Timber Framing and Straw Bale: The Perfect Marriage?

by ziggy on April 12, 2013 -- 4 comments -- Follow

Straw Bale & Timber Frame House 01

Straw bale & timber frame house in the works

I wonder: is timber framing and straw bale building the perfect marriage of two building techniques? Of course, I may be a bit biased, as I am building a timber frame and straw bale house as we speak, but I think there is much to say for the compatibility, efficiency, and beauty of these two systems. I’ll lay out my line of thinking here, including the benefits of timber framing and straw bale alone, and the two systems combined.

Straw Bale & Timber Frame House 02

Timber frame is left exposed on interior when wrapped in bales

The Advantages of Timber Framing

The advantages of timber framing are numerous. Timber frame buildings are more durable and long-lived than any other framing system. They absolutely put stick frame houses to shame, for one — there are timber frames over 1000 years old still in existence.

They also have the advantage of greater fire resistance (think of the difference between burning a sheet of paper, versus a book of paper), and a better resistance to earthquakes and severe weather. (In Japan, timber frames are ingeniously designed so that the frame will fall apart before posts and beams are buckled and damaged in an earthquake scenario.)

The use of timbers can be rather economical, as well. Timbers generally do not travel very far to the building site, meaning local sources of wood are more likely to be used, and whole trees or the majority of a trunk is used in the production of a timber. Despite a higher initial cost in materials and labor, the payoff is a structure that will last exponentially longer than a conventional home.

Straw Bale & Timber Frame House 04

Uninterrupted insulation also protects frame

Straw Bale House Benefits

Straw bale houses pose a number of benefits, many of which should be fairly obvious. Here are a few of the advantages:

  • Straw bales are extremely insulative (they are typically quoted to be an average of R-35 for 18″ of thickness, or “R-Enough”, as some like to say).
  • If well-maintained, straw bale walls can last at least 100 years or more
  • Like heavy timbers, straw is not liable to catch fire very easily.
  • Straw bales are widely available and are a renewable resource, they’re completely biodegradable, and inexpensive
  • Bales are fairly simple to work with, requiring few specialized tools.
  • They have excellent sound isolation qualities.
  • Bales can regulate moisture as they are a vapor permeable medium, and they are appropriate for a range of climates, especially colder or more northerly regions.

Timber Frames and Straw Bale: The Perfect Union?

Now, to speak to my original claim — why are timber frames and straw bales an excellent marriage of two building systems? Let’s look at some of the combined benefits:

  • You can achieve a fully insulative envelope — straw bales work best when they wrap a timber frame, providing uninterrupted insulation. The insulation in stick frame homes, on the other hand, is interrupted at each stud every 16″. And timber frames with infill insulation are more likely to have air penetration at each junction.
  • On a similar note, notching straw bales can be largely avoided when used in conjunction with a timber frame, saving time during the construction process.
  • Straw bales protect a timber frame from weathering — the most critical element of the home, the frame, is protected when fully wrapped in bales. It is way more costly and complicated to repair the frame of the house, versus the walls. Straw bale walls, in a worst case scenario, can be knocked out or replaced without affecting the framing. The timbers, as they are not exposed to the weather, are much more likely to last a long, long time.
  • Aesthetic advantages are numerous, including an exposed frame on the interior, which is visually appealing and functional for dividing living spaces, and posts and beams provide an area for hanging objects. Straw bale walls are thick, and offer creative opportunities in the way of window seats, curved window reveals, and niches.
  • Notably, the use of straw bales and timbers conforms to several of the “patterns” in A Pattern Language, including #160 Thick Walls, #206 Efficient Structure, #207 Good Materials, etc.

Ultimately, a timber frame and straw bale house is very tight with proper detailing and offers excellent energy efficiency, durability, and longevity. The two systems when combined offer superior and uninterrupted insulation, excellent fire resistance, and a much more aesthetically pleasing style than a conventional frame with drywall. The use of these systems provides the builder a better opportunity to use local and natural resources, resulting in less waste and embodied energy costs, and a home that at some far-off date will degrade fairly harmlessly back into the earth.

Straw Bale & Timber Frame House 03

Paying careful attention to a floating window buck

Perhaps the main challenge in this marriage is the framing of doors and windows, these challenges can be overcome with good design foresight and careful attention to detail. Also worth mentioning is the level of attention that must be paid to plaster details around posts and beams, as clay plaster is especially liable to shrinkage and pulling away from framing.

Well, what do you think?

Related reading:

http://www.strawandtimber.com/STRAW_BALE_QUESTIONS.html
http://www.lowimpact.org/factsheet_straw_bale_building.htm
http://www.buildnaturally.com/EDucate/Articles/Strawbale.htm
http://www.strawtec.com.au/page.php?id=5#GoodBales
http://www.timberframemag.com/advantages.html

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  • jay

    Ziggy,

    Great read once more. I am not a fan of SB construction for many reasons, but when it is done in concert with timber framing, as an infill method, that is when it is something else entirely, then I love it. Your builds have been excellent.

    Warm Regards,

    jay

  • ron

    There is a difference between air permeability and vapour permeability.
    Straw bales properly covered in clay allow moisture out but not air.
    Looking fwd to future posts. Thanks.

  • Sophie

    What do you do about termites? I’ve seen straw catch on fire pretty easily, also…. I don’t know about it… I’ve seen traditionally built houses with straw insulation and plaster before that seemed safe enough. Are you guys going to drywall over the straw?

  • Hey Z,

    I get updates whenever someone post more to this article, which of course gets me thinking about it some more. You should really repost this on “Linkedin” in the SB professionals group. You made some wonderful observations.

    As for the plastering, that is a “design issue” that many stumble over, but is rather easy to overcome. Many years ago, while still under my mother’s influence who was a wonderful artist, craftsperson, and designer, I learned about “shadow lining,” in illustration, sculpture, and, most importantly to this discussion, in architecture.

    We get into “cultural mindsets,” which often places us to close to the tree trunk to see the “forest and the trees themselves.” My mother got me into the habit of taking a step back from an “issue,” and really stepping outside “the box” when thinking about it. Thinking about “shadow lines” in this regard applies to where you place the SB, was taking that “step back,” and not thinking about the process as “others do,” but rather “how we could.” Most folks never consider placing the SB 30 mm to 150 mm (1.25″ to 6″) away from their timber frame, there by creating, architectural depth (shadow line,) recesses for MEP (mechanical, electrical, and plumbing)-hidden lighting and fire suppression systems as two examples, and, of course, ease in rendering the walls with whatever method you choose from plasters, to some other cladding.

    As for Sophie’s question, termites in general are a none issue if a structure is designed with “pest management” in mind, or at least not until you start thinking of building in tropical climates. Drywalling (especially with contemporary materials and methods,) would be counter productive to the “natural build process,” as these materials often “out gas” harmful fumes, nor do they breath as they should.

    Till later Z, keep up the good work…

    jay

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