Small rooftop mini split / condenser anchorage

[phillier937]

Can someone help me find a code reference (if any) that says these have to be anchored to the roof or is setting them on blocks OK?

 

[north star]

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phillier937,

What does the manufacturer' installation instructions require ?
Using fasteners to penetrate the roofing membrane \ assembly would
not be a good idea or best practice..........That said, are there any
wind loads in the applicable area ?

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[ICE]

2020 California Mechanical Code
Based on 2018 Uniform Mechanical Code
I am not familiar with Ohio mechanical code.

303.4 Anchorage of Appliances.
Appliances designed to be fixed in position shall be securely fastened in place in accordance with the manufacturer’s installation instructions. Supports for appliances shall be designed and constructed to sustain vertical and horizontal loads within the stress limitations specified in the building code.

303.8.3 Installation of Appliances on Roofs.
Appliances shall be installed in accordance with the manufacturer’s installation instructions. [NFPA 54:9.4.2.1]

The manufacturer's installation manuals do not show, or apparently require, anchorage. The units are depicted sitting on CMU and they are not shown on a roof. People will place the appliance on the ground, on a wall, on a balcony and on a roof.

Contractors have argued that the installation instructions do not require anchorage and the code states that this only applies to appliances that are "designed" to be fixed in place. As an inspector you must use your own judgement as to what is safe.

Mitsubishi:



Bosch:

 

[mark handler]

Ohio Mechanical Code 2017
304.1 General
Equipment and appliances shall be installed as required by the terms of their approval, in accordance with the conditions of the listing, the manufacturer's installation instructions and this code. Manufacturer's installation instructions shall be available on the job site at the time of inspection.
305.4 Interval of PIPING Support
Piping shall be supported at distances not exceeding the spacing specified in Table 305.4, or in accordance with ANSI/MSS SP-58.

 

[ICE]

 

[e hilton]

If you don’t put any slack in the electrical or freon lines, it will stay in place. Add a bead of spray foam for added security.

 

[klarenbeek]

Other than manufacturer's instructions, the only thing the IMC has is 301.15 Wind Resistance. Mechanical equipment, appliances and supports that are exposed to wind shall be designed and installed to resist the wind pressures determined in accordance with the International Building Code.
Clear as mud. Securing it to a pad or sleepers that aren't much bigger than the unit footprint won't help much either, they'll get tipped right along with the unit. Most condensers are pretty stable if on a flat level surface because the majority of the weight (the Compressor) is on the base of the unit. Same applies to most package rooftop units. If they are on a good level curb/base most of them will stay put until you get winds that will be pulling trees out of the ground or maybe ripping up the roofing itself. The exceptions will be narrow higher profile units like minisplit condensers or maybe direct fired makeup air units like you see for commercial kitchens.
Every once in a while I did a rooftop unit replacement where the old unit was screwed to the roof curb. Finding all the screws someone else put in 25 years ago was always a huge pain in the ^$$.

 

[phillier937]

A few years back we had a wind storm and there were 25 units all over the neighborhood adjacent to an apartment unit.

 

[north star]

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If the mini-splits are fastened to the roofing assembly and actually
penetrate the roofing membrane, ...it will be an ongoing maintenance
issue to keep the penetrations sealed..........Plus the refrigerant lines
will also be penetrating the roofing assembly.

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[ICE]

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If the mini-splits are fastened to the roofing assembly and actually
penetrate the roofing membrane, ...it will be an ongoing maintenance
issue to keep the penetrations sealed..........Plus the refrigerant lines
will also be penetrating the roofing assembly.

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RTUs are common. It is on the owner to assure that it is done properly. Placing mini-splits on a roof is a seemingly poor choice.

 

[Paul Sweet]

I've seen mini-splits bolted to 3 ft. long treated 6x6s perpendicular to the unit and sitting on a slip sheet of roofing membrane. The 6x6s add weight down low, and provide a longer lever arm to resist the wind.