Wood Vs. Straw Bale

Which is more green?

This is a source of information regarding the comparison of wood and straw bale construction. We'll discuss the following topics:

• where the materials come from
  
• consequences of harvesting the materials
  
• associated benefits and restrictions of construction
  

While straw bale homes are gaining a lot of green street credit, it is always good to take a step back and examine the whole picture when comparing two types of construction. When you question the viability of the buzz about something green, you are eliminating the possibility of greenwash. That's good! Greenwash is hype about products or services that want to be associated with 'eco-friendliness' but in reality don't have a leg to stand on in the green arena. Firstly, it is important to note that all building, regardless of whether we call it green or not, requires energy and uses resources in one way or another. We are interested in comparing energy/resources used and the respective benefits/consequences of wood and straw bale construction.

Both types of construction can be carried out in 'green' ways. The location of your future home will have a lot to do with which type is more appropriate. In some places, straw bale is readily available down the road while lumber has to be shipped great distances to find your site. Elsewhere, the opposite situation is the case, and lumber is as available if not more readily available than straw bale. Site-harvested timbers are a great option, especially if the trees they came from had to be taken down for the construction of the home. Waste not, want not, right?

Straw bale is a bi-product of cereal grain harvest. It is only locally available to the areas of the country where cereal grain is grown. Furthermore, if it were from a farm that practiced truly sustainable agricultural techniques, it would have been tilled back into the soil to replace the nutrients it extracted during growth. We must also take note that deforestation and soil erosion may have been part of the process of creating the fields where these grains are grown and that most likely harsh pesticides and fertilizers are used to grow these crops. Here's a peek at where grain cereal is grown. The heavily dotted areas should be giving straw bale home construction strong consideration.

That being said, let's move on to the issues facing wood construction, or stick frame. The effects of deforestation are numerous and well known, so we will just touch on the main issues: loss of habitat for birds and other forest-dwelling creatures is devastating for many species on our endangered and extinct lists; we've already declared that soil erosion occurs after clear-cutting; it takes at least seven years to replace trees because they grow slowly, whereas straw growth occurs once every growing season, making it a highly renewable resource. Milling (the process to make 2x4s, 2x8s, etc. from logs) requires the use of fuel
.
On the other hand, close to 100% of waste from this process is recycled. If you have the financial means to specify FSC (Forest Stewardship Council) Certified wood (slightly more expensive) you are helping assure that the wood was harvested using more sustainable wood harvesting methods. The FSC helps influence and convince forest managers to implement responsible social and environmental practices.

The level of quality of the construction and durability of materials are very important issues when talking about the sustainability of your home. If your home is destroyed by water, for example, 10 years after it is built, your home is not considered a sustainable project, even if it scored every possible LEED home point! A shortened life span means it goes to a landfill sooner than expected. How does this add up to big issues? If all the homes in the US lasted twice as long as their expected life-cycle (which is actually only around 25-30 years for standard homes that are built today, 50 years if they're built really well) then think of all the material that we could keep out of the dumpster longer. There were 124 million homes in the US in 2005. That’s a lot of refrigerators (one, maybe two per home). Now think about all the rest of that material: flooring, roofing, timbers, appliances, wiring, lighting, etc. Overwhelmed yet? Well, landfills are overwhelmed. They are busting at the seams and states are making money by selling other states dumping rights. Ugh! What if that were your town they were trashing? We pay other countries to take our trash, too.

According to this site, the US and Canada have stable or increasing forestation rates, making wood a good construction material choice. This means that logging companies are replacing as much or more trees than they cut down. In addition, highly practical and ecologically-sound logging techniques are being implemented in some areas, like underwater logging from forests that have been submerged as an effect of damming or other tidal change over time. It has also been found that by pruning a forest, making it less dense with trees, allows the remaining trees to grow much larger than if they were in a more dense setting. The result: larger trees eat a significantly larger amount of carbon than small or medium sized trees and the forest as a whole will reduce more carbon and produce more oxygen, a vital process to reducing greenhouse gases in earth's atmosphere.

Back to the issue of water damage: stick built walls have a greater ability to dry out quicker than straw bale walls. Straw acts as, well, a straw (think drinking straw) and when water gets through the plaster used to coat the bales, it travels easily up the straws and stays there for a long time. Straw rots much more quickly than wood. Anyone can imagine seeing a stack of 2x4s and some bales of hay left out in the rain for a while. Which one degrades faster? Straw! Moisture can and should be prevented in straw bale construction to the utmost in rainy and humid climates. Foundation walls should keep straw bales far off the ground and above the snow drifts that accumulate in winter. If bales get wet during construction, it leads to problems. The driest method of straw bale building is to bring them straight from a storage facility to the safety of a roof. This means that the home must be designed so that all straw bale walls are NON-load-bearing. If they are load bearing, they must be constructed before the roof is built on top of them, and gives the sky an opportunity to "dampen your day". Unsealed bales should be protected on site by placing a plastic tarp or other water barrier over the exterior of the bales to further protect against moisture should wind drive rain at an angle, under the roof overhang and onto your straw. They should be sealed as soon as possible and the plaster used should be the right type for your climate.

Other ways to compare wood and straw include fire-protection and insulating properties. Straw takes the cake on these issues. Putting up superb test results from studies worldwide, straw bale construction exceeds universal building code fire-rating requirements. The lack of air inside a straw bale wall contributes to this quality. Wood frame homes fuel fires by supplying ample air inside wall cavities and often help fire spread floor to floor through wall gaps.

Straw bale walls produce thermal barriers that are generally three times more effective at insulating interior spaces than typical R-19 wood stud walls. However, beyond R-30, straw bale walls make little difference in the overall energy use of a home because factors like windows, doors, floors and roof conditions affect thermal heat-gain and -loss extensively. So don't get carried away with walls that are over 18 inches thick: there is not much added benefit other than really deep window and door openings, if that is what you are going for.