In zone 4 (Northern VA), what is the best way to keep pipes from freezing in a 2x4 gypsum sheathed wall with aluminum siding?
Picture attached but the vent pipe will be cut out and adjusted to run to the other stud cavity and a 2x6 will be added above the copper to brace a pedestal. There is 2 3/8 inches between copper and exterior gypsum and a little over 1 inch between the pvc and exterior wall. Rain does not hit this wall because it is the house side of a semi-enclosed porch so it has another wall roughly 4 feet in front of it and it has a living space above the porch so it is not open to rain from above.
Secondary to keeping the pipes from freezing my next concern is to protect from moisture build up within the wall. I understand in zone 4 it may be best not to have vapor retarder other than painted drywall yet I think having a vapor retarder behind the pipes may be the best way to keep them from freezing.
Here are the options I am thinking. For all the options I would use pipe insulation on the copper.
1. Put two inch R-10 rigid XPS foam behind the copper pipes and cut it to fit behind the PVC but only install it to the height of the copper pipes. Then install unfaced fiberglass or Roxul in the rest of the cavity including in front of the pipes. This would allow any possible moisture to escape through most of the exterior wall and allow for warm air in the house to pass through the drywall and hit the pipes.
2. Put 2 inch R-10 rigid XPS foam to the full height of the cavity and fill the rest with unfaced fiberglass or Roxul. This would give the highest R value and stop cool air coming in but may cause moisture problems.
3. Use great stuff foam around the studs and fill the cavity with unfaced R-15 fiberglass or Roxul This would allow warm air from the house to pass through the drywall to the pipes and would stop some of the cool air from coming in.
4. Same as number three except use faced fiberglass or in the case of Roxul use a level one plastic vapor retarder. The vapor retarder in both cases would be tucked behind the copper pipes to allow some warm air to pass through the drywall to the pipes.
This is my first post, sorry for the length. I lack knowledge on insulation and would appreciate any advice!
Posted Sun, 10/27/2013 - 01:02
Edited Sun, 10/27/2013 - 05:59
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