C O N T E X T 1 1 1 : S E P T E M B E R 2 0 0 9 41 IHBC Annual School 2009 IHBC Annual School 2009 IHBC Annual School 2009 historic buildings great care must be taken. There can be a very real danger that insulation could give rise to damaging problems, as Ian Brocklebank showed in his article in Context in February 2008. The software programmes that calculate what needs to be done to improve the thermal performance of a wall so that it meets the target in the approved document pays no attention to its actual condition. The reality is often that the wall is fairly damp. If so, most attempts at insulating will have negligible benefits in the short term, and possibly very damaging consequences in the longer term. The starting points for these calculations are the values for thermal transmission given in the CIBSE manuals. Although well founded, these do not take account of individual circumstances in a particular building. In situ U values testing for Historic Scotland has indicated that sandstone walls perform a great deal better than is presumed, although the final report is still awaited. Similar tests are being commissioned in England by English Heritage to cover the many different walling materials used on historic buildings. Insulating roofs Similar considerations apply to insulating roofs. Beside the visual and detailing problems that these changes can make, it is essential to ensure that adequate levels of ventilation protect the roof structure from moisture-related problems. Traditionally roofs, particularly those under tiles and slates, have provided copious amounts of ventilation to deal with excessive moisture generated within the building below. This aspect may become ever more important as buildings are better sealed and roofspaces are increasingly used as habitable rooms. It is also notoriously difficult to fit effective air- and vapour-control layers to prevent this vapour rising up. As with internal wall insulation, the search is on for products requiring a minimal depth that provide the least interference on installation. Some of these look promising, others are suspect. The problem is that judgement is being made on materials that have not stood the test of time and for which scant reliable, independent test results are available. Certainly there would seem to be benefit in considering the use of natural hygroscopic materials; in other words materials that can absorb vapour without impairing their performance. Insulating floors Suspended timber ground floors can be a major source of air infiltration. However, this does need to be established because some historic floorboards have remained undisturbed for centuries and are effectively airtight so do not need to be disturbed. Even if not, it is usually necessary to find a skilled and experienced tradesman to carry out this work if more damage is not to be done. Provided the boards can be lifted quite easily they can be effectively insulated, but it is wise to try to establish what the conditions Further reading English Heritage (2008), Climate Change and the Historic Environment (www.english-heritage. org.uk/upload/pdf/ Climate_Change_ and_the_Historic_ Environment_2008.pdf) English Heritage (2007), Advice for Domestic Energy Assessors (www.englishheritage.org.uk/upload/ pdf/EH_Web_Advice_on_ DEAs_2007.pdf) English Heritage (2007), Energy Conservation in Traditional Buildings (www.english-heritage. org.uk/upload/pdf/ EnergyConservation.pdf) Historic Scotland (2007), Maintaining Sash and CaseWindows (www. historic-scotland.gov.uk/ inform_sash_and_case. pdf) Historic Scotland (2003), Looking After Your Sash and Case Windows: A Short Guide For Homeowners (www. historic-scotland.gov.uk/ sashcase.pdf) Historic Scotland (2002), The Conservation of Timber Sash and Case Windows: Guide for Practitioners 3 (available at www.historic-scotland. gov.uk/index/publications. htm) Chris Wood is head of the building conservation and research team at English Heritage. This article is based on the abstract that accompanied his talk at the annual school. are below the floor. Recent English Heritage research into ventilation indicates that some of these floors are not well ventilated but nonetheless the joists are in good condition. This seems to be due to the buffering effect of the timber in that it absorbs moisture, but heat from above helps this to diffuse away. Insulation will change the environment below the floor and the consequences must be evaluated. Insulating above concrete solid floors usually creates a great number of design problems because of the increased depth that needs to be accommodated. Examples of the use of nanotechnology used in one slim-line system seems to offer potential. The performance of this has actually been tested in situ5. Other issues Renewable technologies offer potential. Some are far more effective than others at present. All of them are invasive to some degree, so English Heritage advocates that carrying out good housekeeping comes first. Considering how to be more economical in the use of energy and carrying out simple repairs and improvements should be carried out initially before installing renewable systems. English Heritage is producing guidance on its website6. Further research is proposed and being carried out to evaluate the effectiveness of benign improvements in occupied buildings and to what extent this influences how people use energy. Human behaviour can be the most important factor in reducing energy use, although this of course is not included within models used to estimate energy use. The most important model in this connection is RdSAP (Reduced Data Standard Assessment Procedure), which is used to produce Energy Performance Certificates,7 which are now required for all domestic properties which are marketed. It is also proposed to be used more widely when the 2010 Part L changes are introduced.The assumptions used in this model are heavily biased against old buildings and could have very harmful consequences unless it is modified. Further research is planned to demonstrate that historic buildings perform better than generally assumed. This will build on the windows and walls testing and other very useful studies. Another novel idea is the use of high-quality acrylic, here applied on the inside of this 18th century window.The acrylic has been precision-cut by laser. There is an advanced dessicant within the space to deal with any possible moisture vapour.The great advantage of this system is that it preserves the original window and is totally reversible and lightweight, unlike double glazing. It achieved a U value of 2.5 in Glasgow.
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