Straw Bale Construction

STRAW BALE CONSTRUCTION

STRAW BALE CONSTRUCTION Straw-bale construction is a building method that uses bales of straw (commonly wheat, rice, rye and oats straw) as structural elements, building insulation, or both.

HISTORY

•

First house in Nebraska(US), 1936.

•

Andaman Earthship in Andaman island

•

Auroville, Pondicherry

CURRENT BUILDING SITUATION AND ENVIRONMENTAL CONCERNS

• High energy intensity required in the manufacture of modern building materials

• Reduction in pollution and green house emission

Comparison of pollutant emissions between SBB and CBB

Energy required for manufacture r-value/ inch

Straw bale Cement brick Clay brick wall .115Gj/tonne 6-8GJ/tonne 2-7 GJ/tonne

1.5

.2

.5

Why build with straw? • Eco- friendly • Energy Efficiency • Ease of Use • Safety

Straw bale

• Size 100 x 45 x 40 cm • usually wrapped with two, sometimes three, or •

more strands of knotted twine Weight 20-27 kg

Straw bales should be •

Dry

•

Dense

•

Well tied

•

Pure

•

Fresh

•

Consistent

Straw baler

Fire resistance •

Bales are typically too dense (lacking in oxygen) to support combustion

•

Dry density varies between 110-128kg/m3

•

High silica content (4-14%) impedes combustion

by charring

Insulative properties • High thermal efficiency reduces the energy

requirements for heating and cooling •

R- value between 30-50

• Sound insulation

Method •

Straw bale buildings use the same foundation, flooring and roofing technologies similar to any conventional type of building

•

Basements, slabs and pier foundations can all be easily adapted to straw bale construction. Similarly, prefabricated trusses can be used to provide the roof structure.

•

a moisture barrier or capillary break between the bales and their supporting platform.

•

The straw bales in the walls are stacked in a manner similar to bricks or concrete blocks, in running bond.

•

Window and door openings are created using wide, rough frame

wooden bucks inserted into the walls during construction.

straw bale wall

1.Post and beam type •

Use timber, concrete or steel frames to support roof load

•

bales are either wrapped outside the framework or in filled between the framing members

•

Straw bales are mainly used as insulation

2. Load bearing wall •

Bale walls themselves support

the roof load

•

Bales are precompressed

before placing to avoid settlement

•

A structural roof plate

is placed on top of the walls.

Wall coverings Types of stucco

• Cement stucco

• Lime plaster • Earth plaster

Lath Galvanized lath should be provided if the wall is to hold stucco

Moisture concerns  Presence of moisture leads to growth of

molds  Moisture barriers and application of wall covering prevent moisture penetration

LIMITATIONS

• High Space Requirements For The Straw • Limited To Two Storeys • Lack Of Codes

• Lack Of Qualified Professionals