Chapter 1: Introduction

Introduction         

The construction Industry has seen continues progress in the last many decades. Research and Development in the field of civil engineering has introduced innovative and sustainable methods of construction that highlights the state of art technology of this century. Architects and engineers continue to build structures and design that offer variety of comforts for the residents. Much consideration is given to the construction times, building sustainability, costs and highest standard of construction materials to be used.

The Frames used for the construction of any building is one of the most influential factors in any construction project. A variety of framings and materials are available. Many factors are considered before the framing and its material is selected for the construction of building; such as costs, weight, accessibility, sustainability, durability and many more. A critical review of the findings is carried out to determine/conclude which frame is best suited for a two-storey residential building. A detailed assessment and evaluation detail for both qualitative and quantitative data collected is presented in the later chapters.

The structures produced with concrete technology are found to be cracked at some point as a result of shrinkage during drying out period. The low thermal conductivity of the material has made it less compatible method of construction in many cases. Intense heat has found to damage the material seriously and consequently the building. When exposed to sea water/vapors the corrosion of concrete has been found as a common side effect. Concrete requires extensive time durations to be prepared and applied to give the final results. The material has high rate of hazardous emissions including NOx, COx and particulate matter and thus its use is highly condemned by the UK environmental safety standard association (Reduce Your CO2., 2007).

Timber and Steel Frames

Timber and steel frames are the two most popular types in the construction industry. Both have their advantages and disadvantages. Steel is said to be the most recycled material on earth and Timber is stated to be the ultimate renewable resource.

All of these factors have prompted the researcher to select the timber and steel frames as construction method for a two storey building, and further analyze these materials of construction. Furthermore, producing/publishing a completive document that highlights all the required information regarding the two most important and sustainable frame construction material could prove to be a helpful guide for many researchers, architects and builders.

The aim of this dissertation is to present the adoption and comparison of Steel & Timber framed buildings and to identify which frame is the best suited for a two-storey residential flat.

Chapter 2: A literature review

Introduction

The two construction methods that have been discussed in this section are timber and steel frame. The other method such as concrete technology can also be considered but it has many shortcomings when compared with two selected methods. Considering the sustainability timber and steel frames are considered to be the most sustainable of the materials.

Timber Frame

A common method of constructing natural structure is called timber frame which consists of heavy and large wood beams and posts which are fixed together through interlocking joints and wooden pegs. The load of the roofs is usually transformed to the foundations which allow the possibility of not requiring interior partition walls for the sole purpose of load bearing. The building structures built with timber are of low weight. Self supporting, strong and durable structures can be achieved by using timber structure which are generally precision-engineered. The readily available supply of timber, frame durability and strength, quick and easy construction and attractive aesthetics make the construction methods more appealing. The diversity of the frame let the design to be used for variety of structures including flats, houses, high buildings, and houses (Timbercraft, 2013; TRADA, 2011).

Many economies prefer the use of timber framed buildings because of its energy efficiency, cost effectiveness and sustainability aspects. Germany, Sweden, Scotland, Japan, USA, Canada and Austria are the biggest economies which are using this method of construction. The frames are easy to erect and take lesser time to be constructed. The Benfield ATT Group has announced timber as the only renewable material in construction industry (FSC Timber Frame, 2013). Furthermore, the timber research and development association (TRADA, 2011) has also declared timber as a renewable material for construction.

Figure 1: Process Flow for Timber Frames (Author and Google image)

The history shows the use of timber as structure frames in many parts of the world since hundreds of years. Centuries ago the method was considered as a basic method of construction in Europe. The structures such as churches, castles, homes and many manors have been and continue to be built with timber. The durable and strong characteristics of the structure has made to it to be used for a long time in the history of many European cultures. Until 20^th century, it has been found that Japan, China and various other countries have built their houses by using timber frame. The Isle Shrine is considered to be an oldest existing structure made up of timber frame. It was 690 AD when the shrine is thought to be built as shown in figure (Timbercraft, 2013). Many interesting and old buildings based on timber frame are still found in Britain. Most of the churches, barns and homes used such type of construction method in past. In history the 13^th and 14^th centuries are the periods of timber framed buildings. Many of the buildings can be still found to be erected even after many alterations decay and repair. The durability and strength of the structure has been proved by the existing structures which have longer life spans than the expected life period.

Figure 2I: sle Shrine (Google Image)

The vast amount of forests surrounding the Britain was one of the reasons of the growing popularity of the timber-frame methods. These forests made the raw material used to construct the timber frames easy to access. The material was easy to be carried to the site as compared to importing from the foreign countries. The simple, easy and fast erection procedures of constructing a timber frame have made it possible to construct timber structured homes in Scotland. The regions with cold climate are suitable with timber structure as it will provide insulation and strength to the given building (Solotimberframe 2010). After the immigration of Europeans to the North America the process of timber framing has now passed from one generation to another. The untouched forests provide the large amount of wood to construct more buildings which will also help the constructors to enhance their skills of building and construction (Whistler, 2011). The continuous cutting down of timber has resulted in the gradual declination of the forests in Britain. The absence of planting new trees has resulted in the reduced timber supply which requires the transportation of the wood from North America to the Britain. Until the 19^th century, the main method of construction of North America was also timber framing (Timbercraft, 2013).

Timber Properties

 Timber has been used as a construction material from the last many centuries. Much research has been conducted in the past to study the properties of timber. The material of construction was categorized into two common groups by Richardson in 1976. The one type of wood that came from the hardwoods and the other that comes from coniferous trees. Different characteristics are attributed to the both types of wood. As each type of wood has distinctive properties therefore it is important to select the particular type according to the structure requirements. The most common properties which are required to be considered while construction include strength, durability, permeability, moisture content, appearance and fire resistance.

Moisture content

The total amount of water present in the wood is called its moisture content. A process of wood drying is a method of separating moisture from wood before it could be used for construction purposes. The moisture within the wood is required to be in equilibrium with the surrounding moisture through the phenomenon of absorbing and desorbing. Many benefits are associated with the drying of wood including;

• More strong wood with lesser content of moisture
• Reduction in the cost of shipping due to the reduction in the weight
• Lesser decay during usage, storage and transport
• Insects are less likely to attack the dry wood as compared to the wood with higher moisture content

The life and strength of the wood can be enhanced through proper care techniques. Thus controlling the moisture content is important as it will help timber to stay safe from the effect of the insects, fungi and consequent decay (Reeb, 1997).

Strength

Every type of timber has different characteristics including their strength.  The wood has been classified according to its strength level. The common classes for the soft wood are C14 – C50 and for hard wood D18 – D70. Where C14; C16 is considered to be a weakest strength class. However the most commonly used strength class in construction is C24. The machines or visual inspections are the methods of grading the different classes of timber. Shakes, knots, splits, grains and wane are the different methods that can be employed to reduce the strength of the timber when required (TRADA, 2006; Richardson, 1976,).

Types of Timber Frames

Post and Beam

The building method which uses the beams and vertical posts is called post and beam methods as shown in figure. The tenon and mortise are used to join the beams and to support the entire building structure. In 1800’s the system of building constructions was most common. The levels are used to be formed for the construction of the beams and posts. All of the floors are independent from each other and erected one at one time (Davis, 2013). In 1830 the method of construction was declined. One reason of this declination was the requirement of the heavy pieces of timber by posts and beams. The declination rate of the availability of the high quality timber resulted in the high costs due to shortages (Nassén et.al, 2012).

Figure 3: Post and Beam Framing (Author)

Thus the construction method become very expensive method and expertise has found a continuous increase in cost of this type of framing method. Another reason of making post and beam method of construction an expensive method is the intensive labor of this building system. Due to these reasons the construction method was reduced to be implemented gradually (Ehow, 2013)

Platform framing

The easy construction of platform farming has helped the method to be used extensively in Canada and USA. It was early in the early 19^th century when the construction method of platform frames was invented and gained popularity in Great Britain. The procedure of construction has given the name platform farming to the construction technique. As shown in figure the method is mostly used to construct houses and other small buildings. The system of building framing which follows the resting of floor joists from every storey on the top plates on the sill of the foundation for the first storey or on the lower storey. The sub floors of each storey bear the partition walls and walls.

Figure 4: Platform Framing (Author)

A platform is generally made a single storey move towards upward to the roof. The exterior walls are then formed by using storey wall studs which are also used to form the other floors and walls. The storey walls studs are also used to join the joists from the floor to the top for the creation of the upper floors (Home, 2013). There are many advantages associated with this method of construction as it is fast, easy and safe to erect, construct and shape the buildings. The method is found to be less expensive as compared to the other construction methods (TRADA, 2002).

Balloon framing

Another type of wood construction method is called balloon farming which was extensively used in Scandinavia, USA and Canada throughout the 19^th century. Long continuous farming members are found to be used in the balloon farming which are also known as studs that can be seen from the foundation sill top to the roof plate top. These structures are usually held together by using nails. There are many problems found in this type of structure farming that has made it be replaced by the platform farming.

Figure 5: Balloon Framing (Author)

The requirement of the studs or long members of farming has made the procedure less popular as the studs are difficult to found and are more expensive. The construction type has found to allow the fire to spread quickly thus a destruction of structure can be expected in no minutes. The height and weight of walls has made the structure difficult to be erected that has reduced the popularity of the method and make it less applicable in most of the circumstances (American Wood Council, 2001).

Cost:

There are many factors on the basis of which cost of the frame construction can be evaluated. These factors include frame design, build location, timber quality, cost of labor and many others. The fluctuating price of the timber is thus the result of all these varying factors. A dramatic increase in the price can be observed when the supply of the product is low and demand is high. The case is more applicable for high quality, long and hard timber. The cost of timber framing also affected by the contractors used to build the structures. The per square meter price for timber is usually range from £500 to £2100 (Homebuilding, 2001

Sustainability

Considering the sustainability factor, timber is considered to lie among top materials. The material has high overall environmental credentials.  The main reason of its high sustainability is the renewable attributes of the material. However the growing problem is the continuous carbon dioxide emissions. The buildings are the major sources of the carbon dioxide emission thus it is important to consider the level of its emission while constructing a house and any building. According to building regulation standards of UK the constructing house produces about 4 tons of carbon dioxide (Sustainable homes, 20113. It is also important to evaluate the building material in order to control the carbon dioxide emissions during overall life span of the building. The release of carbon dioxide into the environment can be reduced greatly by using timber as it is considered as a most sustainable construction material. The reduction in the emission of carbon dioxide has also been found by trees as they are the vital components of the environment. The carbon dioxide is found to be greatly extracted from the atmosphere by the trees. Carbon dioxide will be absorbed by the trees from the atmosphere and stored in their trunks thus helping the environment. More trees would help to extract more carbon dioxide from the environment (Reduce Your CO2, 2007). During decaying or burnt conditions the emissions of carbon dioxide from timber increases.

Advantages of Timber Frame

Timber farming has presented many advantages. The fast, easy and simple method of its usage makes its effective applications widely throughout the world.  Few of its advantages are listed below.

Advantages of Timber Frame

• Since timber frames come in pre fabricated format, they can be erected quickly and easily. Studies have shown that the timber frame construction requires 20 percent less time than other construction techniques and therefore the overall construction process is much faster. Furthermore, the disturbance to the local area and labour cost can be reduced considerably by choosing timber frames. The biggest advantage of these type of frames is the fact they are not weather dependant, allowing speedy production no matter what time of the year it may be (Environ, 2013).
• Timbers frames can be used for different types of structures. Big or small, they can be used in various structures including hospitals, schools, mansions, houses, blocks of flats and hotels. Timber frame is the obvious choice if the soil conditions are deprived.
• The weight of the frame is transferred to the ground in an effort to strengthen the timber frame buildings. This is done as effectively as possible to achieve best results. Strengthening the building is important to deal with the effects of heavy snow load, earthquakes and hurricanes.
• Timbers frames are extremely cheaper as compared to other types of frame. Moreover, the return on investment attached to them is higher because of quicker construction type. Reduced construction time also helps save the excess labour cost. Time frames produce very small amount of waste in addition to being recyclable to landfill. Considering it light weight/structure, the costs attached to the foundation are also reduced significantly.
• Timber framed houses and flats are tough and durable. Buildings or houses using timber frame have an extended lifetime when compared to other types of modern construction materials. According to Enviorn (2013) and Scotframe (2013), timber frame structures are designed to last over fifty years, which satisfies the building codes and requirements.
• Timber is environmentally friendly as it is sustainable and renewable. Forests in the Great Britain, Scandinavia and North America produce the majority of the timber. As tress are cut down to obtain timber, many more are planted to maintain the resources. Additionally, this type of construction material is known to produce less carbon dioxide when compared to other construction materials. By using timber frame for building our houses, flats, hospital and other structures, the damage done to the environment can be controlled considerably (Environ, 2013).

Disadvantages of Timber frames

Unfortunately, there are some disadvantages attached to using timber frames for construction purposes. Some of the drawbacks are listed below.

• As majority of the modern building use steel frames instead of timber frames, it has become increasingly difficult to find people who are aware of this technique of constriction. Moreover, numerous problems can arise if inexperienced labour performs this task with little knowledge about the construction method. Moisture protection and fire stopping are the most important safety aspects which should not be overlooked when constructing building using timber frames (TargetTimber, 2013).
• Another shortcoming attached to using timber frames is the fact this material can catch fire very easily. Appropriate fire protection measures must be taken in an effort to prevent the building from potential fire catastrophe. It is recommended to enclose the timber frame in non combustible materials to tackle fire hazards.
• Studies have shown that timber frame can lose its shape and properties when exposed to water. Therefore, use of timber frames should not be used in parts of the world that experience excessive moisture. Decaying is a noteworthy problem as it can have severe effects on the strength and durability of this material. To ensure safety and health of people inside the building, it is extremely important to install an appropriate moisture protection system.
• Termites and carpenter ants are also known to reduce the strength and reliability of timber frames as these bugs usually feed on wood. If a timber frame structure is affected by infestation, it must be replaced by some other type of construction system (Environ, 2013).

Steel Frame

Steel frames are the most commonly used type of construction material these days. It will not be wrong to say that it is growing in demand with each passing day. Essentially, the steel frame consists of horizontal I breams and vertical steel columns which can be interlocked to hold up the whole structure. Steel frames are used where durability and reliability is required. Warehouses, offices, stadiums, skyscrapers, manufacturing units and bridges are some of the structures that use steel frames. Since steel frame is light and the erection time period is short, it has become the obvious choice for modern day structures and buildings (Lam et al, 2004).

Although timber frame dominated the construction market in the early 1900’s, the use of steel frame has grown tremendously over the last five to six decades. Majority of the civil engineering and mechanical projects are completed using this extremely durable and light construction material. Considering the speedy erection process, their durability, strength and environmental benefits, most construction projects are required to use steel frames.

Japan was the first country to introduce steel frame in construction projects and since then it has grown in popularity across the globe. Steel was readily available in Japan and therefore the country decided to build houses using steel as the construction material. With advantage such as non flammability, durability and strength, steel frame industry experienced a tremendous boom (Ehow, 2013).

Steel frames have been used in the United Kingdom since 1950. The UK started to use steel frames as the first choice for buildings and home following the success of this material in Japan. Similarly in the United States, steel frame was not used as the primary method of construction for homes and buildings until early 1990’s. Steel became the popular choice in the developed world due to its advantages including in-flammability, durability, reliability and energy efficient.

Due to its properties, steel is an ideal choice as the material of construction for modern day structures.  Furthermore, this material is 100 percent recycle which has made it allowed this material to grow in popularity tremendously over the last few years. Buildings or homes, road or railways, steel is being used for a range of application worldwide. Additionally, it is used to manufacture several kitchen appliances including microwave oven, fridges, and freezers and in the card bodies as well. Improved production technologies have allowed for constant supply at an affordable price (TATA Steel, 2013). Considering the reasons given below, steel is now the most preferred building material.

• Durability
• Reliability
• Recyclable
• In flammability
• Retain its properties when exposed to water or bugs

Types of steel frames

Cold formed steel framing

In seismic zones such as the United States, Cold Formed steel framing, also knows the CFS framing is the obvious choice. The CFS framing is strong, reliable and ductile that is ideal for seismic regions. Furthermore, this type of framing can be formed into various sizes and shapes. Studies have shown that the CFS framing is produced by applying the process called roll forming (Lam et al, 2004).

Figure 7: Cold Formed Steel Frame Section (TATA Steel, 2013)

Using this method, sheets of steel are passed through a series of rollers to be shaped as web, C-shape or flange. As the process does not need any heat, the joint and studs used must be strong enough. Since the method does not use any kind of heating, it is known as cold forming. Lower costs and ability to retain its shape are some of benefits of using CFS as the construction material (TATA Steel, 2013). Furthermore, the fact it is termite resistant and non combustible reduce the costs considerably

Figure 8: Cold Formed Steel structure for two storey building (Naked Frames Ltd, 2013)

I-Bream framing

Although using CFS framing for building houses has its own advantages, I beam framing is the most commonly used type of steel framing in the industry. Similar to CFS framing, the I beam framing also has a lot of advantages including durability, strength and low costs.

This type of framing is known as I beam because looks like the letter I. The webs and flanges in I beam frame offer great resistance to shear bending moments and shear forces. They are designed to be able to withstand significant loads. Furthermore, they are available in a range of sizes.

Figure 9: I-beam Steel Frame Section (Google Image)

There are also some disadvantages attached to using I beam frames for building structures.  Although they can be used make large spaces, this type of steel framing can give rise to a number of problems when exposed to heating. Engineers, therefore, are required to use insulation material on the outside for safety concerns.

In addition to being heat sensitive, I beam frames are extremely heavy. They are usually transported using large machinery.

Figure 10: I-beam Steel structure (Google Image)

Volumetric Frame

Unlike other steel frames that are erected on site, the volumetric frames are designed and produced off site. Based on the needs of the project, they can be transported to the required site using heavy machinery or a group of men. The advantages of using volumetric frames are immense. They are extremely cheap when compared to other types of steel framing. Additionally, their quality is higher and reliable (Light Steel, 2013).

Volumetric steel frames are light and therefore the foundation costs can be lowered considerably by using this steel framing. The flexibility and light weight allows the civil engineers to complete complex designs. Some of the most noteworthy benefits of volumetric steel frames are listed below.

• Non combustible
• Environment friendly
• Improved sustainability
• Acceptable sound and thermal insulation
• 100 percent recyclable
• Swift and speedy construction
• High quality product
• Low costs
• Higher efficiency

Figure 11: Volumetric Steel structure (Icarus, 2013)

Costs

With technology improving with each passing day, the manufacturing costs of steel has reduced considerable over the past few years. Not too long ago steel framing was expansive and unaffordable but this is not the case anymore.

Steel itself is cheaper than it was a couple of decades, although it is still considerably more expensive than the timber or wood. Quicker completion of construction projects with steel framing offers better rate of return on investment. Furthermore, with so much competition amongst the labours, the installation and commissioning costs have reduced significantly. When building complex and mega structures such as skyscrapers and bridges, steel is the obvious choice due to its improved strength to weight ratio. It will not be wrong to say that steel frames give excellent value for money. Use of light weight steel can further reduce the foundation costs if needed (NASH, 2013). 

Sustainability

Steel offers excellent sustainability. In fact, it is the most sustainable amongst all types of construction materials used these days. Since it does not lose it properties, it can be recycled even 1000 times if required. According to the figures released by the TATA STEEL, nearly 95 percent of the steel used in the UK is directly recycled or reused. For its sustainability, steel produces negligible amount of waste when compared to timber frame that is wasted completely when exposed to water or bugs (TATA Steel, 2013).

Even the waste produced during manufacturing is reusable. Therefore, using steel as the material of construction is an excellent way to control the amount of waste produced by large civil engineering or construction projects. Although steel can be sent to landfills occasionally, it is reusable and demountable in most cases. If needed, steel framing can be dismantled and reused for creating another structure. Additionally, it hardly produces any dirt, dust or noise during the construction process.

According to sustainable homes (2013), a large amount of carbon dioxide in the UK is caused by construction developments. Using steel frames structure provides better and improved control of green houses gases in the environment due to its higher strength to weight ratio. For being 100 percent recyclable, environment friendly, cheap, steel framed structures are the most sustainable amongst all construction methods.

Advantages of Steel Frame

Although there are a large number of advantage attached to using steel frames for building houses, building, apartments, bridges and mega structures, only the most important and noteworthy are listed below.

Speedy construction

Just like timber framed structures, steel framed structures can be erected in a very short period of time. Depending on the weight of the steel framing used, the foundation development process can be extremely easy and quick. Speedy completion of the building or house also ensures improved rate of return on investment (Steel Framing, 2013).

Non combustible

Steel in inflammable and this advantage cannot be overlooked considering the strict health and safety standards set by the UK government. Steel framed structures do not catch fire and therefore safety of the residents of the building can be ensured.

Flexibility

Steel frames can be used in a variety of structures including street houses, flats, apartments, bridges, mega structures, skyscrapers and railway systems. Its strength and durability allows for design and architectural flexibility.

Cost effective

With steel framed structures, the overall cost of the project is reduced considerably due to quicker projection completion time investment (Steel Framing, 2013). Labour costs are also lowered as the labour is required to spend less working hours on the site. Volumetric steel frames that are fabricated off site offer even better cost affectivity. With steel prices going down (100 percent recyclable), it can now be used even for small scale engineering projects including houses.

Environment friendly

As mentioned previously, steel is highly sustainable and therefore it can be reused as many times as needed. The physical properties of steel are never lost even when exposed to fire or water. Furthermore, it is fully recyclable, which reduces the damage inflicted on the environment tremendously.  Using steel frame structures required lesser transportation needs and therefore the amount of carbon dioxide produced by the vehicles is lowered (Steel Framing, 2013).

Water and termite proof

Due to its properties, steel is resistant to water and bugs. Unlike timber frames that are can be damaged by water and termites, steel retains its structure and provides excellent security against bugs and rain. Steel is the obvious choice in regions which experience extreme weather conditions.

Strength

CFS framing or Cold Form Steel framing offers best strength to weight ratio. Therefore, when the construction material is required to withstand heavy loads, steel becomes the ideal selection.

Disadvantages of Steel Frames

Steel framing costs are considerably higher when compared to timber frames. Furthermore, steel prices in the stock market are not stable. Sometimes, additional insulation and corrosion prevention is also required which adds to the cost of construction project (Steel Framing, 2013).

Conductivity

Heat loss can be a big issue with steel frames as steel conducts heat almost 30 times faster than timber (Ehow, 2013).

Sound transmission

Use of soundproofing system is usually required when using steel framed structures. This is due to the fact that sound travels at great speed through steel.

Insulation

To prevent heat losses, additional insulation may be required for steel framed structures. Unlike timber that offers excellent insulation, steel is not a good insulator.

Corrosion and skill shortage

Due to its properties, steel can suffer corrosion or rust when exposed to aquatic conditions. Furthermore, it is hard to find skilled labour for constructing steel frame (Mehta et al, 2009). 

2.3.          Comparison

Although steel and timber have some identical quantities, there are also a lot of differences between them. One of the main differences between the two types of frame is the fact the steel has the ability to maintain strength over a period of time. Timber on the other hand is vulnerable to excessive amounts of termites and moisture. Therefore timber can experience reduced strength when exposed to water and bugs (Dinwoodie, 2000).

Another notable difference between the steel and timber is the construction and erection time. While timber requires less work and time to construct, steel frames can be very tough and time consuming to construct and erect. Hence steel is the obvious choice where strength, durability and reliability are required. According to a research conducted by Enviorn (2011), a timber frame house can be constructed in 1 week as compared to a steel frame house that needs two weeks for the construction to be completed. Since timber frame is light, labor can continue the construction works even during the rain or snow. Steel frame houses, on the other hand, cannot be constructed under severe weather impact.

However, since majority of the construction projects require higher strength and durability, the steel frames have a big advantage over timber frames. The strength to weight ratio for steel is the highest of any type of construction materials. Skyscrapers, mega structures and tall building, therefore, use steel frames instead of timbers frames, concrete or cement. Furthermore, the effects of rotting or warping are almost negligible when steel is used. This is because the walls remain perfectly straight no matter what the external or internal conditions are. Once constructed and erected, unlike timber frames, steel frames can withhold any kind of weather. Even in events of earthquakes and hurricanes, this type of construction material remains standing, thereby, reducing the damage done to the building and resulting casualties (Scarborough and Armpriest, 2009).  Both steel and timber frames can be damaged significantly when exposed to fire. Timber frames, in particular, are extremely combustible and therefore it is vital to apply the recommended fire protection method to ensure the safety of the people inside the building. Steel frames, on the other hand, are less likely to catch fire. However, when ignited the fire spreads fairly quickly. Fire can demolish steel frames quicker than the timber frames. Heat can pass through the timber more easily compared to steel because timber is a very good thermal insulator. Timber frame buildings stay warmer than the steel frame buildings (Karjalainen et.al, 1994).

Timber is an environment friendly material, which means that it can be sustained. Constructing a building with timber also needs less energy and produce less waste at the same time. However, when damaged significantly it has to be disposed. Steel is also very sustainable. However unlike Timber which is easy to obtain, steel must be produced using highly advanced chemical processes which require needs a lot of energy. Being part of a natural life cycle, timber is a renewable source. It further reduces the carbon emission in the atmosphere as it is sustainable. Timber produces less carbon than any other type of construction material used today in construction industry. It is also recyclable. The waste generated while constructing a timber frame building can be re used if required. Steel is also fully recyclable. The fact it does not lose its physical properties, it can be used a 1000 times if needed.

Constructing timber frame building is considerably cheaper than a steel frame building. This is because the steel itself is very expensive. Timber is available in abundance and therefore it is inexpensive raw material. Steel has to be produced at large chemical plant. The productions costs add significantly to the market price of steel. Furthermore, the costs for fire and corrosion protection associated to steel frames are quite high. Insulation problems in steel building and the additional insulation also increase the expenditure. The fire safety procedures for timber frame are inexpensive to apply (Sathre and Gustavsson, 2009).

Finding skilled labour for steel frame construction projects is very challenging when compared to timber frame buildings which can be constructed by average labour. Cost affectivity of steel frames, however, is many times better as the benefits attached are substantial.

Chapter 3: Methodology

Introduction

A detailed comparison of the steel and wood frame is required to be presented so that the aims and objectives of the dissertation can be achieved. A comprehensive analysis about the sustainability, material properties and cost associated with the construction of each frame is required to b considered through discussing relevant case studies. The presentation of the data of two case studies has been found to be the most appropriate method to understand the aims and objectives thoroughly. The findings from the literature review and case studies have been evaluated by conducting survey through a questionnaire. The results of the survey are found to have vitality for the provision of better understanding of the steel and timber frames and have helped to conclude the whole dissertation.

Case Studies

The two case studies have been analyzed in this section related to the residential buildings in United States. A good comparison between steel framing and wood framing has been presented through these case studies. The material and labor cost has been compared through these case studies. The overall construction cost of the timber framed buildings is compared with that of steel framed in this section. 

Case Study 1

 Demonstration Homes (Beaufort)

The case study of Beaufort Homes has been presented in this section. The steel framed homes were compared with timber framed homes in order to present the material and labor cost of the structures (Historic, 2012).

Table 3‑1 Characteristics

The beaufort homes are erected side by side in the south carolina of the United States. An effective comparison can be made as houses made of timber and steel are constructed at the same location. The floor plans, exposure, dimensions and orientations are same for all sets of houses. Its has been shown in the table that there are two storey residential buildings which are consists of timber and steel framed homes. The length and the width of the homes is same. There are three bed rooms in each home. The foundation, orientation and types of the homes are similar in both cases. The development of the same characteristics of both type of houses was empirical so that they can be compared accurately and reliably. The steel and timber reframed houses are 135 m2 in area which has been illustrated in table. The market value for both of the homes was calculated to be about $182,000 - $199,000 after construction (PATH, 2002).

Table 3‑2Dimensions

Table 3‑3crew composition

Table show the total number of laborers, helpers and foreman required to complete the required jobs. It has been shown in the table that the framing of the first floor required about 6 workers in total for eth steel house which is also same for the timber house. The framing of the second floor required about 7 workers in total for steel and timber houses. For the construction of the non structural walls the timber house requires

two more workers than the steel one. Steel house requires one extra carpenter for performing insulation services as compared to the timber house. The higher number of workers has been calculated for the steel house as compared to the timber house. For the steel house the total number of workers is 116 while for timber house the total number of required workers are 114. So the amount of workers for both cases is almost the same as only 2 extra workers are required in the steel house.

Table 3‑4 total man hours

Table show the total time taken by each home to be constructed. The timber framed takes much lesser time to be built than the steel frame house. Total number of hours required to construct the timber house is about 523 as shown in table above. The total number of hours required to construct the steel house are about 538. The comparison of time has shown that the timber framed house is easy to construct within lesser time period than the steel frame houses. Steel frames take about 15 hours more than the timber frame houses. The table also showed the total time taken by the houses to be completed including inventory. Timber takes about 1359 hours to be constructed while steel framed house takes about 1376 hours to be completed and finished. The comparison has shown that the timber frames can be constructed and completed within lesser time duration than the steel framed house.

Table 3‑5 framing material cost and labor hours for steel house

Table 3‑6framing material cost and labor hours for timber house

Table 3‑7 labor and material cost for steel house (steel framed)

Table 3‑8labor and material cost for steel house (timber framed)

Table 3‑9 Cost Of Labor And Normalized Material That Has Been Paid By The Builder

1 Cost of labor that is included in the cost of material

Cost of the material and labor has been illustrated in above table. Steel house has greater material cost than the timber house as illustrated by data used to discuss case study.

After presentation of data in the form of tables, both frames can be compared effectively. The case studies have shown that the cost for the steel framed house is higher than the cost of the timber farmed house.

Case Study 2:

Demonstration Homes (Valparaiso)

Case study 2 presents data for the demonstrated homes of the Valparaiso. The detailed discussions have been carried out in this section for the sake of comparing to types of frames i.e. timber and steel.

Table 3‑10 The Characteristics Of Every Home

For SI: 1ft = 305 mm

A case study of houses that are erected side by side in Valparaiso United States has been taken to compare two types of frames. The configuration of each type of house is almost same with similar types of the floor plans, orientations and dimensions (Demonstration, 2012).

Table 3‑11 Dimensions for Valparaiso demonstration homes

For SI: 1 ft^2 = 0.093 m^2, 1 ft = 305 mm.

Table 3‑12 Composition Of Crew For Valparaiso Demonstration Homes

Table 3‑13 Normalized hours of labor for Valparaiso demonstration homes

Sheathing is included in hours.

It is adjusted for extra dormer time.

Wood sheathing is included in hours.

It is adjusted for roof size.

Adjusted for Sq. footage of vinyl siding.

Adjustments have been made for porch size.

Table 3‑14 Normalized Labor Of Framing And Cost Of Material For Valparaiso Steel House

Screw cost for framing the walls of the basement is not included.

Cost of material includes floor sheathing, walls and roof.

Table 3‑15 Labor Of Normalized Labor And Cost Of Material For Valparaiso Wood House

Nails cost for framing walls of basement is not included.

Cost of material includes floor sheathing roof and walls

Table 3‑16 Labor Of Normalized Trades And Cost Of Materials

For SI: 1 sq. ft = 0.039sq.m

Hours of living area per sq. ft (2,206 sq. ft)

Include labor cost.

Included in the cost of builder’s material

Included in the cost of builder’s framing labor

Included in the cost of builder’s trim carpentry labor

Table 3‑17 Trades Normalized Labor And Cost Of Material

For SI: 1 sq. ft = 0.039sq.m

Hours of living area per sq. ft (2,206 sq. ft)

²Include labor cost.

³Included in the cost of builder’s material

⁴Included in the cost of builder’s framing labor

⁵Included in the cost of builder’s trim carpentry labor

Table 3‑18 Cost Of Fasteners Paid By the Builder

Drywall screws cost is included in the cost of drywall material.

Table 3‑19 Cost of normalized and actual labor

Labor cost is included in the framing cost.

In the material cost labor cost is included.

It includes cot of labor.

Included in the trim carpentry labor cost

The details for the comparison of two frames have been shown in the form of above tables. In depth comparison has been made for the steel and timber frames. The presented data has shown that the steel frame is expensive to be used for the construction of two storey buildings than the timber framed buildings (PATH, 2002).

Chapter 4: Findings

Introduction

A specialized survey has been created by developing a website. The potential respondents were selected and a link was sent to them to conduct survey.  There were 10 questions in total which were required to be answered by the top civil or construction companies. Considering the limited time, the obtained response was quite satisfactory. The total number of responses was 45. A vital response has been obtained which will be analyzed and discussed thoughtfully in the remaining sections. The results obtained have helped to identify the positive and negative aspects of each structural alternative.

Survey Results

Question 1: 

What is the time taken by each construction type to construct a two storey house?

The graph showed that there are about 45 respondents which have responded to our questionnaire. It has been illustrated in above figure that about 62% of the total respondents has responded that the steel frame takes more time to construct a two storey residential building than the timber frame building. Only 9.8% said that the timber frame takes more time for constructing a house. About 52.2% of the respondents have chosen steel framing over timber framing. The engineering firms have agreed that both frames take same time for the construction of a two storey building with the contribution of the 29% of total respondents.

Question 2:

Which one of the following construction types is the cheaper way to construct a two storey building?

The results from the above graph have shown that it is more expensive to use the steel frame for the construction of a two storey building than the timber frame. About 87% of the total respondents have reported steel as a more expensive construction material as compared to the timber frame. About 6.5% of the total respondents have reported timber framing as more expensive material and remaining 6.5% stated them as equally expensive materials for the construction of a two storey residential buildings.

Question 3:

Which of the construction type requires less number of skilled workers for the construction of a two storey residential building?

There are many factors which determine the number of skilled workers required to construct a two storey building i.e. type of selected material. Heavy material like steel would require more skilled workers. The fabrication and positioning of the frames also determine the required number of skilled workers. The above chart showed that different companies and firms have different opinions for different material of construction. The majority of about 46% of the total respondents has stated that the steel framing needs more skilled workers for the completion of a two storey building. About 36.5% responded that an equal amount of the skilled workers is required for the construction of the two storey building. However the respondents who think that timber frame requires more skilled workers are only 17.5%.

Question 4:

Which of the construction option is more labor intensive?

The determination of the least and more labor intensive material is quite tricky process. The graph showed that about 41% of the total respondents agreed that both timber and steel frames are equally labor intensive. 29% of the respondents think timber requires is the least intensive labor while remaining 30% believes that the steel is a least labor intensive construction material.

Question 5:

Which of the construction type has produces more waste during manufacturing of raw material?

About 60.1% has the opinion that timber has produced more waste during raw material production. 17.8% believes that the steel is a more waste producing construction material. Only 22.1% responded timber and steel has the same effect in producing waste (Buchanan and Levine, 1999).

Question 6:

Considering the carbon emissions, which of the construction type most pollutes and harm the environment during construction of a two storey building?

It has been illustrated from the graph clearly that the steel frame harms the environment greatly and pollutes the atmosphere by a major factor. The amount of carbon emissions is many more in case of steel frames than the timber frames. About 93.1 of the respondents believe that the steel is a more polluting material than the timber frames. No responses have been received for the case of timber which showed it as a best material for the construction of residential blocks. A very small percentage which is about 6.9% believes that both of the frames produce polluting substances equally. The results of the survey have increased the chances of the timber frame to select as a more sustainable material. Requirement of the great amount energy for the manufacturing of steel has resulted in the high emissions of carbon dioxide emissions released into the atmosphere.

Question 7:

Considering the durability of the residential houses, which one of the construction options is the best to choose?

The similar attribute has been responded by about 29.1% of respondents for both timber and steel frames. Steel frame has been found to be more durable as majority of the respondents believed that with the voting percentage of about 63.2%. The remaining 7.7% responded that the timber has less durability than the steel frames. Thus it has been proved that the steel is a most durable construction material when considered for the construction of a two storey house building.

Question 8:

Considering the earthquakes and strong winds such as hurricanes in a two-storey residential building, which one of the construction options has the ability to withstand the most?

The steel frame has been shown to withstand bad conditions of weather including earthquake and hurricanes as more than 56% of the respondents responded this way. The timber frame has lower ability to withstand the harsh conditions of weather and responses gained for this section are about 15.3%. Only 28.7% believes that both steel and timber frames has the same ability to withstand the harsh weather conditions i.e. earthquakes and hurricanes.

Question 9:

Considering the market and climate of the United Kingdom, which one of the building material is best suited for the construction of a two storey residential house presently?

Interesting responses were obtained for this question. Majority of the respondents with the percentage of about 72.3% responded that timber is a best material to be used for the construction purposes in United Kingdom. Steel framing has been considered by only 6.9% of the candidates who think it as a best material to be used for the construction of the two storey house building. The remaining 20.8% believes that both materials are equally suitable for the constriction of residential buildings in U.K.

Question 10:

Considering the market and climate of the United Kingdom, which one of the building material is best suited for the construction of a two storey residential house in near future?

Remarkable results were obtained as outcome of this question. 69.9% of the respondents were found to believe that the timber framing is the best suited material to construct two storey residential building in near future too. Only 5.7% of the respondents believed that the steel frame is a best suited construction material. A significant difference between two frames has been found for the steel and timber frame responses which is about 64.2%. Only 24.4% of the respondents believed that both of the frames are equally suitable to be used as construction materials for the two storey houses in near future.

The survey has showed that the timber is a very useful material and as excellent properties and can be considered as an ideal material to be used for the construction of a two storey residential building.

Chapter 5: Analysis and discussions

Analysis and discussions

The literature review, surveys and case studies have been used to discuss and analyze the data presented in above sections for the comparison of the timber and steel.

The characteristics and the total area of floor (135m²) is exactly the same for both the frames in case study 1 along with the roof areas but the load and non load wall bearings amongst the frames are different as shown in the table 3-1.

More over the results of case study 2 indicates the same characteristics but the difference lies in the floor area which is little higher for steel house rather than the wood house.

In the case study 116 workers were required for the steel house whereas for the timber house, there was a requirement of 114 workers indicating higher number of workers for the steel house as compared to the wood house. However, the results of case study 2 are quite the opposite showing that steel houses analyzing the results of both the case studies, it is understood that both the frames had only slight difference on the total number of workers.

Similarly the results of the survey sort were about the same. From the survey results it is clearly indicated that almost 46% of the respondents agree on the need of more skilled workers for steel framing whereas 36.5% also agrees that both required the same number of workers with a slight difference of 17.5%. Thus, it can be suggested that the judgment for the need of total number of workers between the framed is very difficult and may vary between the projects. On the other hand, the results of this survey suggests that total number of workers required for both frames may be the same during the construction of two-storey residential building having steel framed building. As for the results of case study 1, there is a difference of 3.47% for the number of hours required to construct the timber frame and steel frame, 518 hours for timber frames and 536 hours for steel frame respectively indicating that timber frame is faster to construct as compare to steel frame. Whereas the results of case study 2 showed that 528 hours are needed for constructing the timber frame while the construction of steel frame need 239 hours pointing an increase of 9.3%.

 This again demonstrates the quicker construction of timber frame in comparison with the steel frame. Thus, the results of case study 1 and 2 agree with each other on the fact that timber framing takes lesser time for constructing a two-storey residential building. Moreover the survey analysis results helped us to make a pretty decisive decision. From the results of question 1 of the questionnaire, it is deuced that in order to construct a two storey building, steel frames took more time as compare to timber frames as out of 45 responses 62% agreed on that. Consequently, it is clearly stated that it tool linger period of time to construct steel framed and results of survey and literature review proved that. Case study 2 results also proved the same point of timber frames being cheaper in comparison with the steel framing but the results are of at lower percentage. The results of this case study indicate a difference of 7.4% in the cost of both proving the same point of steel framing being more expensive. Cost has played an important role on the selection of framing along with the factors like labor cost, fitting cost, labor cost, material cost; all are more expensive for steel framing. Question 2 of the survey confirmed that timber frame is less expensive in comparison with the steel frame. A total of more than 87% respondents have found timber frames less expensive. Therefore, it is clear that use of timber frame is advantageous in terms of cost as it is cheaper in all the ways concerned for constructing a two storey building. But the construction intensiveness is tedious and same for both frames. Thus it can be concluded that labor intensity level is same for both the steel and timber frames as most of the respondents chose it as their choice. Similar while considering the terms of durability and strength, it is important for the steel frame. The strength of steel is very high as its strength to weight ratio is high for any building using steel in it (Nucon, 2011). The deisgn life for both the frames is more than 60 years but the strength and durability of steel frame is very high and it can stand extreme weather conditions like hurricanes and earthquakes etc 56% agreed on high durability for steel framing and respondents chose that extreme weather conditions can be withstand by steel framing with more strength in comparison with timber frames. The only source that is renewable and can help in reducing the carbon emissions with the extraction of carbon dioxide is known as timber and it is clear winner in terms of sustainability. Though steel is recyclable but is a non-renewable resource. Moreover the energy required for its manufacturing huge which emits high level of harmful radiations. The results of question 5 also proved the point that it produces more raw materials.

Some similarities and differences are shown by both the frames like the number of workers needed for frame building are same but the cost of both the frames is drastically varying. Depending on the situation, need and cost, some required more cost while others need less. Same is the case with labor intensity. While considering the sustainability both the frames have excellent result but timber wood is more renewable.

Chapter 6: Conclusion

Conclusion

After scrutinizing the whole dissertation we can conclude that the basic aim of the paper has been justified. The best type of the frame has been identified out of steel and timber for the construction of eth two storey building. Previous literature and reports have been assessed critically for the sake of the research objective of this dissertation. There are two case studies which have been analyzed for the identification of the positive and negative aspects of the timber and steel frames. The further information has been gained by the development of a questionnaire which has also supported the findings of the dissertation. Timber frame has been found to be the best frame out of two frames for the construction of the two storey building (residential blocks). The sustainability and price of the frames have made distinguished them otherwise the options were quite similar with each other. Considering the high rise and low rise building, the best frame would be the steel frame as it has the better characteristics suitable for the higher buildings. However for the residential purposes the timber framed structure is found to be more suitable.  Steel frame has not been considered for the fact that the frame is not commonly used in the United Kingdom for the houses and other residential purposes. The main reason of using timber frame is its lower cost and more sustainability than the steel framed structures. The steel framed structure are highly expensive than the timber framed houses. Considering the market of United States, the steel framing has been found to be used abundantly for residential purposes as the researchers there are more aware of the features, quality and properties of the steel frames and structures related to steel. Sustainability is the main reason of the selection of the timber frame as a main structure of construction. The environment subjected to the damage has been saved by using timber frames which has the ability to extract CO2 from the atmosphere. Government encourages to plant two or trees with cutting down of the one tree so that the supply of the timber will not be effected. The harmful gases released during manufacturing of the steel have also made the material less suitable for the residential structure than the timber frames. Considering the price of both frames, timber has been evaluated as a cheaper option for the construction of the two storey residential building. The findings from case studies and questionnaire have proved the timber framed buildings as cheaper and more sustainable. So we can conclude that the timber frame is a best option of the constructional material for the residential buildings.

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