I am building a bathroom in my cuckshed and I want to insulate it. However, there's no room to insulate in between the block wall (goes 3 feet up) and the pipes running to and from the hot water heater. If I insulate on the inside of the pipes, I am concerned that they could freeze on an extremely cold night because they wouldn't be getting much warmth from the inside because the insulation would be in the way. If I don't insulate near the pipes at all I know for a fact they would never freeze, because they'd get so much warmth from the bathroom (it has a register in it) but I'd lose a lot of my heat. What's the best solution?