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HPQ – Will straw houses soon replace brick houses to improve the UK’s Eco-infrastructure and how do they compare with current housing materials?
Contents
Introduction Pg.2
History of straw bales Pg.2
How are straw bales made? Pg.2
What about brick houses? … Pg.3
Advantages
Lightweight and simple to work with . Pg.3
Provides good airtightness with simple detailing .Pg.4
Low-cost renewable material and is widely available from local sources .. Pg.5
Carbon neutrality . Pg.5
Law .. Pg.5
Insulation . Pg.5
Disadvantages
Inconsistent properties Pg.6
Restrictions on detailing .
. Pg.7
Fixings . Pg.7
Allergies .. Pg.7
Safety .. Pg.7
Introduction
Most houses nowadays are substantially made of bricks, which are made of clay, sand and limestone. However, there may be a cheaper and more accessible alternative straw, which is simply dried stalks of cereals, grains and grass. More specifically, straw bales, which are bundles of straw that are compressed, can be used. Therefore, this could be the answer to the UK rapidly deteriorating housing infrastructure. There are many advantages and disadvantages in comparison with brick, and these will influence the future and popularity of straw bale building.
The aim of this investigation is to assess the eligibility of straw bales as a replacement for brick and concrete buildings. Eco-infrastructure or green infrastructure is a term used to describe buildings and transport facilities (such as roads, bridges, tunnels, railways etc) that are made up of sustainable and natural materials, which merge urban and rural life and provide a healthier, greener environment in an urban environment .
History of straw bales
Straw bales have been used in the past to make houses, for example in medieval times. Then most houses were made from straw. However, this building technique died out some time later as many of the houses back then would catch fire and burn. Nowadays, however, the technique has been improved and the binding agents in and between the bales do not allow the bales to burn fully.
Bricks were not used to make buildings again until the early 19th century, when they replaced mud and stone. Bricks were quite complicated to make, especially back then, where clay was quite hard to access, and the process of forming bricks was not too easy as well. However, bricks were much safer to use and build with and were more stable than the previous straw and stone houses that were going out of fashion. Since then, brick houses spread across the world and almost all houses nowadays are made out of brick.
How are straw bales made?
Straw bales are made from dead grass that is compacted together to make certain shapes, such as a cube, cuboid or cylinder. In order for the right straw to be used, a string of 3-5 days of hot, sunny weather is needed . Therefore, in some countries, straw bales are easier to produce, therefore the abundance does vary across the world. However, there is usually enough across the world to supply all farms and straw building companies.
Even when the grass is scorched, there is still some further moisture inside the grass. Therefore, after this burnt grass, which can be called hay, is cut, it is left on the ground for a further 2-3 days to take out all the moisture. After this, to make sure there is no moisture, a roller is used to squash the grass. This crimping of the grass stems allows a more complete drying of the stalks and results in better-quality hay. The reason that so many precautions have been taken to remove as much moisture as possible, as high internal humidity will damage the structural integrity of the bale which could lead to leakage of water if the finishing is not to a good enough standard. The bales that are used near rooves, windows and doors must be chosen specifically and must be of the best quality, as these are the places in a building where most leakages may occur. Therefore, when choosing a bale, it is best to avoid damp or dark bales.
The straw which has been left on the ground to dry for a few days now has to be cut. The length that the straw is cut to depends on the intended use of the straw. For example, if it used to feed animals, the hay is cut into lengths of 1′ or less. This is so when the animals eat it, they don’t waste as much because less will hang out the sides of their mouths4. When the straw is cut for building purposes, the straw is cut to 1.2m or 3.9′. To achieve these accurate cuts, a tractor with a disc mower is used, which has discs that can spread between 3 and 5 metres. The next step is to ted the grass (fluff it up so that the bottom of the grass dries as well as the top) or rake it. Raking is the process of forming rows of concentrated hay, so that the bales are as evenly shaped as possible.
A baler, which is essentially a type of farming machine used to compress a crop like hay or straw into bales and bind them , is then used to produce straw bales. Another additional and helpful feature on a baler is an acid spray, which is sprayed on the bales after they have been compressed, to retard mould if the bales ever get damp again. However, if the bales get damp when they are in condensed form, they dry off very quickly, so the integrity is not overly damaged.
This whole process is quite long because it takes approximately 7 days from normal grass to perfectly compressed and sized bales. The process, however, is not too labour intensive, as farm machinery assists farmers with almost all of the processes. It also does not require many components, as it is only grass, so many things do not need to be bought from other suppliers. The process of straw bale making is much more complicated than what is usually thought, but this is only because they must be specifically prepared for their purpose.
What about brick houses?
Almost all of the houses in the UK are built from brick, which is made from clay, sand and lime. It is the most popular building material, and for good reason as bricks are widely accessible and one of the strongest building materials used in everyday homes. The manufacture of brick is also quite long, but it does require more components, so bricks do have disadvantages as well. Compared with straw, there are advantages and disadvantages, some of which are not exposed to the public as of yet.
Advantages
Lightweight and simple to work with
Straw bales are very light, as they are made up of just dead grass. Therefore, when it comes to transport, it is not too difficult to load and unload these bales. In addition, the vehicles used to carry this will produce less pollution as less fuel is needed to pull this lighter weight, meaning that the carbon footprint of the straw bales will be much lower. Also, the bales can be further compressed so that more can fit inside any vehicle, unlike bricks, meaning fewer vehicles will be used, further reducing the carbon footprint. This is a major reason why straw bales should be considered as an alternative to brick, and also as the future for a greener infrastructure in the UK, by producing a lower carbon footprint and merging rural and urban building strategies.
The simplicity of the bales means that they can be used in many buildings. There are limited ways for building with straw; either finishing with lime or clay plasters5. Therefore, when one does build with straw, the techniques are not confusing, so the work should be completed to a high standard. The lightweight nature of the bales means a reduced load on foundations, reducing the need for materials with high strength and durability, which can be expensive.
The simplicity has also been improved by the concept of pre-fabricated straw panels, meaning that a full house could be put up in as little as 3 days. These panels already have their plaster, and are built to size, and they do not cost much more than ordinary bales.
Provides good airtightness with simple detailing
Aesthetically, straw bale buildings are not easily distinguishable from normal buildings, as they are painted over and finished with either lime or clay. This finishing is also quite simple and provides a modern look to the building that perhaps a brick house may not be able to achieve. The clay or lime finish is applied on the interior and the exterior of the wall, which makes the wall airtight (but the join between the wall and the roof and the join between the wall and the ground must be sealed airtight too). Therefore, the airtight finish does not compromise the aesthetics the building. The idea of the straw bale houses being aesthetically displeasing is prominent among members of the public, but a simple comparison shows that straw bale houses can look comparable to houses made from brick or cement.
Both of the houses above have the same airtightness, and both are quite modern. Aesthetically, the straw bale house does not look of worse quality. Therefore, another factor for the replacement of brick houses should be the relative aesthetics, and straw bales can clearly be used to build something that can rival straw houses, alongside other advantages.
Low-cost renewable material and is widely available from local sources
Depending on the quality and size of the straw bale, the cost can range from ?1.0013 to ?2.50 to ?29.99 . Compared to brick, which is on average ?150 per m2 for materials and labour , it is much cheaper to buy and work with. In addition, overall, less bales are needed in a project than bricks, so for a higher volume, less money is needed. Furthermore, the labour costs are lower, as less materials are needed, and the building techniques require less effort. The building techniques are so simple, that any DIY enthusiast will be able to carry them out with ease.
The fact that straw bales are widely available all over the UK, means that, compared to brick, its carbon footprint is immensely lower, as bricks sometimes have to travels hundreds of miles to be delivered, all while producing more CO2. Also, the straw will be in good condition when it arrives to the buyer, as it does not need to travel very far. This is not the same for bricks though, as they may have to travel longer and may be damaged in transport. The abundance and availability of straw bales, combined with the cheaper price, also means that delivery of bales to building sites will be quicker, and if replacements are needed, they can be obtained easily without overspending too much. The UK will also benefit from these to factors as a whole, as the UK is currently in a huge housing crisis, where not enough houses or accommodation is being built for the rapidly increasing population arriving from overseas.
Carbon neutrality
Straw bales are also 100% carbon neutral. The term carbon neutral means that there is no overall net release or absorption of carbon dioxide, so this is one of the most environmentally friendly building materials available to the public. Straw grows in bulk every year, meaning all of the carbon footprint of the previous straw is cancelled out when the straw finally degrades, and new grass is planted. When the time comes, the straw bales can be ploughed back into the earth. This is the main reason why straw is the correct material to improve the UKs Eco-infrastructure with.
Law
Obtaining planning permission is never a problem with straw bales houses13; the UK councils determine straw bale house proposals at an equal level to brick houses.
Insulation
Straw bale houses provide one of the highest thermal efficiency. The fact that there is more air inside each of the bales means that more warm air is trapped inside the bale, thus retaining large amounts of heat. Therefore, the running costs of living in a straw bale house are decreased drastically, compared to in a brick house. This means that even after the straw house is built, it keeps providing methods to save more money. Straw bale houses therefore save the user money in the short term (it is cheap to buy/build) and it costs less for one to live in it (with lower energy bills).13 Consequently, the dependence on fossil fuels also decreases,
meaning the house continues to be environmentally friendly. The carbon footprint is reduced further because of this, and the eligibility for the material to improve the UKs Eco-infrastructure is further boosted by this.
Evidence of the superior insulation quality is shown below:
Moreover, insulation does not just mean heat, it can also mean sound insulation. Straw is a very good sound insulator as well. The separate straw and the air in between absorb more sound than ordinary walls, as sound travels faster through solid than air. Therefore, as straw bales have more air, in them, the sound travels slower so it is absorbed much better by the straw13.
Disadvantages
However, there have to be reasons why all of the houses nowadays are not made out of straw. There are many disadvantages to building with straw, but the main reason that straw bale houses are not so abundant is the lack of awareness13. Not many people consider straw bales as a good building material, and some people dont know that it can be used at all. The lack of education about straw as a building material at the start of any engineers or builders career means that most building firms do not offer straw services, as it is an obscure building material. Most building firms believe that they are not sturdy and stable enough, meaning a lack of public exposure.
Additionally, with straw, physical disadvantages exist too. None of the following disadvantages occur in brick houses:
Inconsistent properties
As an agricultural co-product, inconsistent properties can be problematic during construction. For example, there may be discrepancies within each bale with the weight, density, moisture content and the exact dimensions. This is because straw bales are completely natural and are compressed. When they are compressed, certain straws have different resistance and elasticity. This means the dimensions will not be completely accurate. The moisture also is not controllable by humans; the straw must dry out naturally. Thus, different amounts of moisture will be present as different bales can hold more or less water. The difference in moisture contributes to differences in weight and density. The density of the bale is dependent on the baler used, and the amount of straw used by the baler. It is hard to control the amount od straw that a baler compresses into bales, but it is measured by weight. The weight itself is subject to minor discrepancies as well, because straw with different age, water content and compression have different weights. All of these discrepancies are quite small, but they can be important enough to cause problems with the stacking of the bales, and the different moistures, in particular, as the internal structure of the bale may be compromised if it is exposed to further moisture, resulting in an unstable part of the wall. However, the bales used to build with are thoroughly checked before use, and straw can make a good, strong wall for over 100 years, so moisture damage is unlikely to occur. Additionally, if moisture damage does occur, changing the bale is not too hard. Nevertheless, this is an important disadvantage, which can deter people who know about this away from considering bales as a brick alternative.
Restrictions on detailing9
Considering the potential damage that excessive moisture can have on exterior straw wall, precautions must be made so that too much water does not come into contact with the wall. Thus, there have to be design limitations. For example, the roof overhang has to be slightly larger than on conventional houses, to stop rain from falling onto the walls. Windows and doors are also placed towards the outer face of the wall to minimise the risk of water penetration, and the walls have to be 450 to 500 mm thick.9 All of these factors do limit the extent of the exterior design. However, there are many solutions to this problem, as shown in Fig.1. The straw bale exterior wall is clad with timber, which can decrease the amount of water that comes into contact with the straw. This also means that the wall must be covered during construction, which can mean extra expenses on scaffolding etc.
Fixings
Any inexperienced straw bale builder may also not know how to fit fixings, and the lightweight nature of the straw will not aid the loos fixing. This can have catastrophic repercussions, especially if these fixings have an electrical connection. If it comes loose, fires can start and spread through the wall.
Allergies13
Many people assume that there may be health disadvantages with straw bales, but, to a certain extent, there arent any. The main fear of allergy comes from hay bales, where pollen is present. However, there is very little pollen present in straw, so only a very severe pollen allergy would be triggered by the straw. This therefore is another disadvantage, even if it is not real.
In reality, the straw bales, even if they had small amounts of pollen would not cause an allergic reaction because the lime or clay plaster stops the pollen from being blown anywhere near a person, so an allergic reaction to a straw house is extremely uncommon.
Safety
There are many theories and misconceptions in the public eye about straw bale houses being weak and being extremely flammable. This is not true however. Before any batch of bales or pre-fabricated panels are sent off for delivery, durability testing is very important. The durability is addressed and tested vigorously on a working and to scale prototype, and it would been blasted by simulated hurricane-force wind loads, soaked in water to simulate flooding and exposed to roaring fires. In 2014, the research culminated in the sought-after industry certificate, which provided the construction sector with scientific proof that straw is durable, genuinely environmentally beneficial and suitable to be insured.
What about other natural materials
There are, of course, other natural building materials, such as hempcrete. Hempcrete comes from the cannabis plant, and the materials are usually obtained via the waste of hemp-fibre production (hemp fibre is used in ropes, canvas and paper). Hempcrete is available as pre-fabricated blocks as well for conventional construction. However, it is usually used as a mix-on-site and cast in-situation material. Hemp and lime are mixed in set proportions to a stiff consistency and moulded into a formwork that surrounds a timber frame . Compared with straw, there are few advantages and disadvantages:
