only
                                                                                                                           required strategically during periods of drought to maintain plant growth.
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                                                                                                                           It is important to note that sloping green roofs produce significant variability in moisture content of the substrate where substrate is typically a dryer
                                                                                                                           medium at the top of the slope and moist and the base which will be an important factor in the irrigation design and water dispersion as well as
                                                                                                                           drainage provisions.

Figure 4 - Roof Drainage Concept (Level 3)
                                                                                                                           Growing substrate
Legend
1. Hardstand / pavements                                                                                                   Native coastal plant species typically prefer sandy soils low in nutrients, with a low pH (3.5-6.5) and a constant supply of moisture. The ideal substrate
2. Pool                                                                                                                    is moderately fertile to maintain a constant plant coverage yearlong. Overly fertile soils encourage competition which may result in uneven coverage.
3. Proposed intercept drains
4. Proposed off form concrete roof sections with down pipes. (where roof pitch is too steep to support planting)           Soil composition for coastal species generally need to be open, free-draining and consider the following properties:
5. Drain outlets - into existing vegetation                                                                                -particle size
6. Roof extent (approx.)                                                                                                   -water holding capacity
7. Site boundary                                                                                                           -air filled porosity
                                                                                                                           -nutrient reserves

                                                                                                                           Note: Actual substrate composition to be specificed by soil scientist during design development phase of the project.



                                                                                                                                                                                                                                     Green Roof Proposal
                                                                                                                                                                                                                                                         Date : 24.09.2014
                                                                                                                                                                                                                Hasler Residence, Seaview Terrace                                       A