Civil Engineering · Engineering Glossary
An impervious surface is any paved or covered ground surface — roofs, parking lots, roads, sidewalks — that prevents rainfall from infiltrating into the soil, causing it to run off as stormwater instead. The percentage of impervious surface on a site drives stormwater volume, peak flow rates, and water quality requirements.
Replacing natural land cover with impervious surfaces is one of the primary causes of increased stormwater runoff from development. Municipal stormwater programs and development ordinances typically regulate the maximum impervious cover allowed, require stormwater management for any increase in impervious area, and may charge stormwater utility fees based on impervious area. Civil engineers calculate the pre-development and post-development impervious percentages as part of the stormwater management analysis. Low Impact Development (LID) approaches — bioretention, permeable pavement, green roofs — reduce effective impervious cover by allowing infiltration. Apex Grid accounts for impervious surface calculations in all civil site development projects.
Apex Grid Engineering maintains this glossary as a resource for architects, contractors, developers, and property owners who encounter unfamiliar engineering terminology on their projects.
View All Engineering TermsApex Grid's licensed PEs provide civil engineering services across multiple jurisdictions — with fast quote turnaround and permit-ready documents.
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