Roof Framing for Future Roof Top Units
Roof Framing for Future Roof Top Units
(OP)
Hello,
I am designing a retail center with leasing spaces. Future tenants will install their own RTUs and ductwork.
Does anyone know how to approach the roof framing design? I don't want to be overly conservative and design specify add'l point load on each joist.
Any idea?
Thanks.
"Be nice to people on your way up because you might meet them on your way down"
I am designing a retail center with leasing spaces. Future tenants will install their own RTUs and ductwork.
Does anyone know how to approach the roof framing design? I don't want to be overly conservative and design specify add'l point load on each joist.
Any idea?
Thanks.
"Be nice to people on your way up because you might meet them on your way down"






RE: Roof Framing for Future Roof Top Units
I would not worry about designing each joist to carry the units via a point load at the middle.
Mike McCann
MMC Engineering
RE: Roof Framing for Future Roof Top Units
I was thinking of using 3' to 4' joist spacing and show typical details of RTU support when the weight exceeds 600#.
Thanks.
RE: Roof Framing for Future Roof Top Units
Regarding "...and show typical details of RTU support when the weight exceeds 600#." If you present it that way make sure to give the upper limit lest someone in the future goes crazy with it and then tries to hold you accountable for it.
RE: Roof Framing for Future Roof Top Units
RE: Roof Framing for Future Roof Top Units
I often go with 6'-8' also with typical Vulcraft Joists when locations of RTU's are defined and I transfer loads to joists/beams accordingly.
On this particular project, we are designing the building shells (up to 8 buildings with approx 12,00 sq.ft each), with slab leave-outs for future tenants to finish their own plumbing, HVAC and stuff. A tenant may want to lease 8,000 sq.ft in one building in which I'd anticipate up to 4 RTU's minimum based on past projects. So the RTU locations are unpredictable.
have anyone heard of constant shear design for this type of application? I know one of my old boss (12years ago) used that expression a lot.
Thanks.
RE: Roof Framing for Future Roof Top Units
RE: Roof Framing for Future Roof Top Units
RE: Roof Framing for Future Roof Top Units
RE: Roof Framing for Future Roof Top Units
RE: Roof Framing for Future Roof Top Units
I think using KCS joists is a reasonable approach.
Adding 10psf live with closely spaced joists to allow the RTU to span over 3-4 joists also seem reasonable to me.
If I were to chose between KCS joists @ 6'-8' on center VS 30psf live load with joists closely spaces @ 3'-0" on center, I think I will go with the KCS.
RE: Roof Framing for Future Roof Top Units
The joist designation would look like 20K 175/100 SP. The 175 would represent you dead + live, the 100 would represent your live / snow. Then direct them on how you want to handle the point loads.
RE: Roof Framing for Future Roof Top Units
RE: Roof Framing for Future Roof Top Units
And in a lot of cases the unit weighs less than the 100 psf and so only minimal reinforcing was required (Some angles or channels to support the unit curb.)