AskCodeMan

We have an individual building a detached garage. The garage will be heated. We live in climate zone 7. The walls and ceiling are insulated properly and there is no living space above. My question is does the garage door require and type of r-value on insulation? Thanks.

This is one of those cases where the code does not address (in its intent): conditioning (heating/cooling) a vehicle garage.

That said, this is what the IRC requires (as stated in the IRC):
- SECTION N1101 GENERAL
- - N1101.1 Scope. This chapter regulates the energy efficiency for the design and construction of buildings regulated by this code.
- - - Exception: Portions of the building envelope that do not enclose conditioned space.

Note that N1101.1 does not state "habitable" buildings or even "habitable spaces" of buildings, the code simply states "buildings" regulated by this code.

That means we must go to the definitions and:
- BUILDING. Building shall mean any one- and two-family dwelling or portion thereof, including townhouses, that is used, or designed or intended to be used for human habitation, for living, sleeping, cooking or eating purposes, or any combination thereof, and shall include accessory structures thereto.

Which says "and shall include accessory structures thereto" - which would include the garage.

All the above actually states that the garage would need to meet the energy code *IF* (when) it becomes conditioned space.

The code does not take into consideration that the garage door is often left open for long periods of time, nor that the garage door defeats any reasonable heating or cooling effect every time it is opened and closed for a vehicle to enter or exit.

The effects of insulating the garage door are far outweighed by the fact that the now insulated door is open ...

Is there anything wrong with insulating the garage door? No. Is it a good idea to insulate the garage door? Yes, whether the garage is conditioned or not.

Is it required by the code to insulate the garage door when the garage is conditioned (your question)? Strictly speaking - yes. Practically speaking - I suspect the code does not intend to address insulating the garage and garage door if a garage is conditioned ... what heat load would you apply for whatever is going on in the garage? What if the garage was used as a pottery making hobby kiln room? I think it is impractical to attempt to determine what R-value would be required for a conditioned garage.