What we need to consider Roof Garden What we need to consider

Content 1 – Safety (Capacity of the roof for the loadings and the actual additional loads) 2 – Different form of roof garden 3 – Legal (necessary for BD approval ?) 4 – Problems from roof garden

1 – Safety – Overload a roof cause collapse

1 – Safety Find out the load capacity of a roof Building design according to CH123B Building (Construction) Regulations Current Regulation 17 Imposed load (1/8/2011) Inaccessible roofs X < 5 deg 2 kPa (where no access is 5 < X <20 0.75kPa Provided) 20 < X < 40 linear interpolation 40< X 0 kPa Accessible roofs X < 20 deg 2 kPa (where access is 20 < X < 40 linear interpolation Provided) 40 < X 0

1 - Safety Building design according to CH123B Building (Construction) Regulations 1975 Inaccessible roofs 0.75kPa (where no access is provided) Accessible roofs 2 kPa (where access is provided and Roof is surrounded with barrier Wall of not less than 1.1m)

1 - Safety 1 kPa = 1000N/m^2 or 101.9 kg / m^2 An adult weight about 75kg If the loading for a roof is 0.75 kPa The capacity of the roof is about 75kg / m^2

1.2mm TPO membrane + 5mm geo-textile 1 - Safety Actual weight of roof garden Items Thickness Saturated Weight 1 - TPO Membrane Waterproof and Root Barrier with 500g Geo-textile 防根及防水層 1.2mm TPO membrane + 5mm geo-textile 1.6 kg/m^2 2 - HIPS 30mm Drainage Layer with Double sides 150g Geo-textile 疏水層 30mm 5.6 kg/m^2 3 - Water Reservoir Panel 儲水層 40mm 21kg/m^2 4 - Top Soil 泥土 density = 2250 kg/m^3 20mm 45kg.m^2 Total 101.7mm 73.2 kg/m^2

1 - Safety Factor of safety for steel structure = 1.8 (BS449) Dead load for City U Roof = 4.25 kPa Designed imposed load = 0.75 kPa Total = 5 kPa Collapse load = 5 x 1.8 = 9 kPa (soil thick 408mm)

2 – Different forms of roof garden

2 – Different forms of roof garden

3 – Legal (Necessary for BD approval ?) Is the Building Regulations required approval of roof garden from Building Authority ? According to Building Ordinance section 2 Building works defined “Building works includes any kind of building construction, site formation works, ground investigation in the scheduled areas, foundation works, repairs, demolition, alteration, addition and every kind of building operation, and includes drainage works.

4 – Problems from roof garden 1 – Soil retain water which will cause leakage 2 – Roof garden obstructed to rain water from drain away cause leakage. 3 – Roof garden obstructed to replacement of the waterproofing. 4 – Root from the plant may penetrated the waterproofing layer.