Changes

*The annual average maintenance cost does not include rehabilitation costs and therefore represents an average of routine maintenance tasks, as outlined in table Green Roofs: Key Components, Descriptions and Routine I&M Requirements, above. As part of these costs, it is assumed that a minor leak is detected in the waterproofing membrane when the roof reaches 10 years of age, and that the leak can be isolated through leak detection tests and repaired through patching. It is also assumed that one minor leak is detected and repaired every 5 years thereafter, until it reaches 40 years of age, when the entire membrane is replaced with new material.  

*The annual average maintenance cost does not include rehabilitation costs and therefore represents an average of routine maintenance tasks, as outlined in table Green Roofs: Key Components, Descriptions and Routine I&M Requirements, above. As part of these costs, it is assumed that a minor leak is detected in the waterproofing membrane when the roof reaches 10 years of age, and that the leak can be isolated through leak detection tests and repaired through patching. It is also assumed that one minor leak is detected and repaired every 5 years thereafter, until it reaches 40 years of age, when the entire membrane is replaced with new material.  

*All cost value estimates represent the NPV as the calculation takes into account average annual interest (2%) and discount (3%) rates over the evaluation time periods.  

*All cost value estimates represent the NPV as the calculation takes into account average annual interest (2%) and discount (3%) rates over the evaluation time periods.  

 

*The costing presented in this section is specific to extensive green roofs only, which are more common than intensive green roofs. Extensive green roofs support low growing plants and have substrate depths ranging from 5-15 cm, while intensive green roofs have growing media deeper than 15 cm (Permeable Pavement Task Committee, 2015<ref>Permeable Pavement Task Committee. 2015. Permeable pavements. American Society of Civil Engineers. hhttps://www.accesswater.org/publications/proceedings/-278801/asce-s-new-permeable-pavements-manual</ref>). The no waterproof membrane scenarios assume that the membrane has already been installed as part of building roof construction and that waterproof membrane leak detection testing is performed by flood tests.  

*The costing presented in this section is specific to extensive green roofs only, which are more

*“Minimum” and “High” life cycle costs estimates are based on two different types of extensive green roof systems; a low cost 10 cm deep without irrigation and water-proofing membrane design and a higher cost 15 cm deep with irrigation and membrane design. For a detailed description of construction, inspection, maintenance and rehabilitation cost assumptions see section 7.1.7 of the [https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-2016-1.pdf LID Stormwater Management Practice Inspection and Maintenance Guide].

common than intensive green roofs. Extensive green roofs support low growing plants and have

*For all scenarios, the CDA (i.e., green roof area) is 2,000 m² and cost estimates include crane mobilization and demobilization to install, deconstruct and reconstruct the green roof. The 10 cm deep growing media bed is planted with cuttings and the “with water-proofing membrane” design is installed with a thermoplastic polyolefin (TPO) membrane and no membrane leak detection system. The 15 cm deep growing media bed is planted with pre-grown sedum mats, includes an irrigation system, and the “with waterproof membrane” design is installed with a synthetic rubber, ethylene propylene diene terpolymer (EPDM) membrane and an Electric Field Vector Mapping (EFVM) leak detection system.  

substrate depths ranging from 5-15 cm, while intensive green roofs have growing media deeper than

15 cm (Permeable Pavement Task Committee, 2015). The no waterproof membrane scenarios assume

that the membrane has already been installed as part of building roof construction and that

waterproof membrane leak detection testing is performed by flood tests.  

 

*“Minimum” and “High” life cycle costs estimates are based on

two different types of extensive green roof systems; a low cost

10 cm deep without irrigation and water-proofing membrane

design and a higher cost 15 cm deep with irrigation and

membrane design. For a detailed description of construction,

inspection, maintenance and rehabilitation cost assumptions

see section 7.1.7 of the LID Stormwater Management Practice

Inspection and Maintenance Guide.

 

*For all scenarios, the CDA (i.e., green roof area) is 2,000 m2 and cost estimates include crane

mobilization and demobilization to install, deconstruct and reconstruct the green roof. The 10 cm

deep growing media bed is planted with cuttings and the “with water-proofing membrane” design is

installed with a thermoplastic polyolefin (TPO) membrane and no membrane leak detection system.

The 15 cm deep growing media bed is planted with pre-grown sedum mats, includes an irrigation

system, and the “with waterproof membrane” design is installed with a synthetic rubber, ethylene

propylene diene terpolymer (EPDM) membrane and an Electric Field Vector Mapping (EFVM) leak

detection system.  

 

*Estimates of the life cycle costs for all green roof design variations and maintenance scenarios in Canadian dollars per unit CDA ($/m²) are presented in the table below. [[LID Life Cycle Costing Tool]] allows users to select what BMP type and design variation applies, and to use the default assumptions to generate planning level cost estimates.

*Estimates of the life cycle costs for all green roof design variations and maintenance scenarios in Canadian dollars per unit CDA ($/m²) are presented in the table below. [[LID Life Cycle Costing Tool]] allows users to select what BMP type and design variation applies, and to use the default assumptions to generate planning level cost estimates.

 

*For all BMP design variations and maintenance scenarios, it is assumed that replacement of the waterproofing membrane is needed at 40 years of age (TRCA & U of T, 2013a<ref>Toronto and Region Conservation Authority and University of Toronto (TRCA & U of T). 2013. Assessment of Life Cycle Costs for Low Impact Development Stormwater Management Practices. Toronto, ON</ref>). Where a green roof is in place, replacement of the water-proofing membrane is assumed to typically involve the following tasks and associated costs:

*For all BMP design variations and maintenance scenarios, it is assumed that replacement of the waterproofing membrane is needed at 40 years of age (TRCA & U of T, 2013a). Where a green roof is in

place, replacement of the water-proofing membrane is assumed to typically involve the following tasks and associated costs:

**Deconstruction of all green roof components and layers;

**Deconstruction of all green roof components and layers;

**For 10 cm growing media bed designs, harvesting 2/3 of the plant material needed to replant

**For 10 cm growing media bed designs, harvesting 2/3 of the plant material needed to replant by cuttings;

by cuttings;

**For 15 cm growing media bed designs planted with pre-grown sedum mats, it is assumed that all mats and associated growing media and plants are replaced with new ones;

**For 15 cm growing media bed designs planted with pre-grown sedum mats, it is assumed that

**Replacement of the water-proofing membrane with new material that meets design specifications;

all mats and associated growing media and plants are replaced with new ones;

**Reconstruction of the green roof layers up to and including the growing media bed with new material that meets design specifications;

**Replacement of the water-proofing membrane with new material that meets design

**Leak detection testing to confirm membrane installation is acceptable;

specifications;

**Reconstruction of the green roof layers up to and including the growing media bed with new

material that meets design specifications;

Leak detection testing to confirm membrane installation is acceptable;

**Planting or installation of new plant material;

**Planting or installation of new plant material;

**Reconstruction of the irrigation system (where applicable) with new materials that meet

**Reconstruction of the irrigation system (where applicable) with new materials that meet design specifications;

design specifications;

**Green roof irrigation system testing to confirm installation is acceptable (where applicable);

**Green roof irrigation system testing to confirm installation is acceptable (where applicable);

**Construction and Assumption inspection work as part of reconstruction work at year 40;

**Construction and Assumption inspection work as part of reconstruction work at year 40;

**Routine inspection and vegetation maintenance work over a two (2) year establishment

**Routine inspection and vegetation maintenance work over a two (2) year establishment period for the [[Green roofs: Planting|plantings]];

period for the plantings;

**Replace plants that don't survive the initial establishment period (assumes 10% and 20% of transplanted plant material does not survive the first year for Minimum Recommended and High Frequency maintenance scenarios, respectively).<br>

**Replace plants that don't survive the initial establishment period (assumes 10% and 20% of

transplanted plant material does not survive the first year for Minimum Recommended and

High Frequency maintenance scenarios, respectively).  

[[File:Mini&high freq green roof.PNG|thumb|center|900px|Life cycle cost estimates for all configurations of extensive green roof design with 10 & 15 cm growing medium, (with/without) irrigation and (with/without) water-proofing membrane with leak detection under minimum and high frequency scenarios (in 2016 $ figures).<ref>TRCA. 2016. Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide. Prepared by the Sustainable Technologies Evaluation Program. Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-7.4-Permeable-Pavements.pdf</ref>]]

[[File:Mini&high freq green roof.PNG|thumb|center|900px|Life cycle cost estimates for all configurations of extensive green roof design with 10 & 15 cm growing medium, (with/without) irrigation and (with/without) water-proofing membrane with leak detection under minimum and high frequency scenarios (in 2016 $ figures).<ref>TRCA. 2016. Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide. Prepared by the Sustainable Technologies Evaluation Program. Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-7.4-Permeable-Pavements.pdf</ref>]]

<small>

<small>

#Estimated life cycle costs represent NPV of associated costs in Canadian dollars per square

#Estimated life cycle costs represent NPV of associated costs in Canadian dollars per square metre of CDA ($/m²).

metre of CDA ($/m2).

#Average annual maintenance cost estimates represent NPV of all costs incurred over the time period and do not include rehabilitation costs.

#Average annual maintenance cost estimates represent NPV of all costs incurred over the time

#Rehabilitation cost estimates represent NPV of all costs related to rehabilitative maintenance work assumed to be needed within the first 40 years of operation, including those associated with inspection and maintenance over a two (2) year establishment period for the plantings.  

period and do not include rehabilitation costs.

#Average annual maintenance cost estimates for the High Frequency maintenance program scenario are approximately 1.82 times the costs for the Minimum Recommended Frequency scenario over the 50 year evaluation period.

#Rehabilitation cost estimates represent NPV of all costs related to rehabilitative maintenance

#Rehabilitation costs for the 10 cm deep filter bed, no irrigation system, with membrane are estimated to be between 1.04 and 1.05 times the original construction costs for High and Minimum Recommended Frequency maintenance program scenarios, respectively.

work assumed to be needed within the first 40 years of operation, including those associated

#Rehabilitation costs for the 15 cm deep filter bed, with irrigation system, with membrane are estimated to be 95% of the original construction costs for both High and Minimum Recommended Frequency maintenance program scenarios.

with inspection and maintenance over a two (2) year establishment period for the plantings.  

#Maintenance and rehabilitation costs over a 25 year time period for the High Frequency maintenance scenario are estimated to be 1.01 and 0.53 times the original construction costs for the 10 cm and 15 cm with membrane designs, respectively.

#Average annual maintenance cost estimates for the High Frequency maintenance program

#Maintenance and rehabilitation costs over a 25 year time period for the Minimum Frequency maintenance scenario are estimated to be 0.55 and 0.30 times the original construction costs for the 10 cm and 15 cm with membrane designs, respectively.

scenario are approximately 1.82 times the costs for the Minimum Recommended Frequency

#Maintenance and rehabilitation costs over a 50 year time period for the High Frequency maintenance scenario are estimated to be 2.87 and 1.90 times the original construction costs for the 10 cm and 15 cm with membrane designs, respectively.

scenario over the 50 year evaluation period.

#Maintenance and rehabilitation costs over a 50 year time period for the Minimum Frequency maintenance scenario are estimated to be 2.04 and 1.48 times the original construction costs for the 10 cm and 15 cm with membrane designs, respectively.  

#Rehabilitation costs for the 10 cm deep filter bed, no irrigation system, with membrane are

estimated to be between 1.04 and 1.05 times the original construction costs for High and

Minimum Recommended Frequency maintenance program scenarios, respectively.

#Rehabilitation costs for the 15 cm deep filter bed, with irrigation system, with membrane are

estimated to be 95% of the original construction costs for both High and Minimum

Recommended Frequency maintenance program scenarios.

#Maintenance and rehabilitation costs over a 25 year time period for the High Frequency

maintenance scenario are estimated to be 1.01 and 0.53 times the original construction costs

for the 10 cm and 15 cm with membrane designs, respectively.

#Maintenance and rehabilitation costs over a 25 year time period for the Minimum Frequency

maintenance scenario are estimated to be 0.55 and 0.30 times the original construction costs

for the 10 cm and 15 cm with membrane designs, respectively.

#Maintenance and rehabilitation costs over a 50 year time period for the High Frequency

maintenance scenario are estimated to be 2.87 and 1.90 times the original construction costs

for the 10 cm and 15 cm with membrane designs, respectively.

#Maintenance and rehabilitation costs over a 50 year time period for the Minimum Frequency

maintenance scenario are estimated to be 2.04 and 1.48 times the original construction costs

for the 10 cm and 15 cm with membrane designs, respectively.  

 

</small>

</small>