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Frequently Asked Questions
What is the junction actually doing?
Three jobs at once.
Carrying the load into the structure.
Keeping water out of the building.
Giving the unit a level base at the right height.
Failure shows as a leak, not a breakage.
It is discovered inside, later.
Why is a curb built to a specific unit?
Its footprint and duct openings must match.
Supply and return penetrations align with the base.
A generic frame does not seal to them.
Manufacturers publish curb drawings per model.
Supply the make and model when ordering.
A curb is not a stock item in that sense.
Why not replace the curb when replacing the unit?
Because the roof around it would be opened.
That is the expensive and risky part of the job.
It exposes the building to weather.
Roof warranties are affected.
An adapter fits the new unit to the old curb.
It is almost always the better route.
What about equipment with no roof opening?
It needs support, not a curb.
Condensers, pipework and cable trays qualify.
Rails and supports spread load without penetrating.
Some sit on the membrane with pads.
Others fix to structure through detailed penetrations.
Choose from whether the roof may be pierced.
How does roof slope affect the curb?
The unit must sit level on a sloping roof.
That requires a tapered curb.
Height differs on each side as a result.
Slope must be stated when ordering.
A square curb on a slope drains wrongly.
It also stresses the unit's base.
What decides curb height?
How the roofing membrane terminates.
The covering turns up the curb side.
It must finish above the water line.
Insulation thickness raises that line.
Roofing systems differ in requirement.
Confirm with the roofing contractor.
Who should be consulted before fixing to a roof?
Whoever holds the roof warranty.
Penetrations and attachments can void it.
Approved details usually exist.
Retrofitting an unapproved fixing is costly.
Structural capacity needs checking too.
Do both before anything is ordered.