Insulate attic to prevent pipes from freezing
Long story short: We have pipes running through the attic of our garage to an addition. The pipes run close to the roof line and then go down an outside wall. The attic rafters are not insulated and the walls above the ceiling line are also not insulated. The floor of the attic where it goes over the house is insulated. The attic portion is open to the garage itself (its kind of like a crawl space), but the pipes will freeze at anything below 32 degrees, so clearly heat is not getting up to the attic from either the garage or the house.
We had shut off valves installed and currently turn the water off to the addition anytime the temperature dips below freezing. While it works, it is a pain and we would prefer to only resort to this in extreme temperatures. The pipes and elbow joints are wrapped with foam insulation. I would like to avoid using anything that requires electricity up there for fear of fires (IE space heater).
Here is my question: We were thinking of installing batt insulation (with proper ventilation using baffles) in the entire area (exterior walls and attic rafters). Is this a waste of time, or do you think it would work? Someone suggested just laying the batt insulation over the pipes, but not insulating the entire area – would that work? Any other suggestions of how to keep these pipes from freezing?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
It would be easier to answer a question like yours (or frankly, almost any question posted here at the GBA site) if we know your Climate Zone or geographical location.
The attic of your garage isn't going to stay above freezing unless you heat the space. Understandably, you don't want to do that.
The correct solution is to run the pipes in a deep trench that runs between your house and the addition on the other side of the garage. This trench should be deep enough to keep the pipes from freezing. Where I live (in Vermont), the pipes would need to be buried in a 4-foot-deep trench. If you live somewhere warmer, the trench could probably be more shallow.
If you don't want to run the pipes in a trench, the usual solution would be to install a length of thermostatically controlled heat tape along each pipe length. (This is a type of electrical wire that heats up whenever the temperature approaches freezing.) After installing the heat tape, enclose the pipes and the heat tape with pipe insulation. The disadvantage of this approach is that it adds to your electricity bill, and the pipes may freeze during a power outage.