Exposed Timber Frame in Straw Bale Houses

Written by Andrew Morrison

exposed timber frame straw bale houseI 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.

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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.

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… Read more »

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… Read more »

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

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… Read more »

Wonderful posts on straw bale & timber frame. I specialize in Timber Framing and can help anyone obtain thier timber frame dreams. Visit Heirloom Timber Framing at
http://www.heirloomtimberframing.com/

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… Read more »

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… Read more »

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… Read more »

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… Read more »