Blue Roof Today: Rainwater Attenuation at Roof Level

Transcription

1 Blue Roof Today: Rainwater Attenuation at Roof Level A CPD seminar presented to CIBSE & SOPHE Engineers by: Alumasc Exterior Building Products Ltd and... Ramboll Consulting Engineers

2 Agenda Introduction and Welcome Blue Roof Thinking Project Drainage Engineering Restricted Flow Control Waterproofing Wayne Willmott (Alumasc) Carl Harrop (WSP) Jassim Daureeawo (Ramboll) Simon Poë (Alumasc Waterproofing) Andrew Lee (Alumasc Drainage) Paul Read (Alumasc Waterproofing)

3 Blue Roofs: Blue Roof Thinking Carl Harrop Associate Director PHE WSP, Property & Development

4 Increasing requirement Storage issues in city centre builds Why? Exposed membrane Paving voids Gravel Green Roofs Many different Approaches Can reduce SW drainage costs by up to 80% Uses the inherent structural strength for snow loads Attenuation for free? Flow devices should provide defined results demonstrable by calculation to the EA etc Anyone can undersize a RW system Maintenance critical Overspill strategy is essential Safety First

5 Blue Roofs: The Project Jassim Daureeawo Senior Engineer Ramboll, Buildings & Design

6 The Importance of Stormwater Management To prevent sewer surcharge and overflow by limiting the discharge of surface water run-off to the external drainage infrastructure To prevent sewer surcharge and overflow by limiting the discharge

7 The Importance of Stormwater Management To Minimise the risk of flooding water courses which subsequently causes damage to surrounding environment

8 The Regulators of UK Stormwater Management EUROPEAN Water DIRECTIVE FRAMEWORK (WDF) Environment agency (EA) Department for Communities AND local government (DCLG) Greater London Authority ( GLA)

9 Main Guidance for Stormwater Management National Planning Policy Framework (NPPF) Planning policy statement 25 (PPS 25) Sustainable Drainage Systems (SUDS)

10 Zenith House Project NEW Residential development (309 dwellings) located in London 9 Blocks of Residential apartments with 20 mews houses NEW Residential development (309 dwellings) located in London 9 Blocks of Residential apartments with 20 mew houses. Block A the tallest block (14 storeys) Overall site area approximately 1.1 HA Requirement to carry out Flood Risk Assessment(FRA) to submit along with Planning Application Implement of stormwater attenuation to meet planning conditions

11 Zenith House Project PROBLEM STATEMENT: Planning conditions limits the maximum stormwater discharge to the sewer to 9 l/s. Need for 600 m3 of stormwater attenuation. 1 in 100 year return + 30 % climate change. Limitations in excavation depth. Limitation in maximum area within the basement for incorporation stormwater attenuation tank.

12 Problem Statement Traditional buried stormwater attenuation tank installation was NOT a viable option due to limitation in excavation depth

13 The Blue Roof Concept AUTHOR S DEFINITION Suitable definition of a blue roof : A roof designed to allow the build-up of water above the roof waterproofing membrane (within various elements), not exceeding the designed hydraulic head, for a defined period of time, to enable attenuation of stormwater at roof level, and which also controls the discharge of rainwater runoff at designed flow rate to meet design requirements

14 Zenith House PROPOSED SOLUTION: Provide 450 m³ of stormwater attenuation at basement level based on maximum floor area available for stormwater attenuation Provide 150 m³ of stormwater attenuation at roof level based on a maximum hydraulic head of 150 mm Maximum discharge from basement pumped system will be 5 l/s and 4 l/s by gravity from the roof attenuation Overall design will restrict the maximum discharge to 9 l/s in line with the planning requirements

15 Zenith House ROOF LEVEL 150 m 3 roof of attenuation TYPICAL ROOF DETAILS

16 Zenith House BASEMENT LEVEL 450 m 3 stormwater attenuation within concrete tank above basement slab BASEMENT SECTION OF ATTENUATION TANK

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18 150mm attenuation with a maximum discharge by gravity of 4l/s though 16 rainwater outlets with integral flow restrictors Rainwater pipes 450 m 3 attenuation with a maximum pumped discharge of 5l/s through dedicated stormwater pumps Combined discharge of 9l/s from gravity and pumped system to external drainage system Stormwater pumps

19 Flow through orifice The flow discharge through an orifice is directly related to the hydraulic head above the orifice. The equation used for the calculations of the discharge, Qo, through the orifice is given by: Where: Qo is the discharge through the orifice (l/s) Ko is Coefficient of orifice D is Effective diameter of orifice (mm) h is the Hydraulic head above orifice (mm)

20 Flow through orifice

21 The Blue Roof Concept Key points: If a build-up of 75 mm is required for roof attenuation, this would require a 0.75kN/m² structural allowance for the water load. This figure is equivalent to the general allowance for snow load. The additional structural load to accommodate a 150 mm of water build-up per square metre is 1.5 kn/m2 which is insignificant as compared to excavation depth to accommodate for same volume of attenuation. Attenuation at roof level can be considered as a design solution for stormwater management, specifically in urban areas with less space on site for stormwater attenuation or limitations in the maximum excavation depth ROOF STORMWATER STORAGE CAN BE SIGNIFICANTLY CHEAPER THAN EXPENSIVE EXCAVATION

22 Blue Roofs: Modelling Detention of Stormwater Simon Poë Product Director Alumasc Waterproofing

23 Sustainable Roof Drainage Green roofs provide complementary drainage capacity and Fulfil all 4 SUDS design criteria (improving water quality, amenity, ecology & hydraulic performance) Soil & plants provide: Retention: Reducing discharge via moisture storage in green roof layers Detention: Reducing peak rates of runoff by elongating time over which runoff occurs due to infiltration time Image courtesy of Blackdown Greenroof

24 Sustainable Roof Drainage Finite capacity of maximum 40 mm Not typically fully available antecedent moisture reduces available capacity Available capacity regenerated via: Evaporation of moisture via heat (solar) energy Transpiration of moisture by plants Response varies as function of: Image courtesy of ZinCo GmbH Green roof configuration Climate (ADWP, Temperature) Green roofs: a valuable component within a SUDS management train

25 Blue Roof Principles Detention of Stormwater Reduce Peak Runoff Drain more slowly Reduce flood risk: Large events Use with retention measures

26 Model Development: Design Storm Design storm characteristics determined using DDF method and FEH values Depth calculated on basis of: Geographic Location Return Period Storm Duration Climate Change Factor Temporal distribution reflects: Intense Summer type storms Gradual Winter type storms

27 Model Development: Blue Roof Response Outlet s discharge rate varies with hydraulic head. Typical equation used: 2 ݔ Outlet response shows 3 phases: 1. Weir entry high discharge 2. Transition 3. Orifice-controlled Phase 3 Phase 2 Phase 1

28 Model Development: Curve fit to derive index Initial tests conducted on 20, 30, 40 & 50 mm outlets Stage Index [x] Based on test results for Q at different outlet diameters & stages, re-arranged equation to identify index values Stage Depth - Index Best Fit Curve Curve-fitted index values 0.65 Derived 2-part exponential equation to predict index with RSQ of 0.98 Model developed with single hydraulic equation, but including index equation Stage Depth [mm]

29 Model Development: Modeled vs Test Results

30 Model Development: Curve fit to derive index New tests on 10 & 15 mm prototypes highlighted lower model accuracy Smaller outlets have quicker, quasilinear transition to orificecontrolled phase Method using curve-fitted index could not predict outcome with accuracy Fitting equations developed to predict discharge from stage relationship, using test results RSQ > 0.99

31 Test Case: 1 Year 6H Design Storm

32 Test Case: 30 Year 6H Design Storm

33 Test Case: 100 Year 6H Design Storm

34 Test Case: 500 Year 6H Design Storm

35 Blue Roof Potential Shift in emphasis regarding roof drainage - no longer about removing rainwater from roof as quickly as possible Green roofs provide multi-faceted benefits, including retention & detention Complementary measures required to mitigate risk of flood for large events Blue roofs attenuate peak runoff for large storm events simply & effectively Green and Blue Infrastructure

36 Blue Roofs: Restricted Flow Control Andrew Lee Specification Manager Alumasc Drainage

37 Simplicity in design is one of those features which people remark upon After they have seen the simple solution, everyone realises that it can be done. Simplicity is the ultimate achievement in design provided all functions are fulfilled.

38 Conceptual Thinking Design Considerations Maximum size of outlets? Building life? Roof construction? 100% instantaneous run off? Void fill rate per m² of roof? Depth of the reservoir? Release rate per outlet? Fixed or bespoke flow rate? Water permanently retained? Outlet double as an overflow? Is silting a potential problem? Allow for outlet maintenance? Moving/floating or electrically operated components? Perimeter baffle or outlet with a removable bore restrictor? Hydraulic Performance Requirements Design Rainfall intensity, duration, frequency? Requirement for retention? Requirement for peak flow reduction? Requirement for peak flow delay? Maximum number of outlets? Maximum size of outlets?

39 Conceptual Thinking Building Fabric Design Requirements Structural tolerances: Zero falls requirement? Waterproofing: Zero falls requirement? Perimeter upstands: Maximum permissible depth for waterproofing? Penetrations: upstand depth restrictions? Roof geometry: existence of obstructions in flow path to outlets? Detailing: Existence of expansion joints? Structural Loadings Maximum permissible dead load capacity available for water storage? Design wind loads? Other Design Criteria Water recycling? Water Quality? Amenity? Ecology? Maintenance: access and frequency?

40 Product (metal gully) Grating with centre hole Vent pipe protector Standard clamp Removal handle Pressure vent pipe Flow restrictor 10mm - 50mm Adapter Standard 100Ø cast aluminium RWO

41 Product (heated gully) Flexible membrane Vent pipe protector Pressure vent pipe Flow restrictor 10mm - 50mm Adapter Standard 100Ø heated RWO with integral thermostat Removal handle Grating with centre hole 240v connection

42 Detailing

43 Detailing

44 Blue Roofs: Waterproofing Paul Read Area Sales Manager Alumasc Waterproofing

45 Zero Falls Warm Roof Green Roof and Paved Roof Both types of roof surface can be used for an attenuation system Leak proof at 150mm water depth Metal or Heated outlets can be used Overflows must be included Access chambers must have solid covers to prevent ingress of detritus Filter sheets essential to prevent washout of fines and congestion at outlet Overflows must be included

46 Double Protection Hot Melt (liquid) Membrane Applied over zero falls roof deck beneath insulation No levelling screed necessary Self healing live membrane PLUS Torch on Membrane Bituminous membrane cap sheet applied over insulation All lap joints minimum 100mm Both systems fully bonded

47 ZENITH HOUSE 1. Zero falls deck 2. Hydrotech hot melt membrane 3. Alumasc GTF insulation 4. Euroroof Thermo adhesive underlay 5. Euroroof Mastergold anti-root 6. Charcon Permavoid crate 7. Alumasc Zinco filter sheet 8. Alumasc Zinco Floradrain 9. Alumasc Zinco filter sheet 10.Alumasc Zinco Extensive sedum bed

48 Blue Roof Today: Rainwater Attenuation at Roof Level The End Thank-you for listening