Additional pad under pedestals?

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Author Message David G. Axt, CDT, CCS, CSI, SCIP Senior Member Username: david_axt Post Number: 2018 Registered: 03-2002 Posted on Friday, May 12, 2023 - 05:34 pm:    In my specifications I specified an additional neoprene pad under the pedestals. On top of the pedestals are 2'x2' concrete pavers. The pedestals are on a single-ply membrane roofing and the pavers only get light foot traffic (ammenity roof deck). The contractor wants to eliminate this additional pad in lieu of the manufacturer's "buffer pad" that is basically just a solid piece of plastic end cap. I told the architect to not eliminate the additional buffer pad. David G. Axt, CDT, CCS, CSI, SCIP Specifications Consultant Axt Consulting LLC Ron Beard Senior Member Username: rm_beard_ccs Post Number: 491 Registered: 10-2002 Posted on Saturday, May 13, 2023 - 03:41 pm:    The pedestals are an extension of the “structural” system and structural systems do not like spongy components. It is suggested that the pedestal manufacturer’s recommendations be followed. What is the lifetime of the of the neoprene pad (“buffer pad”)? Is it the same, or longer, then the pedestal? Typically, membrane roofs under a pedestal system are a fully-adhered sheet membrane applied over a coverboard, over rigid thermal insulation with a nominal 24-psi compressive strength. Depending on the traffic loading, the compressive strength of the insulation may need to be increased; 40-psi, 60-psi, or even 100-psi if used under very large potted trees placed on the pavers. Often food service equipment, ie, ice machines, etc. are placed on the paver system over the years without the Architects knowledge. It makes sense to stay the mfr’s recommendation. "Fast is good, but accurate is better." .............Wyatt Earp Ronald J. Ray, RA, CCS, CCCA, CSI, SCIP Senior Member Username: rjray Post Number: 220 Registered: 04-2004 Posted on Tuesday, May 16, 2023 - 10:17 am:    What is the logic, or science, of the need for the "additional buffer pad"? Is there testing to verify any advantages? Is this a "it seems like a good idea" approach without any research or evidence that it is needed or provides any benefit? David G. Axt, CDT, CCS, CSI, SCIP Senior Member Username: david_axt Post Number: 2020 Registered: 03-2002 Posted on Tuesday, May 16, 2023 - 10:43 am:    I think this requirement came from the acoustical engineer where he was concerned about transmission of noise. David G. Axt, CDT, CCS, CSI, SCIP Specifications Consultant Axt Consulting LLC ken hercenberg Senior Member Username: khercenberg Post Number: 1569 Registered: 12-2006 Posted on Tuesday, May 16, 2023 - 10:44 am:    I've often seen a second layer of single-ply membrane, either sheet or "pads", laid on top of the primary membrane as a protection course when placing pavers and pedestals and am not aware of ever having a problem with it. I prefer using the same type of membrane as the protection course. I have seen others use neoprene pads at each pedestal, again without ever hearing about problems. I am curious as to what thickness pad you specify. ken hercenberg Senior Member Username: khercenberg Post Number: 1570 Registered: 12-2006 Posted on Tuesday, May 16, 2023 - 10:46 am:    If acoustics is the issue, why not place high density XPS on top of the membrane as both protection course and noise isolation? It shouldn't take much thickness. Greta Eckhardt (Unregistered Guest) Unregistered guest Posted on Tuesday, May 16, 2023 - 11:01 am:    I would have thought that the purpose of the neoprene pads was to protect the single-ply membrane from being torn by concentrated stress at the edges of the pedestal feet. If the manufacturer recommends something different in accordance with roof system warranty requirements, it seems to make sense to follow their recommendation, since it is in their interest to protect the membrane from tearing. Ron Beard Senior Member Username: rm_beard_ccs Post Number: 492 Registered: 10-2002 Posted on Tuesday, May 16, 2023 - 04:10 pm:    "transmission of noise"? The whole assembly is sitting on a R-40 (+/-) of foam insulation. Acoustical vibrations should be the least of the system's issues. "Fast is good, but accurate is better." .............Wyatt Earp Ronald J. Ray, RA, CCS, CCCA, CSI, SCIP Senior Member Username: rjray Post Number: 221 Registered: 04-2004 Posted on Wednesday, May 17, 2023 - 12:03 pm:    Over the decades, I have learned that not everything recommended by acoustical, envelope, and sustainability consultants makes sense, or works. Since they make recommendations, I try to weed out those recommendations that fall into the "really?" category. John Bunzick Senior Member Username: bunzick Post Number: 1914 Registered: 03-2002 Posted on Wednesday, May 17, 2023 - 05:04 pm:    I'm going to guess the noise concern was of impact of footfalls, not ambient exterior noise. In the small office area I work in, there is an insulated flat roof (no deck). When maintenance staff is on the roof, you definitely hear them clomping around. I'm not sure how much help neoprene pads may be. Steven Bruneel, Retired Architect Senior Member Username: redseca2 Post Number: 716 Registered: 12-2006 Posted on Wednesday, May 17, 2023 - 07:38 pm:    Most of my work has been in seismically active west coast locations. I look at neoprene pads or other items placed between the roof membrane and the pedestal system as defenses against damage to the roof membrane caused by abrupt lateral movement - what you get in an earthquake. The analogy would be a table with a table cloth on it (roof membrane) and a heavy vase full of water and flowers (pedestal system) sitting on it. Yank the table back and forth (earthquake) and the table cloth will get pulled, stretched and bunch up to one side of the vase. Put a saucer or piece of glass under the vase (neoprene pad) and the vase moves against the saucer, not the table cloth. David G. Axt, CDT, CCS, CSI, SCIP Senior Member Username: david_axt Post Number: 2021 Registered: 03-2002 Posted on Wednesday, May 17, 2023 - 07:52 pm:    Thanks for the responses! I checked with the acoustical engineer and he said that he did not recommend a neoprene pad under the pedestal. David G. Axt, CDT, CCS, CSI, SCIP Specifications Consultant Axt Consulting LLC