Impervious Area

Impervious area is the total surface on a site that rainwater cannot pass through. In Hektar it is calculated as the sum of three parts of your scheme: building footprint, roads, and parking.

Everything else on the site, such as lawns, planting, and permeable ground, is pervious and lets water infiltrate. Impervious area matters because it drives stormwater runoff, and many detaljplaner and municipal rules cap how much of a plot may be hard surface.

What Hektar counts

Hektar sums the hard surfaces your scheme places on the site:

• Building footprint: the ground-level area covered by the volumes you generate with the Building Tool.
• Roads: the internal streets and access you define with the site tools.
• Parking: the surface parking laid out with the Parking Tool.

Add these together and you have the impervious area for the scenario. Divide it by the plot area and you have impervious coverage, the percentage of the site that is hard surface.

Impervious area is not the same as building coverage

Building coverage (BYA) counts only the building footprint. Impervious area is wider, because it also includes the roads and parking around the buildings. A scheme can sit comfortably under a building coverage limit and still exceed an impervious coverage limit once streets and parking are added. Checking impervious area early is how you catch that before it forces a redesign.

Reading it in your project

Impervious area recalculates as you change the scheme, together with the other area metrics Hektar reports in the statistics panel. Increase parking or widen a road and it rises. Pull a building footprint in and it falls. Because it updates live, you can see how close a layout sits to a coverage cap while you are still exploring options, not after the layout is fixed.