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Aerial of the Oak Hills turf field and red running track
Athletic FacilitiesSouthwest OhioCincinnatiTOP-C purple wordmark logo for The Ohio Purchasing Council cooperative purchasing program

Oak Hills Multi-Sport Athletic Complex Construction 2022

Oak Hills High School in Cincinnati has a new lighted synthetic turf field lined for football, soccer and unified lacrosse, with four high-mast light poles, a scoreboard, an elevated press box, a 70-by-40-foot equipment building, team benches, fan bleachers and fencing. Prodigy delivered it design-build under one agreement with civil, architectural and structural engineering in house, from the conditional use submittal and stormwater plan through the drainage base, turf and underground power. The district bought it pre-bid through The Ohio Purchasing Council.

Oak Hills High School in Cincinnati needed a multi-sport field it could schedule — one surface that football, soccer and unified lacrosse could share, with lights, power, seating, a press box and a building to keep equipment in. The district bought the whole thing as design-build on a single agreement, pre-bid through The Ohio Purchasing Council: engineering, architecture, materials and installation from one party rather than a designer hired first and a builder bid against the drawings afterward.

Prodigy carried the civil, architectural and structural engineering in house. Civil covered the preliminary site plan and due diligence, the conditional use submittal, a partial location, topographic and utility survey, the stormwater pollution prevention plan, the detention as-built and easement plat, and construction staking. Architecture covered preliminary design and building elevations for the pole barn and press box, a code review and risk analysis, and the permit and construction documents. Structural provided the general notes and design stamps the Hamilton County permit process required for the barn, the press box and the light poles.

The built work starts underground. Existing dirt and spoils come out, the subgrade is graded and compacted to the site plan, HDPE perforated pipe is laid, a permeable geotextile liner goes over it, and #304 and #57 gravel is laid and compacted, all contained by a reinforced concrete curb poured around the turf. On top of that goes a synthetic turf system of at least 360 by 180 feet with permanent lines for all three sports. Around it sit four high-mast light poles on poured footers and bases with a Wi-Fi lighting control unit, a roughly 70 by 40 foot pole barn with two overhead and two man doors, an elevated press box about 10 by 8 feet with sliding windows and a scoreboard control desk, a scoreboard, fencing along the west and north boundaries, two team benches and two mobile fan bleacher sets. Power reaches all of it by underground boring from the school's existing electrical room.

Oak Hills stadium at dusk under the new field lighting
Aerial of the new Oak Hills turf football field with the school logo at midfield
Newly installed Oak Hills turf field with site work still underway
Oak Hills field and track alongside the school during construction
Press box and bleacher structure under construction at Oak Hills

Technical Discussion

The stone under the turf is the detention basin

A synthetic field is sold as a carpet. It is a drainage structure with a carpet on top, and on this project the civil design asked that structure to do a second job: hold stormwater, so the site would not need a separate detention basin.

Section through the Oak Hills synthetic turf field: turf carpet over open-graded #57 stone with about 40 percent voids, dense-graded #304 stone with perforated HDPE pipe, a permeable geotextile and compacted subgrade, contained by a reinforced concrete curb. A one-inch rain on the 64,800 square foot field is 5,400 cubic feet, a little over 40,000 gallons.
Figure 1 — The voids in the stone base hold the storm, and the pipe releases it slowly.

How much water a field collects

The turf is a minimum of 360 feet by 180 feet, which is 64,800 square feet, or about one and a half acres that shed nothing sideways. One inch of rain on that area is 5,400 cubic feet of water, a little over 40,000 gallons. Natural grass absorbed some of it and released the rest slowly. A turf system passes all of it straight down, within minutes, so something below has to slow it before it reaches the storm sewer. That is what detention means, and new impervious area is what triggers the county's requirement for it.

Open-graded stone is mostly air

The base under the carpet is two stones doing two jobs. The #304 is dense-graded: it compacts tight and holds the shape and grade of the field. The #57 is open-graded, clean stone about an inch across, and roughly 40 percent of its volume is void. Every inch of #57 can therefore hold about 0.4 inch of rain, and a one-inch storm fits inside 2.5 inches of it. Perforated HDPE pipe at the bottom collects the water and lets it out at a controlled rate, and a permeable geotextile keeps soil fines from migrating up and filling the voids. A reinforced concrete curb around the perimeter contains the whole section like the wall of a shallow tank.

Why the order of work matters

Compaction of the subgrade comes before any of it, because a soft spot under the stone becomes a low spot in the carpet three seasons later. The four light pole foundations were poured in the same operation as the base for the same reason: they are the only other elements that pass down through the drainage layer, and cutting them in afterward means cutting the tank.

Using the stone as detention kept a basin off the site and kept that land usable. When you plan a turf field, ask the civil engineer early whether the base can carry the detention volume, because the answer changes how deep the stone is and whether you lose ground somewhere else.

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