LID opportunities in industrial, commercial and multi-residential types

This section identifies source areas typically found on industrial, commercial and multi-residential properties and gives advice on which LID practices are (usually) ideal for each land-use type. Source areas include parking lots, roofs, pedestrian walkways, common areas and landscape areas. The section also discusses LID retrofit opportunities and constraints accompanying these source areas and provides a table for each land use group identifying common, possible, and unlikely retrofit options.

If the site features listed below do not apply to your site, select the most appropriate category or use a combination of two or more categories to screen LID options. LID practices are scalable, so applying alternate LID practices to those identified for each land use group may be a possibility after detailed evaluation of site constraints (i.e. field testing conducted during pre-design). Choosing an appropriate LID practice can be an iterative process, as additional site information becomes available in the pre-design phase.

High-rise and mid-rise sites

LID options for high-rise and mid-rise sites

Mid- and high-rise sites (four storeys or more) share common features. These buildings are often for residential use and include apartments or condominiums. Leasing companies or condominium associations usually operate these buildings. Many office buildings also belong to this category. Office buildings may be operated by an independent site owner, but often commercial land management groups own and operate them.

Parking lots

Mid- and high-rise buildings have higher user occupancy densities than other sites and require significant parking area. To conserve site area, these parking lots are typically located underground. Mid- and high-rise buildings usually have flat roofs that drain internally to onsite storm sewer networks. They typically have common areas, but their size and function vary. Bioretention: Parking lots

Common areas

Pedestrian and common areas are outdoor features found on most mid- and high-rise sites. They provide access and egress to buildings and allow pedestrian movement around the property. Most mid- and high-rise buildings will have common areas at their entrance and can include garden features, planters and benches. On residential sites, common areas may include parks or parkettes, playgrounds, sports facilities, sidewalks and pathways.

Landscaped areas

Landscaped areas commonly surround mid- and high-rise buildings They can also be found adjacent to parking lots and internal roads. These areas are often grassed and may include plantings. These areas are ideal for establishing bioretention areas, soakaways or bioswales if conveyance is preferred. If grading allows, landscaped areas adjacent to the parking lot can easily be retrofitted to provide quality control and water balance benefits. Often located within the pedestrian areas adjacent to a building, target these areas can for accepting and infiltrating clean roof drainage. Cisterns for rainwater harvesting can also be located in landscapted areas, either buried or above ground. Utilities may be buried within landscaped areas on your site - not always just adjacent to the building) - so get your locates before digging.

Roof areas

In many municipalities, the rooftops of mid- and high-rise buildings are not visible. Developing LID practices on these surfaces will provide benefits but will be more difficult to promote, since a benefit of green roofs is their aesthetic appeal. The exception is major urban centres where a significant number of high rises offer views of other buildings' roofs.

LID options for high-rise and mid-rise sites
(** = Common, * = Possible, o = Unusual)

Source area	Permeable pavements/sidewalk	Bioretention	Bioswales	Soakaways	Perforated pipe systems	Rainwater harvesting	Landscape alternatives	Prefabricated modules	Green roofs	Pollution prevention
Roof area	o	o	o	o	o	**	o	o	**	o
Pedestrian / landscaped / common areas	**	**	*	*	*	o	**	**	o	*
Parking area	**	*	*	*	*	o	o	**	o	**

Low-rise residential sites

LID options for low-rise land use

Low-rise residential sites include townhouses and apartment complexes with fewer than four storeys. Management groups or condominium boards usually operate these sites. Common landform features of low-rise residential sites include small parking lots, significant pedestrian walkways and landscaped areas. Townhouses have peaked roofs with external drainage, while low-rise apartment complexes have flat roofs with internal drainage.

Landscaped areas

Low-rise residential sites typically have significant landscaped areas. On townhouse sites, landscaped areas tend to be spread across the complex as gardens, parking islands, and strips of lawn. Park or community green spaces areas may also be present. Due to lot grading, it may not be practical to convey road and parking lot runoff to landscaped areas around the building’s perimeter. These areas can, however, be retrofitted to provide water balance benefits by infiltrating roof runoff via bioretention, soakaways or bioswales.

On sites with larger green spaces, LID practices for accepting runoff from more substantial catchment areas will likely be feasible. Parks can also be retrofitted with most LID options. LID options such as infiltration chambers won't sacrifice park function, while highly visible practices like bioswales or bioretention enhance their aesthetic value.

Parking areas

Parking areas on low-rise residential properties are often small and well-used by residents. These parking lots are graded to catch basins which connect to onsite storm sewers. Due to their smaller, decentralized design, parking areas for townhouse developments typically convey runoff overland to internal roadways equipped with storm sewers. Permeable pavement is a retrofit option for both types of parking facilities and for internal roads.

LID options for low-rise sites
(** = Common, * = Possible, o = Unusual)

Source area	Permeable pavements/sidewalk	Bioretention	Bioswales	Soakaways	Perforated pipe systems	Rainwater harvesting	Landscape alternatives	Prefabricated modules	Green roofs	Pollution prevention
Roof area	o	o	o	o	o	**	o	o	o	o
Pedestrian / landscaped / common areas	o	o	o	o	o	*	**	o	o	o
Parking area	**	**	*	*	*	o	o	**	o	*

Large commercial sites

LID options for large commercial sites

Large commercial sites include big-box stores, warehouses, and shopping malls. Often located in highly urbanized commercial centres, they are usually owned and operated by land management companies.

Large commercial sites are rarely more than two storeys in height. Typically they have large and often underused parking lots and flat roofs that drain internally through the building to onsite storm sewers. Though these sites are expansive, they rarely have complex networks of pedestrian walkways and often rely on vehicular traffic to get site users onsite.

Parking areas

Not all parking areas are used equally. At large commercial sites parking spots may be reserved for people with disabilities, visitors to the site, expectant mothers, families with young children, specific employees, deliveries, motorcycles, electric cars, taxis and public transportation. When considering parking areas for LID retrofit locations, identify and respect these special areas during the design process. Be sure to understand how site parking is used throughout the week.

Parking spaces close to building entrances are used more frequently than those in moderate and peak demand areas. If grading and other site-specific factors allow it, investigate installing permeable pavement in infrequently used areas to extend the system's lifespan. The social benefits of green features may be underappreciated in areas that are not frequented by site users, so aim to implement practices like bioswales or bioretention areas closer to the entrance of the building to maximize biophillic benefits. On many sites existing drainage patterns dictate where parking lot source controls can be located.

Roof areas

The roof areas of large commercial buildings are large impervious surfaces. Controlled roof drains have become a widely utilized tool for stormwater management with the commercial development industry. While these devices do attenuate flows, they do not significantly reduce runoff volumes. By simply directing roof runoff to a soakaway pit, you can provide a great amount of volumetric stormwater control. Consider going one step further and storing this water in a cistern for future use. Commercial rooftops are relatively clean, and complex filtration is not required for most non-potable uses.

LID options for large commercial sites
(** = Common, * = Possible, o = Unusual)

Source area	Permeable pavements/sidewalk	Bioretention	Bioswales	Soakaways	Perforated pipe systems	Rainwater harvesting	Landscape alternatives	Prefabricated modules	Green roofs	Pollution prevention
Roof area	o	o	o	o	o	**	o	o	**	o
Pedestrian / landscaped / common areas	**	**	**	*	o	o	**	**	o	*
Parking area	**	**	**	**	*	o	o	**	o	**

Small commercial sites

LID options for small commercial sites

Small commercial sites include strip malls, small private enterprises, car dealerships and residential sites converted to commercial facilities. While site features vary significantly with these small sites, typical features include small parking areas and limited pedestrian and common areas. On these sites roof areas can be flat with internal drainage or peaked with external drainage.

While often owned and operated by the site user, land management companies also own and operate a significant portfolio of small commercial sites in Ontario.

Landscaped areas

Landscaped area retrofits on small commercial sites are limited due to high impervious surface coverage. Landscaped areas can often be found near the site perimeter. Where open channel conveyance systems like ditches and swales exist, bioswales are often a suitable retrofit option. Bioretention may also be a suitable option along green site perimeter areas. On many sites, drainage is conveyed towards site perimeters and away from the building, allowing for the capture of parking lot runoff.

Roof areas

Small commercial buildings roofs are large impervious surfaces and offer excellent opportunities to intercept runoff. Whether drained by internal or external means, rainwater harvesting is a viable option to achieve water balance benefits. Harvested water is useful for irrigation and for pressure washing of hard surfaces. Indoor non-potable uses - e.g. toilet flushing - are viable options on roofs with internal drainage pipes. Green roofs are an alternative, as is directing roof leaders to bioretention areas, soakaways or even permeable pavement.

Parking areas

Like large commercial sites, parking patterns on small commercial sites will include areas of high use close to the buildings, as well as areas used only during periods of peak demand. Due to lower vehicle speeds and fewer heavy loads, parking lots are ideal locations for permeable pavement installations. Bioretention areas are options for areas enclosed by curbing. Consider directing parking lot runoff to LID practices external to the parking lot, such as perimeter bioswales or soakaways. Infiltration chambers installed under parking lots would provide runoff volume reductions. Utilities, frequently electrical lines for lot lighting, may be buried within parking lots, so be sure to get locates before digging.

LID options for large commercial sites
(** = Common, * = Possible, o = Unusual)

Source area	Permeable pavements/sidewalk	Bioretention	Bioswales	Soakaways	Perforated pipe systems	Rainwater harvesting	Landscape alternatives	Prefabricated modules	Green roofs	Pollution prevention
Roof area	o	o	o	o	o	**	o	o	**	o
Pedestrian / landscaped / common areas	**	**	*	*	*	o	o	**	o	*
Parking area	**	*	*	*	*	o	o	**	o	**

Light industrial sites

LID options for light industrial sites

Light industrial sites include light manufacturing, warehouse, warehouse-manufacturing, laboratories, and food production and processing facilities. Common landform features include buildings with less than four stories, maintenance yards, shipping and receiving areas, flat roofs with internal drainage, and vast but often underused parking lots.

Light industrial sites present unique challenges and opportunities. When evaluating the LID retrofit opportunities on a light industrial site, give preliminary consideration to pollution prevention, especially in and around shipping and receiving areas, and product or waste storage areas.

Storage / shipping and receiving

Light industrial lands often have storage and shipping and receiving areas located immediately adjacent to buildings. Due to the intensive use of these areas, they are significant contributors to pollutant loading.

Often, the simplest and most inexpensive way to reduce pollutant loading from such areas is implementing pollution prevention (P2) practices. P2 includes non-structural solutions that reduce pollutant loading by changing site practices. For example, reducing the amount of de-icing salts used in the winter can significantly improve runoff quality. Changing the location of product or waste storage from the perimeter of the site to a controlled catchment area or within the building can also improve runoff quality. Modifying loading and unloading practices by changing equipment or implementing weather policies can also be extremely effective in reducing the stormwater impact of a site.

Structural P2 practices for these areas could include spill containment structures used to temporarily detain materials or liquids until collection and disposal can occur. Spill containment structures should be part of a site-specific spill response plan. These systems may include subsurface vaults and oversized pipes with shut off valves. Staff training is mandatory for operating these systems.

Outdoor material and waste storage areas can be upgraded with covered storage bins, shelters, or containers to prevent rain from coming into contact with materials that impact stormwater quality.

Establishing buffers around surface conveyance features can also provide significant improvements to runoff quality. These buffers may include physical barriers, such as bollards or curbs, for preventing conveyance features from being used as storage areas.

Staff parking areas and rooftops

These areas represent the best opportunity for establishing LID practices on light industrial sites. Runoff from these catchment areas can be treated with the same suite of LID options for commercial lands.

LID options for large commercial sites
(** = Common, * = Possible, o = Unusual)

Source area	Permeable pavements/sidewalk	Bioretention	Bioswales	Soakaways	Perforated pipe systems	Rainwater harvesting	Landscape alternatives	Prefabricated modules	Green roofs	Pollution prevention
Roof area	o	o	o	o	o	**	o	o	**	o
Pedestrian / landscaped / common areas	o	o	o	o	o	*	o	o	*	*
Parking / storage / loading and unloading areas	**	*	*	*	*	o	o	**	o	**

Institutional sites

LID options for institutional land use

Institutional sites include colleges, universities, long-term care homes and retirement homes. While site features can vary significantly, typical features include multiple-storey buildings, large parking areas that comprise a smaller percentage of overall area than commercial sites, flat roofs with internal drainage, and significant pedestrian and common areas for public interaction.

Some institutional sites, including university campuses, will include vast networks of buildings and interconnected pathways. Institutional sites typically have dedicated landscaping and/or operations and maintenance staff who can be trained to provide the required long-term maintenance.

Parking areas

Parking lots on institutional sites represent a significant source of stormwater pollutants. LID designers should target these areas to improve runoff quality and reduce runoff volumes. LID options suitable for parking lot runoff include bioretention areas within parking lot islands or along the parking lot perimeter, bioswales along the perimeter of the parking lot, and infiltration chambers buried underneath the parking lot or along adjacent green space. Consider modular units, especially as part of a treatment train with other LID practices.

Permeable pavement is another viable option for institutional parking lot retrofits. On sites with several parking lots, consider the feasibility of modifying operations for LID practices. A site partially retrofitted with permeable pavement will likely require two separate parking lot maintenance plans: one for the conventional asphalt and one for the permeable pavement.

Landscaped areas

Institutional sites present many opportunities for landscaped area retrofits. Often found along pedestrian pathways and adjacent to buildings, landscaped areas are ideal for establishing highly visible LID practices like bioretention areas or bioswales. Gardens and parking islands in close proximity to buildings can be converted to bioretention areas and/or irrigated via a rainwater harvesting system.

To reduce site maintenance costs on large properties, site owners should consider alternative landscaping to a high-maintenance lawn. No-mow or naturalized areas require minimal maintenance compared to mown grass areas and can greatly reduce site runoff by encouraging interception by tree canopies and evapotranspiration by green vegetation. Naturalized areas with cleanly mowed edges and colourful plant species can still give the impression of an orderly and attractive landscape.

LID options for large commercial sites
(** = Common, * = Possible, o = Unusual)

Source area	Permeable pavements/sidewalk	Bioretention	Bioswales	Soakaways	Perforated pipe systems	Rainwater harvesting	Landscape alternatives	Prefabricated modules	Green roofs	Pollution prevention
Roof area	o	o	o	o	o	**	o	o	*	o
Pedestrian / landscaped / common areas	**	**	*	*	*	o	o	**	o	*
Parking area	**	*	*	*	*	o	o	**	o	**

Go back to Screening LID Options

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

Natural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).

Tank used to store rainwater (typically roof runoff) for later use.

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

The natural features of the landscape, dictates flow patterns, runoff velocities and discharge rates.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

Ground depression acting as a flow control and water treatment structure, that is normally dry.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.

An underground water storage reservoir into which stormwater is directed and allowed to percolate into the underlying native subsoil.

An excavated area lined with geotextile filter cloth and filled with clean granular stone or other void forming material, that receives runoff and allow it to infiltrate into the native soil; can also be referred to as infiltration galleries, French drains, dry wells or soakaway pits.

Tank used to store rainwater (typically roof runoff) for later use.

The technique of removing pollutants from runoff as it infiltrates through the soil.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Stormwater management following the hierarchical approach: Source Control measures, Conveyance Control measure and End of Pipe treatment to achieve the water quality and water balance target for lot level development of the preferred strategy.

A combination of lot level, conveyance, and end-of-pipe stormwater management practices.

A mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

The interception, storage and eventual evaporation of rainfall from vegetation canopies.