A Wolf or Whirlwind Won't be Able to Blow This House Down

Now there is a plethora of options to consider when it comes to building components for the walls of your home. Instead of going into the pros and cons of each one I would rather discuss the general building principles to keep in mind and maybe introduce you to some new materials that you might not be familiar with. Because one again, there is no one size fits all answer to what is best, it will depend on the variables of your needs and priorities. The overall main concern is air infiltration and the R-value (resistance to heat flow).

Air infiltration happens all over the house with the wall cavities only contributing a small amount (14%). To solve air infiltration you need to address air flow throughout the structure, with the most important places being gypsum board, gaps, and penetrations, not the cavity. To get a continuous air barrier you need to seal under sill plates, fill band joists, and seal around penetrations such as recessed lights and electrical boxes. Also you need to seal all edges of your gypsum board and exterior structural sheathing. All of which are typically not done in the residential construction industry.

The optimum wall insulation value is an R30+, while industry standard and typical building codes only call for an R19. There is a myriad of options when it comes to insulation, such as: spray foam, clothing insulation, rigid insulation, extruded polystrene (EPS), expanded polystrene (XEPS), Cellulose, even straw bale and the most commonly used fiberglass. I learned as a child not to play in the fiberglass "pink" stuff because you will be very itchy afterward. Each material has various R-values, pros and cons. Which material you choose to use will depend on your needs, wants, concerns, budget and also the construction of your wall. Once again beyond just the typical stick framed home there are many other options such as metal framing, structurally insulated panels (SIPs), insulated concrete forms (ICF), straw bales and even rammed earth. One system I would like to discuss more in depth is the straw bale home. It is currently being touted as the greenest, most energy efficient cost effective way to build.

Straw bales 2’ thick stacked on top of each other in a running block pattern like bricks are plastered inside and out. It eliminates the need for insulation and is entirely non toxic. The California Energy Commision officially regards a plastered straw bale wall to have an R-value of 30, while other studies have shown straw bales to have as high as a R-53 value. It matters little whether the final truth about the R-value of straw bales walls is R-33 or R-43 or even R-53. Above R-30, the differences are minor and will usually be overshadowed by windows, floors, doors and ceiling/roof details. Whatever the value, it is at least three times better than the average “R-19” wood studwall system. Rice, barley wheat or flax straw bales can be used. Rice is an optimal choice because it has silica which is resistant to fire and because of the sand in it it is less prone to rot.

As odd as it sounds to build a home out of straw bales Dr. Burritt in 1938 in Hunstville, AL used straw bales as insulation in between a post and beam structure when building his mansion. The idea came to him while making rounds he stopped in a barn to rest. He noticed how cool and comfortable it was and decided to build his house this way. His home is a historical landmark and can still be toured today. Straw bales are less prone to rot or burn than a typical stud. It is less likely to burn because it is very dense, there isn’t space inside wall for fire to travel. Regular walls are 90% air and fire races through it. It also creates a healthy indoor are quality. The wall is breathable so water vapor can move in and out of wall and water doesn’t condense and create a breading ground for mold. It is roughly the same price of installation alone. Also you can get this product directly from the farmer which gives it an extremely low embodied energy. It is also an fantastically affordable product, approximately $2,600 for 4,000 sq. ft. home. Take into consideration you will need to have a post and beam structure instead of a typical stick framed home, but on average your post and beam structure with straw bales will cost you half as much a lumber package and go up twice as fast.

Whatever construction products you choose to build your walls out of keep in mind the goal of minimum air infiltration and maximum r-value while keeping a healthy environment for your family. Who knows, maybe the three little pigs were onto something when they built their house out of straw. And yes, all the homes featured on this post were built out of straw bales.