Insulating ceiling of unheated basement garage

[austin]

This post is related to the thread, "hot air register inside double wall". Why shouldn't there be heating wires on concealed pipes? I see that the pipes that pass through the unheated garage ceiling do have heating wires on them. The cord pokes through the ceiling and plugs into the wall. Clearly, the previous owners had a lot of problems with freezing pipes. I don't know what the guy was thinking who did this installation. The ceiling of the garage is drywalled. I took some down the other day to see what was in there. There is about 4" of insulation strapped to the underside of the floor above. It is sagging. Needless to say, the room above the garage is colder than the rest of the house. The water pipes and heating ducts run under that insulation, so they are pretty much exposed to the cold. Winter temperatures can go to -40. I'm thinking that I should fill up that entire space with insulation. Any suggestions as to how to go about doing this?

[Dean]

Besides being a big fire hazzard, you can't really depend on electric heat tapes to continue to keep working and eventually they will burn out or loose power and will no longer be protecting the pipes from freezing but you won't know it until it's too late.

A lot of people think water pipes should be wrapped to prevent freezing but the best way is to leave pipes uninsulated in an area where they can get any warmth at all even though the area may not seem to be very warm.
In other words only insulate between the cold area and the pipes but not between the warmer area and the pipes.

Probably one of the most important things to do though is to keep any draft off the pipes which usually can be done by stuffing insulation or rags into any cracks that wind can blow through.

I tried to draw a rough sketch to demonstrate.