RTU on Sleepers on Polyiso
RTU on Sleepers on Polyiso
(OP)
I have 2800lb chiller that an owner wants to put on a roof (i-beams and metal deck)
As we are going to be installing the unit near a bearing wall, the roof structure has plenty of capacity to carry the weight.
The roof is metal deck w/ 5" polyiso and a membrane. The owner does not want to penetrate the membrane for support legs.
I proposed to lay down double 2x12 flatwise over the beams that carry 6x6 pt beams perpendicular that support the unit.
The 2x12's are intended to distribute the load over polyiso. Based on their surface area, I get a bearing pressure of less than 4 psi. The polyiso is reportedly has a 20 psi rating which, is my understanding, the load that will cause 10% deformation in the foam. Assuming a linear relationship, my load would cause 2% deformation or 1/10"
Does this sound like reasonable approach?
Thanks
As we are going to be installing the unit near a bearing wall, the roof structure has plenty of capacity to carry the weight.
The roof is metal deck w/ 5" polyiso and a membrane. The owner does not want to penetrate the membrane for support legs.
I proposed to lay down double 2x12 flatwise over the beams that carry 6x6 pt beams perpendicular that support the unit.
The 2x12's are intended to distribute the load over polyiso. Based on their surface area, I get a bearing pressure of less than 4 psi. The polyiso is reportedly has a 20 psi rating which, is my understanding, the load that will cause 10% deformation in the foam. Assuming a linear relationship, my load would cause 2% deformation or 1/10"
Does this sound like reasonable approach?
Thanks






RE: RTU on Sleepers on Polyiso
I would also check wind load trying to tip the thing over.
DaveAtkins
RE: RTU on Sleepers on Polyiso
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: RTU on Sleepers on Polyiso
Not enough wind or seismic to slide or tip the unit.
RE: RTU on Sleepers on Polyiso
When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.
-R. Buckminster Fuller
RE: RTU on Sleepers on Polyiso
RE: RTU on Sleepers on Polyiso
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: RTU on Sleepers on Polyiso
Mike McCann, PE, SE (WA)
RE: RTU on Sleepers on Polyiso
ASCE 7-10 section 13.4 prohibits using friction from gravity loads to resist seismic loads on non-structural components.
RE: RTU on Sleepers on Polyiso
@WannabeSE - Thanks for the info. I have refrigerant lines and electrical conduit anchoring it :> Seriously, we are in a low seismic area and even if it moves a little, it should not be a problem.