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Frequently Asked Questions
Why not simply replace the curb?
Because it means opening the roof.
The curb is built into the roof covering.
Removing it exposes the building to weather.
It disturbs a warranted roofing system.
A roofing contractor joins a mechanical job.
That is the expensive part, not the unit.
What is the first question when replacing a unit?
What is underneath it.
Not which unit to buy.
Manufacturers change footprints between generations.
Like-for-like often does not fit its predecessor's curb.
Establish the curb before selecting.
It changes what is economic to choose.
What information does an adapter need?
Two sets, and both must be right.
The existing curb's dimensions and opening positions.
The new unit's curb drawing.
Measure the curb on the roof, not from drawings.
Drawings are frequently out of date.
That measurement is the whole risk.
What happens if a measurement is wrong?
The adapter arrives on a roof with a crane booked.
It does not fit and nothing can proceed.
Refabrication takes weeks.
The old unit may already be removed.
Measure twice, by two people.
Photograph the openings as well.
How does it affect the unit's height?
It raises it by the adapter's depth.
Weather termination heights change.
Step-over and service access change with it.
Duct connections inside may need extending.
Check clearances to anything above.
Confirm before ordering.
Does the adapter need insulating?
As well as the curb it sits on.
Otherwise it is the thermal weak point.
Condensation forms on its inner face.
That drips directly above the ceiling.
Insulation and sealing are specified together.
Do not treat it as a plain steel frame.
Can an adapter correct for slope?
Some can, and it is worth asking.
A tapered adapter levels a unit on a slope.
That avoids replacing a square curb.
It adds height on one side.
State the slope with the measurements.
It is a common requirement on older roofs.