Cost Comparisons of Conventional and Urban Mining Design Constructions Petra Riegler-Floors, Annette Hillebrandt
Are loop-compatible constructions inherently more expensive, as is generally assumed? In order to answer this question, the following discussion will study the entire lifetime of a construction, including its erection, necessary upkeep during the use phase, demolition and waste disposal. During a building cost analysis, all design participants typically focus exclusively on the construction phase. The use phase, if it is considered at all, is usually viewed only from the perspective of energy. Most of the time, the demolition costs are given no attention. However, since expenses are nevertheless incurred for upkeep as well as for demolition and waste disposal, the following analysis will take into account the expenditures for all life phases of the construction in the calculation of its total cost (Fig. B 7.1). As this chapter focuses on the physical structure, the operational costs of supply, cleaning and maintenance as well as running repairs will not be considered here – in contrast to the life cycle cost analyses in the assessment methodologies [1]. In an experimental set-up presented at the end of the chapter, three examples featuring conventional and recyc ling-compatible construction versions are compared with one another (p. 128ff.). Determination of Project Costs The costs for construction are taken as much as possible from the current Construction Cost Index (BKI – Baukostenindex) [2]. For the few newer or less well-known materials not listed there, costs were determined by combining the price of the material (manufacturer’s list price) with the labour costs for the installation of a comparable material from the BKI. Material and installation costs
Costs for materials and their installation form the basis of construction costs. Material costs Recyclable materials have a reputation for being generally more expensive than their commonly used, less loop-compatible coun 120
terparts. Figure B 7.2 shows a comparison between different insulating materials in terms of construction and demolition as well as waste disposal costs (see “Insulation”, p.86ff.). A significant price advantage can be seen in the case of blow-in cellulose insulation. All mat- or panel-based insulation materials are in approximately the same price range, with jute insulating mats (made from used coffee or cacao sacks), rather than a mineral oil-based insulation, representing the least expensive variant. The differences in material costs, however, carry less weight overall because of the relatively high labour costs. Installation costs Many detachable joining techniques were not developed in order to facilitate dismantling by material type, but rather to allow for faster and predominantly weather-insensitive instal lation, reflected in labour, construction site provision and pre-financing cost savings. The comparison of two different joining techniques in facing masonry (Fig. B 7.4) illustrates the advantage of detachable connections: The installation time and associated labour costs of a newly developed dry bricklaying system are about one third less than those of the traditional mortar bonding method (see “Mortarless system for brick curtain walling”, p. 50). At the end of its life cycle the dry-laid facing wall is just as easy to disassemble again, and the clinkers can be sold for reuse (see “Facing brick shell on a load-bearing exterior wall”, p. 108f.). In addition, the work required to remove old mortar adhesions from the bricks before reuse is completely avoided. Upkeep costs: life cycle of the construction and product life
The product lifetimes used in the following studies are mostly taken from the BKI [3], the table “Service Lifetimes of Building Components” of the Federal Institute for Research on Building, Urban Affairs and Spatial Development (BBSR) [4] and (for green roofs) from a project report compiled by the Fraunhofer Institute for Building Physics [5]. For a few of the newer or less well-known materials not