Inlet boxes are a critical part of any stormwater management system, ensuring that storm water and runoff are captured and directed safely into a drainage system. Whether installed in a roadway, intersection, or parking lot, these structures prevent surface area flooding and protect communities from costly water damage. Engineers often specify different types of inlet boxes depending on flow requirements and site conditions. Among the most common are Type 5 and Type 7 inlet boxes, each with unique applications in modern stormwater management systems.
What Is an Inlet Box?
An inlet box is a precast concrete structure designed to collect surface runoff and connect to underground drain pipes. Depending on site design, inlets can take the form of precast concrete curb inlets, precast concrete drop inlets, or precast drainage inlets. They are built with openings like a grate inlet, curb inlet, or box inlet that allows storm water to enter the system.
These inlets prevent debris from entering and clogging downstream storm drain basins or underground detention systems. Engineers may add curb inlet protection to reduce sediment buildup, and designs are often paired with catch basins, storm drain grates, and drainage grates for added flow capacity.
Type 5 Inlet Boxes
A Type 5 inlet box is typically a precast curb inlet with a curb inlet frame and grate. It is installed along roadway edges, where runoff flows along the curb before it enters the system through the inlet grate.
Why Engineers Specify Type 5
- Hydraulic flow: Ideal for capturing runoff moving in a single direction along the curb line.
- Safety: Reduces ponding on road surfaces that can cause hydroplaning or freezing hazards.
- Efficiency: Smaller footprint than a large storm drain box, making it cost-effective.
- Durability: Manufactured as precast inlets with options for bituminous coating and A LOK fittings for watertight drain pipe connections.
Use Cases for Type 5
- Residential streets where water follows the curb.
- Highways and arterials where frequent inlets are needed to manage continuous curbline flow.
- Urban developments where curbs define drainage paths.
Type 7 Inlet Boxes
A Type 7 inlet box is usually a larger grated inlet or combination inlet with a storm drain grate set directly in pavement. Instead of capturing flow only at the curb, it collects water across a wide drainage area.
Why Engineers Specify Type 7
- Capacity: Designed to manage higher volumes of water than Type 5.
- Coverage: Captures sheet flow across surface areas like intersections or parking lots.
- Safety: Minimizes ponding in areas where standing water can disrupt traffic or pedestrian movement.
- Flexibility: Can be integrated into precast concrete storm drain boxes, storm drain basins, or concrete catch basins.
Use Cases for Type 7
- Parking lots with large paved surface areas.
- Intersections, where sheet flow crosses multiple lanes.
- Industrial sites, where large paved yards require heavy-duty stormwater management systems.
Engineering Factors Behind the Choice
An engineer’s decision between Type 5 and Type 7 comes down to hydraulics, site layout, and compliance:
- Hydraulics: If calculations show concentrated curbline flow, Type 5 is chosen. For wide sheet flow across pavements, Type 7 is preferred.
- Safety: Type 7 inlets are often ADA compliant and bicycle safe, with larger openings that reduce ponding hazards.
- Maintenance: Type 7 inlets offer easier access points for maintenance and inspection compared to smaller Type 5 inlets.
- System Integration: Both types connect to catch basins, storm drain boxes, or stormwater detention systems that store runoff and slowly release it downstream.
Eagle’s Precast Advantage
At Eagle Concrete, inlet boxes are manufactured as precast concrete curb inlets, precast drainage inlets, and precast concrete storm drain boxes. As part of Prime Contractor Supply, Eagle holds PennDOT concrete certification, ensuring every unit meets state and municipal standards.
Key Benefits of Eagle’s Precast Inlets
- Custom and standard sizes: Available in standard DOT-approved designs or tailored dimensions for unique projects.
- Durability: Made from precast concrete with options for bituminous coating and chemical-resistant finishes.
- Flexibility: Compatible with A-Lok fittings, catch basin grates, and concrete catch basins.
- Compliance: Designed to meet ADA, municipal, and state standards.
- Efficiency: Precast manufacturing reduces field labor, speeds up installation, and ensures consistent quality.
Eagle also manufactures complementary structures, including precast concrete manholes, manhole risers, and catch basin risers, so contractors can source an entire drainage solution from one supplier.
Use in Stormwater Management Systems
Both Type 5 and Type 7 inlet boxes tie directly into larger stormwater management systems. These systems may include:
- Underground detention systems, where water is stored and slowly released to prevent downstream flooding.
- Storm drain basins and catch basins for drainage, which intercept runoff.
- Stormwater detention vaults connected with triple wall pipe or single wall corrugated pipe for long-term durability.
By combining inlets, storm drain basins, and catch basins, Eagle’s products form a comprehensive management system that keeps roads, parking lots, and communities safe.
Conclusion
Choosing the right inlet box type is about more than compliance — it’s about performance, safety, and long-term reliability. Type 5 inlet boxes excel along curb lines, where they efficiently capture concentrated flow, while Type 7 inlet boxes manage wide sheet flow across intersections, parking lots, and industrial sites.
Eagle Concrete delivers both options in precast concrete, certified through PennDOT concrete certification, and built for durability with protective coatings, strong materials like cast iron, and designs that prevent debris from entering the system. With precast concrete curb inlets, drop inlets, storm drain boxes, and full catch basin assemblies, Eagle provides the flexibility engineers need to design effective stormwater management systems that protect communities and infrastructure for decades.
For more details on Eagle’s inlet boxes or to request a quote, simply reach out through our email address or place an order — most products are ready within standard business days.