outside drains and pipes

[Marisa Somma]

I have an 8 unit property in PA. I have had an issue with the bathroom pipes freezing in one of the apartments. The bathroom portion of this apartment sticks off the back of the building and has storage area just below it. The Storage area is not insulated at all. I can see the water supply lines and the drain pipes near the ceiling of the storage area. The water supply lines come out from the wall and go up into the ceiling and the drain pipes come out from the ceiling down the wall and to the ground. It has been suggested to me to insulate the entire storage area. Trying to save money I was thinking I should just concentrate on the area where the water supply lines are and may be even box off that area. The other pipes going all the way to the ground are drain pipes, do those need to be insulated as well? I'm being told they should but I cant find any information supporting that.