A techno-economic case study of external timber wall assemblies in Swedish single-family homes

Abstract: Decisions made at the early stage of building design can significantly influence theenvironmental, energy and economic performance of buildings. Future homeowners anddevelopers often have to make decisions concerning the design and specification of thebuilding. These choices are usually governed by functionality, aesthetics, cost, materialavailability, etc. Except for decisions related to long-term performances, they are relativelyeasy and straightforward to make. Long-term performance assessments that consider theimpact of a product over its lifetime, requires thorough research. Due to the lack of studies onthe long-term benefits and performance of different building design options, homeowners anddevelopers often base their decisions on short-term financial benefits, ignoring long-termbenefits. This may lead to incorrect decisions that are difficult to correct.Within this context, the aim of this study is to compare the long-term economic viability ofdifferent external timber wall construction types. By doing so, our goal is to address the lackof techno-economic studies within the construction industry and thus, to assist the decisionmakingof Swedish homeowners and developers. We evaluate the economic performance ofthree wooden wall construction alternatives—that of IsoTimber, cross-laminated timber(CLT), and timber frame walls—via thirteen wall assembly scenarios and two case housesfrom Bysjöstrand eco-village, Sweden. The scenarios account for variations in wall type andwall thicknesses. Our study utilizes an approach based on life cycle costing (LCC) andconsiders the capital cost and the present value of heating cost. The latter is calculated for 1m2of heated area of each case houses over a 40-year period. Indoor Climate and Energy software(IDA ICE) is used to estimate the heating energy use and the Bidcon program to estimate thematerials and labor costs for all cases. The study considered reasonable economic parameters,but to see their impact on the results and feasibility of wall constructions improving, sensitiveanalysis has been done using different values.The main finding of this thesis is that timber frame wall construction is the most economicchoice in the long term. In contrast, IsoTimber wall is the least economic choice, in general,and for two-story homes, in particular. Moreover, the present value total cost for IsoTimber intwo-story building is 5% higher than for a single-story building that has a similar U-value. Incontrast, it is 3% and 7% lower for CLT and timber frame walls respectively. Also, the resultsindicate that although the present value heating cost decreases with increasing wall thickness,this increase is considerably smaller than the increase in the capital cost. Finally, assumedeconomic factors affect the results greatly, but in general, improving the U-value of CLT wallconstruction might be the most profitable then timber frame comes after, and then IsoTimbercomes in the last. Along with, return economic benefit from the improvement of all studiedwall constructions in single-story building is higher than the benefit in two-story building.