The Building Conservation Directory 2023

34 T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 2 3 | C E L E B R AT I N G 3 0 Y E A R S C AT H E D R A L C O M M U N I C AT I O N S BUILDING PERFORMANCE EVALUATION A retrofit workflow and its application at New Court CAROLINE RYE and CAMERON SCOTT B ACK IN 2011 when we founded ArchiMetrics Ltd, it seemed that very little was known about the performance of older buildings. Our aim was to improve understanding through the physical measurement of the buildings themselves and where possible to check these findings against the performance predicted by theoretic building models. Building monitoring is still a relatively niche occupation and understanding how a building performs is not necessarily part of standard architectural design or construction practices. Nevertheless, we are regularly contacted by people who wish to carry out some form of performance assessment, often within the context of the energy efficiency refurbishment of a traditional or historic building. The workflow diagram opposite has been created in response to these enquiries with the aim of enabling refurbishment or retrofit project teams to work with those carrying out building performance evaluation to determine an approach for their projects. Specifically, this workflow is of relevance to projects where insulation is being considered as part of a retrofit and where modelling and/or monitoring might be used to help manage potential risks. This article, written to accompany the workflow chart, uses the description of a retrofit project of a Grade I listed building, New Court, Trinity College, Cambridge, to illustrate some of the pathways set out in the diagram. The retrofit was completed in 2015 and has now been monitored for seven years, giving us a clearer picture of the performance of the retrofitted building, including the reduction in fabric heat losses and moisture balances within building materials, old and new, as well as air quality and comfort levels within the refurbished rooms. Where a traditional building is to be insulated, the assessment needs to be bespoke – that is to say all the stages of an evaluation process should be worked through. This includes, for example, devising a monitoring and/ or modelling scheme, designing and building the measuring equipment, installing it, capturing the data, creating the analyses and reporting the findings. This approach is aimed to ensure a high level of detail and understanding of the buildings and materials we are dealing with, but its bespoke nature also means that the process is very much driven by the particular concerns and specific questions relating to a project. These questions often arise in relation to certain risks that may have been identified by the project team, particularly if it is felt that these risks may not be fully understood. When the investigation of retrofit proposals began at New Court in 2011, it was the effects of applying internal wall insulation (IWI) to solid walls that were the issue. In particular, the team needed to know what might happen to moisture within the protected walls and the timbers embedded within them if the building fabric was internally insulated. Specifically, would moisture accumulate within the fabric to such an extent that it risked rot and mould growth? As well as answering this primary question, the subsequent monitoring also provided information that was of use across a range of design questions. MONITORING AND/OR MODELLING Early on in the project hygrothermal (WUFI) modelling had been used to try to make an assessment of the moisture risks for the insulated fabric. This had indicated that there might be a moisture accumulation problem for the walls, particularly if a PIR (polyisocyanurate) board was used as the insulation material. However, there was a great deal of uncertainty as to the relevance of the model: in particular, the material property inputs pre-loaded within the modelling software might have little relevance when applied to an older UK building. Therefore, to address these uncertainties the team, led by 5th Studio, decided to engage in an investigative process whereby, in the first instance, monitoring was used to assess the ‘base case’ performance – that is to say the performance of the existing fabric prior to intervention. Completed in 2015, the retrofit of New Court, Trinity College, Cambridge has now been monitored for seven years, giving us a clearer picture of its effects on fabric performance and comfort levels. (Photo: Tim Soar)