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Minnesota Stormwater Manual

Assessing the performance of green roofs
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Green Infrastructure: Green roofs consist of a series of layers that create an environment suitable for plant growth without damaging the underlying roof system. Green roofs create green space for public benefit, energy efficiency, and stormwater retention/ detention.

Because exact maintenance requirements vary from roof to roof, we do not recommend developing maintenance specifications, but recommend developing example maintenance performance requirements, as described below.

For acceptance of installation

Set the following requirements for, for example, 30 days after Substantial Completion, for roofs established using cuttings, pre-grown modules, or mats:

  • minimum percent cover of specified plant species required;
  • maximum percent cover and patch size of weed species (if any);
  • maximum square feet of bare area allowed; and
  • minimum thickness of media.

All areas that do not meet Performance Standards 30 days after installation shall be re-planted with original plant species and densities within 14 days of notification unless weather conditions are not suitable for planting as determined by Owner’s Representative.

Set the following requirements for, for example, 30 days after Substantial Completion, for roofs established using plugs, or pots:

  • minimum percent of plants that are healthy as determined by Owner’s Representative;
    • crowns of plants level with top of media;
    • vigorous foliage;
  • root balls broken and integrated into the soil;
  • maximum square feet of area of bare area allowed (excluding any areas that have been established from seed alone); and
  • minimum thickness of media

All areas that do not meet Performance Standards 30 days after installation shall be re-planted with original plant species and densities within 14 days of notification unless weather conditions are not suitable for planting as determined by Owner’s Representative.

For acceptance of maintenance

Set the following requirements for acceptance of maintenance:

  • minimum percent cover of specified plant species required for each year of the maintenance period;
  • minimum number of species present on the roof each year of the maintenance period; can also specify desired minimum percent cover needed to count as species diversity if desired;
  • maximum percent cover and patch size of weed species (if any); and
  • maximum square foot of bare area allowed each year of the maintenance period.

Vegetation will be replaced with species and densities acceptable by Owner’s Representative anytime vegetated cover requirements are not met during the maintenance period.

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