Roof replacement shall include the removal of existing layers of roof coverings down to the roof deck.

Exception: Where the existing roof assembly includes an ice barrier membrane that is adhered to the roof deck, the existing ice barrier membrane shall be permitted to remain in place and covered with an additional layer of ice barrier membrane in accordance with Section R905.

The installation of a new roof covering over an existing roof covering shall be permitted where any of the following conditions occur:

1. 1.Where the new roof covering is installed in accordance with the roof covering manufacturer’s approved instructions.
2. 2.Complete and separate roofing systems, such as standing-seam metal roof systems, that are designed to transmit the roof loads directly to the building’s structural system and do not rely on existing roofs and roof coverings for support, shall not require the removal of existing roof coverings.
3. 3.Metal panel, metal shingle and concrete and clay tile roof coverings shall be permitted to be installed over existing wood shake roofs where applied in accordance with Section R908.4.
4. 4.The application of a new protective roof coating over an existing protective roof coating, metal roof panel, metal roof shingle, mineral surfaced roll roofing, built-up roof, modified bitumen roofing, thermoset and thermoplastic single-ply roofing and spray polyurethane foam roofing system shall be permitted without tear-off of existing roof coverings.
5. use this link to read more about Idaho codes.  2020 Idaho Residential Code - CHAPTER 9 ROOF ASSEMBLIES - R908.3 Roof replacement. (iccsafe.org) 
6. certain cities require a city inspector to come out to your house and make the roof was installed to Idaho's specific building code. some counties require the contractor to make an appointment before we start your desired project. We always verify with the county you are in before we start. check your local county requirements about city inspections for roof replacements.