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Crafting Green Roofs


Green Roof Vocabulary

In short, This is a glossary with frequently used words used in the Green Roof industry, particular to construction of such or in relation to Green Infrastructure.

Over all, the aim of this Green Roof Vocabulary is to provide a brief overview of terms and makes no claim to completeness. The Green Roof Vocabulary only occasionally updated. Of course, we appreciate suggestions and/or additions to our Green Roof Vocabulary.

Learn online about the most important terms related to Green Roofs.
This is a short version of a Green Roof Vocabulary, done by others. Especially nice for students and newcomers as a starting point.

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This is a screen shot of a light version of Green Roof Vocabulary


  • Adaptation - In the context of climate change: an adjustment in natural or human systems in response to actual or expected climate or their effect. And which moderates harm or exploits beneficial opportunities.
  • Aggregate - Non-organic fragments that make for instance up parts of growing medium.
  • Allowances - An amount established in the contract documents for inclusion in the contract sum. Covering the cost of prescribed items not specified in detail and providing for the variation between the predicted cost and the actual cost of construction.
  • Ballast - A material, for example used to hold loose laid roofing materials in place.
  • Bidding - When a general call is issued to contractors to propose a competitive budget to complete a given project. (GRHC)
  • Bidding, Pre-qualified - When an owner issues an invitation to bid to a selection of qualified contractors. (GRHC)
  • Built-in-Place Systems or Wall-to-Wall Green roof which is constructed / assembled directly at the final destination. The most efficient solution in regards of costs, environmental, general green roof benefits. Also the Best Management Practice. Tray systems are delivered per-assembled off-site.
  • Bid Securities - Insurance that provides the owner a mechanism for financial recovery should the low prime bidder default upon its bid. In the absence of a bona-fide and substantive error. (GRHC)
  • Bid Shopping - Given enough time the general contractor will immediately begin shopping the lowest bidder in order to procure a "final and best offer" from all bidders. Because to avoid this process, subcontractors withhold their bids to the general contractors until the last minute. (Bruce, 2005)
  • Biodiversity - The variety of life in the world or in a particular habitat or ecosystem.
  • Blue Roof - Blue Green Roofs - In fact, transforms low sloped roofs into the the most efficient means to manage stormwater volume. On Blue Green Roofs water is retained and detained in an optimized drainage layer within the Roof, Green Roof,or Solar Garden Roof system.
  • Bonding of Subcontractors - Payment and performance bonds are written by a surety or and insurance company and insure faithful performance of the work contracted and pull payment to those companies that provide services or materials for the project. (ASPE 2003 : 30)
  • Cation exchange capacity - The quantity of positive ions (cation) that can be absorbed by growing medium. (GRHC)
  • Carbon Footprint - Measures the total amount of greenhouse gases (GHG) caused by an activity or a person’s day-to-day life. Overall, through the burning of fossil fuels for electricity,cooling, transportation etc., and is generally measured in units of tons (or kilograms) of carbon dioxide equivalent.
  • Climate change - Change of climate that is attributed directly or indirectly to human activity that alters the composition of the global atmosphere. Additionally to natural climate variability observed over comparable time periods.
  • Chain of Custody - A process involving the assignment of quality assurance responsibilities for the entire construction process. (GRHC)
  • Critical Path -A sequence of tasks that need to be carried out in order for a project to reach substantial acceptance and completion. (GRHC)
  • Commissioning -A process of achieving validating and documenting that the performance of the complete building and its systems meet the design needs and requirements of the owner. (Demkin 2001)
  • Compaction - Increase of density mainly used with growing media.
  • Counter-flashing -Metal sheeting placed at the base of a parapet wall to protect the roofing membrane against environmental impact to pro-long the lifespan.
  • Control joints - Joints which accommodate the movement in the surface component of the roof.
  • Curtain wall - A non-structural outer wall, often of glass or steel
  • Dead Loads - All permanently placed materials on and below the roof (e ,g. green roof materials, green roof plants, ceiling fans). (GRHC)
  • Design Build -When a single firm is responsible for both the design and construction of a given project.
  • Direct Green Roof System a.k.a Built-in-Place - Is a system where the vegetation is not planted in containers or modules, but onto specially designed layers. These are placed on top of the existing roof. Often called seamless system, wall-to-wall system or monolithic system. Direct green roof systems are the most efficient solution for greening roofs with the best protection for the roof.
  • Drainage Layer - such as granular drainage material (bulk), drainage boards/sheets, drain pipes placed above a protective layer and under the growing media with a Filter Fabric in between. Granular drainage layers are a mineral growing media because of the absence of organic materials but sufficient space to promote root growth. In general all drainage layers have a specific drainage characteristic, stormwater retention, and stormwater detention capacity with a plant suitable Air-to-Water ratio. (Breuning)
  • Drain Access Chamber or Inspection Box - a device installed around roof drains that protects the roof drains and remains accessible. Typically with a perforated, removable cover for inspection and potential surface water. Ideally Drain Access Chambers are connected with each other by subsurface drainage channels to  ensure proper function all time. (Breuning)
  • Ecosystem services - The direct and indirect contributions of ecosystems to human well-being.
  • Erosion Blankets or Erosion protection layer - Protective sheeting or woven fabric placed on top of growing medium to protect against erosion by wind and water. Experience showed that such layers are very ineffective and counter productive for healthy plants. (Breuning)
  • Ethylene Propylene Diene Terpolymer (EPDM) -EPDM material is a thermosetting synthetic elastomeric membrane (RCI).
  • Evapotranspiration - The sum of water loss through evaporation and plant transpiration.
  • Expansion joints - Joints which are an extension of membrane and allow the structure to expand and contract without breaking.
  • Extensive Green Roof -An extensive green roof system is a shallow system with hardy and often succulent type of plants without permanent irrigation system. (Breuning)
  • Fertilization -The application of nutrients to plants. Depending on the Green Roof Type the application time and amount varies. Fertilizer can be solid/granular or liquid and mineral or organic. The preference shall be on organic fertilizers to avoid nutrients to run-off and pollute the stormwater. (Breuning)
  • Filter Cloth, Filter Fabric -A synthetic, mineral or organic material laid over the drainage layer creating a separation to avoid infiltration of dead organic content and fine mineral content from the growing media layer.
  • Food Security - Food security refers to the availability of basic foods and how accessible they are.
  • Friction coefficient - a scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. Friction coefficient is used on sloped roofs but also in stormwater retention and stormwater detention.
  • Green Roof Assembly - Everything above the roofing (and root barrier). Typically consisting of a protection layer, drainage layer, filter cloth/fabric, base medium and/or growing medium, and the vegetation on an impervious surface. (Breuning)
  • Green Infrastructure - Green infrastructure refers to the array of technologies and practices, such as green roof habitats, that use naturals systems to enhance overall environmental quality and provide ecosystem services, such as filtering air pollution, carbon sequestration, and stormwater attenuation.
  • Growing medium - Growing Media - Green Roof Soil - is top layer or the substrate that anchors and promotes the vegetation from the beginning. Later the plant growth will be sustained by the engineered combination of all layers. (Breuning)
  • HVAC systems - Heating, ventilation and air-conditioning systems.
  • Hydrodynamic membrane -A membrane that relies on gravity to shed water. (GRHC)
  • Hydrostatic membrane -A membrane that is able to withstand pressure exerted by a fluid due to its weight. (GRHC)
  • Intensive Green Roof, Garden Roof, Roof Garden - Is a Green Roof type that supports a high variety of different plants including shrubs and trees. Typically Intensive Green Roofs are equipped with a permanent irrigation system that is ideally placed in the drainage layer or based medium. (Breuning)
  • Irrigation System (temporary or permanent) - Systems which deliver moisture to the plants in different ways. Sprinkler or surface irrigation has high evaporation rates and should be avoided to protect resources. 
  • Life-Cycle Cost - The capital and operational cost of a construction item or system during the estimated useful life of a structure (e.g. building). (Breuning / GRHC)
  • Life Cycle Costing Analysis (LCC) - The capital and operational cost of a construction item or system during the estimated useful life of a structure (e.g. building). (Breuning)
  • Live Load - All equipment, amenity items and people on the roof. These are not permanent elements and cause the weight on the roof to fluctuate.
  • Loose Laid Green Roof System, Built-Up Systems, Monolithic Systems, Wall-To-Wall Green Roofs - Green roof which is constructed / assembled directly at the final destination. The most efficient solution in regards of costs, environmental and general green roof benefits. See additionally Monolithic Platform Systems. (Breuning)
  • Membrane Protection Layer- Protection Layer - A material used to protect the waterproofing membrane, root barrier, and/or an insulation layer against mechanical impact during the construction and over the operational time. It also reduces friction between roofing and green roof layers or elements. (Breuning)
  • Mitigation - In the context of climate change, a human intervention to reduce the sources or enhance the sinks of greenhouse gases. In the context of stormwater, a technique to reduce stormwater run-off. (Breuning)
  • Modular Green Roof System, Tray System, Pre-vegetated Planters, Prefab Sectional System - A roof greening system which combines one or more layers in a pre-manufactured and pre-vegetated container (e.g. drainage, growing mediums, and plants). Pre-vegetated modular systems are a costly alternative for small projects and hobby gardeners and only in one-size-fits-all. (Breuning)
  • Monolithic Platform System - Green roof which is constructed / assembled directly at the final destination where an engineered platform creates 100% roof protection during the construction of the building. The monolithic platform is considered as a second roof deck where all other roof parts (HVAC, railings, pavers, PV systems, gazebos can be anchored in. All monolithic platform systems are Blue Roof ready. (Breuning).
  • Moisture Retention Layer - a layer of mineral wool or thick poly fabrics installed above or below the drainage layer which is supposed to increase water retention. Unfortunately these retention layers often create over-saturated (no air) barrier where plants suffer more than they benefit from. (Breuning)
  • Negotiation - When an owner decides to hire a contractor as a sole-source provider based on previous experience or reputation.
  • Overburden -A term used primarily by roofing professionals to refer to the entire Green Roof system above the waterproofing, receptive root barrier. (Breuning)
  • Packaging Process -Process involving the establishment of a hierarchy of responsibility between the trades. (GRHC)
  • Plenum -The space that is used for air circulation in heating and air conditioning systems, typically between the structural ceiling and the suspended ceiling or under a raised floor. The plenum is typically used to house the communication cables for the buildings computer and telephone network(s). (GRHC)
  • Pre-Grown Mats - Vegetated Mats - vegetation on a carpet-like and fully vegetated element to install vegetation as an instant green. Typically these mats are filled with growing medium where most of the plants roots grow. Vegetated Mats can come in rolls or slabs like grass sods. Some mats have an additional plastic mesh to increase the strength. (Breuning)
  • Pre-bid conferences -Conferences held in order for the owner and design team to clearly communicate information, be it technical or procedural, to bidding contractors. (GRHC)
  • Punch List - A list of items of work to be completed or corrected by the contractor after substantial acceptance. (GRHC)
  • Polyvinyl Chloride (PVC) - A synthetic thermoplastic polymer prepared from vinyl chloride often compounded into flexible and rigid forms through the use of plasticizers, stabilizers, fillers, and other modifiers; rigid forms are used in pipes, flexible forms are used in the manufacturing of sheeting a roof membrane materials (RCI).
  • Schedule of Values - A statement furnished by the contractor to the architect reflecting the portions of the contract sum allocated to the various portions of the work and used as the basis for reviewing the contractor's application for payment. (AIA 2001)
  • Staging - A specified area used to store materials during construction. In some cases the green roof layers allow staging on top because of the excellent protection function.
  • Supersaturating – is reached when all Green Roof layers contain excessive water and/or surplus water than can't reach the drain (fast enough). This can be wanted or unwanted depending on the engineering part behind.  Roofs are designed to have emergency overflows if supersaturation is not wanted. (Breuning)
  • Quality Assurance - Actions taken to ensure that standards and procedures for the implementation of a system or product are adhered to, such that they meet technical requirements. (GRHC)
  • Retrofit - When a Green Roof is engineered and built on to an existing roof.
  • Roof Assembly - is the combination the Green Roof where all roofing components, including the roof deck, membranes, insulation, covering, root barrier etc, are combined. (Breuning)
  • Root Repellent Layer - Root Barrier - A barrier that eliminates roots to grow in the roofing layers below. Ideally the roofing shall be root resistant in the first place to avoid the use of barrier that are not proven for the purpose and may create more damage. Separate root barriers must be compatible with the roofing systems. (Breuning)
  • R-value -The measure of thermal resistance. R = K·m²/W. Although Green Roofs may help under certain climate conditions but they don't have a consistent R-value. (Breuning)
  • Shop Drawings -Depict the conditions of installation throughout the construction process, including a profile schematic, details, information, and accurate dimensions and configurations. (GRHC)
  • Submittals -Product data, supplier's technical literature, MSDS, a statement by the supplier that the product is suited to, and approved, for the proposed use, samples, soil samples and test reports, cost estimate, and shop drawings. (Breuning / GRHC)
  • Urban Heat Island Effect -This is a phenomenon whereby urban areas experience higher temperatures than the surrounding countryside. This is caused primarily by the change in land cover from green open spaces to buildings, roads and other infrastructure which absorb solar radiation during the day and releases it as latent heat during the night. (Breuning)
  • Value Engineering -A meeting of minds between owners, designers, and contractors to reduce the costs of a project by substituting materials or construction methods with "approved" alternative products or methods that will provide acceptable results of equal or mostly lower quality. (Breuning)
  • Vitrify -To make a surface non-porous. (GRHC)
  • Water Holding Capacity -The maximum volume of water that a Green Roof system can hold before creating run-off. (Breuning)
  • Water Permeability - is the quality or state of being permeable, able to be penetrated or passed through by a water or air. The layers of Green Roofs different levels of permeability on purpose and to meet FLL requirements. (Breuning)
  • Water capture -The quantity of water that is retained in any layer of a Green Roof system after new water additions have ceased and that cannot escape the roof except through evaporation or plant transpiration. (Breuning / ASTM e2397 -05: 3.2.1)
  • Wind uplift - an upward force that occurs when the pressure below a roof is greater than above it.