Unitised timber envelopes. A novel approach to the design of prefabricated mass timber envelopes for multi-storey buildings

Abstract

Tall timber building is today both possible and desirable due to the advantages that timber construction offers the industry in terms of productivity gains and sustainable development. Prefabrication certainly represents a unique opportunity for timber technologies to lead the construction sector's shift towards a more industrialised approach, and new solutions need to be put in place for future generations of tall timber buildings. This paper examines the design of newly-conceived timber-based envelope systems for multi-storey buildings, which are fully preassembled off-site to maximise construction efficiency and safety. The prefabricated external wall assemblies are provided with all functional layers (including windows and cladding) to enable site installation from the constructed floor without scaffolds or any action from the outside of the building. An aluminium/gasket frame system is integrated within the external walls to guarantee air and water tightness at panel interfaces and guide the installation of the “mega-panels” on-site. The technical solution is presented in the form of 2D technical drawings and a three-dimensional model, developed for the application in a load bearing CLT-based envelope configuration. A full-scale (though small-size) mock-up was assembled to account for fabrication and installation issues, as well as to demonstrate the versatility of the solution for the use-case of a non-load bearing curtain wall configuration. The research innovation is found in the systematic and novel design approach to the development of industrialised timber-base envelopes, rather that in the specific instance of the design outcome presented and analysed here. This is a particularly important innovation because, as the key mitigating barrier for buildings, envelope design is context-related and has to be conducted on a case by case basis. This article presents the most substantial design outcome of the first author's doctoral research and is now being further developed as part of an industry embedded research project investigating industrialised construction and tall timber buildings.