Sustainable Masonry Seminar
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On the occasion of the Society AGM, a Technical Session was held with the title Sustainable Masonry Construction and was attended by some fifty members and guests.
The new President, Cliff Fudge, chaired the proceedings and introduced Martin Clarke and Michael Driver from the Modern Masonry Alliance who started the session with a paper entitled Modern Masonry – the optimal solution for Sustainable Communities. Martin explained the mission of the Alliance was to ensure a future for the masonry industry by ensuring it was the first choice as a method of building. One of its first tasks had been to prepare a response to the consultation draft of the Code for Sustainable Buildings. There had been 444 responses to the Code and the comments are being summarised by BRE. The Alliance view that whilst there was much in the code that could be supported for example on energy and water management there was a lot that masonry had to offer which perhaps was not reflected so strongly, for example, future proofing against climate change, fireproofing, absence of toxic mould etc. One key element which works against masonry is the assumption built into the life cycle assessment element that masonry buildings last for sixty years whereas the reality is we expect them to last for centuries, the base should be 125 years to be realistic. Martin mentioned the Arup study which showed that in a future subject to climate change lightweight constructions would begin to overheat to an unacceptable degree by the 2020’s. This was returned to by Colin Marshall later in the morning.
Martin introduced Ian Abley, an architect who would be studying the re-engineering of the masonry construction process as an Engineering Doctorate student at Loughborough University. The first event linked to Ian’s appointment is an MMA part-sponsored one-day workshop at Kingston University entitled Superbia – the case for Suburbia held on 23rd September.
Michael Driver gave a thoughtful presentation based upon the premise that “sustainability is the issue of our time” but not just sustainable construction in the narrow sense but that our challenge was to produce sustainable communities. The issue was how could we do this and he gave some examples of how communities have developed, for example by the Romans about the road system and by Houseman in Paris where a series of focal points were established and communities formed the infill areas. However it was done we needed places that people understood and people do respect scale, they like masonry materials because they do enhance our communities.
David Hills gave a manufacturer’s view of clay brick from his perspective as Chairman of the BDA Sustainability Committee and used some examples from his own company, Ibstock Brick. David felt that there was a lot of emphasis from the government to “do more with less” and that there was a lot of conflict between short and long term considerations. A significant point is that since 1990 the energy demand from our housing has increased by 18%, this largely due to the increase in single person dwellings. The latter creates a major problem as, although the £60k house might be a reality, there was a huge problem in siting such houses, especially in times of problems over water supply. A major question is what can be done about the increase in demand for energy? Most new technologies have a very long payback period and green technologies cannot offset the increase in demand. David reflected that from the Arup study if we persist in using lightweight construction we will make things worse as greater amounts of air conditioning would be needed. He also touched on the 60 year life issue and provided some findings from a BDA supported PhD project at Leeds Metropolitan University that showed in a sample of 860 buildings the average period before replacement of clay bricks exceeded 150 years. Ibstock is actively working with communities near its factories to improve local conditions in a sustainable way. Brick factories do have potential impacts on the communities around them as there is the potential for dust emissions, lorry movement, noise etc. David showed a number of examples of how Ibstock had invested in projects to reduce the impact of the community. Apart from those things that are needed for compliance with legislation such as flue gas scrubbing there were many where the investment went way beyond what was strictly required. For example the inclusion of wildlife retreats during quarry rehabilitation, the use of willow weave and rammed earth instead of concrete to stabilise a river bank, river re-routing, fish stocking, lorry wheel washing etc. An important benefit to Ibstock is that there has been an improvement in employee satisfaction as measured by independent survey since the policies were implemented, so it seems that the whole community including the workforce are benefiting from the approach.
Colin Marshall from Tarmac Topblock talked about The Sustainability of Masonry in relation to Part L and Thermal Mass. He explained the UK commitment to reducing the energy used in our buildings and how this was being approached in the new Approved Documents to the Building Regulations. The approach now is that the overall emission rate for the building is controlled rather than each element. The Design Emission Rate must be less than a Target Emission Rate which is set at a value of 20% lower than the requirements in 2002. Typically a wall U value will need to be 0.27-0.3 W/m2oK in order that buildings comply although issues of heater control efficiency and air leakage have now been introduced. Colin also discussed the outcome of the Arup study in to the effect of high thermal mass in limiting the occurrence of uncomfortably high internal temperatures. A key point is that the whole focus on embodied energy is a short term consideration whereas the mitigating effects of high thermal mass may not be felt for 11-25 years when climate change has developed further.
Malcolm Bell from Leeds Metropolitan University discussed the experience in recent field trials of the Air tightness of Masonry Dwellings. One study was based on measurements on 25 houses which were then fed back to developers and improvements made on a second batch of dwellings which were also tested. The second looked at trying to achieve a 30% CO2 reduction from 2002 levels (10% on 2006). The requirement to achieve 10m/h@50Pa leakage was considered in relation to several international examples, e.g. the Passive House, Hanover (0.29m/h) and Scandinavian practice (1m/h) and also the second project at Stamford Brook in which the airtightness target was 5m/h@50Pa. What was clear from previous work was that although some air leakage could be attributed to direct air movement through components such as windows and through obvious services penetrations, by far the largest proportion could not be attributed to any particular leakage route. Experience from the field trials suggested that much of this unaccounted for leakage was through hidden paths provided by the air voids in partitions, floor spaces, eaves voids and, most importantly, behind plasterboard dry-lining. It was pointed out that traditional wet plastering is a good way of minimising some of this air movement but that there is understandable reluctance by housing developers to use it. The consequence of dry lining is that the air space behind the lining connects the numerous air paths and leakage points and results in some very complex and hidden air flows. The field trials demonstrated that, attempts to reduce air movement behind dry-lining by the application of continuous ribbons of adhesive were rather futile as it was almost impossible to achieve in practice. The key message was that designers and constructors need to understand the principles of air barrier design and construction. In particular, serious consideration needs to be given to the way the air barrier in the different elements is linked together at junctions so as to ensure its continuity. It is very easy to lose continuity when one part of the structure meets another. Room-in-the-roof designs and other areas of complex geometry and structure present a considerable challenge in this respect. Malcolm concluded with the view that airtight construction required understanding at all levels of construction from concept and detail design to site management and operatives. Without such a cultural shift, the significant improvements in airtightness that are needed to produce sustainable homes are unlikely to take place.
As Michael Driver said “Sustainability is the issue of the Day” and certainly the speakers held the interest of the audience over two hours on varying aspects of the subject. At 12:30pm the President brought the session to a close. The audience warmly thanked the speakers and made their way to the Club Bar prior to a return to the Ballroom shortly afterwards for the Society’s Annual Lunch.
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