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Estimates of the life cycle costs of inspection and maintenance have been produced using the latest version of the [[Cost analysis resources|LID Life Cycle Costing Tool]] for three design variations (full infiltration, partial infiltration and no infiltration) to assist stormwater infrastructure planners, designers and asset managers with planning and preparing budgets for potential LID features.

Estimates of the life cycle costs of inspection and maintenance have been produced using the latest version of the [[Cost analysis resources|LID Life Cycle Costing Tool]] for four design variations

to assist stormwater infrastructure planners, designers and asset managers with planning and preparing budgets for potential LID features.

Assumptions for the above costs and the following table below are based on the following:

Assumptions for the above costs and the following table below are based on the following:

*Design variations for permeable pavements can be broken down into three main categories:  

*Design variations for [[Green roofs]] can be broken down into four main categories:  

**Full Infiltration design, where the pavement drains through infiltration into the underlying subsoil alone (i.e., no sub-drain);  

*#Extensive, 10 cm deep growing media bed, no irrigation system, no waterproof membrane;

**Partial Infiltration design, where drainage is through the combination of a subdrain and infiltration into the underlying subsoil (i.e., with a sub-drain); or,

*#Extensive, 10 cm deep growing media bed, no irrigation system, with waterproof membrane;

**No Infiltration (i.e., filtration only design) that includes an impermeable liner between the base of the BMP and the underlying native sub-soil, where drainage is through a sub-drain alone (i.e., with a sub-drain and impermeable liner).

*#Extensive, 15 cm deep growing media bed with irrigation system, no waterproof membrane;

*For permeable pavements it is assumed that rehabilitation of the pavement surface will be needed once the BMP reaches 30 years of age in order to maintain surface drainage performance at an acceptable level. Included in the rehabilitation costs are (de)mobilization costs, as equipment would not have been present on site.  

*#Extensive, 15 cm deep growing media bed with irrigation system and waterproof membrane;

*Design costs were not included in the rehabilitation as it was assumed that the original LID practice design would be used to inform this work. The annual average maintenance cost does not include rehabilitation costs and therefore represents an average of routine maintenance tasks, as outlined in Table Permeable Pavements: Key Components, Descriptions and Routine I&M Requirements, above. 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 permeable interlocking concrete pavers (PICP), as defined in the Tool. This product has been selected for costing due to its popularity and well understood maintenance needs.

*For green roofs it is assumed that replacement of the water-proofing membrane protecting the roof structure will be needed once the roof has been in place for 40 years

*For all permeable pavement design variations, the CDA has been defined as 2,000 m² of which 1,000 m²  is impermeable pavement draining to the pavers, and 1,000 m² is permeable pavement. The impervious area to pervious area ratio (I:P ratio) used to size the BMP footprint is 1:1, which is in accordance with recommendations in the [https://sustainabletechnologies.ca/app/uploads/2013/01/LID-SWM-Guide-v1.0_2010_1_no-appendices.pdf LID SWM Planning and Design Guide (CVC & TRCA, 2010)].

*Rehabilitation costs are those related to deconstruction, replacement of most materials (assumes 2/3 of cuttings needed to replant the 10 cm deep growing media bed design can be harvested from the previous roof), and reconstruction including (de)mobilization costs, as equipment would not have been present on site. Design costs were not included in the rehabilitation as it was assumed that the original LID practice design would be used to inform this work.  

**The Full Infiltration design does not include a sub-drain and assumes a native sub-soil infiltration rate of 20 mm/h. The base granular reservoir is 350 mm deep and is capable of storing runoff from a 61 mm rain event over the CDA. A monitoring well is included for inspection purposes.

*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 Partial Infiltration design includes a sub-drain and assumes a native sub-soil infiltration rate of 10 mm/h. The base granular reservoir is 350 mm deep and is capable of storing runoff from a 9 mm rain event before the stored volume reaches the perforated underdrain pipe located 50 mm above the native sub-soil. Although a flow restrictor is recommended to maximize infiltration, the cost of this feature is not included due to its relatively low cost.

*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 No Infiltration design includes a sub-drain pipe installed on the bottom of the sub-surface water storage reservoir and an impermeable liner. All other features are the same as the Partial Infiltration design variation.  

 

*Estimates of the life cycle costs of PICP permeable pavements in Canadian dollars per unit CDA ($/m²) are presented in the table below. [[Cost analysis resources|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.

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

**For all BMP design variations and maintenance scenarios, it is assumed that rehabilitation of the pavement surface will be necessary when the BMP reaches 30 years of age to maintain acceptable surface drainage performance. Rehabilitation of PICP pavements is assumed to typically involve the following tasks and associated costs:

***Remove pavers, bedding and joint fill and top 5 cm (2”) of base aggregate and replace with new material that meets design specifications

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

***Construction and Assumption inspection and testing associated with rehabilitation work to confirm that materials meet design specifications and installation is acceptable, including compaction and surface infiltration rate testing. <br>

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

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

 

*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.

 

*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;

**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;

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

specifications;

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

Leak detection testing to confirm membrane installation is acceptable;

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

design specifications;

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

High Frequency maintenance scenarios, respectively).  

 

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[[File:Minimum & hig hfreq cost p.p.PNG|thumb|center|900px|Life cycle cost estimates for all infiltration types of PICP [[permeable pavements]] an 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>]]

'''Notes:'''

'''Notes:'''

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

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

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

metre of CDA ($/m2).

#Rehabilitation cost estimates represent NPV of all costs related to rehabilitative maintenance work assumed to be needed after 30 years in service, including those associated with inspection.

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

#Full Infiltration design life cycle costs are lower than Partial and No Infiltration designs due to the absence of a sub-drain to construct, inspect and routinely flush.

period and do not include rehabilitation costs.

#Rehabilitation costs for Full Infiltration designs are estimated to be 54.8% to 55.6% of the original construction costs for High and Minimum Recommended Frequency maintenance program scenarios, respectively.

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

#Rehabilitation costs for Partial Infiltration designs are estimated to be 53.5% to 54.3% of 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 No Infiltration designs are estimated to be 47.4% to 48.1% of the original construction costs for High and Minimum Recommended Frequency maintenance program scenarios, respectively.

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 Minimum Recommended maintenance scenario are estimated to be 22.3%, of the original construction costs for Full Infiltration design, 22.6% for Partial Infiltration design, and  20.0% for No Infiltration design.

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

#Maintenance and rehabilitation costs over a 25 year time period for the High Frequency maintenance scenario are estimated to be: 39.0% of the original construction costs for Full, 38.9% for Partial Infiltration designs, and 34.5% for No Infiltration designs.

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 Minimum Recommended Frequency maintenance scenario are estimated to be approximately: 1.07 times the original construction cost for Full, 1.06 times the original construction costs for Partial Infiltration designs, and 93.9.% the original construction cost for No Infiltration designs.

scenario over the 50 year evaluation period.

#Maintenance and rehabilitation costs over a 50 year time period for the High Frequency maintenance scenario are estimated to be approximately: 1.43 times the original construction cost for Full, 1.41 times the original construction costs for Partial Infiltration designs, and 1.25 times the original construction cost for No Infiltration designs.

#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.  

 

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