When selecting the right rooftop curb for a new or replacement Rooftop Unit (RTU), you’re faced with a wide range of options. Each curb design exists for a specific purpose—structural, airflow, vibration control, wind resistance, or roof compatibility. Here is a concise breakdown of the most common curb types and what sets each one apart.
Knockdown Curbs
- Ship unassembled
- Easy to store and transport
- Lowest-cost curb option
- Assembles quickly in the field using basic tools
- Ideal for contractors who keep inventory on hand
Welded Curbs
- Ship fully assembled for faster installation
- Factory-set squareness, supports, and deck pans
- Higher freight cost due to volume
- Often requires a crane for rooftop placement
- Saves time at the job site
Adjustable Pitch Curbs
- Designed to compensate for up to 1″ of pitch per 12″ in any direction
- Ships knockdown for easier transport
- More economical than fixed-pitch welded curbs
- Provides flexibility when exact roof pitch isn’t known until arrival
Platform Curbs
- Features insulated metal cladding and a full wood nailer
- Designed to support horizontal rooftop units, split condensers, and similar equipment
- Can be roofed-in or anchored directly to a slab
Horizontal Curbs
- Accepts a standard down-discharge RTU
- Redirects airflow out of side or end openings
- Converts downward airflow into a horizontal configuration
- Ideal for retrofit projects where duct orientation changes
Structurally Calculated (Seismic) Curbs
- Required when jobs call for structural integrity under seismic conditions
- Engineered and stamped by a Professional Engineer (PE)
- Typically based on IBC and California building codes
- Designed to maintain structural performance and safety after seismic events
Vibration Isolation Curbs
- Equipped with heavy-duty steel spring isolators
- Standard deflection: 2 inches
- Reduces noise and vibration transfer into the building structure
- Used for packaged or mechanical equipment mounted on roofs
Wind Curbs
- Engineered for high-wind or hurricane-prone regions
- Securely anchors the RTU to the curb
- PE-stamped
- Requires specific field anchoring procedure
- Originally grew in popularity after Hurricane Andrew due to updated safety requirements
Metal Roof Curbs
- Designed specifically for ribbed metal roof panels
- Always built with roof pitch incorporated
- Usually installed without a full perimeter wood nailer
- Requires additional sealing due to exposed construction
- Provides proper alignment and watertight integration with metal roofing profiles
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