Single Apartment over Commercial Tenant

Downtown Main Street is trying to make a comeback, but what can we do with the existing space? Housing is in high demand these days, but sprinklers are expensive. Wisconsin's one- and two-family dwelling code, the Uniform Dwelling Code, doesn't require sprinklers but isn't that just for houses and duplexes? Per State Statute 101.01 the commercial building code is for public buildings and places of employment; a public building has occupancy by the public or 3+ tenants. This means there is the possibility of a hybrid Commercial Building Code (CB) / Uniform Dwelling Code (UDC) building, with one tenant each. But how would that work?

• The Commercial Building code will cover the structure for engineering loads and construction type.
• Each tenant may be considered separately for thermal compliance or COMcheck 2015 may be used for both (unless the UDC is updated).
• The Commercial tenant may require sprinklers, but there is no sprinkler requirement in the UDC.
• The aspects of exiting, HVAC, windows, etc. are addressed by each tenant's respective code.
• The upper apartment would contribute to the height, number of stories, and fire area unless an occupancy separation to the commercial tenant is provided.
• The only enforceable separation requirements are currently related to the Commercial Tenant:
• Do you need an occupancy separation because of limits to height, number of stories, fire area?
• Do you have fuel-fired equipment requiring separation?
• Do you have a garage?
• Note that the Commercial Building Code has separation requirements for an R-3 (if there are 3 or more tenants, 1 or 2 apartments would be classified as an R-3).
• The Uniform Dwelling Code has separation requirements for an accessory structure, another dwelling, a garage, or property lines - just nothing specific to a Commercial Building.
  A good designer will provide an appropriate separation, instead of achieving the D- of code minimum.

Code references:
 Separation:
 Separated occupancies per IBC 508.4 (use R-3), OR:
 Fuel-fired equipment separation per IBC 509
 Garage separation per IBC 406
 Fire Area separations per IBC 707 & 711
 CB Note: Non-separated for CB for an R-3 follows 420.3
 UDC Note: UDC separates dwellings from other dwellings, garages, outbuildings, property lines, etc. in SPS 321.08 Ceiling separations noted in 321.08(1)(a)1.b. & 321.08(2)(e)
 Sprinklers: Not required for UDC, check CB tenant
 Structural loads per CB: Walls, roof, floor, etc.
 Height –no limits for UDC, check CB:
 The upper unit is considered a story, IBC Table 504.4
 Upper unit inc. in building height, IBC Table 504.3
 Construction type per IBC 602 includes enclosing walls of the dwelling unit
 Thermal Envelope:
 Calculate individually or most restrictive for both
 May 2025: CB is more restrictive (UDC update may change this) CB: COMcheck 2015 IECC > UDC: REScheck IECC 2009
 UDC for exiting, HVAC, windows, etc.
 CB for Commercial Tenant

This is not an all-inclusive list, but it provides a good starting point to consider adding a single apartment over a single commercial tenant!

More Info PDF: UDC Over CB