Question 1

What causes drainage problems in parking lots?

Accepted Answer

Insufficient slope (under 1%), clogged/undersized catch basins, and pavement settling. Poor drainage is the #1 cause of premature failure, cutting lifespan from 20 to 12 years.

Question 2

How much does a parking lot drainage system cost?

Accepted Answer

Catch basins + pipes: $2.50–$5.00/sq ft. French drains: $4.00–$8.00/sq ft. Permeable pavement: $8.00–$15.00/sq ft. Complete system for 50,000 sq ft: $40,000–$120,000.

Question 3

What is the minimum slope for a parking lot?

Accepted Answer

1% minimum (1 foot per 100 feet). 1.5–2% recommended. ADA spaces: maximum 2% in all directions. Slopes over 5% require energy dissipation at discharge.

Question 4

Does permeable pavement work for parking lots?

Accepted Answer

Yes — reduces runoff 85–95%. Costs $8.00–$15.00/sq ft but can eliminate $50,000–$200,000 in detention pond costs. Requires quarterly vacuum sweeping.

Parking Lot Drainage Solutions