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Unread 03-21-2018, 09:35 AM   #34
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Join Date: Jul 2005
Location: Fairfax, Va
Posts: 3,076
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Speaking of plumbing - insulating it?

The entirety of this 14X7 bath is over an unheated 2 car garage. Original supply and waste lines were in the 2X10 joist cavities, and original vanity against a North facing 2X6 framed exterior wall with the supply lines coming up in the stud bay. The 3/4" lines that feed the bathroom originate in a crawl space and make the trip to the bathroom through a 2X4 framed load bearing wall between the house and garage, and that wall is insulated with R13. It appears the pipes are held close to the warm side, as they were in the vanity stud bay. In the vanity stud bay they were wrapped in some deteriorating foam pipe insulation.

We've been here for 18 years and have never had a pipe break, and it does get cold here in the DC region. When I opened up the floor and wall I didn't see any evidence of prior repairs. The insulation work was best described as shoddy; many gaps, much compressed, sections completely missing. See photo below.

The new set up will be largely the same, pipes in the floor and the exterior wall, but with much greater care spent on sealing and insulation. I installed 2 continuous layers of R13 under the supply lines in the floor, though it did get compressed a bit in some spots so I am figuring on an overall R value of 23 or so. I still have enough depth to lay in more R13 (though it too would be slightly compressed).

Here's the question (finally, right?): should I add more insulation over the supply lines in the floor? Will any heat from the finished floor radiate downwards enough to add any degree of warmth to the pipes (adding more insulation would effectively block that heat)?
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If I recall correctly my memory is excellent, but my ability to access it is intermittent.
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