Concrete parking lot building in Sherwood OR - a lot that stays flat and drains

A national trade group's guide sets the thickness by the lot's regular traffic, with thinner slabs for passenger cars and light trucks and thicker ones for heavier commercial and industrial trucks. Its lighter tiers allow an occasional heavier truck, so plan for what parks there every week, not the rare visit. The same guide says lots for heavy industrial trucks should be designed one project at a time.

Start by working out how many vehicles will use the lot and how that number may grow, because one industry group recommends the owner supply those loads so a civil engineer can set the concrete strength, joints and drainage. The same group has a geotechnical engineer, a soils specialist, recommend the thickness from how well your ground supports it, so plan on both. Leave some room in the schedule too, since one trade guide calls for pouring only on ground that isn't frozen and a cold snap can push the date.

Make the ground under the slab even all the way across, with no sudden changes from hard to soft, because a concrete slab spreads its weight so widely it puts very little pressure on the ground. National industry guidance says site work that makes the upper ground uniform matters more than making it extra firm. That's where our crew puts its effort, getting the subgrade, the ground the slab sits on, even from one end of the lot to the other.

The stormwater side runs through the Site Development Permit process of Clean Water Services, the agency whose stormwater standards cover Sherwood, which reviews storm sewer, water quality facilities and erosion control on sites larger than one acre, and sites one acre or larger also need a DEQ 1200-C/CN permit. The agency has proposed new standards for applications accepted on or after November 1, 2026, so when yours is filed may decide which rules apply. For zoning and other permit questions, the state sends you to the local building department first, and we'll go over all of it at the estimate and agree on who applies before work starts.

Yes, in general. The state's Construction Contractors Board says Oregon law generally requires anyone paid for construction that improves real property to be licensed, so ask any contractor bidding your lot about theirs. One trade group's specification also has the paving contractor tell the owner in writing before the pour if any pre-job site checklist item isn't met, and that's a fair thing to ask about too.

The cost comes down to the lot's size, how thick the slab has to be for your traffic, how much digging and grading it takes to even out the ground, and what the drainage and stormwater work involves. The big swings usually come from what's underneath, which is why I walk the lot before putting anything on paper, and the written scope lists each step so you can see what you're paying for. Longer term, an older industry guide notes concrete has fairly simple upkeep and isn't much bothered by oil and fuel drips, which is worth weighing when you compare paving types.