From 2012-2013, my partner April and I took on the work of building a new home for ourselves. After living in a less-than-warm cob house in a cold northern Missouri climate, we quickly decided in favor of using straw bale for the wall construction to provide insulation in our new design. That left the frame in question, but we quickly decided that it had to be a traditional timber frame, and I'm glad we made the choice.
Advantages of Straw Bale Building
The union of straw bale building and timber framing is a harmonious one, and there are numerous advantages of employing the two systems in collaboration. Straw bale and timber frames are highly compatible, beautiful, and the efficiency and longevity of using these natural building techniques is superior in a cold climate setting.
The use of straw bales in home construction is actually rather "new", relative to the historical longevity of other natural materials, especially stone, cob, adobe, wattle and daub, and others. All of these long-lived materials have one thing in common -- they are all massive, and do not provide much in way of actual insulation values (R-values). If your goal is to maximize insulation and minimize the amount of fuel you burn to keep comfortable, straw, and specifically straw bales are an excellent option to pursue.
A two-string straw bale is typically quoted to be an average of R-27.5 for its 18" of thickness when used on-flat. (Oak Ridge National Laboratory, 1998). Though there are other materials with a higher R-value per inch, I would argue that straw bale is a highly effective choice of insulators, considering all other factors involved.
Straw: A Local Building Material
Those other factors include local availability, fire resistance, ease of use, moisture regulation, and longevity. Straw is widely available across the country, and not too surprisingly, the same places where wheat and cereals are grown are those same places where people usually benefit from living in a well-insulated home. That includes places like the cold north, midwest, and northeast United States.
In an era where nearly everything is shipped great distances during its manufacturing and delivery, choosing the local option is increasingly important to cut down on carbon emissions. In the case of our straw bale home, we were able to acquire all of our bales from a farmer a mere 7 miles away -- that's one trip with a truck and trailer (plus fuel to cut and bale the straw), compared to an almost unaccountable distance most industrial products have traveled.
Fire Resistance, Ease of Use, and Moisture Regulation
Straw bale walls have been subjected to valuable fire-rating tests by the American Society of Testing and Materials (ASTM), and the results have proven valuable. Two different clay plastered and lime plastered walls have successfully passed code-recognized testing, and proven to be much superior to conventional stud and fiberglass walls in terms of resistance.
The advantages of straw bale extends past local availability, good insulation values, and fire resistance. Working with bales requires few specialized tools, making the work very accessible to unexperienced individuals. Clay and lime-plastered bale walls are vapor permeable, meaning in the best case scenario, the home will self-regulate moisture and remain comfortable throughout the changing seasons. Acoustic isolation is another benefit attributed to straw bale walls, and depending on where you are building, this could be an attractive boon.
Last but not least, straw is 100% biodegradable, and at the end of a straw bale building's lifespan, the material can gracefully return to the earth, leaving no toxins behind. We can drill more deeply into these advantages, but since my goal is to provide an overall illustration of the benefits of straw bale when combined with timber framing, let's look ahead.
Advantages of a Timber Frame
When comparing a timber frame to a conventional stud frame, the myriad advantages make an easy argument. Like straw bales, materials for a timber frame are best acquired locally. Whereas most dimensional lumber used in conventional construction and available at every home supply store across the country comes from only a few (and frequently overexploited) regions (namely, the northwest), a timber frame encourages local use of readily available materials. Shipping large timbers is cost-prohibitive, and it only makes sense to work with local sawmills to produce wood for a frame. I would argue that choosing the timber frame route encourages working within your area, creating stronger connections with your neighbors and local economy.
A Frame For Generations
Another big benefit not to be underestimated is the inherent and potential longevity of a timber frame structure. Timber frames are more durable and long-lived than any than any other framing system, hands down. 500-750 year old timber frame homes are not uncommon in Europe, where maintenance and care of these structures is common. When the wood in a frame is well-protected from the elements and maintained during its lifetime, there is no reason a house should not last well beyond your lifetime. This is in stark contrast to the disposable model of conventional home building today, where homes are simply not expected to last.
Like straw bale, timber frames offer superior fire resistance ratings. Heavy timber construction is given a two hour fire rating by NFPA, the National Fire Protection Association, which is vastly superior to a stick frame insulated with fiberglass. In fact, you may be eligible for lower home insurance costs based on the higher fire rating.
Between the longevity, durability, increased fire resistance, and excellent potential for use of local materials, timber framing is a highly desirable natural building option.
The Meeting of Straw Bale and Timber Framing
I've pinned down a few individual advantages of both straw bale and timber frames. But why do they go so well together?
If kept dry, a timber frame should last almost indefinitely. To maximize your home's energy efficiency, your insulation should be uninterrupted. This is where straw bale and timber frames make for a beautiful combination. A straw bale wrap provides a continuous wall of insulation around the timber frame, providing excellent energy efficiency and protecting the framing from weathering. With a sound roof and foundation, this combination should result in a very long-lasting home. The use of large timbers means that the straw bales do not need to be notched, saving on labor, and leaving the frame exposed on the interior is aesthetically appealing and a functional way to divide living spaces.
The benefits of straw bale and timber framing are highly complementary, and the best aspects of each can be fully realized when the two are in combination. This is why I have come to believe that this is a building system very worthy of pursuit, especially in colder climates.