Curbs vs Dunnage

[zeppy]

what is the difference between curbs and dunnage relating to a rooftop unit - is there a distinction between these terms




is one moreso used for spit systems vs those systems that are not split systems?

[btuhack]

Curbs are permenent/fixed in place package unit supports, factory or field fabricated, that are properly flashed, sealed, and secured to roof structure to support said unit. A curb could support a downflow package or a split with a structural curb cap.

Dunnage is scrap wood used temoparily to support and/or elevate something during the building process, ie: during a crane lift, etc.

Sleepers are rooftop structural devices used to spread the weight load over a larger existing structural area. Sleepers can be integrated into the roof membrane and capped, or bare and simply lagged into the structure. Side discharge package app or common for rooftop condenser apps.

[zeppy]

is dunnage used to support an rooftop a/c (say 5 ton unit)?


looks like railroad ties that have flashing draped over them and then the compressor unit is bolted to the flashed wooden beams.

[bradgill]

We can use treated (but cured) 4x4 here a code compliant support. In many cases they prefer it because we can get them 12 foot or ten foot even, real important for underbuilt roof trusses. The engineering can prove certain PSF loads, fact is in reality the live load information isn't usually properly understood. A vibrating peice of refrigeration or hvac equipment is a live load. Roof curbs are always preferred for new construction, unfortunately they dont provive displacement area support, but fortunately they are rather well aceepted and seal up plus look way better.
Some commercial curbs for replacement have to be made, all pitched roof curbs are always custome made with 20 G plus sheet metal or even some as nice as stainless steel welded. Insteresting all the ways I have seen things supported flashed or sealed.

[btuhack]

is dunnage used to support an rooftop a/c (say 5 ton unit)?


looks like railroad ties that have flashing draped over them and then the compressor unit is bolted to the flashed wooden beams.

You are describing sleepers.

[bradgill]

nothing like rubber slippers