Hybrid, Prefabrication Volumetric Framed

Hybrid, Prefabrication Volumetric Framed Design Technology Student Number: 14002245 2015-2016 10-05-2016

BE 1339

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Table of Contents I.

Introduction ............................................................................................................. 3

II. History of prefabrication ........................................................................................ 3 III.

Timber systems ................................................................................................... 4

IV.

Large panel high rise residential buildings ....................................................... 4

V. Advantages of hybrid, prefabrication volumetric frame ..................................... 5 A.

Procurement .................................................................................................................. 5

B.

Design process.............................................................................................................. 6

C.

Craft quality ................................................................................................................... 7

D.

Time saving ................................................................................................................... 9

E.

Cost ................................................................................................................................ 9

F.

Hard costs...................................................................................................................... 9

G.

Soft costs ......................................................................................................................10

H.

Building performance ..................................................................................................10

I.

Sustainability ................................................................................................................11

VI.

Disadvantages of prefabrication volumetric frames and modular ................ 11

A.

General image...............................................................................................................12

B.

Perceived performance ................................................................................................12

C.

Customer expectation ..................................................................................................12

D.

Quality ...........................................................................................................................12

E.

Undesirable layouts .....................................................................................................12

F.

Total construction cost ................................................................................................13

VII.

Prefabrication volumetric modular designs .................................................... 13

A.

Foundation ....................................................................................................................13

B.

Walls ..............................................................................................................................15

C.

Floor ..............................................................................................................................15

D.

Roof ...............................................................................................................................15

VIII. Mechanical, Electrical, and Plumbing System ................................................ 17 A.

Heating and cooling systems ......................................................................................18

3 B.

Prefabricated stairs ......................................................................................................18

IX.

Conclusion ......................................................................................................... 19

X. References ............................................................................................................ 20

I.

Introduction

Construction has been made easy by offsite construction techniques where building assembling components are delivered on site for assembly only due to prefabrication technology. Prefabrication can be defined as the technique in which houses or building’s assembling components of a structure are developed in factory according to the desired construction architecture, where they are then transported to the construction site to be assembled into the designed or desired building. Prefabrication can also be defined as modular construction which is a type of construction where the factory-produced preengineered building units are delivered to the construction site where they are then assembled according to the approved plan or client’s design (Admin,2016). The factory produced pre-engineering modular can be made various forms such as complete rooms, parts of rooms, or even separate high serviced units such as lifts, kitchens and washrooms. For buildings that are not tall the discrete modular units usually do support themselves but on tall buildings some architects do like to support using structural framework to enhance their strengths (Lawson, Ogden & Goodier, 2014).

II.

History of prefabrication th

Prefabrication construction is said to be dated back earlier than 20 century where bridges, house, churches and hospitals of the colonies were made from factory fabricated materials from the factories which were assembled at the construction sites. For example, in the UK in 1779, it is believed that the first iron bridge which was built at Colebrookdale was from fabricated materials. Then the technique of prefabricated materials started being embraced after the First World War when the necessity of provision of new houses which could not be handled by traditional building methods or trades system. Then shortly after First World War in 1928, prefabrication did not manage the competition with traditional building methods which made developers to cease its use and switch to traditional methods of building.

After the Second World War, there was need for houses that were destroyed from war, and also there was political pressure to provide homes for solders returning from war which required creative thinking and design work. Due to political pressure, the government of UK formed a committee which was charged

4 in considering materials and methods of construction which was suitable for building flats and houses, with consideration to efficiency, speed of erection and economy. The committee then passed the Temporary accommodation act which enabled the government to develop 157,000 temporary houses from imported parts which were developed from factories where then the committee appointed a team to erect the imported parts.

III.

Timber systems

For the timber system built frames, they were introduced in the United Kingdom in 1920s after the First World War so that it can respond to the shortage of labor when building the buildings external walls which were made from solid timber planking or heavy framed panels which were cladded using timber. Between 1927 and 1941 is when the first panels made of timber on the external walls were built where the highest building they could erect when the panels were extended was two story building. When using the timber panels, the frames were overlaid with a breather type membrane of building paper or bituminous felt, and then cladded with timber boarding nailed directly to the frame (Smith,2010,p.9). Then plasterboard and fiberboards were used to line the frames over the timber boarding. Then in 1945 there was shortage of timber which lead to forming rationing hence leading to using separate materials such as bricks backed by cavity, where stressed skin panels were fabricated in factory as per the client’s design then transported to be assembled on site. Between 1945 to 1965 timber gain popularity since it’s easy to form panels using timbers where 20,000 timber frame dwellings were developed. By 1975, timber frame system was widely developed where more than 80,000 timber framed dwellings were developed with loadbearing timber frame panels and external wall cladding.

IV.

Large panel high rise residential buildings

Within the late 1950’s there was a major push in United Kingdom to increase the number of houses within a restricted site space and a very short period of time which led to development of Large Panel Systems (LPS). The LPS were used to erect the first building in 1965 where nine buildings each twenty two floors were erected. The durability assessment of using large panels system in erecting buildings with many floors depends on the rate of corrosion of any embedded steel reinforcement and the cladding elements that have clades the panel’s external envelope. Some of the problems that large panels also suffered from are water penetration since the joining materials ages and poor thermal performance, the bridges had frequent condensations, which some of them were facilitated by poor workmanship at the fabricating factory, or even poor architectural design.

Use of fabrication in construction industry has been currently been accepted by construction stakeholders where due to the advanced in technology and creativity of the architectures in designing, various building with variety of performance requirements depending on the needs of the client, complexity of the required building with variation on shapes, form and size can be erected. Due to advancement of

5 technology, prefabrication can be accomplished from virtually any material where they determine the element, system and building type that can be developed. The most common type of materials for prefabrication can be categorized as wood, aluminum or steel, polymer, composite and concrete. The materials to be used in prefabrication should have performance characteristics and properties which will depend on where and how they will be used in building and what functions such as attachment, structure, thermal resistance and infiltration they will perform when used in building. For example, for prefabrication structures the materials suitable are steel and concrete since they are readily and easily available and affordable, for non-bearing load enclosure materials such as polymers, glass and aluminum since they offer light transmission and they are light weight, and for small buildings wood is used for closure and also for structure

V.

Advantages of hybrid, prefabrication volumetric frame

Prefabrication volumetric frame do have great benefits when specifically viewed on the client’s point of view. Some of the needs are;

A.

Procurement

On this benefit, prefabrication technology increases the ability on collaboration and responsibility on single point. The procurement process on prefabrication construction is easier since ready made products are easy to procure than the procurement of construction materials that are all raw materials that will be used to custom design the building at the site during construction period. On the prefabricated materials which can be both readymade and custom designed, slight adjustments can be done at the procurement process to fit various procurement methods. Some of the construction procurements methods that can be used in procurement of hybrid prefabrication volumetric framed are; 

Design-bid –build procurement method, where under this method, the client proposes a design which is designed by the architect and is bid among contractors. The bidding documents are produced by the architect where the successful contractor is forced to select a sub-contractor for supplying the prefabricated materials. The limitation of this method is that it does not save time, as the main intention of prefabricated technology is to save time. The bidding documents for this procurement methods requires the approach where they are designed using manufacturer’s standards, they are designed using prototypical or performance based, and designed using a custom prefabricated system since most prefabrication manufactures do have their own system on which they design and manufacture the prefabricated frames (Smith,2010).

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Negotiated bid procurement method, where under this method the client and the architect do select the prefabricated manufacturer or a contractor from the prefabricated manufacturer so that they can have maximum collaboration between the prefabricated manufacturer, client and the architect. Then the three makes the following arrangements on the client’s project will be provided with general contractors;

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Implementation of a single point procurement where the prefabricated manufacturer provides general contract directly to work on the client’s project.

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The prefabricated manufacture together with the client and the architect do use competitive bid procurement to select a contractor.

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Design- build procurement method where the client searches and makes a contract with the prefabrication manufacture for him or her to provide full or partial design services on top of the construction services. This procurement method takes two permutations which are;



Traditional design build where the prefabrication manufacturer provides the client with in house design services by using the manufacturer’s architecture team or by collaborating with an outside architecture firm on behalf of the client, where then the manufacturer’s architectural team provides the final document that they will use in construction (Smith,2010).



Design build with bridging documents method where the architect provides the bridging documents for the manufacturer to complete the client’s building, if the drawing set has reached a stage of completion between the 50% construction documents.

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Strategic partnering procurement method where the client engages the prefabricator manufacturer for an extended period of time on multiple projects. This procurement method is mostly engaged if the client has high volume of repetitive work.

B.

Design process

Prefabrication volumetric framed has various benefits on design process for clients and architecture where some of the design process benefits are; 

On pricing the prefabrication volumetric frame do provide upfront design pricing where it provides guidance on the entire project costs, it provides early estimates on design phase, and it provides a basis on negotiated bid procurement.

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On logistics prefabrication volumetric frame to provide the client and the architect the transparent means and methods of construction that can be used in predicting and monitoring the quality of work on the building.

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On resource and consultants, the design processes required for fabrication volumetric framed where the manufacturers do easily recommend the client with qualified and experienced consultants and other resources such as engineering services according to the client’s project.

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The design process also provides the client’s with effective prototyping and mock-ups mechanisms which allows the clients and architects to predict the outcome of the project with high degree of certainty. The benefits of prefabrication frames prototypes is that they can be much more cheaper, real and fast, exactly replicates the project, and more clear than the prototypes for the in-situ methods of construction.



The design process on this method of construction provides the client with construction documents that are integrated with manufacturer’s designs, documents that are streamlined according to the client’s

7 specifications, documents that have no design and drawing redundancy, documents that are combined with shop drawings which eliminate the needs to produce the latter as a separate process, and documents that are 100 % perfect and reliable. 

The design process of prefabrication frames provides the architect and the client the usability of advance architectural software such as;

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Revit for building information modeling (BIM), which provide more accurate and reliable information to project team members, decreases the documentation errors, improves accuracy and speed of estimating, expedites the drafting process, and which in general reduces the cost and duration of the project. Also this software provides an effective collaboration mechanism between the prefabrication manufacturer and the architect by the software interface, generation of models, and real-time collaboration functionalities.

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Shop drawing which its basis for reinterpretation it uses architectural drawings by tradespeople into their own drawings.

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Intelliwall where architect and manufacturers design light gauge steel framing designs. The advantage to design process that this application provides to the architect is that it automatically generates steel studs that are most efficient, effective bill of materials which includes dimensioned drawings.

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Solidworks software which provides the most effective parametric design capabilities and computer numeric control integration for prefabrication that are made from metal.

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Catia or NavisWorks which provides the architect and the client capabilities on onsite building process such as animation of the building model which demonstrates how the site will be set up, including even the cranes movements when lifting the delivered prefabricated modular.

C.

Craft quality

Craft can be defined as “construction of a building with skills and with careful attention to detail” (Smith,2010). The craft quality benefits that prefabrication volumetric framed method of construction offers both to the client and architect are; 

Increased skill level and cooperation of constructors where most prefabrication manufacturers can be seen as union workplace where they have dedicated employees who guarantee quality performance, and it provides highly skilled and specialized workforce consistently hence the client with high volume of prefabrication project can be assured of constant and consistent workflow of skilled workers. Also craft provides increased stability of the workforce since most prefabrication manufacturers do have long-term employees who are craftsmen who are dedicated in their work, and who have experience in the prefabrication volumetric frames development and connection.

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Most prefabrication manufacturers have constant repetition of work which have optimized in time-motion studies of indication workstations for improvement of quality and standards, they have intuit since they have been continuously working on the same type of project which makes the manufacturer’s workers to know exactly where to place the needed tool, to have rapidly increasing knowledge, skills and experience.

8 Also the intuit craft’s advantage allows uninterrupted concentration of tasks on which the workers are working on hence saving time which has positive cumulative effects on time. Repetition of work also provides increased opportunities’ jigging hence improves how employees use apparatus in guiding machine tools and hold work to work. 

Craft allows the client and architect to have improved physical access to work by having a team that has already been exposed of the client’s project by concealing on their previous prefabrication frames assemblies. Also the client’s project can be inspected from two sides when its being assembled since the prefabrication modular exposes more spaces and surfaces when being assembled. Also improved physical access guarantees improved ergonomics which allows the team erecting or assembling the prefabrication modular to work without strain or impediment. Finally, the improved physical access provides the assembly team with fewer confinements, disruption or interferences since the working area is not subjected to many constraints from interior space because it will be surrounded by factory spaces.

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Craft provides improved working environment where the prefabricated materials are developed. The team manufacturing the materials do enjoy indoor working environment which eliminated outdoor working conditions such as weather or temperature variations which guarantees consistent quality of product. Also the team enjoys increased control of pollutants and hazards since prefabrication manufacturers do provide working areas with ventilation and effective air control mechanisms, and specialized safety and emergency equipments which also motivate the team in providing quality and high standards products.

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Craft provides access to technology such as stationary technologies which allows the prefabricated modular and frames to be developed with exact fitting dimensions, to be, packaged, shipped and delivered on site. Also, prefabrication volumetric frames and modular have increased security at the construction sites since modular and frames are large blocks which cannot be easily stolen.

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Crafts provides the client and architect with effective and efficient monitoring and quality control by providing accessibility and visibility of work since at the construction site there is inspection of any component due to improved physical access to the work. On the quality control prefabrication model of construction allows the ability to closely improve the quality of work by closely monitoring at each assembly station. This guarantees the client with quality project product since it reduces time needed to perform quality checks and reduces errors at the construction sites.

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Crafts assure the construction stakeholders with tolerances where tighter tolerances can be achieved since factory methods improve crafts construction. The tolerances achieved by prefabrication modular and frames are inner-module which achieves tolerance on finishes and walls within a modular frame, and assembly tolerance which is the process of placing the prefabricated modular on site and the tolerance on the prefabricated modular frames themselves.

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D.

Time saving

Prefabrication volumetric frames and modular saves time for building houses since almost all the parts are created at the factory and transported to the construction site for just assembly. Some factors that make prefabrication save time are; 

Construction scheduling where prefabrication saves time by ensuring that project team has the capability of performing building construction and site work simultaneously. For example, when comparing prefabrication construction and in-situ construction is that the activities for in-situ construction are start-up, substructure, superstructure, interior works, services, finishes, commissioning and project hand over which for small project it can take up to 25 weeks . For prefabricated modular construction, the activities that can be carried out are production planning, manufacturing modular, site works, site finishing, commissioning and project handover, where for a small project which is similar to in-situ mode of construction can take only 10 weeks. The time taken of in-situ construction are 25 weeks and that for prefabrication constriction is 10 weeks which shows that prefabrication constriction saves time by 50% to 70% of the time that the construction project could have been taken if the project in-situ or commonly mode of construction.

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Prefabrication volumetric frame or modular saves time due to factory time efficiency which decreases the time required to perform a site on prefabrication factory much more compared to a specific cost that could have been done on an in-situ construction environment.

E.

Cost

Prefabrication volumetric framed and modular reduces the cost of construction on basis of time that it reduces to complete a building, and on basis on to value- to volume ratio which compares the total value of equipments, finishes etc. With high value to volume ratio, prefabrication mode of construction reduces the cost of construction by offsetting the relatively fixed costs such as setting and transportation.

Construction costs that are reduced by prefabrication volumetric frames and modular can be classified as hard cost and soft costs.

F.

Hard costs

On client’s point of view, hard costs can be defined as the costs such as factory overhead, robustness and redundancy that the client pays the contractor. Prefabrication modular and frames save hard costs by; 

Factory time efficiency which lowers labor costs since manufacturers use machine or mostly automated activities to develop the modular hence reducing manpower needed which on in-situ construction method the manpower takes almost 50% of the cost.

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It lowers the labor rate since the modular and frames are lifted using cranes joining them requires less labor.

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Decreased general conditions where prefabrication modular and frames allow fewer components which are used for a short time.

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It reduces fewer incidences of components damage, error or theft since the prefabrication modular when from the factory have exact dimension which reduces errors, they are in bulk hence they cannot be easily stolen, they cannot be easily damaged by workers carelessness, and their storage is much easier since one can be placed on top of the other, which reduces the costs that the contractor allocates as miscellaneous costs.

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Transportation costs where prefabricated modular and frames do have lower transportation costs by 5% of the in-situ costs since a single transport carries a module which on in-situ the materials for mixing so that the same module can be made would require various transportation trips.

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It reduces redundancy and robustness costs which are caused by additional use of materials that the one which were anticipated since in prefabricated frames and modular construction the materials needed to develop the building are known, unlike the in-situ construction model where materials needed to construct a building are just estimations which can be lower than the actual quantity.

G.

Soft costs

These are costs based on the lost revenue or expenditures that occur in construction industry. When using prefabricated modular and frames, soft costs are reduced based on the how they restructure the delivery and assumption of the entire project. The soft costs reduced are; 

It reduces construction loan costs loans since modular construction is can be developed with less than half time of what the in-situ construction method can be developed, hence it reduces the interest on construction loans by reducing loan period if it’s based on the duration of each individual draw.

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It reduces out-of-service time costs which are significant costs specifically for institutions which need urgent buildings, since the construction duration is reduced by less than half, hence reducing out of service time.

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For income generating project, prefabricated modular and frames fastens the return on investment since the duration of completing the project is very short.

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It reduces design processes costs since it reduces the construction estimating costs, engineering fees, construction administration costs, and costs for making and processing construction documents.

H.

Building performance

On building performance, the prefabricated modular and frames facilitates by;

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They have acoustical characteristics where the insulate sound since they have their own framing which prevent sound from being transferred to adjacent surfaces through the frames. Also for areas that total sound insulation is required, the prefabricated modular can have acoustical quilts be efficiently and easily integrated between the frames or modular.

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They have thermal and moisture characteristic where in addressing issues of thermal bridge, the building envelope are made on modular which are designed to achieve a thermal resistant that is uniform by provision of continuous insulation. This can be achieved by the fact that the modular walls, floor and roof are made of various layers of materials which some of the materials are insulators to prevent thermal bridge (Smith, 2010). In addressing issue of light, the open sides of the modular and frames which make up the building’s envelope can be modified to windows where clear glasses can be used to provide adequate light during the day time hence reduce the cost of lighting the house.

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On robustness, the prefabricated modular and frames can be able to withstand craning forces, vehicle braking and road vibration since they are built to be stronger naturally with functionalities such as increased seismic resistance, durability, strength and future additional loading capability more than in-situ building elements.

I.

Sustainability

Modular construction has sustainability attributes since it includes whole life measures such as minimizing energy in use since it provides thermal insulation for human comfort, it has effective and efficient cooling and heating systems, and it saves energy by effective control systems. Another sustainability measure is that it has effective energy measures of saving energy since its effective to manufacture. Another sustainability indicator is that it this method of construction has effective materials and resource use since the modular has been reinforced with steel which has high strength compared to its weight ratio, its modular have effective design in material use, its design is long lasting, it has low maintenance, the modular can be recycled or reused, and that the modular provides future adaptability (Staib, Dorrhofer, & Rosenhal, 2008). Also, when it comes to structure relocatability, this mode of construction increase the possibility of moving the structure assembled into a new location. Also, on neighbors’ disturbance, the method reduces the neighbors’ disturbance and also increases the construction area cleanliness.

VI.

Disadvantages of prefabrication volumetric frames and

modular Apart from having advantages prefabricated volumetric frames and modular do have various disadvantages which create barriers in adapting them. Some of the disadvantages are;

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A.

General image

In some parts of the United Kingdom, prefabrication method of construction has not been accepted due to the previous image that it had set in 1960s which were issues of workmanship where there were building were collapsing due to poor assembly on the prefabrication systems,

B.

Perceived performance

The buildings that were erected using prefabricated modular and frames in the United Kingdom between 1946 and mid 1970s were viewed to have shorter lifespan than the buildings which were developed using the in-situ traditional methods. Since then some people have had the perception that prefabrication frames and modular do provide non-permanent building solutions hence causing barriers on procurement options of the prefabrication building components.

C.

Customer expectation

The customer expectation disadvantage is facilitated by the perception that the customers wants buildings or houses that have traditional finishes such as bricks, where on the previous prefabricated timber modular were finished by plain timber cladding.

D.

Quality

Some prefabricated modular and frames may be developed using low quality materials and construction methods hence having non conducive thermal characteristics such as they can have unvented attic which can be making the houses hotter in the summer season and cooler in the winter season. Also the low if the floors are made from low quality materials and construction process, they can be sagging or have inadequate electrical service panels.

E.

Undesirable layouts

The prefabricated buildings do not have flexible designs such as in-situ buildings where one can mold a building in various designs and shapes since when being manufactured the prefabrication volumetric modular and frames are built as trailer homes with fixed layout. The fixed layout nature of the prefabricated modular and frames can lead to inconveniences to some customers who have limited and fixed land, where they can have challenges in how to strategically place the heating and cooling ventilations, or other drainage channels. For example prefabricated modular do limit the clients from customizing parts of their buildings such as the circular floor plans on some areas of the houses.

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F.

Total construction cost

For complicated designs where the client wants a more flexible layout design the prefabrication method can cost the client higher in adjusting the building to fit his or her creative needs that the in-situ traditional conventional construction method. Also, the cost of prefabrication modular and frames can be higher in some areas where the government has limited the permissible road widths and height which can force the transporters to split the prefabricated modular into small manageable modular which increases the costs of transportation.

VII. Prefabrication volumetric modular designs Prefabricated modular can be developed as masses where they can be non-attached by being solo or field, semi attached where they can be field joints or pods within other framework, and attached modular where they can be mate or stack modular combination. There are various designs in which the prefabrications should be designed so that the load can be distributed evenly within the building. Some of the designs involve using conventional structure where each load is directed directly at each column that supports the frame or module, or the forces can be distributed at the four corner columns of the module.

When designing the modular, the architects does not consider shear forces on the opening and glazing since all the loads are transferred to the end columns (Smith,2010).

The modular can also be designed as interstitial truss modular where they provide structural support for additional space and for larger clear spans on vertically stacked modular. Also the modular can be designed using light gauge steel as non-load bearing pods such as plant rooms and bathrooms which when being developed they are independent on the super structures.

A.

Foundation

Foundation can be defined as the interface between the supporting soils and the building which provides support for vertical gravity loads of the contents of the building and from the weight of the building. It also provides resistance to horizontal sliding which can be caused by ground movements or vertical loads at the end of the walls. When designing the foundation on which the prefabricated house is to be developed, there are various considerations that should be done by the architect which are the soil conditions of the area, site topography, building load that will be on the above, retaining requirements, decay expose, speed of the wing and termite.

The average foundation of a building that is designed to be more than one story in an expansive soil condition should be excavated on an approximate depth of 1.5 meters from the ground level after the expansive soil will be removed and the area filled with hardcore and compacted to the required level (Riley & Cotgrave, 2009). The foundation will be made strong so as it may provide continuous vertical support, to minimize movements or damages which can be caused by passive and friction bearing at the

14 interface between the soil and foundation and foundation to house interface, and also to provide stiffness and strength which can be able to resist both vertical and horizontal loads on the building. The various types of foundations that can be used on prefabricated modular and structures erection are; i.

Strip foundation which is a continuous strip of concrete which will support the walls bearing the load of the building. On the new center, the minimum dimensions for the strip foundation will be a minimum of 450mm wide and at least 200 mm deep (Frassetto,2012).

ii.

Trenchfill foundation where if this type of foundation will be used, the foundations will be dug to a point where the subsoil will provide a load bearing capacity that is sufficient.

iii.

Raft foundation where it can be used if the soil on the ground that the prefabricated structures are being developed is very weak and expansive such as clays or peat.

iv.

Pad foundation which can be used if the load needs to be supported. For example they can be used on the prefabrication modular and framed building if it will use steel frames since it requires a condition where the load is concentrated on small area (Frassetto, 2012).

This mode of construction needs a deep and strong pad foundation system since the modular places a point load rather than a distributed load on its foundation. The modular will then be set on a ¾” or 1” steel bearing plates and leveling steel plates which will be embedded in the reinforced concrete foundation.

Concrete can be defined as a composite material which is composed of mainly sand, cement, ballast and water where they are mixed together to form a fluid mass that can be easily molded into various shapes according to the molding used. Reinforced concrete can therefore be defined as concrete which has been reinforced by materials having higher tensile strength and durability such as steel bars. The pad foundations after being casted together steel plates and stub, it will be raised to approximately 18” from the ground and bottom of joist on which the modular will be connected to the foundations so that it can leave a crawl space for service connections. The parameter foundations on which the modular will be placed on are as shown in the diagram below;

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Figure 1 Author drawing

B.

Walls

The walls of the prefabricated modular and frames for building have a standard height of 2400 mm with a dimensional unit of 300mm being adopted for vertical and horizontal dimensions specifically for the exterior walls. The exterior walls for the prefabricated modular can be from various materials depending on the client’s choice such as having boards on the inside, then a meta-line gap in between, and cladding on the outside according to the client’s decisions.

C.

Floor

The floor for the prefabricated modular do have a standard dimension of 450 mm where it can be composed of various materials such as boards, floor joist, insulation, optional boards, ceiling joist, and concrete on steel from deck depending on the manufacturing factory or the client’s tastes and preferences.

D.

Roof

On roofing there are several options that are available for roofing modular buildings. Some of the options that the clients can decide to be included in the design of his or her house are; 

Separate roof module where a roof module can be constructed independent of the modular where they are then set on building at the construction site.

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Integrated roof where the roof can be integrated together with the upper most modular at the factory where they are compete and just placed as complete roofed module. For the integrated roof the most ideal due to transportation from the factory to the construction site is the flat-roof or a roof that has a lowsloping (Staib, Dorrhofer, & Rosenhal, 2008).

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Hybrid roof which is a combination of integrated approach and separate module where a portion of the roof are included as the module is being constructed at the factory and then the other part is constructed independently. This option is advisable for roofs that are steeply pitched (Staib, Dorrhofer, & Rosenhal, 2008).

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In-situ roof where roofs are constructed using pre-fabricated trusses which are then placed on site and covered using the client’s choice of covering materials. This option of roofing is ideal for multi-unit construction.

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On site off building roofing where on this option the roof is construction conventionally at the site but not on the building where then after it’s lifted using cranes into place. Also this option is ideal of multi-unit constructions but with sites which have adequate working space for construction of the roof (Staib, Dorrhofer, & Rosenhal, 2008).

An image showing a prefabrication volumetric framed showing the building’s envelope which in this case will be the roof, wall and floor is as shown below;

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Figure 2 Author drawing

VIII. Mechanical, Electrical, and Plumbing System Factory manufactured systems do have decentralized systems where its cost- time benefits are on mechanical, electrical and plumbing systems installation. The prefabricated systems enable the architect to design the modular with plug and play options where they are more or less self-contained. Also, the decentralization functionalities on the prefabricated systems to avoid complexities when making the field connection and when routing systems. When making electrical connections on the modules a junction is

18 used as the main connection of the module where it becomes the point of connection for the module and the power supply (Smith,2010).

The prefabricated modular do have hookups capabilities which allows floor, walls and roofs panels to be removable so that mechanical, electrical and plumbing systems to be connected between the modules.

The hookup capabilities allows the modules to have design of access points and chase enclosure so that when doing building finishes the connections can be effective, and so that future maintenance and systems replacements can be easily carried out on the prefabrication volumetric framed buildings.

A.

Heating and cooling systems

The fabricated volumetric elements will allow package wall units which allows the buildings to have proper ventilation, and that so that they can allow HVAC systems to be easily installed for quiet, effective and effective temperature regulation. Also, to regulate the temperature the prefabricated units do allow terminal conditioner units where centralized condensers units are used to pipe water to the terminal units which can be regarded as the most environmental sustainable solution for prefabricated structures. Also, a high velocity small duct mechanism can be applied to regulate the prefabricated buildings temperature where air is supplied to the desired locations using small flexible ducts which reduces the need for large shaft spaces. Temperature at the prefabricated buildings can also be regulated using plenum ventilations where space between the modules can be created, and by use of radiant heating and cooling system which are little vertical space consuming machines which use low energy and with effective air conditioning outcomes (Smith,2010).

B.

Prefabricated stairs

Prefabrication manufacturers also do make prefabricated staircases which are of standard sizes of 225mm to 250mm and risers between 150 mm to 175mm. The fabricated stairs can be from steel where there are various shapes or profiles such as curved, spiral and straight where the client can choose from.

In cases of semi-detached houses and terrace, the staircases can be fabricated in three ways where the client can select the way that he or she wants. The three ways are type A for flight only, type B for flight and top landing, and type C for flight and base landing. Prefabricated stairs provides the clients with better productivity, quality and accuracy since they can be easily and quickly installed which eliminates the messy caused by cast-in-situ. When fixing and installing prefabricated staircases, they it can be done by prefabricating the stairs and landing different and installed on site, or it can be done by prefabricating both of them together and be delivered to the construction site as one module.

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IX.

Conclusion

Prefabrication construction where most of the significant part of construction happens at the factory, has many advantages over the traditional mechanism of construction specifically if prefabrication is adopted on large projects where it will save cost by reducing the time taken into less than half. If well adopted on the construction industry prefabrication has the capacity of making a difference in terms of social, economic and environmental terms. If well adopted the benefits that it can have on the client, architect and the contract are that it can assure the client that high quality building will be delivered, it can assure the contractor and the architect of profitability and improved productivity due to reduced number of manpower, and it can has more environmental benefits that the in-situ mode of construction.

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X.

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