insulation of water pipes behind the wall of a finished attic


We live in the Boston area. We bought our current house a year ago. The attic is finished with heat. This past winder, all the water pipes to the attic's bathroom got frozen on a very cold day. We had some temporary solutions so that the pipes didn't freeze again.
Now I am trying to find a perminant solution. I opened the attic bedroom's wall and found that the water pipes laying on the floor of the unheated trangular area behind the wall. Because of the ventilation required, I guess the area where pipes are can get very cold. Currently there are some tapes wrapped around the pipes but not completely.
I am thinking of buying more tapes and wrap the pipes more carefully and tightly. Also, put some extra insulation on top of the pipes. Is this enough? Last winder the lowest temp was -10F here.
If not, what's a good solution of the problem.
Thanks,
-Mike
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Mike wrote:

Don't just put insulation on top of the pipes, you need to leave the pipes exposed to the heated space to keep them from freezing.
What I did in our finished attic was to put the pipes inside the knee wall and then add a second set of studs in the knee wall directly behind the existing studs, basically a wall as thick as two 2x4s. I put insulation in the outer section of 2x4s, with the pipes between the insulation and the heated space, and the insulation is the barrier between the pipes and the unheated "exterior" triangular space behind the knee wall.
Ken
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Mike wrote:

You need more than insulation. All insulation can do is to slow cooling.
When you run water in the pipes they warm up. Assuming they are in an area that is below freezing, they will then start cooling towards freezing. If you run water often enough, they don't freeze. Adding insulation slows the freezing, but it will not stop it.
You need to add heat to those pipes. That means heating the areas they are in or using an electrical heat tape made for that use to keep them warm.
--
Joseph Meehan

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Another solution might be to install a hot water recycle pump up there. You could put it on a t-stat so that it would run on the coldest days. And or add a push button for getting hot water up to the area faster. These connect under the sink and it pull hot water and injects into the cold water pipe. Moving water does not freeze as fast.
I grew up in Iowa and we had a well, if it stayed below -10 for a couple of days dad would just put the kitchen sink on slow drip so that during the night the pump would have to turn on and run a couple of times.
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I agree, especially if the system is one that returns the (cooled hot) water through the cold water line rather than a dedicated hot return. If you use a hot return pipe, you can couple the pipes together so the hot pipe can keep the cold one from freezing.
If rebuilding the pipe space (to keep it in the heated space), or hot water return are not practical solutions then an electric pipe wrap would be apporpriate. Basically an electric blanket for the pipe. Need to inspect it yearly the verify its always working though as they can deteriorate over time.
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You want to insulate between the pipes and the cold side. You want to let the heated air in on the room side.
Insulating the pipes may not help over time. If the pipe is wrapped and no other heat source, the heat will eventually travel from the water to the cooler area and freeze the pipe. It just takes longer if insulated but if no heat is added, it will lose what heat is there.
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Thanks, guys.
Looks like the simplest suggested solution is to use heat tape. I was hesitating to use them because of the safty concern. Are they safe?
For the more complicated suggestions, I will do a little more research to decide on one.
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move the pipes and/or use pex

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Mike wrote:

No. Heat tape causes plenty of house fires.
MM

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Add to that the cost of a wireless or wired smoke detector with lithium battery (10 year life). a pair of wireless smoke detectors goes off at the same time but are pricy at $80 a pair. Wired detectors are cheap but you have to put in a wire which is not easy.
Hence my recommendation for yearly inspection (at beginnnig of cold season)

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