Impervious Coverage in Finnish Single-Family House Plots
Potential of Low-Density Residential Areas in Stormwater Management and Creating Urban Green Spaces
Single-family house areas account for a significant percentage of the total square area of cities. Where statutory land use planning is concerned, single-family house areas and single-family house plots in Finland are usually addressed only in terms of housing, even though the impervious surfaces their construction creates also determine the cause of stormwater runoff and urban green spaces.
This study will explore the specification of impervious surfaces in the single-family plots of modern-day Finland. Impervious surfaces are a key factor in causing stormwater runoff and the deterioration in the condition of catchment area streams. At the same time, impervious surfaces seal the ground surface and prevent vegetation from growing at each site. The research subject involved three plots in a housing fair area and their garden plan (N = 63), which represent sites completed in the same area. Housing fairs present individual consumers with the ideal of single-family housing as proposed by commercial developers.
Permeable and impervious surfaces and their detailed breakdown into different surface types were measured in the plans. Although a considerable percentage of the impervious surface area in a modern-day Finnish plot is formed by garden surfaces, vehicle parking and various types of shelters and roofs also play a role in the formation of imperviousness. Used as a tool in statutory land use planning, plot density does not specify plot permeability, in which the roof square area is the primary factor. When defining the area of imperviousness, statutory land use planning could make use of the maximum allowable roof square area and/or the maximum allowable amount of impervious surface coverage as well as reduce the need for surfaced passageways by placing the parking space and residential building centrally within the plot. Setting guidelines for the amount of green space within a plot is more challenging, because the changing needs of residents significantly influence plot landscaping.