Heritage Retrofit

BCD SPECIAL REPORT ON HERITAGE RETROFIT FIRST ANNUAL EDITION 33 such vernacular and humble houses, some terrible 20th-century replastering, painting, patch rebuilds and hard cement pointing had been carried out. There were even areas of glistening moisture on interior wall surfaces and large areas were black with mould. Also, the ground floor skirting boards had rotted through. At this point, some basic humidity readings were taken in June 2015 (Figure 2). The work began with internal faces of the exterior walls being stripped of their coatings and then relined with insulating and humidity-buffering mineralised woodchip panels created especially for the project, and then plaster finished with a Vivus plaster skim. Outside, the walls were depointed of cement and repointed with Vivus mortar and lime-washed. It was clearly demonstrated that the material can be applied quickly. Pure lime skims were applied and finished in the same day. The skims contained no aggregate of any kind nor any other additive – they were pure air lime. In some rooms, purely for the experiment, panels were fitted to the walls and then skimmed and finished on the same day without issue. The north- and south-facing external walls were also finished in the same timescale, repointing and initial coat of limewash completed on day one and subsequent coats applied on day two, completing the work, front and back – sunshine with wind (south front) and cold damp shade (north rear). The two walls were completed in the same manner, clearly demonstrating the setting property of the materials used. Inside, the walls were paper lined and then decorated with a modern ‘fully breathable’ soft paint. Although this will not affect the insulation per se, it will undoubtedly reduce the ability of the walls to absorb humidity. However, many owners and tenants will expect to be able to use these finishes, so this was added as part of the experiment. It is expected that the house will remain humidity free, even with the walls lined with paper. A key element of the demonstration lay in showing the effect of humidity, contained within a structure, on the insulation performance. This moisture can reduce the effectiveness of any insulation by up to 30 per cent depending on the levels. Successfully dry out a building and maintain that humidity, then it will be warmer. Take an insulation that buffers humidity while also helping to equalise the humidity by being diffusive, and apply it to a wall that because of its manner of construction, acts in the same way, then we will have achieved many things simultaneously. The insulation and humidity control abilities are now being monitored with sensors installed at the property. The data taken thus far has shown a very beneficial effect. The average humidity levels recorded in the building had dropped 24 per cent from June 2015 to April 2016, and it is estimated that the energy efficiency of the walls has increased by more than 30 per cent. Empirically, the house is now warm and dry, even though the building was not inhabited all winter following the works. The temperature remains fairly constant, feeling cool on hot summer days and warm and dry on damp cold days. The monitoring will continue for another two years to show the long term effect over winters and summers with the building being regularly used and inhabited. Feedback from the occupants will also be sought. HARRY CURSHAM (harry@vivus.solution s) has spent the past 27 years working with, experimenting with and learning about air lime materials. He is a director of Vivus Solutions Ltd (see page 34). The full Welsh Government SBRI report is available from the author on request. FIGURE 2: Humidity readings – June 2015 AREA POSITION HUMIDITY(%RH) Ground floor First floor Internal west wall Low level 96.35% 88.50% High level 88.99% 88.50% Internal north wall Low level 94.89% 79.50% High level 78.56% 79.50% Internal east wall Low level 93.02% 89.99% High level 89.90% 89.55% Internal south wall Low level 89.95% 88.70% High level 87.05% 88.70% Mill Cottage on completion of repointing and lime-washing using Vivus materials Fireplace and window details, with insulated walls, plastered and finished Sample data recorded following the work at Mill Cottage showing a marked fall in dewpoint (black) and relative humidity (green) from December 2015 to April 2016, while temperatures (blue) rose. During this period the house was uninhabited and the weather in this exposed location was particularly cold and wet. FIGURE 3