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How Straw Bale Houses Work


Straw Bale Additions and Retrofits

Say you're interested in straw bale building, but you're already settled in your house. You can still use straw bales for additions and retrofits.

Straw bale house mid-construction
Photo courtesy StrawBale.com
Straw bale construction

Straw bale additions are accomplished by tying the addition to the existing structure. After laying each row of straw, place a lath, which is a sheet of metal mesh, over the bales and attach it with dowels or landscape pins. Then, fold the lath at a 90-degree angle and staple it to the frame of the existing house. If you've built a straw bale addition with wooden frames, then the frames can just be attached directly to the frames of the house. Plastering the addition is completed in the same way as straw bale construction.

A contractor can assist with matching up the exteriors of the house and the addition. In laying foundation for an addition, consider the thickness of both the bales and the plaster so that the finished addition will line up with the existing house.

It's possible to wrap your existing home in straw to achieve better energy efficiency. As in building a new straw bale home, the design for a retrofit must ­consider how to prevent moisture from getting into the walls. Straw bale s feature large roof overhangs to protect the walls from rain, so a retrofit may require changing the current roof of a home. This may be accomplished by changing the slope of the roof and extending it.

You may have to create a larger foundation for the house so that the foundation can support the additional width of the bales. This new portion of foundation can be attached to the existing one with epoxy (or anchor) bolts [source: Morrison]. Then, toe-ups should be built to keep the bales off the ground as they are in house construction. However, instead of stacking the bales and then plastering, as is done in straw bale construction, the bales should be dipped in an earthen-based plaster before stacking. This way, plaster is on the bales before they are set up against the home. The bales also can't be tied right up against the house because of the risk of moisture from the siding of the existing house getting into the straw bales. Use a wire netting between the house and the bales to create ventilation [source: Morrison].

When you have bales on the outside of an existing home, you'll have to do a little work on windows and doors; otherwise, using bales 18 inches wide will set windows and doors into deep wells. You can avoid this extra work by retrofitting with the bales on the inside of the house, which is done in much the same way; however, doing so would reduce the space within the house by the width of the bales.

Although creating a larger foundation, changing your roof line or undertaking any of the other tasks necessary to incorporate straw bale construction may seem prohibitively expensive, remember to weigh those costs against the energy savings achieved over the lifetime of the house.

To learn more about straw bale construction, visit the links on the next page.