ZEMCH 2015 - International Conference Proceedings | Page 337

solutions that better satisfy the requirements of reducing waste and the components variety. This
investigation is part of a broader research with the objective of searching for suitable design to
sustainable low-income housing in developing countries.

Rationalisation and Material Waste in the Construction Industry
The design phase plays an important role in both the product quality and the production process
(Franco and Agopyan 1994). Most of the rationalisation measures to reduce cost and time and to
improve the product quality depend on the design phase (O’Connor and Davies 1988). Although
the importance of this phase is recognised, the design decisions are usually taken without considering production aspects. The high level of material waste in construction sites is partially due
to this situation.
Formoso et al. (2002) argue that measuring waste is an effective way to assess the performance
of the production process, since it allows identifying causes of inefficiency and opportunities
for improvement. In this context, waste must be understood in a broader sense. Skoyles (1974)
and Formoso et al. (1996) classified material waste in two categories: direct and indirect material
waste. Direct waste is a kind of actual material loss and the wastage generated usually must be
removed from the site. In the indirect waste, materials are not lost physically but a monetary loss
occurs. Examples of indirect waste are: substitution of material and the use of a greater amount
of material caused by the inefficiency of the production process. In this case, the waste remains
incorporated to the product, although it does not add value to the client.
According to Whitt1, 1974 apud Soilbelman, 1993, decisions during the product design aimed at
reducing the variety of components, improving the dimensional coordination and facilitating
the production process contribute to constructability and, consequently, to enhance productivity and to eliminate materials waste. In industrialized building systems, the dimensional coordination of the components is even more necessary because of the higher value of the material
in comparison to conventional building systems. These issues are the key to producing a large
amount of affordable low-income housing.
The empirical study presented in this paper focuses on the description of the decisions taken in
the product design phase with the objective to reduce material waste of an industrialized building system to be adopted in low-income housing projects. The decisions here described are restricted to waste reduction of the wall components.

Industrialized Building System – Light Wood Frame
There are two variations of the building system discussed in this paper: Light Wood Frame (LWF)
and Light Steel Frame (LSF). In these systems, the walls consist of a light frame with a sheathing
(Oriented Strand Board - OSB) nailed to each side of the framing which provides strength, rigidity,
a space for piping and insulation and also a framework for supporting interior finishing and exterior components (Canada Mortgage and Housing Corporation 2014).
Two kinds of wall panels are possible: (1) bearing walls are those supporting loads of the building
(can be external or internal wall); (2) non-bearing walls are internal partitions or external walls
supporting no load. The framing is comprised of horizontal (bottom and top plate) and vertical
(stud) components. The plate distributes the weight of the building to the foundation. In bearing
walls, top plates are double, but a single top plate may be used where roof rafters or trusses bear
directly above wall studs (AWC 2001). In order to suit the size of the OSB, the spacing of vertical
components (stud) is 400 or 600mm on centre, depending on the load the wall supports.
According to AWC (2001), studs in bearing walls are nominal 50x100 millimetres with the 100 millimetres dimension forming the basic wall thickness. Studs in a non-bearing wall are nominal 50x75

Reducing waste in the construction of light wood frame low-income housing

335