Equipment service access

The project is a new high school in New Orleans. Cooling is provided by three large chillers mounted in a mechanical well at the top (third) floor, open to the sky and surrounded by walls on four sides to roof height (about 15 feet). The units are mounted on steel frame supports elevated six feet above the 3rd floor level to permit maintenance of the roofing material below. The AHJ has called for a service catwalk at the height of the supporting frame, citing IMC 306.5 which I have excerpted below. My interpretation is that the units would have to be elevated 16 feet above the level of access to require this. The AHJ disagrees, saying that because the units are located more than 16 feet above grade the catwalk is required.

Any experience or opinions would be appreciated.

IMC 2006: 306.5 Equipment and appliances on roofs or elevated structures.
Where equipment and appliances requiring access are
installed on roofs or elevated structures at a height exceeding
16 feet (4877 mm), such access shall be provided by a permanent
approved means of access, the extent of which shall be
from grade or floor level to the equipment and appliances’level
service space.
Original Post
a graphic would help, of course, but step back and consider this:
the 'correction' may be citing an incorrect code section, but the logic is correct...
how would you service the equipment that is sitting on a structure that is 6 feet above the accessible roof surface, and thus must have serviceable parts as high as 12 feet above that roof...
? a portable ladder
try imagining yourself as the service personnel working on the equipment, carrying tools/parts, etc., and doing this from a portable ladder step about 8-9 feet in the air...
? is this a reasonable solution... safe... meet the intent of the code (which is for service personnel to be able to safely perform their work)

a catwalk around the equipment (or at least on the 'working side') seems to be an approach that meets the intent of the code, and will reducee the building owners risk and insurance costs...

am i missing something about this configuration that makes my comments moot?

Thanks for responding. Your comments will seem "reasonable" to everyone except my client, who will have to pay for the unnecessary catwalk structure. The fault in the logic of the AHJ is this: according to his interpretation the units could be 16 ft above the ground and not need a catwalk, but six feet above a concrete floor surrounded by a 14 ft high barrier, and the catwalk is required. This makes no sense to my client, and I have to agree. It seems clear that the intent of the Code is to provide for the safety of maintenance personnel by limiting the height that they will be required to work above a stable surface. The 16 foot limitation is understandable - it is a common length for an extension ladder. But whether the ladder is on the ground or inside a room on an upper level is not relevant.

These units may require some maintenance or repair every few months or years, and they are equipped with hinged panels to facilitate this. At six feet elevation, the serviceable parts can easily be reached by a person on a stepladder as safely as changing a lightbulb. If more extensive repairs are required, presumably this would be done by a trained technician with special tools and skills and appropriate risk management and safety measures included in the contract scope.

Would the catwalk be safer and more convenient? Absolutely. But is it the highest and best use of funds on a project with a limited budget? I would argue that the benefit will never equal the expense, unless of course that is what it takes to obtain the Certificate of Occupancy.
not sure we are on the same page...
what type of equipment?
if major equipment, with serviceable electrical and mechanical parts, don't mechanical and electrical codes require there be a level area in front of the equipment for service personnel to stand on while servicing the equipment, for safety purposes?
the code section you cite says, paraphrasing, provide a permanent ladder from grade to the 'level' service space...
the catwalk would be the 'level' service space...
how does a stepladder provide a safe 'level' space for servicing of major equipment...
in the instance of a roof that is, for example, 12 feet above grade, a temporary ladder can be used to reach the roof level itself, but don't you still need the 'level' service area?


The equipment in question is three large chiller units. All code required and mfg recommended clearances are provided at the level of the 3rd Floor mechanical well where the units are located. Access to the well is the same as the remainder of the 3rd floor, via permanent stairs and elevators. The issue seems to be whether the "level service space" is at the 3rd floor slab or somewhere above it. My interpretation of the language in the IMC is that unless the equipment is elevated more than 16 ft above the floor, the level service space IS the floor.

For example, in my experience mechanical units are always placed on curbs or housekeeping pads or frames elevated above the adjacent floor or roof level by some distance ranging from a few inches to several feet depending on the conditions. Rarely have I seen a service platform or catwalk constructed around such units. The presumption is that the units can be accessed safely up to a certain height (16 ft, according to the IMC). If the mounting height is greater than the prescribed limit, something must be done to reduce the height (add a platform).

It seems clear that the intent of the Code requirement is to limit the elevation of the equipment above the level of access, regardless of where the level of access is relative to grade.
we agree, up to a point...

i agree that raised pads and racks are common...

however, i disagree that the level service area is the roof surface that is (in your analysis) anywhere from zero to 16 feet below the actual equipment, and its access doors/panels, etc.

in my opinion the electrical and mechanical requirements are that a level surface, 3 feet in 'depth' be provided in front of the equipment (the sole purpose of which is to provide a stable surface upon which the electrician or mechanic can stand) while he/she services the equipment, replaces parts, etc.

in order for this to occur the level surface must be such that the access door/panel of the equipment is within customary reach/height...

in my experience two solutions are common: a) provide a housekeeping pad or similar platform that is sized larger than the equipment itself, with the equipment mounted so that there is a level 3 foot service area on its 'business end'; b) provide a separate elevated walkway (catwalk structure or similar) on the 'business end' of the equipment... these solutions both afford a stable standing surface/platform for the service personnel (the 'level service area')...

i agree the code section you cite would allow one to use a temporary ladder from the roof to the 'level service area' if the equipment is less than 16 feet above the roof surface... however, although the code might allow this, i disagree that this is a safe arrangement... i have not looked at OSHA to see what it says on this issue, but i would speculate OSHA would frown on a service person having to shlep tools, equipment and parts up a ladder to a service platform 15.9 feet above roof level... i would also speculate insurers would frown on this arrangement...

since you don't provide a graphic showing the arrangement of the equipment, framework, roof, clearance to parapet, etc. it is not possible for me to understand all the constraints you are dealing with... all i can do is provide my designer's perspective on what i believe is the intent of the various regulations, and common sense from the perspective of the service personnel...

? input from any code regulators out there ?

Hil, your analysis, as noted by Eskew, is clear and logical however we are dealing with someone whose client's only concern is dollars.

As a % of total construction cost, it seems however that provision of the catwalk is a no brainer. I agree with the B.O.

Damn the minimums, consider risk management and do it right. Chillers require large tools and regular servicing to stay within warranty (check the manufacturers recommendations too.)
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