Heritage Retrofit

8 BCD SPECIAL REPORT ON HERITAGE RETROFIT FIRST ANNUAL EDITION The thermal performance of the building envelope was quantified before and after the improvements using in situ U-value measurements, co-heating and air pressurisation tests. The improvements were also modelled using the government Standard Assessment Procedure (SAP) for the energy rating of dwellings, and the outputs compared with the measured results (see Further Information for details of the research report). In addition, sensors were installed behind the internal wall insulation in 16 locations to monitor heat and moisture at the interface with the wall. In a heated building the addition of internal wall insulation will make the existing wall colder because it gains less heat from the interior of the building. As the wall Measuring the moisture content of the dowels manually, using a resistance moisture meter. The dowels are connected to terminal blocks located to suit the spacing of the pins on the moisture meter. This enables repeated measurements to be made quickly and easily. Hygrothermal monitoring set-up at Shrewsbury Flaxmill Maltings: the dowels are cut into three sections isolated by epoxy resin. The ends of the dowels are also sealed with epoxy resin. In each section there is a pair of embedded electrodes which enable the electrical resistance to be measured remotely to provide a moisture profile through the thickness of the wall. The interior of the flax mill: the line of short cast iron columns once held the drive shaft to power the looms. becomes colder, its humidity increases. This prompts two questions: does the wall remain sufficiently wet for long enough to harm building fabric? And does moisture tend to accumulate over time? The sensors installed measure temperature, relative humidity and the moisture content of a small block of wood (page 7). Moisture monitoring at New Bolsover has been carried out continuously since 2011. During this period seasonal fluctuations have been observed, with walls becoming wetter in winter and drying out during the summer months. So far, no conclusive evidence of moisture accumulation behind either insulation system has been observed, but monitoring is continuing. (The results of the work to date will be published in an interim research report report which will be available for download from Historic England’s website). GEORGIAN FLAX MILL, SHREWSBURY Historic England has also been monitoring site trials to assess the effects of internal wall insulation on the hygrothermal behaviour of brickwork at Shrewsbury Flaxmill Maltings, Shropshire, (also known as Ditherington Flax Mill). The internationally important historic site comprises seven listed buildings, including the main mill (Grade I listed), built in 1797 to the designs of Charles Bage. It is the world’s first iron-framed building – a forerunner to the modern skyscraper. The site ceased trading in 1987 and became derelict. English Heritage acquired it in 2005 and carried out emergency works to halt the decline of its buildings. Plans to bring the site back into sustainable beneficial use as a mixed-use commercial and residential development are in preparation. In this context questions have arisen about the extent to which wall insulation might form part of the energy strategy for the buildings, providing an ideal opportunity for further research into its effects. Two systems of internal wall insulation, similar to those used at New Bolsover, have been installed in trial areas on three exterior walls in a room in the engine house adjoining the main mill. The 1½-brick thick walls face south, east and west respectively. The monitoring set-up is similar to that at New Bolsover, except that wooden dowel moisture sensors have been installed in holes drilled in the walls to within 50mm of the external faces. This allows moisture profiles through the thickness of the wall to be obtained, in addition to heat and moisture transfer