WCEL > Issues > Urban Growth and Development > Smart Bylaws Guide > Part 6 > Use Site Resources Wisely > Site Coverage & Impermeability

Smart Bylaws Guide – Use Site Resources Wisely – Site Coverage & Impermeability

Zoning and subdivision standards can establish the amount of impervious (non porous) areas allowed on individual lots.  This ensures that a certain amount of rainfall is returned to hydrological paths through the soil to recharge aquifers and streams.   As imperviousness increases, the amount of rainwater that returns to the soil, aquifers and creeks decreases.  Several municipalities are distinguishing between total imperviousness (amount of site coverage) and effective imperviousness (the effect of the site coverage where measures are taken to return rainwater from the site into the soil on the site).  Adequately sized houses on smaller lots, although having more total imperviousness, may have less effective imperviousness if, for example, rain leaders are directed to drain in the front yard or a rock pit, and paving materials are porous.

In single family smart growth neighbourhoods site coverage is generally 50 percent, with an allowance for an increase to 60 percent if a detached secondary suite or coach house is built. In multifamily smart growth neighbourhoods site coverage is generally 50 to 100 percent of a lot. Even with these figures for site coverage effective imperviousness can be significantly less if rainwater from the buildings and paved areas is infiltrated into the uncovered areas of the site.

Examples of Site Coverage Standards Include:

1. The maximum site coverage for buildings shall be 50 percent of the site area.

2. For the purpose of this section, site coverage for buildings shall be based on the projected area of the outside of the outermost walls of all buildings and includes carports, but excludes steps, eaves, balconies and sundecks.

3. Except where the principal use of the site is a parking area, the maximum site coverage for any portion of the site used as parking area shall be 20 percent.

4. Except for multiple dwellings, the area of impermeable materials, including building coverage, shall not exceed 60 percent of the total site area.

5. For the purposes of section 4 of this Schedule, the following materials shall be considered impermeable: the projected area of the outside of the outermost walls of all buildings including carports, garages, accessory buildings, covered porches and entries; asphalt; concrete; brick; stone; and wood.

6. Notwithstanding section 5 of this Schedule, gravel, river rock less than 5 cm in size, wood chips, bark mulch, sand set pavers and other materials which, in the opinion of the Director of Planning, have fully permeable characteristics when in place installed on grade with no associated layer of impermeable material (such as plastic sheeting) that would impede the movement of water directly into the soil below, are excluded from the area of impermeable materials.

7. The effective imperviousness of the site shall not exceed 10 percent.

Or

1. All portions of the lot not covered by buildings, structures, and non-porous or paved surfaces shall be landscaped. This landscaping shall be maintained. 

2. Non-porous or paved surfaces, including a driveway, shall not cover more than 30% of the lot area that is not occupied by the principal and accessory buildings or structures. 

3. At least 50% of the area of the required front yard shall be landscaped, which shall not include any non-porous or paved surfaces, provided that the amount of the required landscaped area may be reduced to a minimum of 30% of the front yard for a pie-shaped lot.

Vancouver’s RS-7S Zoning pp.6-7
Zoning and Development By-law 1 January 2001 – Amended to July 6, 2004

4.8 Site Coverage and Impermeability

4.8.1 The maximum site coverage for buildings shall be 40 percent of the site area.

4.8.2 For the purpose of this section, site coverage for buildings shall be based on the projected area of the outside of the outermost walls of all buildings and includes carports, but excludes steps, eaves, balconies and sundecks.

4.8.3 Except where the principal use of the site is a parking area, the maximum site coverage for any portion of the site used as parking area shall be 30 percent.

4.8.4 Except for multiple dwellings, the area of impermeable materials, including building coverage, shall not exceed 60 percent of the total site area except that where developed secondary vehicular access to a site is not available, the Director of Planning may exclude from the area of impermeable materials an amount not exceeding:

(a) for the first parking space, the product of the distance, in metres as measured along the driveway centre line, from the point where the driveway crosses the property boundary to the point where it meets the nearest side of the approvable parking space times 3.1 m; and

(b) for each additional parking space, 67 m² to accommodate vehicular access and manoeuvring.

4.8.5 For the purposes of section 4.8.4 of this Schedule, the following materials shall be considered impermeable: the projected area of the outside of the outermost walls of all buildings including carports, garages, accessory buildings, covered porches and entries; asphalt; concrete; brick; stone; and wood.

4.8.6 Notwithstanding section 4.8.5 of this Schedule, gravel, river rock less than 5 cm in size, wood chips, bark mulch, and other materials which, in the opinion of the Director of Planning, have fully permeable characteristics when in place installed on grade with no associated layer of impermeable material (such as plastic sheeting) that would impede the movement of water directly into the soil below, are excluded from the area of impermeable materials.

The District of Metchosin's Bylaw for the Protection and Management of Rain Water sets explicit limits on maximum effective impervious area (see section 3.5).

The City of Port Coquitlam's Zoning Bylaw, at section 519, uses the local government jurisdiction over drainage and impervious areas to establish a requirement for a green roof on large (>5000 sq. m.) commercial and industrial use buildings.