A straw bale building is wonderful for us. It provides us with a super-insulated house. The buildings went up quickly and were easy on the budget. Building a house out of natural material that is a by-product of food production gives us a good feeling in terms of environmental kindness. All good stuff.
However, no matter how tight the bales, those golden grass stems don’t offer much in the way of purchase and strength for hanging a shelf for a row of heavy plates, glasses, and bowls. Even sheet rock expansion fasteners punched through the plaster aren’t strong enough to guarantee that you won’t wake up to the sound of crashing crockery some night.
Here are some tips on securing shelving, electrical outlet boxes, and even attaching additions and porches to a straw bale building. We used these techniques for both our straw utility building and our straw bale home. Our cabinets and shelves are rock solid, our electrical boxes don’t wiggle when you pull out a plug, and neither the front porch nor my workshop have blown away.
There are essentially three techniques we incorporated in building for these attaching needs. One is for shelves and cabinets, another for electrical outlets, and another for attaching rafters for a porch or addition. Each of these is our adaptation of procedures used in a variety of natural building books.
Materials for installing one shelf hanger include:
a 2 x 4 cut to length
2 - 3’ sections of all thread
4 - flat washers at least 1” diameter
2 - 4” x 4” piece of 3/4” plywood.
The length of your 2 x 4 will depend on the shelf bank or cabinets being installed. In our utility room, we installed hangers vertically about 3’ apart and from floor to ceiling to provide for adjustable shelving. In our kitchen, we installed one hanger the length of our cabinets, about 10” below counter height and built a 1”x4” nailer into our home-made cabinet boxes.
Tools we used included a battery powered saws-all, 1 1/4" spade bit, 1/2" twist wood bit, power hand drill, bolt cutter or hack saw, hammer, and wrenches.
With the saws-all, cut out a cavity in the inside straw bale wall a bit wider than your 2 x 4, maybe 5” wide, for the length of the hanger. Excess cutting will be filled by plaster so don’t try for precision. Just make sure that the 2 x 4 is flush or a little recessed with the plane of your wall.
Drill two holes to just allow passage of your all-thread through your hanger, spacing them for even pressure. We put them in about two feet from top and bottom in an 8’ run (more in a longer hanger). With your 1 1/4” blade bit, cut a countersink hole to prevent the fastening nut from sticking out from the plane of the board.
Place a steel washer and nut on the end of a section of all-thread, push the other end through the hanger, insert the hanger into the cavity and, using a piece of scrap wood over the end of the all-thread, drive the section through the bale wall as straight as possible.
With the saws-all, excavate around the protruding all-thread on the outside wall to a depth of about 2” and large enough for your 4” plywood piece. Drill a hole in the center of the 4 x 4 plywood and slide it onto the all-thread, put on washer and nut and tighten finger tight.
Repeat the process for the other hole(s). Secure the nuts very firmly, keeping in mind the need to keep the hanger evenly mounted. With bolt cutter or hack saw, cut off excess all thread. You may want to file down any sharp cutting burrs to save some skinned knuckles when plastering.
Electrical outlets are installed in somewhat the same manner. However, instead of piercing the wall, wedges are cut and driven into the bale after a cutout slightly larger than the electric box is made in the straw with a saws-all. I make my wedges by ripping a piece of 2 x 6 about 12” long in half. I then make wedges from the 2” x 2 1/2” pieces.
Be sure to cut your wedge with two beveled sides to insure a flat surface for mounting your electrical box. Drive your wedge into the bale with the wedge point parallel to the orientation of the straw. Don’t wedge between bales. It will be impossible to get enough contact to provide a secure foundation.
There are many methods of cutting the wedges. I use a table saw and a home-made jig. It is slower and less efficient than a commercial jig, but it only cost pennies to make.
Drive the wedge into the bale so that your box will mount about half-way into the wall. If you use adobe plaster, as we did, the plaster coats will be about 1 1/2” thick. You don’t want to tunnel into plaster to mount your electrical box plate. Ask me how I learned this one!
When the wedge is secure and driven in the bale to the proper depth, attach the box to the face of the wedge. I simply screw in a couple 1 1/4" sheet rock screws.
Attaching a porch or small addition
We really don’t recommend that you attach a porch or addition to straw bales, although we join interior stud walls using the shelving hanger process described above.
For an add-on, we take advantage of one of the building elements of a straw bale building. That is the bond beam that is installed at the top of the bale wall. It is fastened mechanically to the stem wall using one of a variety of techniques (more of this in another blog). The bond beam that we use is a simple box with interior cross pieces made from 3/4” plywood and 2 x 6 dimension lumber.
The bond beam is securely attached to the wall and further stabilized by the attachment of the roof trusses or rafters. To the outside 2 x 6 of the bond beam box, we simply attach another 2 x 6 as a plate with carriage bolts. The plate will be exposed after the wall is plastered and provide a secure anchor for rafters attached with joist/rafter hangers. We have used this method for our workshop, our potting shed, and all our porches.
It is important to remember that there are many building techniques for DYI straw bale buildings. These are just some that we have used successfully. We wish anyone undertaking the building of their own house, straw bale or not, all the best. There are few more personally satisfying adventures.