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Inspection and Maintenance: Green Roofs (view source)
Revision as of 19:48, 11 August 2022
, 1 year agono edit summary
*For green roofs with [[Green roofs#Irrigation|automated irrigation systems]] using municipal/drinking water, schedule watering to occur at night or early in the morning to minimize the loss of water to evaporation;
*For green roofs with [[Green roofs#Irrigation|automated irrigation systems]] using municipal/drinking water, schedule watering to occur at night or early in the morning to minimize the loss of water to evaporation;
*For green roofs with [[Green roofs#Irrigation|automated irrigation systems]] using cistern water, irrigating during the day when evaporation rate is high will make greater use of stored rainwater, thereby freeing up more storage in the system for the next rain storm and helping to reduce site runoff volume.
*For green roofs with [[Green roofs#Irrigation|automated irrigation systems]] using cistern water, irrigating during the day when evaporation rate is high will make greater use of stored rainwater, thereby freeing up more storage in the system for the next rain storm and helping to reduce site runoff volume.
==Rehabilitation & Repair==
Table below provides guidance on rehabilitation and repair work specific to green roofs organized according to BMP component. <br>
</br>
[[File:Spray-Irrigation.jpg|thumb|340px|Picture of a spray nozzle used in an automatic spray irrigation system on a green roof. When the irrigation system shows sings of leaking, either from the distribution line, fitting or sprinkler nozzle then [[[Testing#Green Roof Irrigation System|testing and repair work]] must be scheduled shortly to identify the problem area. (Photo Source: Vegetal I.D., n.d.)<ref>Vegetal i.D. n.d. Green Roof Irrigation. Accessed May 10 2022: https://www.vegetalid.us/green-roof-technical-resources/extensive-green-roof-design-guide/270-green-roof-irrigation.html</ref>]]
{|{| class="wikitable" style="width: 900px;"
|+'''Green Roofs: Key Components, Typical Issues and Rehabilitation Requirements'''
|-
!Component
!Problem
!Rehabilitation Tasks
|-
| rowspan="3"|'''[[Green roof media|Growing Media]]'''
|Eroded growing media area ≥ 30 cm in length or other damage is present
|
*Restore [[Green roof media|Growing Media]] to required depth with material that meets design specifications, replant and irrigate bi-weekly or as needed until [[Green roofs: Planting|plantings]] are established. If problems persist, consider covering with matting or other [[Construction: erosion and sediment control measures|erosion control measure]] until plantings are established or adding parapets or other wind break structures.
|-
|Surface ponding remains for > 3 hours after the end of a storm event because water does not infiltrate through the growing media
|
*Aerate (i.e., rake) or replace growing media in problem areas taking care not to damage the drainage or protective layers.
|-
|Surface ponding remains for > 3 hours after the end of a storm event because the drainage layer is [[Clogging|clogged]].
|
*Consult with green roof designer or product manufacturer/vendor to determine corrective actions.
|-
|'''[[Vegetation]]'''
|
[[Green roofs: Planting|Plants]] are not thriving and [[Green roof media|Growing Media] is low in [[organic matter]] (< 3 %) or available phosphorus (< 2.2 mg/kg)
|
*Amendment or [[Phosphorus testing in media|fertilizer application]] should be prescribed by the medium manufacturer or product vendor.
|-
|'''[[Overflow|Overflow outlets]]'''
|
Surface ponding remains for > 3 hours after the end of a storm event because [[overflow|overflow outlet]] is obstructed.
|
*Remove the obstruction which may require the use of a pressure washer or drain-snaking service.
|-
|'''[[Green roofs#Irrigation|Irrigation system]]'''
|
Distribution line, fitting or sprinkler nozzle is leaking, damaged or misaligned.
|
*Identify the location of the damaged system component through [[Testing#Green Roof Irrigation System|testing]] (i.e., running the system in each zone while making observations). Turn off the system and schedule the repair work.
|-
|'''[[Testing#Green Roof Leak Detection Testing|Protective Layers]]'''
|
Water-proofing membrane has reached 40 years of age and is due for [[Testing#Green Roof Leak Detection Testing|replacement]].
|
*Deconstruct the green roof, replace the water-proofing membrane with new material, and reconstruct with materials that meet design or product specifications.
|}
==Inspection Time Commitments and Costs==
Estimates are based on an extensive green roof with 15 cm of growing medium, irrigation and water-proofing membrane with leak detection system; estimates for other combinations of these variables are described in the [https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-7.6-Green-Roofs.pdf Low Impact Development (LID) Stormwater Management Practice Inspection and Maintenance Guide]<br>
</br>
[[File:Task Cost estimates.PNG|thumb|left|400px|Per-task cost estimates for maintenance and rehabilitation of an extensive green roof design with 15 cm growing medium, irrigation and water-proofing membrane with leak detection (in 2016 $ figures).<ref name="example1" />]]
[[File:Maintenance and Operation green roofs.PNG|thumb|400px|General time commitments and costs for inspection of an extensive green roof design with 15 cm growing medium, irrigation and water-proofing membrane with leak detection (in 2016 $ figures).<ref name="example1" />]]
[[File:Life cycle cost estimate green roof.PNG|thumb|center|400px|Construction and life cycle cost estimates for extensive green roofs with 15 cm growing medium, irrigation and water-proofing membrane with leak detection (in 2016 $ figures).<ref name="example1" />]]<br>
</br>
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:
*Design variations for [[Green roofs]] can be broken down into four main categories:
*#Extensive, 10 cm deep growing media bed, no irrigation system, no waterproof membrane;
*#Extensive, 10 cm deep growing media bed, no irrigation system, with waterproof membrane;
*#Extensive, 15 cm deep growing media bed with irrigation system, no waterproof membrane;
*#Extensive, 15 cm deep growing media bed with irrigation system and waterproof membrane;
*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
*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 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.
*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.
*“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].
*For all scenarios, the CDA (i.e., green roof area) is 2,000 m<sup>2</sup> 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 ($/m<sup>2</sup>) 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.
*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, 2013<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:
**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 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;
**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 material that meets design specifications;
**Leak detection testing to confirm membrane installation is acceptable;
**Planting or installation of new plant material;
**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);
**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 period for the [[Green roofs: Planting|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>
</br>
[[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:'''
<small>
#Estimated life cycle costs represent NPV of associated costs in Canadian dollars per square metre of CDA ($/m<sup>2</sup>).
#Average annual maintenance cost estimates represent NPV of all costs incurred over the time period and do not include rehabilitation costs.
#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.
#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 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>
==Inspection Field Data Sheet==
Feel free to '''download''' (downward facing arrow on the top righthand side) and '''print''' (Pinter emoticon on top right hand side) the following [[Green roofs]] Inspection Field Data Form developed by TRCA, STEP and its partners for the [https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-2016-1.pdf Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide]<ref>STEP. 2016. Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide. https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-2016-1.pdf</ref>.
The 4 page document prompts users to fill out details previously mentioned above on this page in other sections about various zones associated with [[Green roofs|Green roof]] features (i.e. Growing media, vegetation, overflow outlets, etc.) and describe why each area is a pass or fail, and if remediate action is required and under what timeframe it would be completed by. Furthermore, the forms prompt the reviewer to determine what type of inspection is being conducted for the feature in question: Construction (C), Routine Operation (RO), Maintenance Verification (MV), or Performance Verification (PV). <br>
<br>
[[File:Planting on green roof.jpg|thumb|340px|Planting new suitable [[vegetation]] species is on a green roof to ensure vegetation composition, coverage and condition remain optimal (The Scott Arboretum at Swarthmore College. 2014. Planting Green Roofs: Sowing Seeds<ref> ]]
<pdf width="900" height="800">File:LID-IM-Guide-2016-1.pdf Green Roofs inspection.pdf</pdf>
==References==