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straw bale and condensation around pipes?

Posts: 2
Location: 乯畭, New Caledonia
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Hi folks....a quick question for you straw bale experts! Do you have any specific treatments to where water pipes and drains come in and out of the house? With the possibility of condensation due to differing temperatures do you have a trick to isolate this potential issue,
Posts: 35
Location: Jacksonville, OR
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In response to Alex’s question about water and drain lines in a straw bale wall and the concern for condensation, there’s a chapter in Straw Bale Construction Details: An Illustrated Guide for Design and Construction that covers plumbing in a straw bale wall but we don’t delve into condensation much—mostly because we recommend not running water lines in straw bale walls!

The concern is as much for a leak damaging the bales as much as for water vapor in the walls condensing on the water line and possibly damaging the straw.  

Water lines generally enter from under the building through the foundation, and we try to bring water to the building’s utility room where it gets distributed to sinks, toilets, showers, washers, etc. under the floor, through interior partition walls, or the attic space.  Good planning during design pretty well eliminates the need to pass water lines through the straw bale wall assembly except for very short runs (the wall’s thickness) to supply a hose bib (aka spigot, outside faucet, sill cock, hydrant).  

In that situation we recommend that the line pass through a sleeve sloped to the exterior so that if a leak should occur water would drain to the outside.  If there’s any concern for condensation the water line can be wrapped with insulation and passed through an oversized sleeve.  Or the sleeve itself could be wrapped with insulation.  Some builders will fabricate an insulated chase for the water line to pass through, although I think in most cases the sleeve itself is enough.  Nowadays most buildings seem to be plumbed with flexible PEX tubes, and we use PVC or ABS pipe for the sleeve.

A related concern is that water lines near the exterior of a straw bale wall could burst during freezing weather.   Frost-free hose bib valves used in conventional construction place the actual valve inside the conditioned space so that’s unlikely to occur; when the valve is turned off there’s no water in the line that remains inside the wall.   But straw bale walls are  thicker than the longest frost-free hose bib assembly (14”) that I have seen so far.  Still, using a 12” or 14” long frost-free assembly places the valve well into the wall where it’s not likely to freeze.

But in places that experience extremely cold winters there’s another solution.  “Trunk-and-stem” water line systems are the most common in North American residential plumbing, but they can be wasteful of hot water.  Another kind of system called a “home run manifold” system allows each water using fixture to be turned on and off at a manifold inside the house.  As winter approaches water lines that serve a hose bib can be drained after the line has been turned off at the manifold.  

Drain lines generally exit through the floor—I haven’t seen a drain line in as straw bale wall yet, but if one had to pass through, as with a hose bib supply line, a sleeve might not be a bad idea.  Drain lines aren’t pressurized, but if the drain pipe needed to be replaced a sleeve would facilitate that.  

Plumbing waste fixtures like sinks and toilets use traps that prevent sewer gases from leaking into the house.  The waste lines must be vented, and these vents are much easier to run through an interior partition wall and pass through the roof, but they can be run through a straw bale wall, too.  
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