The Roof Cut You Might Not Need
When an old rooftop unit comes off, it can be easy to assume the existing roof curb has to come off with it.
But replacing the entire curb can add another layer of work to an RTU replacement. Depending on the project, it may involve disturbing the roof membrane, coordinating roofing work, addressing flashing, and creating a new transition between the roof and the replacement equipment.
Sometimes that work is necessary.
Other times, a properly designed curb adapter can allow the existing curb to remain in place while creating the transition needed for the replacement RTU.
The key is knowing which approach fits the actual conditions on the roof.
This guide explains when a curb adapter is worth considering, when a new roof curb may be the better choice, and what information should be reviewed before making that decision.
Relax… It’s Curbco.
Figure 1: Curb adapter vs. full roof curb replacement. What each approach involves.
What Does a Curb Adapter Actually Do?
A curb adapter creates a transition between an existing roof curb and replacement rooftop equipment when the two are not directly compatible.
Depending on the application, the adapter may account for differences in:
- Equipment footprint
- Supply and return opening locations
- Curb dimensions
- Equipment support requirements
- Utility routing
- Transition geometry
When the existing curb and roofing conditions allow, an adapter can provide a way to install new equipment without replacing the entire existing curb.
That can mean less disruption at the roof and fewer modifications during the retrofit.
➡️ [Explore Curbco Custom Curb Adapters]
When a Full Roof Curb Replacement May Be the Better Choice
A curb adapter is not the right solution for every project.
There are situations where removing the existing curb and installing a new one should be evaluated.
1. The Existing Curb Is Damaged
If the existing curb shows significant corrosion, deterioration, structural damage, or other conditions that may compromise its ability to support the replacement equipment, installing an adapter on top of it may not address the underlying problem.
The existing curb condition should be evaluated before determining whether it can remain in service.
2. A Reroof Is Already Planned
If the building is already scheduled for a reroof or membrane replacement, the project may provide an opportunity to evaluate the existing curb at the same time.
Depending on the building and equipment requirements, installing a new curb as part of the roofing scope may make sense.
3. The New Equipment Requires Significant Changes
Some replacement RTUs differ substantially from the equipment they replace.
Changes in footprint, weight, airflow openings, or other equipment requirements may make a new curb more appropriate than adapting the existing one.
The right answer depends on the specific equipment combination and field conditions.
4. Project Requirements Call for a New Curb
Applicable codes, engineering requirements, specifications, roofing requirements, or other project conditions may require a new curb.
Those requirements should always be reviewed before deciding on an adapter-based solution.
When a Curb Adapter May Be the Better Fit
When the existing curb is structurally suitable, the roof is not scheduled for replacement, and the replacement equipment can be properly adapted to the existing conditions, a curb adapter may offer several advantages.
1. Less Roofing Work
A full curb replacement can require additional work around the roof opening, membrane, flashing, insulation, or surrounding roofing system.
When an adapter can reuse a suitable existing curb, some of that roofing work may be avoided.
That can simplify coordination and help keep the RTU replacement focused on the equipment transition.
2. A More Efficient Installation
Replacing a curb introduces additional demolition and reconstruction into the project.
An adapter-based installation can reduce that scope when the existing curb is suitable for reuse.
For schedule-sensitive projects, reducing unnecessary work can make installation planning easier.
3. Less Disturbance to the Existing Roof System
Removing an existing curb may require disturbing the roof membrane, flashing, and surrounding roofing system.
When an adapter can reuse a suitable existing curb, the project may require less roofing work.
Always confirm roof warranty requirements with the roofing manufacturer, roofing contractor, or warranty provider before modifying an existing roof system.
4. Reduced Building Disruption
Roof work can affect more than the crew working above the building.
Depending on the project, demolition and roofing work may introduce additional noise, access requirements, weather considerations, and coordination with building operations.
Reducing that scope can be especially valuable on occupied facilities.
Figure 2: Curb adapter or new roof curb? Key conditions to evaluate before choosing the right approach.
What Makes a Curb Adapter Solution Work?
A curb adapter is only as effective as the information used to design it.
Before an adapter goes into production, key conditions should be confirmed, including:
- Existing curb dimensions
- Curb height
- Roof pitch, where applicable
- Existing curb condition
- Replacement unit footprint
- Replacement unit weight and support requirements
- Supply and return opening locations
- Transition geometry
- Utility considerations
- Economizers, dampers, or other accessories that may affect the application
Good information upfront helps reduce assumptions during design and surprises during installation.
📐 Not sure your existing curb conditions are documented accurately? [Learn About Curbco’s Curb Measurement Service]
How Curbco Approaches Curb Adapter Design
Every retrofit starts with two realities: what is already on the roof and what the replacement equipment requires.
Curbco uses the project and equipment information provided to design custom curb adapters around the specific application rather than treating the transition as one-size-fits-all.
That includes considering the existing and replacement equipment configurations and the supply and return opening geometry provided for the project.
Contractors, distributors, and engineers can turn to Curbco for:
- [Custom Curb Adapters] designed around specific equipment combinations
- [Roof Curbs] when a new curb is appropriate for the project
- [Curb Measurement Service] when existing conditions need to be documented
- Project and equipment information review
- [FastPass] expedited production for qualifying time-sensitive projects
- [KurbHub] to simplify the quoting and project workflow
Our goal is not to push every project toward an adapter.
It is to help provide the right Curbco solution for the conditions you are working with.
Relax… It’s Curbco.
Not Sure Whether You Need a New Curb or an Adapter?
Start by gathering:
- Existing RTU manufacturer and model number
- Existing curb dimensions
- Photos of the curb and surrounding roof
- Replacement RTU manufacturer and model number
- Replacement equipment submittals
- Information about planned reroofing
- Relevant structural or project requirements
With the right information, the application can be reviewed before the installation reaches the roof.
📁 [Submit Your Drawings] so the Curbco team can review your project information.
Need help documenting the existing curb?
📐 [Learn About Curbco’s Curb Measurement Service]
Related Resources
Continue planning your retrofit with:
- [Curb Adapter vs. Roof Curb: What’s the Difference?]
- [Complete Guide to RTU Replacement Projects]
- [How Contractors Measure Existing Curbs Before RTU Replacement]
- [10 Common Rooftop HVAC Retrofit Mistakes and How to Avoid Them]
- [How to Avoid Costly Change Orders During RTU Replacement]
- [Understanding Static Pressure Changes During Rooftop Unit Retrofits]
Relax… It’s Curbco.
