Straw Bale Housing
The IronStraw Group - page 2
Straw bale building typically consists of stacking rows of bales (often in running-bond) on a raised footing or foundation, with a moisture barrier between the bales and their supporting platform. Bale walls can be tied together with pins of bamboo, rebar, or wood (internal to the bales or on their faces), or with surface wire meshes, and then stuccoed or plastered, either with a cement-based mix, lime-based formulation, or earth/clay render .... (more)
This is the second of three 'mirrored' pages of sections of the Web Site of the USA based IronStraw Group (Cashmere, Washington). Permission was received to copy the information on the pages. You can visit The IronStraw Group by clicking on the logo. More information about The IronStraw Group is provided at the bottom of this page.
The IronStraw Group
Building Technical Info
This is the fourth section in this series about building strawbale homes. Many times we focus on the technical aspect of building and forget about why we build this way.
We will try to include photographs of finished strawbale homes or details within homes so you can see the beauty in these strong buildings.
Because the walls are two feet thick, it is possible to make wonderful window seats built right into the walls that look very natural as in the photograph on the left. Just add pillows or cushions, coffee and a good book. We loved sitting and looking out this window to the forest behind our house. Nature and all the wildlife can be observed if we take the time to slow down and look. This is part of strawbale building also, don't forget to nourish the soul.
Raising the Walls - continued
In the previous section we showed several photographs of the wall going up during a workshop and how hectic it can get. Pinning bales is an integral part of your home's stability and can easily be overlooked. Someone needs to check this - that's why we recommend wall captains for each wall. Starting with the first course, all corners must be pinned together. One method is to use rebar bent into a "U" shape approximately 2' along the base with 6"-10" legs. We recommend #3 rebar because it is easier to make the tight bends of the "U". This pin can easily be pushed into the tops of the two corner bales to secure them together.
It is advisable to have all window and door frames complete and ready to install on the work site before you have your workshop. This will make your wall raising go much smoother and faster. Preparation of the frames also includes corner braces so everything stays square during installation and further bale stacking.
Corner braces can be made from any kind of scrap wood on your site, or salvaged from past projects as long as it is strong enough to keep everything in place. We like to brace as many corners as possible, with some on the inside and some on the outside. We think that two is a minimum if they are fairly large.
This photograph shows a window/door frame combination installed with several courses of bales stacked in place. Keep in mind that stacking the bales should start at your door and window openings as well as your corners. Always stack towards the center away from your openings and don't force bales into your walls. A nice snug fit will help keep your frames in place and square. Too much cramming and jamming of bales in the wall can cause your corner posts to move or your window/door frames to go out of square. The wall raising will go quickly, make sure your wall captains know how snug the bales should be and that they check each course.
When the 4th course is complete it's time to pin everything together. This is the time to inspect the wall to insure it is straight and that there are no bales sticking out where they shouldn't. Line up all bales - use a large sledge hammer to move stubborn bales. Some people have made "bale whackers" using a sledge hammer size handle and a large block of wood (4"x8"x12"). This can be great fun! Run a string between your corner posts at each course to be a guide. Each course of bales should have been inspected and aligned before the next course went on top, this is an extra check.
Once you are happy that all the bales are ready to be pinned it's time to pound rebar. We recommend using #4 rebar to pin the bales. Some people have used bamboo and wood stakes and they work well; however, if you have had to convince your building official that the strawbale walls are really safe, then they will usually prefer rebar. As long as your building official is satisfied with your choice, use the material you prefer. We will talk about using rebar since it is widely available at local lumber yards and inexpensive. The added stiffness of #4 rebar is suggested here rather than the flexibilty of the #3 used for the corner "U" pins.
Tools to aid in pounding rebar are illustrated in Build It With Bales (Buy this book at the beginning of your planning and read it - see details below.) During the wall raising assign two people to cut rebar in 5' lengths. You will need 2 pieces for each full bale (if you have 30 bales around the house, you need 60 pieces.) This rebar gets pounded down through all 4 courses tying every bale to the ones above and below.
This procedure will be repeated for every course upward. If your walls are 6 bales high, you will need another 120 pieces of rebar. the photograph above shows a 7 bale high wall ready to be covered in plastic at the end of a day. This wall has a 30 degree bend in the middle of it.
The IronStraw Group
Building Technical Info
This is the fifth section in this series about building strawbale homes.
Wall raising continued
We emphasised the importance of pinning bales and making sure the bales are stacked straight in the last article. This is really important at this stage - it will make your job much easier later on. Wall captains, or someone should be diligent about checking the straightness of your walls. Make sure the corner guides have not moved and the door/window frames have not been pushed out of square. Be patient and check this and fix any problems as the walls go up. We recommend that the owner builder not have any assigned tasks except to oversee this part of the wall construction.
This will payoff (and it's so much easier now) making box beam placement and eventually stucco-ing much easier. Don't pin a course of bales until you are satisfied that it is straight and just the way it should be.
Which brings us to box beams, or as described in Build It With Bales, rigid beam assemblies. No matter what you call them, for load-bearing walls, something has to be on top of the wall for your roof structure to sit on. We have used many of the variations in Build It With Bales and prefer a box beam made of 2x4, 2x6, or TJI (in order of least to most rigid) all combined with plywood tops and bottoms and stuffed with straw. Assemblies are made to various lengths to fit your walls.
*NOTE: This drawing is not meant to be a substitute for your drawings to be submitted to your building official, it is a general drawing to give you an idea of how a box beam is constructed.
Depending on each individual building design, one of these beam assemblies is usually a good choice. Now is a good time to mention structural engineers who will remind us about the length of the span for openings, or the distance between trusses and the roof dead load and the snow load, etc., to determine the appropriate beam assembly. If you have not had any building experience it is a good idea to have your plans reviewed by someone who can calculate or verify that your structure is safe. This does not mean you need to spend thousands of dollars hiring architects and structural engineers. (Although they are highly trained professionals that will ensure your building is safe.)
During our last workshop, one of the volunteers told us about a very reasonably priced engineer familiar with strawbale buildings that he highly recommended. Contact us if you want to hire an engineer and we'll pass along his information.
Here's an example of a wall during construction showing many of the things discussed here and in previous articles. So take a look. This is a load bearing wall with a load bearing door frame. The door frame will support all the weight of any bales and the roof loads above it. This type door frame does not require a separate lintel (as long as you have calculated the wood needed to support across the distance of the door opening.)
Also note the temporary support to keep the wall straight. Here the "box beam" is in place but not connected down to the foundation yet. The hole between the bales just above the door to the right will be stuffed with straw after the wall is secured.
This is a 6 bale high wall using 3 string bales. The resulting ceiling height is about 8'-6". Also note the sill plates under the bales, two 2x4's to give a 3" step up for the bales to sit on. It is inexpensive insurance against future water damage from flooded floors.
Which brings us to wall tie down systems, or strapping. We have favored high strength poly strapping rather than metal strapping because it is much easier to work with and less likely to cut hands. Another alternative is wire fence material and Gripple wire rope connectors. This is really a personal choice so we suggest you participate in some building projects, either through workshops or volunteer on a site. You will want to do this anyway before you tackle your project, so it would be a good time to check the method used on the work sites you visit.
This photo shows the green poly strapping on the far wall (if you can see it...). This runs under the sill plate (anchor bolted to the footing) and up over the top of the box beams on top of the walls. You can also see the radiant infloor heating tubes (red) and the rough plumbing. All this ready for the concrete floor to be poured. We used rigid 2" insulation under the entire floor.
In the next section we'll show you some trusses and talk about getting the roof on your walls as quickly as possible to protect your straw. Post and beam construction gets your roof built before the walls, so protecting your straw is not as much of an issue.
If you are planning to build where it is rainy all the time you might want to consider post and beam. We have always built in climates that have some time of year that you can count on it being sunny and dry to build.
Matts Myhrman and Steve MacDonald, Build It With Bales, Version 2. Out On Bale, 1037 E. Linden Street, Tucson, AZ 87519 USA. [Price US$29.95 plus S&H]
If you are interested in building, see our consulting page to see how we can help you. You can e-mail Michael Thomas, Co-Founder of IronStraw Group in the USA at thomas(at)ironstraw.org
For more information click on the IronStraw logo or e-mail