Combined life-cycle cost assessment of roof construction

This paper compares the combined life-cycle costs of four different types of roof construction common in New Zealand. Two cladding options have been chosen, namely steel sheeting and concrete tiles, supported by two different types of framing, namely softwood timber trusses and lightweight structural steel framing. The material quantities, embodied energy and CO2 emissions of each roof configuration have been assessed using simplified life-cycle models. The combined life-cycle cost of each roofing system has been determined by adding the material costs with the estimated 'costs' of the embodied energy and CO2 emissions. Material costs have been determined based on current installed prices and the maintenance costs discounted to net present values. The embodied energy and CO2 emissions have been calculated using previous input-output models developed for New Zealand building materials. It was generally found that concretetiled roof structures had lower overall combined life-cycle costs when compared to the steel sheeting options, mainly owing to the greater durability and lower embodied energy content of the concrete tile cladding. It is hoped that this paper will aid housing developers and stakeholders in making sustainable choices in their selection of roofing materials.