I posted this exact message as a response to a question on the Podcast blog entry. For those of you who read it there, sorry for the duplication. After receiving a couple more questions about how to bale with exposed posts and beams I thought it was worth publishing this under its own heading.
Timber frame is a beautiful compliment to straw bale construction and it has been done several times in the past. The biggest thing to be aware of is that traditional timber frame is not cheap. A standard frame house may cost $6-$10 per square foot to frame while a timber frame home runs about $65 per square foot to frame. That is a major difference and the cost adds up quickly. It is possible to build exposed post and beam instead which is much more affordable and less of a specialty framing system. When doing this, a foundation must be poured for the bales out side of the posts or their load must be incorporated into the floor framing engineering.
Another consideration with running the framing on the inside of the bales is how to finish windows and doors and how the roof attaches to the building. Windows and doors are most easily handled by using bucks for their installation, boxes built for the windows that lay directly on the bales (or the floor for doors). By using bucks you can place your openings anywhere in the wall. In terms of roofing, it is always a good idea to have a large overhang (2′ or more) on bale walls. That is made a bit more difficult because the overhang has to cantilever from the inside face of the bales all the way out over them and that creates a weak spot for the roof frame. A simple truss design is a good idea (if post and beam) and the bent design for timber frame can also handle this. It is, however, important to be aware of this design issue before you complete the home design.
Another issue of concern is the plaster on the inside of the home. It will have a tendency to crack at every post if you are not careful. I like to use expanded metal lath (plaster lath) on the back side of the posts that extends out beyond them by about 6-8″ on either side of the post. This has to be installed before the bales. In addition, the bales need to be attached to the frame so more lath can be stapled to the back side of the post and then bent at 90 degrees and stapled into the top of a course of bales. Done at every course, this provides adequate attachment for the bales. The lath that was applied first allows the plaster to have a strong attachment point at the joint between the posts and the bales. A color matched caulk along that joint is a good idea too.
27 Responses
Hello.
I’ve signed up for your online newletter and check your blog pretty often. THANK YOU for what you are doing to promote and educate about straw bale construction. I am trying to educate myself as our family dreams of pursuing this in a few more years. We want a house that is “green” and efficient. We also love the style of timberframing, asthetically. What are your thoughts of combining straw bale and timberframing? Do you know of any sources about this that I could look into? We are wondering both about the environmental effects and just the feasibility of combining the two.
THANKS so much.
Katie
Thanks for the feedback Katie. I appreciate it. Timber frame is a beautiful compliment to Straw Bale construction and it has been done several times in the past. The biggest thing to be aware of is that traditional timber frame is not cheap. A standard frame house may cost $6-$10 per square foot to frame while a timber frame home runs about $65 per square foot to frame. That is a major difference and the cost adds up quickly. It is possible to build exposed post and beam instead which is much more affordable and less of a specialty framing system. When doing this, a foundation must be poured for the bales out side of the posts or their load must be incorporated into the floor framing engineering.
Another consideration with running the framing on the inside of the bales is how to finish windows and doors and how the roof attaches to the building. Windows and doors are most easily handled by using bucks for their installation, boxes built for the windows that lay directly on the bales (or the floor for doors). By using bucks you can place your openings anywhere in the wall. In terms of roofing, it is always a good idea to have a large overhang (2′ or more) on bale walls. That is made a bit more difficult because the overhang has to cantilever from the inside face of the bales all the way out over them and that creates a weak spot for the roof frame. A simple truss design is a good idea (if post and beam) and the bent design for timber frame can also handle this. It is, however, important to be aware of this design issue before you complete the home design.
Another issue of concern is the plaster on the inside of the home. It will have a tendency to crack at every post if you are not careful. I like to use expanded metal lath (plaster lath) on the back side of the posts that extends out beyond them by about 6-8″ on either side of the post. This has to be installed before the bales. In addition, the bales need to be attached to the frame so more lath can be stapled to the back side of the post and then bent at 90 degrees and stapled into the top of a course of bales. Done at every course, this provides adequate attachment for the bales. The lath that was applied first allows the plaster to have a strong attachment point at the joint between the posts and the bales. A color matched caulk along that joint is a good idea too.
Hi – having trouble getting your podcast; window won’t load? But thanks for your most excellent blog it’s teaching me a lot of things I want to know for if/when we get to build what we want.
— Leslie, Ruch
Quick Question: Can load bearing straw wall get building permits as easy as post & rail.
–Peter
Peter,
Good question. The answer is no. Post and beam structures are easier to pass through building departments because the inspectors understand the structural elements of the frame a lot more than they do the merits of the bales as a structural system. There is a code in Oregon and other states that allows for load bearing construction, however, you will likely have to do some convincing nonetheless!
Have you had any experience with Eastern Redcedar as a structural support? I’m wanting to use fresh, debarked timbers as the post in a post and beam strawbale barn frame.
Cor,
As long as it meets your local codes for structural support, that will be fine…and beautiful!
i’m designing a straw bale/timber frame home with an exposed frame. i’m planning on a 4×6 raftered roof with each rafter hanging out 18″ past the outside of the bale wall. i’m wondering if you have any suggestions as to how to join the top of the bale wall to my roof system (notch the bales around the rafters, then what?). i know from past experience that bale walls have the tendency to settle a bit and i’m trying to figure out a way to prevent a gap from opening at the top of the wall. any thoughts would be much appreciated. thank you.
Hi Ethan. I suggest you don’t try to notch the bales around the rafters. Remember that the strings will be on top and so that will make it all but impossible to notch the bales. Even if you were to stack on edge (which I don’t recommend), notching is still not the best option.
Build a soffit at the top of the wall that extends down from the roof assembly. The soffit should have a flat surface for the bales to stack up to. The area above the soffit floor is insulated with whatever insulation you are using in the house other than bales: wool, cotton, spray, fiberglass, and so on. The face of the soffit should be covered with plaster board so that when plastering, there is a seamless transition between the bales and the soffit. This is the easiest way to avoid any settling because you can cram the last course of bales in tight to the bottom of the soffit thus minimizing any sag that might otherwise occur. It also give you a channel to run some electrical if you need it. Good luck.
Hey Andrew,
I have a friend who plastred behind his exposed posts to limit cracking and for continuity. They used eye bolts to tie the bale structure to the backs of the posts. It was labour intensive for the plasterers to say the least but the finish is fantastic. He and I were talking the other day and wondered about the possibility of attaching masonry board with the plaster lath to the back of the posts. It seems like this would be a little more rigid to cracking and would give a seal behind the post without having to plaster behind. What are your thoughts?
Andrew,
Another quick question on window bucks on the bales. Is it better to carry the window bucks to the floor like the doors or is there no difference for crack reduction etc?
Also related to my last querry above, do your DVDs cover exposed interior post and beam techniques as well?
Again…. Great site Andrew, you’re doing great things for demystifying bales.
Thanks!
Pete
I like the idea of using plaster board behind the posts along with the blood lath. This would, as you say, make for a rigid installation. Sounds a little labor intensive, but perhaps not so bad in the end. Be sure it is relatively thin so you don’t have to notch the bales around it at every post.
In terms of the bucks, I prefer to carry mine to the floor if I can, again to minimize cracking; however, if they are anchored well to the bales and reinforced with the lath, they would be fine as a load bearing window buck, just floating on the bales.
My DVDs do not specifically cover the system you are talking about.
This is about as close a topic as i could find to my question. I have been designing a straw structure for abour 3 years, and i have yet come to any info on the type i want to use. I am planning on using post and beam but my posts will be approx 6 feet outside the bale wall, this gives us an exceptional overhang, and a wrap around porch space as well. however, it is very difficult to find info for foundations on this type of build. while the post and beam will handle all of the weight of the roof and ceiling, and some of the floor as well (we were planning on interior posts to support the ridgeline, which would also be tied to the ceiling and floor joists). the bale foundation will have to be tied in to the floor joist system and ceiling system as well. We have a 30″ frost depth in our build codes and i really dont want to put down a 2’x2.5′ chunk of concrete. for all the obvious reasons. Is there any input you could give me to help me with this? I would be ever grateful.
That’s a tough one. I would suggest rubble trench technology for sure. I think this is more of a question for an engineer though. You might try contacting Nabil (Nah-Beel) Taha at 541.858.8500. Good luck.
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I have also been planning a Post and Beam Strawbale construction and have purchased your entire DVD set and am anxious to recieve your new version of the Post and Beam Infill. Do you recommend a specific book that will get me started in how to Timber Frame? I was just about to push the button on “A Timber Framer’s Workshop: Joinery, Design & Construction of Traditional Timber Frames” but thought that I should check with you first. Also, I absolutely love the idea from Eric above and was wondering if he ever got any farther with his plans?
I don’t have any specific recommendations on timber framing. I have never done the art myself (with my own hands) so can’t really comment on it. Not sure how things went with Eric, I never heard an update.
When you say it cost $65/sq. ft. for post and beam – does that include the straw bales and such or is it just the post and beam frame? Also, is that using kiln dried wood? What about using rough-hewn lumber?
This is just the timber frame cost. Not sure how the lumber differences would influence the cost. I don’t do enough work with custom timber frame to answer that question well.
I have a post and beam restoration under way the task is to insulate the in between the rafters which are about 2 ft apart at most and merely 4″ deep.
I thought about baling these then sheet rocking allowing for 1/2 of rafter to show through in between. However being in the NY Northeast region w/36 R value required is tough.
I looked into spray foaming which would have been the most expedient and practical manner to address my needs, however, after 2 days of research I do not want to risk the off-gassing concerns and orders thereof.
Any suggestion how to approach this challenging task?
most other alternative insulation e.g. denimun and cellulose insulation are price prohibitive.
Open to healthy and eco-creative solutions.
TY
How much depth is there in the rafter cavities (the spaces between the rafters)? In order to get a high R value, you will need adequate space to place the insulation. Bales are not a good idea to add unless you increase the frame as they are very heavy. They add approximately 40 pounds per square foot to the frame loads, which is a lot. Insulation is very lightweight and thus well suited to the job. You may have to go with a formaldehyde free fiberglass insulation if budget and weight restrictions are in place. You can get an R-42 in a 12″ rafter bay with that material. Keep in mind that in most areas, the code for ceilings changes if they are vaulted and you are restricted to the rafter bay depth. It is often lowered to R-30. I always go with the R-42 in a vault, personally, as the roof is where most heat is lost in a building.
It should be no issue to use the foundation slab to build the frames on. I personally would rather clad the walls once standing. Insulating and breather membrane is certainly easier with panels flat, so do that, but perhaps leave the cladding off.
The frames would have to be up before the bales are stacked. Keep in mind we don’t use a commercial vapor barrier, only the plaster and the plaster is the cladding as well.
all these different ideas,what about zoning, that shoots down so many things one could do.
Zoning is really only in charge of what type of building you can put in a specific area. If you want to build a house in a residential area, that should be fine whether it is built of conventional means or straw bale. If you want to put a car dealership in that same area, now you’ll have a problem. Planning, on the other hand, can create all kinds of issues for people building with bales because they may not understand the process or may have a personal belief that it is a bad idea (typically based on not understanding the concept or its viability as a home construction technique). For that, you may need to get your building engineered (almost always solves the issue) or simply do some more leg work in showing that your home design does in fact meet and/or exceed the code provisions in place. This is one major reason that people in the straw bale world have been working hard to get a bale specific code provision approved within the International Building Code (IBC) and the International Residential Code (IRC). Helping to support that effort is a great way to preemptively solve the potential issues that you could encounter at the planning level.
Dear Andrew,
Been gleaning loads of information and tips from your posts and video’s, thanks :D..
Currently i’m in the process of designing a small straw bale house which I’ve recently reconsidered for permitting issues here in Portugal to include timber frame structure.
This reconsideration has opened up a whole load of new issues including basics such as internal/external frame? not sure which is better suited for a novice builder? I’ve completed the Rubble trench and am about to pour the reinforced concrete bond beam 60cm w x 30cm h. Will this be suitable to mount the frame with the right connectors? .. too many unanswered questions and no real experts about here in Portugal.. Help!
Thanks for your message. As long as the foundation you have provides enough depth and width for the frame to attach to, you will be fine. I don’t know the requirements in your area for depth of foundations nor the minimal width required for a frame to attach. Sorry I can’t help with that specifically. I find that an internal frame is the easiest to work with. Exterior frames are tough in terms of weather proofing. Good luck and sorry I don’t have a better answer.