There are several design requirements that must be met in order to provide a transformer room within the building for your project.
First, the fire ratings of the walls and ceiling must be a three hour assembly. Ventilation must be provided as well as street access that is “reasonably” level (level enough to be able to lift the transformer with equipment sitting on grade outside) with a removable curb.
The ceiling height of the room is a particularly sensitive one as they like to have 30″ of lift clearance when the transformer is hoisted on the hoist beam. Xcel would like to see 18′ of room height (that’s right, eighteen feet) to accomplish this, however, an engineered system of spreader bars for the hoist mechanism can reduce this up to several feet. Be prepared to spec the hoist and spreader bar assembly to prove your system will work.
The hoist beam must be able to extend all the way to the face of the building, which poses some interesting structural solutions. Don’t forget the oil containment tank below the floor with the inspection tube as well.
Finally, you must always meet the “open to sky” requirement outside the ventilated opening to the room to allow potential smoke from the room to escape vertically above the ventilated opening. No operable doors or windows are allowed above this opening, and they even restrict deck spaces with inset doors in this region. This will impact a multifamily design considerably.
These are very complicated little rooms with several disciplines involved. Do yourself a favor and have a meeting with Xcel (or whoever your utility provider is) well in advance as many of these design constraints will dramatically impact the adjacent spaces. Only they can approve your final design for permitting, so consider these tips as a starting point and verify everything in your design with the utility provider as well as the local code official. Or just hire EVstudio for your project because we’ve been there.