NEC Definition - SRO Units W/cooking but no bathrooms

[derekk]

Hello:

I am currently doing service calculations for a building which contains ~150 residential units and I wanted to get some opinions on how they should be classified. These are small single-room occupancy apartments, rented out long-term. The contain a sink, but no bathroom. The owner wishes to prepare the units to permit small "mini-kitchenette" units to be installed in the future. The kitchenettes combine a sink, small UC refrigerator, and two electrical cooktop burners and require only a single 120V, 15A circuit. These units will NOT have separate utility meters. Heating is via steam and there is no air conditioning (which precludes using the Optional Calc).

I'm going back and forth between calling these dwelling units (which would require including 3,000VA for SABC's to each unit) and including the mini-kitchenette's as fixed appliances (meaning only a 75% demand factor for the appliances to the service under 220.53) vs considering them to be more like dormitory units without the SABC's and using a 65% demand factor under 220.56. Unfortunately, the Article 100 definitions for both Dwelling Units and Guest Rooms require "sanitation" which these units do not have and, although used in the 2014 NEC, Dormitory Unit doesn't have an Article 100 definition.

I'm just curious if anyone else has done similar units before and could comment? I think I'm forced to treat these as Dwelling Units due to the cooking (even without a bathroom) but the combination of (2) SABC's and only being able to use a 75% load factor on the kitchenette's is going to require a very large service relative to how these units are actually utilized.

We're much more used to doing traditional multi-family dwelling or hotel units so I've never had to include one of these small "all in one" kitchenettes before but I realized that they create kind of an odd calculation issue. The total cooking load for this unit is only 1500W, which is less than the 1750W minimum required to use the demand factors in Table 220.55. Since this is fastened in place, it must fall under 220.53 and this results in a very large load. If the manufacturer increased the load of these units to include 1750W of cooking, then the total demand load in our example would drop from 169KVA (1500VA*150 units * 75% demand) to only 79KVA (1750VA * 150 units * 30%). This is quite a large difference. Since these are a planned future load anyway, I may well add in a future window PTAC unit for each unit too. This will allow me to use the Optional Calc's and with the 220.84 demand factor this produces a much lower load (basically free air conditioning from the NEC).

Thanks in advance for any comments.

 

[jumper]

If the dorms do not fit the definition of a dwelling unit, then you cannot use the resi calc options.

They are not hotel guest suites if they are attached to an institution such as a school or similar. They would have to be commercial open rentals.

The dorms would still need AFCI per 210.12. Only section I know that even mentions dorms IIRC.

 

[derekk]

Jumper, these units are not attached to an institution, although university-level students would be the majority of the tenants.

I think that technically you would be right in that this would be a commercial occupancy although philosophically, I'm not sure that it should be. Take a generic 300-room hotel with most of the guest room load at 2VA/ft per table 220.12 with 40% or 30% demand factors from 220.42. Now, you take the same 300-room hotel but move the dedicated bathrooms into shared hallway bath's instead. I'd argue that the overall load on the building service would be the same in these two scenarios (assuming the same type of traveler). Under 220.42 we'd be at 100% demand factor but there also isn't an adequate category to use under table 2201.12 for these rooms, so anything we come up with could easily be challenged. Despite the lack of a bathroom in the units, I would probably still calculate these as hotel guest rooms including the 220.42 demand factor and add a statement that the occupancy doesn't directly correspond to one of the table 220.12 categories so we're going with the closest one (guest rooms). If we did this WITHOUT also using the demand factors from 220.42 for a hotel then we'd way overshoot the service and feeder sizes as the use of the space is identical among the two scenarios.

How would you calculate something like this?

 

[jumper]

I do not mean this unkindly : please hit the space bar more often, large chunks of text are hard to read.

So, these rooms have no baths. Hard to call them guest suites.

So, not dwelling units nor hotel guest suites.

Not good for calculating purposes.

You gotta ask your inspector. I have no clue what answer you will get.

How is this building zoned per IBC or whatever code applies to your area?

 

[derekk]

Sorry about the spacing. I have very large monitors so what looks like 3 lines on my screen might be 10 for other people.

Occupancy is R-2 on floors 2+ (where these units are located) with various commercial A and B spaces on the ground floor.

I don't see them often, but I managed to dig up two other projects I've seen recently (that were designed by other MEP firms).

These were both traditional short-term hostels and they treated the spaces purely as hotel rooms, probably didn't even consider that the lack of a bathroom means that they don't meet the NEC definition.

I don't usually mind coming up with conservative calculations but in this case we need to have our service "fit" into a maximum of 2500A@208/120V in order to use a sidewalk transformer vault.

Our MAX 15-min average load on the entire existing service (with close to 100% occupancy and taken from 2 separate 30-day periods) was below 350A, so this is definitely a case where we don't want to artificially overshoot the calc's over some kind of an arbitrary definition in the NEC.

I can't think of a valid reason why the proximity to the nearest bathroom should completely alter the calculations. We do need to discuss this with the AHJ first, of course. Fortunately, our local utility is often glacially slow so we should have plenty of time.