4. contract due to change in temperature when

4. Construction
Materials

Based on the concept in which
the earthship is constructed it is necessary to choose the construction
materials based on their properties, thermal mass, cheap, environmental
friendly etc. the material should be such that it is easily available locally
and should not be transported from far place as it involves burning of fuels
and gets expensive. The material should be non-hazardous to both environment
and as well as to inhabitants and should not consume lot of energy while
manufacturing it. It should have a good thermal mass so that it can store heat
and help to maintain the temperature. Durability also plays an important part
as the structure should withstand the nature and should be resilient especially
in seismic prone areas.

Some of the materials which
can be used are discussed below

4.1
Roof

Roof consists of three parts
viz, Roof Shingle or tiles, Roof rigid insulation and Roof Deck.

Roof shingles are overlapping induvial
elements which covers the roof from being exposed to the outer atmosphere.  Shingles made of different materials are
available in European market. Some mostly used are listed below

·        
Ceramic Shingles- Made of ceramic is the most
used type for residential buildings in Europe. These Shingles are durable and
comes with different shapes and sizes. They do not expand or contract due to
change in temperature when compared to other types like asphalt and metal
roofing. They cost around 120 to 250 per square meter area to install.

·        
Wood Shingles- Machine Cut or hand Cut from
blocks of wood. They are mainly used to give good looks to the roof but hey
last only up to 10 years. They are avoided in cold and humid conditions as they
are vulnerable to growth of moss due to water. They are cheap and cost in
between 50 to 100 euros per square meter area, but repairing is expensive.

·        
Asphalt Shingles- There are two types of
Asphalt Shingles available one with fibre glass and second one with Organic mat
based. They are very light in weight and easy to install. These are cheap, but
life time cost is higher as they last only for 10-12 years. Installation cost
about 30 to 70 Euros per square meter.

·        
Metal Shingles- Metal shingle is generally made
of metals like alloyed steel, aluminium, copper. They are available in both
shingle sections and wide panels. It is a good fire resistant, light weight and
now days metal with zinc coating is available which is high resistant to
rusting. they can be made of recycled materials and can be recycled at the end
of its service life. This type of roofing is best suited for shedding rain
water and snow as it has a smooth surface when compared to other types.
Fastenings systems are provided so that stresses are not formed in the metal by
expansion and contraction due to change in temperature. Care should be taken
while installing the metal shingles or roof space there is a solid sheeting
below the metal roof because it can be noisier during rain when installed
directly over living space or open framing. The cost of installation depends
mainly on the type of metal shingle or roof is made of. Copper is the expensive
one costing in thousands per square meter. With general metal like galvanised
iron and other alloyed metals cost in the range of 50 to 150 euros per square
meter for installation.

·        
Solar Shingles- Manufactured for the first time
2005, these shingles are basically photovoltaic cells made to look like
traditional shingles and act as one. They function as a convention roofing
material, have smooth surface and generate electricity. These shingles are two
or three times more durable than the regular roof tiles and can be installed in
any type of climatic conditions. They can withstand massive impacts of nature
like high temperature, wind, hail storm. By using these tiles, one can avoid
using traditional solar panels which take extra space and structural elements
like frames. Some manufactures claim that their solar cells can generate energy
just by daylight when it is cloudy. It helps to reduce once electricity bills
by 40 to 60 percent. They are expensive than the ceramic tiles, costing around
250 to 300 euros per square meter area for installation. But they are good
option for a structure which wants to be off grid.

 

 

 

After looking at pros and cons
off all the above types of roof shingles, Solar shingle and metal shingles
provide to be better option than others for an earthship. Metal shingles has
good qualities like smooth surface, cheap, recyclable, durability but in case
of solar shingles, with all those qualities it can even generate electricity.
Which avoids providing traditional solar panels that often takes extra space.
But for an earthship the roof is sloped and the front side on the structure
will be facing south direction so that maximum sunlight can enter the
structure. Since the roof is sloped and the higher end being on the southern
side some part of light will be able to fall on the solar shingles. Hence solar
shingles can be avoided. So metallic wide panels are the best option for an
earthship in European Conditions.

 

Roof Deck is a base on which
roofing system is laid. This roofing system include roof shingles and roof
rigid insulation. Its function is not just to hold them together but to resist
wind loads, snow loads and impact loads.  These roof decks are supported by columns and
beams. Some of the available types in Europe are discussed below

·        
Concrete Decks/Slabs- Generally called as
slabs, they are mostly used for flat roof. This can be cast insitu or
precasted. They are available in both RCC and pre stressed concrete. They are
not often used for sloped roof but mainly for carrying heavy loads like open
terrace where often people will be using it for sitting. Not recommended for
pitched single floor buildings.

·        
Steel Decks- They are wide panels of metals
which can be directly used without shingles. They are to be welded to steel
supports if the deck is to transfer loads to sheer walls or columns. One of the
main disadvantage of this roofing is that it has very low R- Value (thermal
resistance) and a good insulation layer has to be provided to compromise it.
They are generally used for industrial buildings and economical residential
buildings. Cost of installation depends on the quality of material opted and it
can be cheap. It is very easy to install.

·        
Wood- comes in different types like wood boards
and plywood. Plywood are made of thin layers of wood adhere together such that
grain of each layer is perpendicular to adjacent layers. This gives greater
strength and stability to its dimension. Wood Boards can also be used instead
of plywood. But the main problem with the wood is they can swell and shrink if
it absorbs moisture. This can be caused by lack of ventilation in the building.
An extra layer of thermal insulation is to be provided in between roof deck and
shingles

·        
Structural Insulated Panels- SIPs are made from
sandwiching 3 layers of structures. They have the same strength as a wood deck
can have. The two outer layers are usually made of oriented standard boards and
the core layer is an insulation layer generally made of different materials by
different manufacturer. Some of the used core material are Expanded Poly
Styrene, polyurethane, polyisocyanurate. Polyisocyanurate has the best
insulation property. Many other insulation materials are available, each with
different heat resistance, fire resistance and cost. They are eco-friendly,
have good strength, cheaper than plywood, has good moisture resistant and easy
to install.

 

By
comparing the all the available deck materials in Europe SIPs prove to be good
choice as it can act as both roof deck and also a thermal insulator. For other
types of deck an extra roof rigid insulation is to be provided. So SIPs suits
better to an Earthship.

 

4.2 Beams and Columns

A beam
is a horizontal structural spanning between two supports which withstands load
by resisting against bending. Two types of internal forces act in a beam which
are bending moments and shear force. The vertical loads from roof is carried
horizontally by the beam and transferred to columns and walls. Whereas column
is a vertical structure which transmits compression loads from roof, slabs or
beams to footings.

The
most used material for constructing columns and beams are as follows.

·        
Timber- Timber is a wood which is suitable for
carpentry, building and other engineering purposes. Construction by timber is
very easy and quick which reduces site labour. By using timber construction,
site waste can be minimised by controlled manufacturing. Wood does not expand
due to heat like steel does but it is a hygroscopic material i.e it loses
moisture to air by absorbing surrounding condensable vapours below the fibre
saturation point. It is 400 times more thermal insulator than steel and 14
times better than concrete. Wood may get deteriorated by some fungus,
chemicals, insects and water. Timber don’t have a great life span as concrete
and steel.

·        
Reinforced Concrete- Reinforced concrete is a
concrete embedded with rebars, plates or fibres. It is the most commonly used
construction material. Both the materials act such that the compression
strength of the concrete and tensile strength of the act together to resist the
stress all over the body. One of the main cause to loose strength of the
concrete is shrinkage, so care must be taken while casting.it has a high
compressive strength compared to other building materials like steel and
timber. It requires less skilled labours to erect a concrete structure while in
case of steel it is the other way around. Concrete has a good fire and thermal
resistance. It costs around mid-range being cheaper than steel and bit
expensive than timber.

·        
Steel- Steel are widely for big structure since
it has high strength-weight ratio. As it has high ductility it provides large
reserve strength by undergoing large plastic deformation and also they have
good fatigue strength. Erection of steel structure can be done rapidly but only
by skilled labours. Since steel has a high strength-weight ratio it is more
susceptible to buckling due to slenderness. Steel structures should not be
exposed to water and air as it may start corroding. Regular painting is to be
done to prevent this problem. One of the main disadvantage is its cost. Steel
structures are very expensive.

 

 

Since steel is used for big
structures and is expensive it is not advisable to use for an earthship. But on
the other hand Timber has all the good qualities but to get timber tress are to
cut down which effects the environment. Therefore reinforced concrete is
suitable material for columns and beams.