Replies

1. 
   user-2310254 | Oct 29, 2016 09:21am | #1

   Ronnie. Where do you live? How thick is your XPS foam?

2. 
   Dana1 | Oct 29, 2016 09:52am | #2

   2" of foam is aobut R10, 6" of fluff is abotu R20. At the above-grade section the temperature at the drain will split the difference roughly 1/3-2/3 of the indoor & outdoor temperatures. So, if it's 60F inside and 0F outside the drain would be about 20F. If it's 20F outside and 60F inside it will still be above freezing.

   In a cold climate where there's a chance of going for a full week or more of temperatures that never exceed 20F there is a potential for frost/ice plugging the drain, assuming the foam is only 2" thick.

   So, as Steve asked, how thick is the foam, and where is this house?

3. 
   Jon_R | Oct 29, 2016 12:24pm | #3

   I predict that the heat in the drain water will be more than enough to prevent freezing. But you could omit the fiberglass covering the above grade pipe area.

4. 
   Dana1 | Oct 29, 2016 12:56pm | #4

   I've seen existence proofs that this can freeze up if the R-ratio isn't off. Drains drain, the amount of residual heat transferred the water is small. Unless the drain flow is an abnormally high duty cycle, it's not enough.

5. GBA Editor
   Martin Holladay | Oct 30, 2016 06:00am | #5

   Ronnie,
   The principle that Dana Dorsett is invoking is a good one: in general, you want plumbing pipes to be on the interior side of the insulation. So I would vote for no fiberglass.

   If you want more insulation, just glue some more rigid foam to the existing layer of rigid foam to make the foam thicker. Then put your plumbing pipes on the interior side of the rigid foam.

   For more information on insulating basement walls, see this article: How to Insulate a Basement Wall.