Insulation for Pex rain shower head in attic, insulation options?

[Jmpage2]

Greetings forum,

I’ve seen variations of this question asked but I wanted to start my own thread on it to see if I can get a couple of specific things answered by the experts here.

I’m in the midst of a bathroom remodel and my general contractor is installing 3/4” Pex for new fixture lines for the master shower. One of the lines is for a rain head that must run through insulated attic space, about 40” from the interior wall.

What is the best approach for insulation of the Pex line as we are in a cold climate where temps can dip below zero periodically in winter and the very well insulated attic can still get below freezing?

The mechanical sub contractor who helped install the new Kohler digital valve proposed that what would be considered “standard” in the trade is to put a 6” vent in the ceiling to allow warm air from the bathroom to help keep the rain head shower line from freezing but this seems like a terrible idea to me as it will result in constant loss of heat and moisture from the bathroom into the attic.

I saw another thread where it was proposed to build an insulation tent with rolled insulation over the line so that warmer air from the room below will keep the line from freezing… not sure what is considered the current best approach for this.

Any useful input especially from any pros who have dealt with this situation is very much appreciated, thanks!

 

[wwhitney]

An intentional air leak is not a good idea. You could add a vent under the PEX and then add an air sealing detail above the PEX, but that's unnecessary.

All you need to do is ensure that the plumbing is within the thermal envelope. So if you are insulating the attic floor with, say, 10" of fiberglass, and you have PEX lines within that framing, where the insulation hits the PEX lines, all 10" of insulation goes on the cold side of the PEX.

Now, if the indoor temperature is 65F, and the attic temperature is 0F, if you put 4" of insulation below the PEX and 6" of insulation above the PEX, then the PEX temperature should be 60% * 65F = 39F, above freezing. So in theory that would work, but there's no good reason to cut things that close. Just put all 10" of insulation above the PEX.

Cheers, Wayne

 

[Sponsor]

 

[Chad D.]

An intentional air leak is not a good idea. You could add a vent under the PEX and then add an air sealing detail above the PEX, but that's unnecessary.

All you need to do is ensure that the plumbing is within the thermal envelope. So if you are insulating the attic floor with, say, 10" of fiberglass, and you have PEX lines within that framing, where the insulation hits the PEX lines, all 10" of insulation goes on the cold side of the PEX.

Now, if the indoor temperature is 65F, and the attic temperature is 0F, if you put 4" of insulation below the PEX and 6" of insulation above the PEX, then the PEX temperature should be 60% * 65F = 39F, above freezing. So in theory that would work, but there's no good reason to cut things that close. Just put all 10" of insulation above the PEX.

Cheers, Wayne

This^^^. In other words, “tent” the insulation over the piping so it is all on the warm side of the insulation. If you have blown-in insulation in the attic, lay some regular batt insulation over the pipe before fixing the disturbed blown-in. You don’t want the insulation under the pipe because you’re looking for the heat transfer through the ceiling to keep this small pocket warm.

This is how we keep our residential fire sprinkler systems from freezing in attics. The water in our piping (hopefully) never moves, so even tougher to keep from freezing!

 

[Jmpage2]

Thanks fellas I appreciate the very helpful information.