AskCodeMan

I've been asked to detail the method of separation for a R-1AAA zoned property in which we are constructing an apartment over an existing, detached garage.

Any suggestions on the proper answer? Is this in reference to the four hour fire wall?

The existing building is only a detached garage?

The zoning classification is not applicable to anything I can address as zoning classifications are local government created and their designations and meanings vary greatly from locality to locality. What is necessary is the following: a) the building code which is applicable to your area, year and IBC or other?; b) type of construction; the building occupancy.

As I am envisioning the question, especially with the phrase "detached garage", I am thinking that it is residential, such as under the IRC (or a code which is IRC based, many are, some still have not updated to the IRC or even using the IRC as a base for a locally amended version of it) and that there is a dwelling unit to which the detached garage is an accessory structure to the dwelling unit.

And that an apartment is to be constructed or converted (from whatever) above the detached garage.

The required separation between the apartment above a detached garage which is an accessory structure to a dwelling unit has greatly reduced separation requirements, and egress requirements, than an apartment over a garage which is not an accessory structure to a dwelling unit under the IRC or IRC based code. A detached garage which is an accessory structure to a dwelling unit which is under the IBC or IBC based code would have greater separation requirements under the residential occupancy of the IBC, and an apartment over a detached garage which is not an accessory structure to a dwelling unit under the IBC would have even significantly greater separation and egress requirements.