End Product Defects in Residential Building Construction

For the past decades, construction firms have been facing problems such as high cost pressure, shortened project time and increasing in competition. Moreover, the construction industry in many parts of the world suffers from problems such as workmanship defects, time and cost overrun (Harrington et al., 2012). In addition, contractors are usually more inclined toward the profit generation rather than quality improvements, especially if they have already met the minimum requirements for quality (Low and Teo, 2004). Clients are demanding better quality because in many construction projects, clients often find themselves paying high prices for defective works that do not satisfy their needs (Low and Sze, 2005). The cost of defect and damage can be minimized by a proper preventive tool instead of the corrective action. Moreover, Ilozor et al. (2004) pointed out that some defects caused several other defects and preventing those defects could eliminate many other defects.

Ms. Kobdao Maneejak made a case study aimed to:

1. Investigate and classify root cause of defects.

2. Study the behavior of defects during the architectural stage.

3. Develop preventive measure tool to minimize defects.

With the complexity of construction methods, high quality of end product and involvement of many trades, defects are found when moving from architectural and M/E to end products. In order to minimize defects, site managers have to understand the behaviors originated defects both activities within and across the work package. The findings indicated that defects in residential building construction in Thailand caused from pressure to rush the product to market.

This chapter summarizes the results in brief of three case studies. The identified defects from three project case studies were investigated the root causes and the defect behaviors during architectural stage to end products in residential building.

Conclusion

Twenty-eight (28) work activities under 7 work groups from architectural stage to end products were listed to investigate the root cause of defects. Main root causes of defects were identified by site managers including project engineers, site engineers and foremen. Four main root causes of defects are design, workmanship, materials and lack of protection. Once the root causes of defects were investigated, site managers identified each defect, its causation and its root cause. All identified defects were registered with photographs and short noted. For in-depth discoveries, site document were scrutinized. From data collection, defects were found in all work groups: wall, floor finishing, wall finishing, ceiling, painting, sanitary and M&E.

           

Workmanship and lack of protection were found to be two most critical factors causing defects during architectural stage. Defects which caused by workmanship were under the following work groups: wall, wall finishing, floor finishing, ceiling, painting, sanitary and M&E. Defects were also found during the finishing stage. Floor finishing, wall finishing and sanitary were the most three common work groups where the defects were identified by site managers. Moreover, defects originated by materials such as using wrong equipment/tools or defective materials were found under these work groups, wall element, ceiling and sanitary wares.

During an investigation, the relationship among defect, rework and damage were observed. Three types of defects, based on the level of correction, were derived; corrective defect, rework defect and corrective defect. Corrective defect needs only a minor correction while rework defect needs a rework process. The corrective actions of defects are negotiated between an owner inspector and a contractor to either perform minor correction or rework. Another type of defect is damage defect. Damage defect is defined as once a defect occurs and it is either corrected or reworked, it affects the element which is not related to correction, or rework activities.

After in-depth analysis of defects, corrective defect and rework defect were commonly found at sites. Majority of corrective defects were generated from ceiling, painting and M&E work group. Masonry work, wall tiling, in-wall M&E installation were the critical activities causing rework defects. Also, M&E installation in ceiling was often found as the rework defect causation. However, for damage rework, only few items were found during data collection. From case study, wrong sequencing activity and poor protection were the main cause of damage rework.

Recommendation

Moreover, it was found that most defects were repetitive. Their occurring behaviors were quite the same. Activity sequencing was used to capture and understand defect behaviors. Wall plastering was found to be the most critical in generating or hiding defects. Strict measures of quality assurance must be designed and applied in this bottleneck activity including critical point inspection, agreement on area transfer between trades, and protection of easily damaged products. Wrong activity sequencing occurs when many subcontractors from different trades are performing works in sequences. Without proper crew balance based on synchronized production rate, immediate succeeding activity will move pass its predecessor causing many subsequent defects.

Site managers should develop the schedule which concurrently involves only 2-3 trades at maximum to reduce the number of work package contractors/subcontractor so that complexity and interdependency can be reduced and defects can be easily detected.  Moreover, each work package contractor/subcontractor before commencing their work has to agree that there will be a zero defect and provide protection to their finished work upon leaving their work areas.

In conclusion, critical quality inspection is the most essential measure to minimize the occurrence of defects. After the transferring of structural stage to architectural stage, zoning the work area by using different shades of color, green, yellow and red, is recommend to minimize the possible damage defect. Only workers who wear the color-matched armbands are allowed to the work area. For green zone, all work activities under architectural stage can be performed and all workers can enter the green zone. After all works are performed, protection is needed. For yellow zone, only carpenters and furniture crews can enter the work area, before start working, both crews have to accept that the work area has zero defects. For red zone, anyone who needs to enter the work area has to get permission from site engineers to get into the work area; critical inspection is checked both before commencing the work and after the completion of the work every single day. Moreover, both yellow and red zones required all workers taking off their shoes before entering the work area.

Her thesis abstract is copied below. 

Abstract

This paper identifies and presents findings derived from in-depth investigation of work behaviors causing defects during architectural and finishing stage of residential building construction. High-rise building construction projects were investigated. Data were collected by structured interviews of on-site managers, direct observations of work activities, and quality inspection records. Activity sequencing, quality inspection, and correction of defects were analyzed.  When a project team force for progress toward the finishing stage, defects are commonly found because wrong activity sequencing, especially when architectural and M/E activities are interfaced. Perceiving that surface finishing can cover up prior defects, improper quality inspection on preparatory works occurs mostly in surface finishing activities. The work sequence and nature of defects are applicable in residential building construction in Thailand where prefabricated components are not much used, except exterior facade. The study result can be applied to improve planning and quality assurance system for defect reduction.

Keywords: Defects, End product, Activity sequencing, Buildings