Components of green roof design

Transcription

1 Components of green roof design Eric French The first and most important component of any green roof is its design. Green roof design is typically initiated under two circumstances: 1) The owners of a structure desire to add a green roof to their existing building. 2) The owners of a building in the design stage are interested in a green roof and ask the design team to include the green roof in the design. Beginning with the first scenario, adding a green roof to an existing structure poses a special set of design challenges that must take into considiteration: 1. Available excess load for the green roof. 2. Age and condition of existing membrane. 3. Existing mechanicals and utilities on the roof. 4. Access needed for future building maintenance. 5. Access to roof for installation purposes. 6. Condition and efficiency of roof drains. An onsite roof inspection is a critical first step. 1

2 Get on the roof to assess the conditions first hand. Do not rely on someone else. After our site inspection, we need to calculate the excess load available for a green roof. These calculations must be done by a licensed structural engineer. The calculation looks something like this: Structural load capacity minus dead load minus live load minus snow load Equals the allowable weight for a green roof It is critical that we keep the weight of the green roof under the allowable excess load for the roof. The other important factors to consider when looking at an existing roof are the age, type, and condition of the existing waterproofing membrane. Roof membranes older than three years are considered too old to receive a green roof. Some manufacturers will nullify their warranty if a green roof is added over an existing membrane without their consent and input. It is critical to inspect every aspect of an existing roof to determine its condition before you agree to add a green roof. 2

3 Often you will find HVAC units and their associated utilities on an existing roof laid out in a seemingly random manner. These units need to be maintained on a regular basis and access to them must be designed into the green roof to avoid damage to the green roof plants. Access is also needed for other building maintenance activities such as window washing and lamp bulb changing. Allowances need to be made for existing utilities such as gas lines, power lines and condensate piping so not to bury them in the plantings. Common items to inspect are: Seams and flashings Drains, valleys and crickets Future access requirements Patches and variations in elevation 3

4 Penetrations Utilities Access to an existing roof is often more complicated than one under construction. Sometimes it becomes necessary to use large cranes for hoisting materials to the roof. Gaining access for large cranes in the urban environment will often require street closings and off peak work hours. If a roof can be designed using fewer components or faster installation systems, substantial savings can often be accomplished. Working in the city requires a lot of upfront planning and coordination with public safety agencies. 4

5 Using bulk planting mix saves considerable time and expense, if you have the room to set up the equipment. The final item we want to verify on an existing roof is the adequacy of the existing drains to assure water is not ponding on the roof during storm events. If the roof has a history of ponding, additional roof drains may need to be added before installing a green roof. A green roof is not intended to become submerged because the additional weight to the roof of standing water is problematic. If insufficient drainage can not be rectified then the building is not a candidate for a green roof. This is not a well designed drain. 5

6 Designing a green roof for a new structure is vastly simpler than adding a green roof to an existing structure. Work backwards with engineering once the type of roof desired determined. Selections can be made regarding roofing materials and methods to optimize both efficiency of maintenance and cost of installation. Construction access is often much easier and hoisting is less of a problem. After we determine if our structure can accept a green roof and what excess load we are working with, we need to start our design process. Green roofs are made up of the following components: Waterproofing membrane and associated flashings Root barrier to protect the waterproofing membrane Drainage layer to allow the growing medium to drain Growing medium - typically light weight engineered media Vegetation These are the very basic requirements. Additional components of a green roof can be: Supplemental insulation / contouring foam Water drainage channels Water retention mats Gravel vegetative free zones with edgings Stepping stones / access paving Irrigation Additional amenities are often: Patios, fountains, railings, lights and furniture. 6

7 Preliminary designs can be done in SketchUp for impact. Regional building codes must be taken into considiteration. The city of Pittsburgh now has a green roof ordinance: I Extensive Green Roofs Extensive Green Roofs are lightweight veneer systems of thin layers of drought tolerant self-seeding vegetated roof covers. (1) Extensive Green Roofs permitted by-right shall not have more than five (5) inchesof soil medium. (2) All Extensive Green Roofs shall have at least a one (1) foot perimeter of vegetation-free zone around the edges of the roof and around all roof penetrations (i.e. skylights, pipes, etc). (3)For Extensive Green Roofs with projected live loads of higher than fifteen (15) poundspersquare foot, consultation with a structuralengineeris a requirement J Intensive Green Roofs Intensive Green Roofs are heavier than Extensive Green Roofs. For the purposes of this code the term means any Green Roof with soil mediums greater than five (5) inches. A consultation with a structural engineer is required for all Intensive Green Roofs. Vegetation Height on Intensive Green Roofs shall not exceed five (5) feet over the maximum height of the zoning district. (3) All Intensive Green Roofs shall have at least a one (1) foot perimeter of vegetation free zone around the edges of the roof and around all roof penetrations (i.e. skylights, pipes, etc). 7

8 No uniform or national building code exists for green roofs in the United States. American Society for Testing and Materials (ASTM) has developed the most comprehensive set of guidelines in the US. The German Society for Landscape Research, Development and Construction, the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau (FLL) has created a German national standard for green roof construction and performance which is used in the US as the reference standard. First we can discuss roof membranes. There are many types of water proofing systems used today. The only systems that are suitable for green roof applications are water impermeable membranes: 1. Fluid applied membrane such as coal tar or asphalt 2. Polymer Modified Bitumen or MB 3. Single Ply Membranes 1. Thermoplastic: TPO, PVC, and PVC alloys 2. Thermoset: Most commonly EPDM It is highly recommended that any single ply membranes be fully adhered to reduce leak migration. 8

9 This is a fluid applied membrane going down on a roof along with the reinforcement layer. Photo courtesy of American Hydrotech Once a membrane has been installed it should be thoroughly leak tested either by flood testing or electronic vector mapping to assure the integrity of the waterproofing. Chain of custody is critical at this point to assure no damage occurs to the waterproofing. The green roof contractor should start installing the green roof as soon as the leak test has been completed. Root barrier should be immediately installed along with the drainage layer. The drainage layer can be as simple as a synthetic wicking layer to a multi functioning all in one composite layer. 9

10 After installation of the root barrier over the waterproofing membrane and the drainage layer is installed, installation of the vegetation free zone typically occurs. Photo courtesy of American Hydrotech Foam contouring occurs on top of the drainage layer if variations in elevations are desired. Installation of the green roof media occurs after the contouring foam is covered with another layer of fabric. 10

11 After the soils are in place it is time to install the plant materials. These are plugs ready to go on the roof. Plugs require regular watering after planting and require 18 to 24 months to fully grow in. Sedum sod is a roll out pre-vegetated mat providing an instant green solution for an extensive roof. 11

12 Sedum Sod requires immediate regular watering for the first month or two. Pre-vegetated trays are a great option for small projects and require almost no transitional maintenance. Green roofs are everywhere. Sometimes where we least expect to find them. 12

13 There are may ways to build a green roof. Have fun, be creative, innovative but. Remember everyone is watching: We need to get it right the first time! 13

14 Allegheny County Office Building Green Roof Demonstration John K. Buck and Darla Cravotta October 4, 2011 Darla Cravotta Allegheny County Speaker Introduction John K. Buck, CPSSc Project Manager, Civil & Environmental Consultants 2 Project Information Client: Allegheny County, Pittsburgh, PA Location: Allegheny County Office Building 542 Forbes Avenue, Pittsburgh PA, Support From: Penn State Engaging Pittsburgh Pennsylvania Environmental Council Conservation Consultants, Inc. 3 Rivers Wet Weather ( USDOE and Federal Stimulus funding (ARRA) 3 1

15 4 5 Green Roof Benefits What is a Vegetated Green Roof? A roof intentionally designed to support the longterm growth of plants on its surface Why a Green Roof? Environmental Benefits Financial Benefits Looks cool, is cooler 6 2

16 Green Roof Benefits Societal Reduced Stormwater Runoff Reduced CSOs Cooler Urban Environment Improved Aesthetics Parkland on Rooftops Carbon Sequestration Financial Extended Roof Life Lower Energy Costs Lower Stormwater Management Costs Image (e.g. LEED) Property Value Green Space Incentives 7 Project Information Allegheny County Program Goals: Reduce CSOs by speeding adoption of green infrastructure Public Private Demonstrate Benefits of Green Roofing Lead by example Support optimized design Support educational initiatives 8 Selection Process Project Execution Team: Project Information Allegheny County Darla Cravotta, Dan Onorato Cuddy Roofing (A Scalo Company) Prime Contractor EislerLandscapes Green Roof Design and Installation Civil & Environmental Consultants Monitoring System, Engineered Soil Design 9 3

17 Green Roof Benefits Combined Sewage Overflows (CSOs): Sewage and stormwater are combinedinto one pipe, all sent to [or toward] sewage treatment plant In wet weather, what can t be treated gets dumped directly into the river a Combined Sewage Overflow (CSO) Green roofs and other green infrastructure reduce stormwater volume, intensity, and CSO pollution 10 CSOs 11 Green Roof Runoff Reduction Reducing CSO Pollution with Green Roofs: Mechanism: Soil acts as sponge to soak up rainfall that drives runoff and CSOs Some succulent plants also behave like sponges (e.g., Sedum spp.) Commonly % runoff reduction 12 4

18 Green Roof Heat Island Benefits Urban Heat Island Effect: Impervious surfaces absorb heat by day, reradiate heat day and night Re-radiated heat make cities hotter Re-radiated heat increases cooling costs 13 Cooler Surface and Subsurface Temperatures Peak Summer Surface Temperatures: Green Roof o F Cooler Building City Building Peak Temp. Delay 14 Aesthetics Intensive green roofs are generally elaborately planted and commonly used as habitable spaces. Carnegie Mellon University 5

19 ACOB Structural Limitations Types of Green Roofing Extensive Semi-Intensive Intensive 2 ½ -4 Depth 5-8 Depth 8 + Depth Leak Detection (EFVM) 6

20 Monitoring: Demonstrate Benefits Click to edit Master title style Overview Web Site Allegheny County Office Building Green Roof Project Overview: 20 Overview: Allegheny County Office Building Green Roof Monitoring Program 8,400 SF of 20,200 SF converted to green roof in June 2010 Remainder conventional control roof Monitoring weather, temperature and water relationships using 95 sensors linked to internet 21 7

21 22 Details of Allegheny County Office Building Green Roof Monitoring Program Green Roof Types: 1. Tray Extensive (4 soil, pre-grown sedum) 2. Extensive (4 soil, sedum sod) 3. Semi-Intensive (~6 soil, plugs and pots) 4. Intensive (>8 soil, plugs and pots) Green Wall to hide cellular switchgear 23 Details of Allegheny County Office Building Green Roof Monitoring Program L L L L H L Extensive (4 ) H H L H Intensive (8 ) L Semiintensive H (6 ) 24 8

22 Details of Allegheny County Office Building Green Roof Monitoring Program Legend Climate Control Roof Green Roof Climate and Microclimate 25 Intensive & Semi-Intensive (~6-10 ) Tray Extensive (4 ) Extensive Sod Roof (4 ) 26 Details of Allegheny County Office Building Green Roof Monitoring Program Monitoring System Features: Microclimate and design differences considered High and Low slope positions monitored 95 temperature, moisture, and weather sensors monitored Real-time internet-accessible data Transfer relevant data to inspire, educate, advance state of art 27 9

23 Details of Allegheny County Office Building Green Roof Monitoring Program Sheltered Exposed Sheltered 28 Before 29 Installation of Drainage Mat 30 10

24 Drainage Wetness Sensor 31 Lateral Drains to Roof Drains (Over Composite Drainage Blanket) 32 Sensor Wires in Conduit 33 11

25 Closed-Cell Styrofoam for Lightweight Contouring 34 Wire Shelves to Support Microcosms 35 Crane Lifting Engineered Soils 36 12

26 Crain Lifting Engineered Soils 37 Filter Fabric and Soil over Styrofoam Mounds 38 One Year Later (6/10/11) 13

27 Before 40 After 1 month 41 After one year 42 14

28 1 Month After Planting H H L 43 One Year Later (6/10/11) Details of Allegheny County Office Building Green Roof Monitoring Program Microcosms Comparisons in Same Microclimate: Highly-monitored miniature green roof alternatives Set in same microclimate Interpretive display value 45 15

29 4 Control Details of Allegheny County Office Building Green Roof Monitoring Program Microcosms Comparisons in Same Microclimate: Measure: Percolation to drainage blanket (runoff) Soil Moisture (3 depths) Soil Temperature (3 depths) Solar radiation, air temperature, rainfall 47 16

30 Runoff Over Soil Roof Drainage Through Soil Microcosms Soil Drainage (to drain tube) Soil Surface Runoff (to drain tube) Soil Drainage Lysimeter (to rain gauge)

31 52 53 Sensing and Sampling Area 54 18

32 One Year Later (6/10/11) 56 ACOB Microcosms 57 19

33 Dielectric Soil Moisture Sensor (Decagon EC-5) 58 Soil Sensors Dielectric Soil Moisture Sensor Soil Temperature Sensor 59 Sedum Sod Monitoring 60 20

34 Control Temperature Monitoring 61 Control Roof Measurements Air Temperatures at 6, 18 a.g.l. Solar Radiation Roof Wetness Roof Surface Temperature 62 Cooler Roof Temperatures 40 o F Cooler! 63 21

35 Cooler Surface and Subsurface Temperatures Peak Summer Surface Temperatures: Green Roof o F Cooler Building City Building Peak Temp. Delay 64 CMU Heat Flux Comparison (Wang and Becker, 2011) Heat Flux Comparison H H L Extensive (4 ) H L H L L H Intensive (8 ) L L Semi-intensive (6 ) 65 ACOB Heat Flux Analyses (Wang and Becker, 2011) Carnegie Mellon Univ. Student Analyses of Temperature Flux Differences (Wang and Becker, 2011, David Dzombak, Ph.D. Advisor) Considered insulation components and temperature gradients across green roof and control roof layers to calculated heat flux Found Greatest Energy Benefit in Warm Weather Cooler Roof Temperatures Reduce Heat Gain to Building (75.3% difference in heat flux (gain) between green and control roofs in June-August) Found Modest Energy Benefit in Cold Weather (8.2% difference in heat flux (loss) between green and control roofs in November 2010-April 2011) 22

36 Heat Loss or Gain at ACOB, MJ/M 2 (Wang and Becker, 2011) 67 Green Roof Hydrologic Monitoring Forecasting Stormwater Capacity: Monitoring green roof soil moisture and roof runoff Can forecast how much stormwater green roof soils can absorb 68 Water Balance Monitoring Monitoring Rainfall & Runoff vs. Soil Water Content 69 23

37 Green Roof Soil Moisture Storage Relationships Monitoring Green Roof Soil Stormwater Storage 70 Rainfall (blue), Roof Drainage (red) and Soil Volumetric Moisture Content with Depth Runoff Reduction Runoff Delay 24

38 Rainfall, Roof Drainage, and Soil Moisture Relationships /31/110:00 9/10/110:00 9/20/110:00 9/30/110:00 Date / Time Inches of Rainfall or Roof Drainage Soil Water Storage (volumetric) Total Rainfall During Rain Event Total Roof Drainage During Rain Event Total Apparent Soil Water Storage (0-7" BGS) Rainfall and Roof Drainage Main Roof Microcosms (inches) Rainfall (inches) " Soil Roof Drainage (inches) 6.5" Soil Roof Drainage (inches) 1 0 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 10" Soil Roof Drainage (inches) % 90% 80% 70% 60% 50% 40% 30% 20% 10% 4.46 Runoff Reduction - Main Roof Microcosms " Soil % Runoff Reduction 6.5" Soil % Runoff Reduction 10" Soil % Runoff Reduction Rainfall 1 0% Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct

39 Green Roofs: Reduce stormwater volume and intensity, prevent water pollution (CSOs) Keep buildings and neighborhoods cooler Save money Summary 76 Questions??? Darla Cravotta Allegheny County John K. Buck, CPSSc Project Manager, Civil & Environmental Consultants