There are many different approaches to framing a straw bale house; however, there is one in particular that I have used on the vast majority of my projects over the years. It is a post and beam frame system with roots in conventional framing techniques. Because I came to straw bale construction many years ago as a general contractor practicing conventional construction, I brought some of that detailing over. I should preface this article by saying that there are right ways of framing and wrong ways of framing. The system I describe in this article lands in the “right way” column, but so do many other styles. As long as you are working with a structurally sound and safe system that brings you the best results possible for your style of building, then go for it.
One of the first details that often surprises people is the spacing of the posts in the system I use. I hear people talk about wanting to reduce the amount of notching in the bales by spreading their posts out as far as possible. I disagree with this approach and instead keep my posts relatively close together: no more than 6’ apart. One reason for this is that when the bales are stacked in between posts that are set far apart, there is no point of attachment for the bales other than the top and bottom of the wall. As such, the wall becomes weak as it is stacked higher. When posts are set closer together, the notches at each location provide a point of connection to the frame and make the wall much stronger both during construction and for the life of the structure.
One way I keep the posts close together is by incorporating them into the window and door frames. By using 4×4 posts as the king studs I end up with wider nailing surfaces on either side of the opening. This allows me to attach the finish trim, plaster channel and/or plaster lath, and welded wire mesh around every opening with positive attachment to the frame. These king studs serve two purposes by providing the nailing surface and by acting as part of the overall structural frame. Because windows and doors are placed in many locations around the home, and because I otherwise limit my post spacing to no more than 6’, I can minimize the wall beam size as a result. This minimal wall beam is important because the bigger the beam, the more expensive it will be. Further, larger beams are made from larger trees (unless an engineered beam is used) and I want to reduce the size of the trees I am using in my projects for environmental reasons.
Okay, let’s take a look at how the system works and why it can save time and money in your building process. I’ll simply lay out the process so you can see, step-by-step, how it comes together.
Use 8d nails to tack (just barely nail) a 2×4 top plate to your bottom plate (in this case, a 4×4 which will be part of your toe-up system). Complete the framing layout on the two plates just as you would in conventional construction. For those of you not familiar with this process, start with wall openings (window and door locations) and partition walls. Mark the king stud of the wall opening with the letter K and the trimmer studs with the letter T (see diagram below for window framing details). Use the letter P to mark any partition walls that intersect the main frame. You need only mark the P on the top plate as there will not be a framing member attached here, only a notch cut in the top beam. I’ll discuss this in more detail below.
Next, mark a line across both plates at one edge of the location of all the posts and strike either a dash or an X on the side of the line to represent the post location. (Note: I use 4×4 posts throughout my structures to save time and money. A major reason is that anything bigger gets into the plane of the strings, which either need to be cut and retied or pulled out of the way. A 4×4 post will notch into the bale without any adjustment to the strings, thus saving labor.) For studs that are truncated by windows or doors, mark the plates with the letter C for cripple. I know this is not the most PC labeling system, but it is the industry standard.
The reason I start with the windows, doors and partition walls is that those locations are typically specific and not something that I want to start moving around at this stage of the process. In addition, you may find that a post lands on or very near a window/door frame. In this case, you can often eliminate the post and simply use the wall opening frame as your structural element. This saves you some additional lumber and time in both the framing and baling phase. Be careful not to remove posts that are too far from the wall opening frame as this may create a situation in which the beam becomes “over-spanned” and undermines the engineering of the structure.
With the layout complete, separate the two plates and place them on the floor system (slab, framed floor, etc). Insert your window frames and posts per the layout and attach them to the plates. Use at least two 16d nails to attach through the top plate into the posts and frames and use four 8d nails to toe-nail the frames to the bottom plate. Do not attach any wood in the location of the partition walls because the intersecting walls will not actually make it all the way through to the exterior frame. The only place this is not true is when the partition wall is used to create a water isolation wall against which the bales will stop. You can learn more about water isolation walls on our website.
Now stand the wall in one long section, or several sections depending on the wall length. Be careful not to lift too much at once as that can be dangerous. Lift only as much as you and your helpers can do safely. After all, standing one long wall can be faster than standing two shorter walls, but not if you end up in the hospital along the way.
Building the walls on the ground speeds up the process tremendously, and here’s why. One of the big problems with traditional post and beam construction is that each post has to be plumbed in two directions and then braced in that position. Once the posts are braced, the beams are laid into position, often nudging the posts out of plumb. After some fine-tuning of each post, the frame is up and braced; however, no windows or doors are installed. Those would have to be framed in to a standing wall, which is much harder and slower to accomplish than framing them on the ground.
With the system I use, the wall is built completely on the ground and raised as a single unit. Once it is lifted into position, the bottom plate is moved onto a chalk line snapped on the floor system and anchored into place. If anchor bolts are part of the equation, i.e. you are framing on a slab, then those locations can be pre determined, drilled, and fully prepared ahead of time so that the wall can literally be raised, lifted and then dropped onto the bolts. If framing over a wood deck, simply attach the bottom plate to the frame (not just into the plywood decking) with long structural screws, like those used in SIPs construction [Trufast or Timberlok screws].
This is where things get even better: plumbing the wall. Because the layout was marked in exactly the same location on both plates, plumbing the end of the wall will translate down the entire length of that section. In other words, by securing the corner of the wall in a plumb location, the entire wall section is plumbed in one step. This is much faster than plumbing each post. Continue around the structure plumbing each corner and bracing the wall sections in position with long diagonal braces (typically 2x4s) attached to the exterior of the frame.
For longer walls, raised in multiple sections, be sure to brace each section in line with the adjoining section so that any changes made to one will translate to the other. I break my walls so that the junction is split evenly over a post location. This allows me to stand one section with a post in place, and then attach the adjoining section directly to the post so as to make the wall sections perform as one. With all of the walls in position and braced, add steel strapping plates to connect each post to the bottom plate. I use plates on both sides of the posts to ensure a solid connection as relying on toenails alone isn’t strong enough.
The final step of the frame assembly is to lay the beams on top of the 2×4 top plates and nail them together (nail from the 2×4 into the beam). Once the beams are in place, you can straighten the walls as necessary. Because the corners are already plumbed, straitening the walls will transfer that plumb line down the wall and keep the frame straight. Here’s a quick tip: if you buy beams that are really straight to begin with and you don’t leave them around the site for long before they are installed, you won’t have much work to do in order to get the walls straight.
Install the partition walls and make sure that everything is tied together by clearing out a section of the beam (basically creating a dado) equal to the depth of the 2x interior top plate as shown in the diagram. Lay your partition wall top plates into the dados and face nail down through the intersecting plate to tie the two walls together permanently. This adds a level of “out of plane” strength to the bale walls and also transfers shear strength from the partition walls to the bale walls.
I leave the last stud, closest to the bale wall, off of my partition walls when completing my initial framing. This allows me to access the bale wall with ease during the baling phase so that I can place, plumb, and clean up the bales without getting trapped behind a stud. Once the bales are fully prepared, I attach the last stud assembly of each partition wall to the bale wall by nailing it at the toe up and top plate. The image below shows a mock up partition wall with a minimum ½” plywood backing, covered with roofing felt. This provides a vapor seal at the wall intersection and a nailing surface for both the field mesh and plaster lath and creates a high quality transition between the partition wall and the bale wall while firmly connecting the partition wall to the bales without having to drive a single dowel into the bales.
The process of baling is either improved or impeded by the framing system into which the bales are applied. Take the time to properly frame your structure and you will save time and money throughout the rest of the project. After all, having adequate nailing for mesh, plaster lath, and finishes is more than just desirable, it is imperative. Whenever one aspect of the build has a positive effect on one or several following details, the process is improved. As I mentioned at the start of this article, this is one way to frame, not the only way. That said, I believe in this system and have used it on many, many projects with great success. I find that it is fast and effective and provides for a strong wall system and I know it will do the same for you.
Andrew has a passion for straw bale construction that is matched only by his desire to teach his knowledge to others. With nearly 20 years of building and contracting experience, he has now moved his practice entirely to consulting and teaching. He shares his knowledge with thousands of people via his DVD series, blog, and hands on workshops. To learn more, please visit www.StrawBale.com.