Keep as much of the plumbing out of the bale walls as possible. That’s it, end of lesson. Okay, so there’s more to it than that, but that is perhaps the most powerful tip I can offer. If you can manage to keep all of your plumbing inside of interior, stick framed walls, you will eliminate most of the hassles associated with plumbing in straw bale structures. In fact, if designed properly, a straw bale house will differ very little from a conventional house as far as the plumbers are concerned. There are three areas that can be difficult to address in straw bale structures because the plumbing in those areas simply cannot be kept out of the bale walls. It can, however, be isolated from them.
A typical problem area is the kitchen sink because most home owners want a kitchen sink with a view which, by design, tends to place the sink against an exterior wall. A simple solution is to bring the water lines up through the floor and cabinets; however, the vent line still needs to exit through the roof. In some scenarios the plumber can “wet vent” the lines to allow them to exit the building through a framed wall; however, I find that the best way to deal with this situation is to frame in the area behind the cabinets with standard materials so that the water and vent lines can all be run in the same location. This completely isolates the plumbing from the bales and eliminates the risk of water damage.Once plastered, the area will be completely hidden and nobody will know the difference.
Another plumbing detail commonly used in conventional homes is the placement of the tub and/or shower against an exterior wall. The extent of the risk is proportional to the permeability of the finish materials for the shower. In other words, if a drop in fiberglass unit is used to create the walls of the shower, the bales can be adequately protected with minimal extra effort. On the other hand, if some porous tile or natural stone is used, the substrate will have to be protected with extra care as water will find its way through the finish. There are many options out there including tile (well backed), solid surface material like that used on counter tops, metal roofing, natural stone, glass, drop in fiberglass units, and others.
Whenever it is not possible to protect the bales from contact with water, consider framing the area out and creating a section of faux bale wall, similar to what we did in the kitchen. By matching the depth of the bales with framing and insulation that can be wrapped in waterproof materials that drain to the exterior, the bales are isolated from the potential risk. The diagram to the left shows how this is useful in the case of a tub unit. Note that the isolation walls completely separate the bales from the tub and the framed wall is insulated and protected from water intrusion with conventional detailing.
Another location where water isolation walls, or in this case a water isolation box, is essential is around hose bibs located in bale walls. The only option for separating the water lines from the bales is to place the pipe in a water isolation box as shown here. The box should be as tall as the surrounding bales and once completed, flush with both the interior and exterior planes of the wall. Give yourself enough room to work inside the box without making it bigger than you really need. Wrap the box interior with a waterproof material (roofing felt or visqueen work well) and then cut your bales to fit around it during the baling process.
Finally, follow standard practices for wet locations in the design. Keep kitchens, bathrooms, laundry rooms and other wet areas close to each other to minimize costs and material use. When building with a concrete slab, locations on the first floor need to be accurate and well planned as they will literally be set in stone once the concrete has been poured.