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Straw Bale House Construction - Part 4

Updated on April 20, 2017
Ashish Dadgaa profile image

Ashish Dadgaa is a Construction Manager with 10 years of experience in the Industry. He writes about Home Improvement and maintenance.

Insulation

Straw Bale Wall Insulation
Straw Bale Wall Insulation

Straw bales are very famous because of their high insulation property. They don't require any extra insulation materials as they has high insulation value than brick and concrete blocks and they works far better than that commercially manufactured insulation. Insulation of the building envelopes, such as doors, windows, walls, floor, and a roof is required to prevent the displacement of heat by conduction. Insulation in the fabric (doors, windows, walls, floor and roof) of a building is needed. The highly insulated straw bale walls will keep a building cool in summer and warm in winter by saving energy, as well as, it will minimize the carbon dioxide emission and electric bills.

Approximately, straw bale walls have U-vales from 0.13 W/m²K to 0.20 W/m²K. It’s U-vale mainly relies on the bale’s quality. As per sustainable homes code-5 and code-6, U-value of wall requires around 0.18 W/m²K for code-5 and 0.11 W/m²K for code-6. To accomplish these U-values it always needs high tech and expensive insulations and construction methods. Thus, straw bales grant a low-tech solution for achieving highly insulated walls in the house, which needs less energy to keep inner environment comfortable. So, this will run straw bale houses cheaply, with a savings of at least 75% on yearly energy demand of house. Now, the farmers don’t have permission to burn those 4 million tons of surplus straw, which is producing every year in the UK. If these 4 million tons of surplus straw utilize in building construction then it will minimize the carbon for the lifetime.

Fire

Fire Testing on Straw Bale
Fire Testing on Straw Bale

Fire safety is one of the essential considerations in straw bale construction. As it is flammable material, it requires detail consideration to keep it safe from the construction phase to its completion phase. However, straw bale construction techniques have come up with an idea of tightening straw into the dense blocks, which effectively minimizes the oxygen the straw. In additionally, when straw bale walls are plastered externally and internally, the blend of insulating interior and non-flammable plaster skins would make the straw bale walls fire resistive.

The various fire tests had done on the plaster straw bale walls to determine its fire resistance performance. In 2001, the Vienna Technical Institute conducted F90 fire test on straw bale walls and which produced plastered straw bale wall 90 minutes of rating. In 2009, the students of Bath University built straw bale house as their research project and which they kept under fire resistance test. The house revelled under temperatures of 1000°C for two and half hour, which was longer than legal requisite and though it stood firmly. The tested houses confirmed that straw bale wall’s performance is acceptable for residential construction.

Durability

Straw Bale House Load and Durability Test
Straw Bale House Load and Durability Test

In the Nebraska, the houses have been abided more than 100 years due to its good construction. However, a life of straw bale house mainly relies on the original construction quality and maintenance of the house throughout its life. The type of straw utilized in the construction of the house is also made a huge difference in its durability. Straw may be consist of the stalks of wheat, rice, oats, rye and barley. The rice straw is one of the best for long durability of the house, as it has a higher amount of silica level in it which makes its drying process quicker.

The load bearing structures are less durable than the timber frame/ infill structure. In load bearing structures within the short duration of construction, cracks and leakage are likely to see on the plastered walls. Whereas, in timber frame/ infill structure these problems are rarely noticeable. In load bearing structures, walls are an essential structural element, as they have to carry not only roof load but also live and dead loads of upper floor in the house, which all enhance chance of cracks and water penetration inside the walls. This all leads to furthermore risk of insect, rot, and infestation in the structure.

Affordability

Straw bale is a cost effective material. It is easily available as it is an agricultural product. Bales of straw are cheaply available for just £1 each, especially if it is bought from local vendors. It has been estimated that three bedroom straw bales house can be built in less than 20% of the cost of a conventional house. However, for the big construction project expense will likely to enhance as transportation, handling and storage cost will be incurred. One specific reason of low-cost straw bale houses is that occupants are constructing their houses with the help of friends and family. If they hire professional labors then the labor cost would be similar to the traditional construction. There is some possibility that demand for straw bale houses would increase in future then the straw will not be seen as a waste product and it will lead to increase in the cost of straw. On the other hand, some experts are anticipating that in near future lots of straw bales houses will be seen as food price has risen so more rice, wheat, oats, and barley will being produced and it will result in more surplus straw would utilize for building and housing.

Unique Design Feature

In the straw bale house, the rammed tire foundation would be utilized, as the best sustainable alternative to a concrete foundation. It would be an excellent sustainable step toward minimizing carbon emission.

What is Rammed Tire Foundation?

The rammed tire foundation is a sustainable, low-impact and environmentally friendly building technique. It is a totally carbon-free foundation, as builder or contractor would reuse car tires with rammed earth. It has a straightforward construction process, first place the tire into the trench then fills the central hollow area of a tire with rammed earth and compact it with ramming equipment. Once all three tires are in place, the lime render is laid on top of them for the rigid floor. Moreover, its expected life is 30,000 years, which is considerably longer than environmentally high impact concrete foundation. The tire foundation first utilized in the UK for family house construction near Brighton with full Building Regulation and Planning approval.

Why Rammed Tire Foundation?

It has been estimated that over 440 million cars tires are thrown away in the UK every year. Around 55 million tires are either taking space in our landfills, or they are being thrown illegally in private properties or on the side of the road. If they are stocked up in the landfills it creates health and environmental hazards as after few months in landfill tires starts to get deteriorate, and it spread disease due to mosquitoes and breeds in tire piles. When they move in some manufacturing plant, and they burn under special conditions, they emit dangerous fumes and an awful smell, which affects weather extremely. However, the advantage of re-using tires is minimizing in energy consumption and pollution. Furthermore, according to research from Cornell University says that the houses that are built on the used tired foundation can be worked as an earthquake-resistant element. It acts as a shock absorber between the house and quivering earth.

In addition, the rammed tire foundation is very cost effective; it only requires charges for transportation from the garage, rammed earth infill materials and few working tools. The foundation of semi- detached three bedroom house can be easily done under £1000.

What sort of structure can utilize tire foundation?

It can be utilized as a foundation for any well designed, low-impact structure. This incorporates houses, studios, garages, workshops, offices and sheds. It can easily utilize for the building up to the 200 sq/m.

Ground Bearing Pressure

The bearing pressure on each pile of car tire foundation with a span of 2.5m increases to about 250KN/sq m instead of the regular 60 to 80KN/sq m for a continuous foundation.

Tire Foundation Construction Method:

1

Dig the trench about 700mm to 800mm until the rock soil strata and Level the bottom of a trench throughout.

2

Lay the tire into the trench, fill the central hollow area with a rammed earth, and gently start packing underneath the rim of the base of the tire before progress further.

Ramming earth inside the rim with hammer
Ramming earth inside the rim with hammer

3

Keep pouring rammed earth into the tire until the top, after that use feet, hands or compacting machine for appropriate compaction and then ensure that the tire’s rim is filled.

4

Verify the height of all tires with the levelling tube and ensure all tires are at the same level, if not adjust accordingly.

Leveling of tires
Leveling of tires

5

Place the second and third tire appropriately onto the first and fill in the similar way.

6

Level off the top of the tire with rammed earth.

7

Once it is finished, lime plaster should apply for the rigidity and protection from the weather.

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© 2017 Ashish Dadgaa

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