Lucy Pedler. Director: The Green Register
Since June 2010 we’ve been running our ‘Eco-refurbishment and The Green Deal’ seminar where ‘warts and all’ presentations of residential case studies give delegates in-depth information on how to retrofit their buildings in a sustainable, low carbon way. But one of the frequently asked questions raised in these seminars is ‘what are the risks of interstitial condensation when applying insulation to an existing building?’
As the economy plummets but fuel prices sore, construction professionals are increasingly working on upgrading their clients’ properties rather than new build projects but are very concerned that by adding roof, wall and floor insulation this will move the dewpoint and cause moisture to build up within the fabric of the external envelope. This can cause damp to build up, mould to grow and potentially damage the fabric – or worse still, structure – of the building elements. Alarm bells start to ring and no professional wants to be faced with a possible lawsuit for negligent practice.
Other concerns repeatedly raised in our Eco-refurbishment seminars are ‘Which is the best way of insulating an existing external wall – inside, outside or the bit in between’, ‘How can I achieve airtightness when refurbishing buildings?’ and ‘How can the design team and builders effectively communicate to achieve best practice detailing?’
As always TGR loves to respond to our delegates’ requests for more, unbiased information and we decided to tackle these issues head on by running a series of new ‘All in the Detail – achieving Best Practice Detailing for Eco refurbishments’ seminars around the UK.
Our first seminar was held in London with over 40 delegates attending the whole day. The speakers were chosen firstly because of their in-depth knowledge of eco-retrofit projects and secondly because they were all experienced practitioners and could share some of their practical experiences of building airtight, well insulated refurbishments but with little or no risk of interstitial condensation.
The first – and judging by the delegates’ feedback by far the most well received – speaker was builder Rafael Delimata, director of Bowtie Construction – contractors with a passion for sustainable building. Rafael used a combination of teaching techniques to explain how his company has consistently achieved best practice detailing in retrofits. Using full size construction mock ups of wall and roof junctions he had made especially for the seminar, Rafael illustrated how to achieve very stringent airtightness standards and the challenges of getting continuous, unbroken layers of insulation, vapour checks and breather membranes.
Rafael also used videos to demonstrate examples of difficult detailing such as at roof hips and valleys, dormers, window and door reveals. Architects’ drawings were displayed (anonymously of course!) to show where detailing was tricky and how better communication – both through drawings and between site managers and operatives – would achieve better standards of airtightness and insulation.
The best thing about Rafael’s presentation was that he could prove that his retrofit jobs actually worked using a combination of careful site practices, good communication and a thorough understanding of the technical information on tried and tested building products.
Finally, Rafael addressed the thorny issue of the cost to install low impact building materials, hidden costs like wastage and storage, delays if products need to be reordered and how builders save money compromising on quality or using substitutes.
The next speaker was Mick Morris from Airseal insulation who talked about moisture control in existing buildings and what happens when insulation is added, particularly when it is non-breathable. The risks and dangers of moving the dewpoint and trapping airborne moisture in elements of a retrofit project were also covered.
Next on was Valentina Marincioni, a scientist from NBT who shared some fascinating research she is working on with University of Central London on moisture movement in buildings. Valentina explained that there are three key principles to delivering low energy refurbishment solutions through the building fabric: thermal coherence, air-tightness and moisture control. In order to insure that a fabric solution is delivered correctly NBT have developed a Material System based approach and Valentina outlined the importance of one of these areas, fabric moisture control and the use of moisture modelling software WUFI to assist in the retrofit design process. The research shows that it is a very complicated subject and that the WUFI software systems take into account subtle differences such as location, orientation and even different types of bricks.
Our final speaker was Jean Pierre Wack, director of eight associates who used an extremely interesting case study of a passivhaus standard retrofit house in London to demonstrate quite how far we would have to go to achieve this very stringent standard.
With The Green Deal’s somewhat underwhelming launch on the first of this month (rumour has it that January will see a revamped relaunch) this seminar could not have been more timely as it has helped construction professionals understand the complexities of introducing green measures into existing buildings, something we are going to have to increasing get our heads around as the impacts of climate change on our poorly performing building stock become evident.