What Is an Adjustable Pitch Roof Curb?
An adjustable pitch roof curb is a variation of a knockdown curb designed to compensate for a roof pitch of up to 1 inch per 12 inches in any direction. This flexibility makes it an ideal choice when:
- The roof pitch is unknown or difficult to measure precisely.
- Multiple roof slopes exist on the same building.
- Rooftop units are installed in different orientations.
Instead of ordering a fixed-pitch curb for each slope, adjustable pitch curbs can be leveled on-site — saving time, cost, and confusion.
Why Roof Pitch Matters
Even a slight roof slope affects how rooftop HVAC units operate. Ignoring pitch can lead to performance issues, safety hazards, and long-term damage.
1. Uneven Weight Distribution
A rooftop unit sitting on a steep pitch places uneven stress on the curb. This imbalance can cause the curb to buckle, especially under heavy loads or strong wind conditions. Improper leveling increases the risk of tipping, which could result in equipment damage, injury, or even collapse.
2. Excess Vibration
Motors and compressors are designed to run level. When tilted, they generate excess vibration, which can:
- Loosen tubing connections, causing refrigerant leaks.
- Increase wear on bearings and fans.
- Create unnecessary noise and shorten equipment life.
3. Compressor Oil Problems
Like a car engine, a compressor relies on oil for lubrication. If the unit isn’t level, oil may pool on one side, starving parts of lubrication and causing overheating or damage. Over time, oil can separate from the refrigerant and coat the inside of coils — reducing heat transfer and overall efficiency.
How Adjustable Pitch Curbs Work
Unlike fixed-pitch curbs, which are manufactured for one specific slope and direction, adjustable pitch curbs feature two interlocking assemblies:
- Bottom Assembly – Mounted directly to the roof and follows its slope.
- Top Assembly – Slides over the bottom like a sleeve and can be leveled independently.
Once leveled, the top section is secured in place using Tek Screws, locking the curb’s angle and creating a stable, level platform for the HVAC unit.
Installation Overview
MicroMetl adjustable pitch curbs are shipped knockdown-style (disassembled) in a single compact package with all required hardware.
Assembly Steps:
- Assemble the Curb – Connect sides and ends with sheet metal screws using the pre-punched, embossed holes.
- Square the Frame – Measure diagonally corner-to-corner to ensure equal distances.
- Level the Top Assembly – Slide the top over the bottom and raise the downhill end until level.
- Secure in Place – Fasten Tek Screws around the entire perimeter to lock the top assembly.
- Install Duct Supports and Gasket – Prepare for rooftop unit placement.
Height Guidelines
There’s no maximum height for adjustable pitch curbs, but there is a minimum height requirement based on roof slope.
Formula:
Minimum Height = (Longest Curb Dimension ÷ 12) + 1″ overlap + 1″ clearance (for duct supports)
Example:
For a 70″ x 40″ curb:
70 ÷ 12 = 5.83″
+1″ overlap = 6.83″
+1″ clearance = 7.83″ minimum height (rounded to 8″).
Taller curbs can always be ordered to meet specific job requirements.
When to Use Adjustable Pitch Curbs
Adjustable pitch curbs are ideal when:
- Roof slopes vary slightly across different sections.
- Rooftop units face multiple directions.
- Pitch or orientation details are unknown at the time of order.
They allow one product type to fit multiple conditions, eliminating the need for several fixed-pitch curb variations.
Benefits at a Glance
- Eliminates guesswork for roof slope and unit orientation.
- Reduces custom ordering costs.
- Provides a level, secure platform for rooftop units.
- Simplifies installation and inventory.
- Available in most small-to-medium curb sizes.
Conclusion
Adjustable pitch roof curbs are a practical, cost-effective solution for variable roof slopes. They ensure safety, improve equipment performance, and simplify installation by removing the need for custom-sized, fixed-pitch curbs.
MicroMetl’s adjustable pitch curbs are engineered for flexibility and reliability — giving contractors and installers peace of mind on every project.
For a simpler introduction, see our article:
[What Is an Adjustable Pitched Curb? – Basic Overview]
