Prefabrication is a double-edged sword. While it speeds up the process of prefabricating building components under controlled conditions, thus increases their quality, it requires skilled labor, factory environment and hauling materials to the prefabrication site. Its is not forgiving in terms of design, production, and construction tolerances , which requires accurate workmanship. Another caveat is the necessity for using heavy equipment, resulting in intensive energy consumption. Depending on the level of expertise in a given society, it may be better to begin with the existing technology and incrementally develop it to the point when highly technical methods make sense in terms of budget, and skill levels.

In my point of view, it depends on what kind of prefab... My research group is working on a woodframe prefabricated house in order to reduce flows and non value adding activities on site. Prefab can reduce waste as well as physical fadigue for workers.... we are starting design process on this issue. We are doing literature review yet. So, it's only our guess.

I see the role of prefabrication increasing in low lost housing solutions for developing countries.

I am happy to hear this from Hirota.But have we thought of the cost implications on procuring the raw materials for prefab,cost of technology,training of human resources to use the technology etc.I quite agree that it will speed up the process of construction and reduce especially insitu waste but the cost of even transporting the preb components should be look at.What materials are we proposing for Sonal,s prefab and in what geographical location are we considering?This is becuase the cost of steel especially in Africa regions is quite expensive and the entire regional is becoming a desert hence timber spices are in trouble and therefore even if you get the timber the cost and method of preservation is very scarry.Also environment factors and human behaviaral factors also posses a threat to timber prefab.But in all its save time and energy as Hirota said.

The concept of prefabrication followed by site installation is very popular when it comes to steel structure. The cost effectiveness of the technique increases with the quantum of the job.

Coming to reinforced concrete structures, the concept is developing rapidly. Given the advantages of a controlled environment of the prefabrication facility, excellent quality control can be exercised in the fabrication. This will give rise to structures with a much higher durability as compared to conventional cast in situ structures.

Now about cost in case of RC structures. Costing can be broadly divided in the following categories. 1> Architecture and Design Cost, 2> Fabrication Cost, 3> Transportation Cost, 4>Installation Cost and 5> Maintenance cost. Say it is decided that a huge housing company has to construct numerous residential buildings. The buildings in such a case are essentially identical having the same architectural configuration. for a given site conditions a similar design can be adopted for all the buildings. In the design and architecture stage itself, attempts shall be made to keep as few number of different structural components as possible. Since the number of independent structural components is less, and their quantities are large, the effective cost of prefabrication will go down. Furthermore due to the excellent quality control, the maintenance costs will also go down. Thus when applied at a large scale, the effective cost of prefabricated construction will be low.

One point of caution for RC structures. Connections techniques between structural components are still in a development stage. Although the methods under gravity loads are well established, a lot needs to be done to have suitable procedures for extreme loads like winds and earthquakes. However, where these things are not an issue, i.e. low rise structures in seismically stable areas, the option can be conveniently chosen on a large scale.

I am looking for solutions in multi-disaster zones say a combination of flood and seismic occurrences as in Himalayan upper reaches of India.I am looking forward to engineered timber construction(CLT panels) with a certain degree of prefabrication as well as customization possibilities to suit the local population needs.Local mass production facilities may reduce the needs of expensive transportation.The participation of users in construction of course with proper training can also reduce the labour costs.But then there may be the question of supplies as timber essentially means the cutting of trees and the whole issue can be easily discarded.Can anyone provide some more insight in the context of India?

In my opinion, precast concrete structures are a very good option.

Cost of production is relatively small, high durability, and relatively low maintenance costs.

Two years ago, the fib Commission 6 issued a Bulletin 60, entitled "Prefabrication for Affordable Housing" - I recommend it.

@Francis Bondinuba

I agree with your views regarding the obstacles in the use of timber even with the increasing cost in other conventional construction processes using steel or concrete.Conventionally timber has always been looked upon with suspicion regarding its structural capability and durability with respect to fire and/or insect attacks.And the decreasing availability of it with increase in desertification also seems to go against it.But can we not invest in captive timber forest production leaving aside our natural forests.It will serve the dual purpose of alternative afforestation and timber production?Given the advantages of timber with regards to its low embodied energy and role as an effective carbon sink.It may also be sustainable and with participation of local population which can be trained in modular construction ,mass housing activities can be taken at low costs.

When we talk about costing in AEC industry, we need to know that there is a life cycle cost, so we have CAPEX (capital cost) and OPEX (operation and maintenance cost). Indeed the prefabrication will reduce waste in materials and time. Also, we have clear scope of work, which means no changed in decisions and designs. So you are dealing with product, more products lower cost and low products high cost (vice versa). We are agree there is low cost in OPEX. However, it cannot reduce the cost of OPEX, because prefabrication is hards to deal with if we don't have the same materials that fabricated in the factory which might be need to upgrade the facility after 5, 10 or 15 years. We need to consider the flexibility for the materials that will use not now but in the future, we live in technology revolution. Also, the flexibility should be considered through deign for housing especially in developing countries, because the family is growing and the facility might be upgraded or expanded....

It is great idea if we think in a compressive aspects.

Using reused and recycled materials for all components and structures like as: recycled concrete/ mortar which uses recycled aggregates from construction demolition waste for precast structures, concrete bricks, mortar,...

I think Sonal is interested to fulfill the need for housing in a disaster effected areas such as Bhuj in Gujarat, India or Latur in Maharashtra, totally destroyed by a killer earthquake. For these areas prefabricated constructions were carried out on large scales where industries came forward to manufacture many types of components. These components are being built by using mixtures of many materials including fly ash on large scales. Even today many states are engaged in providing low cost houses for rural population. Even after flood devastation such construction is very popular to rehabilitate a large population in short notice at less cost. A better understanding of this type of construction can be acquired by visiting some industries such prefab components are manufactures and observing their model construction. Hope I am on line with your subject...Thanks

Prefabrication is a double-edged sword. While it speeds up the process of prefabricating building components under controlled conditions, thus increases their quality, it requires skilled labor, factory environment and hauling materials to the prefabrication site. Its is not forgiving in terms of design, production, and construction tolerances , which requires accurate workmanship. Another caveat is the necessity for using heavy equipment, resulting in intensive energy consumption. Depending on the level of expertise in a given society, it may be better to begin with the existing technology and incrementally develop it to the point when highly technical methods make sense in terms of budget, and skill levels.

Prefabrication has to go along with industrialization. Prefabrication may not be cheaper but generally would improve quality, reduce construction waste, increase speed of conostruction and render cleaner working environment on site. In advanced countries, this could also reduce labour cost. However, prefabrication is effective only if a large number of identitical components are to be manufactured in a factory so that the manufacturing process could be mechanised and automated. Logistic management is also important but most civil engineers are no good in logistic planning and management. Moverover, many prefabricated components are broken during handling and transportation. The lifting arrangement by more than three wires is actually statically indeterminant but only static analysis is applied to determine the tension in the lifting wires. This has been causing damages and cracking of concrete during lifting but usually the materials engineers are wrongly blamed. We need civil, structural, mechanical, ligistic and business engineers (preferably one engineer who knows all these) to work together to make prefabrication a viable solution to construction.

Traditionally, the locally available materials were incorporated into houses.

These included rock, mud, straw, trees, bamboo, grass, palm fronds, and

volcanic materials.

Perhaps we are looking at this the wrong way.

How can we employ efficient modern machinery to utilize

locally available materials to build traditional elements

for housing rapidly, then teach, and let the locals build their own houses

from the elements left behind.

Adobe bricks could be made from modified concrete highway paving

machines, and old cement mixers filled with mud, and straw or grasses,

or pampus grass, or chopped bamboo.

The paving machine could have several side by side extrusion molds with

one vibrator in each mold. The bricks would be left behind as continuous

long strips of extruded mud and straw, and a chopper behind the

paver molds would cut the strips into uniform lengths that are longer

than the width.

The roofs could be prefabricated in a factory as panels that slip lock

together on the edges. Two panels and two cables and two vertical

struts from the peak down to the horizontal cables. Tent shaped.

There would need to be a way to attach the roof to the walls that would

work in a high wind.

I suggest you also consider the cost and time saving advantages of digitally simulating your construction model. In a recent company meeting, we learned that a company called SHoP Construction, has been able to go from design to build of prefabricated homes in Brooklyn, NY, in about 4 months. This relief is in response to so many homes being destroyed by hurricane Sandy last year. The company was able to do this so quickly because of being able to use software to design and simulate the process. Sorry but I cannot find an article about this on the web, but it was highlighted in this internal R&D presentation.

@Albert Kwan: I think that prefabrication effectiveness doesn't depend on number of identical components, but inversely - allows to see and distinguish identities (or better - similarities) hidden in whole product. What is the most important, we talk about manufacturing (technological) similarity, not geometrical. Thus, both the similarity of prefabricated components manufacturing and similarity of assembly operations.

Similarities of assembly operations are invisible before assembly sequencing, resorces planning, scheduling, etc.

My research focuses on the production of steel structures, but the essence of prefabrication is similar to civil engineering.

I think we should define the meaning of low cost housing in developing countries first and then what is the solution of them. We cannot generally say as global issue.

I think prefabricated elements is good idea to minimize cost and improve quality control of produced products. this is particularly important for developing countries

Prefabrication of mass housing is not a novel idea, we have only to look at the post-WWII housing in the UK. There was considerable experimentation with materials, component assembly, unit size (single vs towers). It was NOT entirely successful in saving costs, and the quality and durability has not withstood the test of time. There were many lessons learned that can inform current efforts. These may include the prefab of mechanical pods, or specific wall assemblies. But the final solution is an optimization of prefab, transportation, local labor and materials.

I can add perhaps a few points from the context of prefabrication attempted in India in the past few decades. The Hindustan Housing Factory in New Delhi, the Central Building Research Institute, Roorkee & the Structural Engineering Research Centre, Chennai, several IITs, & private construction giants like L & T have taken pioneering leads in this effort But the dissemination of the technique has not pervaded the industry to appreciable levels. Reasons are far too many. Few of the essential factors that inhibit the large scale adoption to affordable housing listed below need to be addressed, if large scale adoption is desired..

1. Projecting elements like Sunshade(chajja) are usually not included in prefab, for

ease of stacking.

2. Even buyers of affordable housing do like variety/exclusivity of features. Stereo

typed identical "pigeon holes" being forced down their throat is not relished.

3. In prefab environment, the pre-determined location of fixtures like electrical &

plumbing fittings, etc are unalterable thus denying the buyer's choice of having them

at the desired places as per their individual taste.

4. Historically only in countries where the state built & allotted housing is the only

possibility, the prefab technique had it;s way.

5. The Economics of prefab has already been discuussed by many already. In

developing countries lacking handling machinery especially in country side

adoption of prefab is found difficult. Also, perfecting the joints between wall-to-wall

& wall-to-floor/roof has to be achieved by proper training.

F the state and its companies have the capacity to achieve the prefab (human and material resources), no doubt it will be a very good solution, because this technique has the advantage of saving time (serial production) and money (low losses of materials and a huge amount of production).

It is a good solution for accelerating population growth but it needs infrastructure for such a process. Which means skilled labor, energy, studying social side of residential compounds, environmental consequences of such a process (waste management, water and waste water).