hey a little help would be appreciated

i got a call today from a big client,they asked me if i could install a curb around a 24by 24 exhaust vent.i have never heard of a curb and ive been in buisiness for 13 years.this is on a flat roof.my guess is that they want me to in install the whole vent from the roof because it is a flat roof.but i thought he was talking about like a rain diverter but you dont need that on a flat roof!

Lanny - you brought up another issue. Your explanation covered a roof ventilator whereby the base incorporates a flange that overlaps the curb. However, centrifugal fans anchored to the roof creates a whole host of problems. We would isolate these fans by installing a wooden platform over a curb, and waterproof same w/ suitable roofings. Thus, in the event of leakage in that area, examination would be basically limited to 4 mounting screws. Oftimes, pitch pans are used, which IMHO are a pain in the arse.

You mentioned it was an exhaust vent. Even more important - how hot is it. If it is a flue of some sort, the curb should be isolated from touching it. It may be necessary to contact clients insurance company, if they require class "A" or "B' construction. These vents also require counter flashings, which are just as important as the curbs.

No offense intended, but, Holy Moly..... 13 years and never heard of a curb? Then it seems doubtful that you would know how to tie one in either. Do the client a favor and decline.

This may be helpful http://www.roofcurb.com/