I have a hot and cold pipe that is located in an attic space above my garage that is accessible from the back side. The problem is this pipes are running through the wall studs and keep freezing in cold weather. I have this pipes insulated with pipe insulation as well as wall insulation and a second layer of wall insulation that runs over the studs. Is there any way to put some sort of heat tape on this pipe even though it runs through the walls?
Insulating a pipe in a cold space does pretty much nothing. Insulation simply slows the transfer of heat. The only way to insulate pipes is to have them on the warm side of the insulation and if your garage isn't heated you're not going to be able to solve it with insulation. If your climate is not normally freezing you could heat the space with a small electric heater (plug in radiators are safest) on the cold days. Otherwise you need to relocate the pipes or your building envelope so that the pipes are within your conditioned space. It's a potentially serious issue as frozen pipes often burst.