The 'Healthy Retrofit' talk was hosted by Cullinan Studio in their new BREEAM 'Excellent' retofit offices.
Brendan Sexton of Cullinan Studio introducing the evening and our latest annual sustainability report.
Johnny Winter of Cullinan Studio began the evening with a talk on the retrofit of
our Baldwin Terrace studios, including some of the lessons learnt from the process.
Neil May's talk on (a seemingly dry subject) - 'How sustainable products can assist with moisture control in retrofit' - was particularly timely.
Neil May of ASBP.
29% of UK housing stock is solid wall construction. As a nation we have to upgrade it successfully if we are to reduce our carbon emissions and provide comfortable homes that people can afford to heat.
Under the Green Deal, this widespread form of construction is labelled 'hard to treat'.
It's an odd situation to be in. At last, and for all the Green Deal's faults, something is being done to tackle the challenge of widescale retrofit of our existing housing. Now there is a growing pressure to get this work underway. But do we actually have the technical solutions?
The general 'golden rule' for the Green Deal is that the cost of carrying out improvement works is matched by savings in fuel bills. 'Hard to treat' properties can't meet this rule: the cost of insulating solid wall properties far exceeds the savings in fuel bills. To get this work done, additional subsidy is needed. This comes from the utility companies' 'Energy Company Obligation'. This subsidy is not given away but is paid for by a general increase in all our fuel bills. The utility companies are obliged to meet set carbon reduction targets, hence the pressure to get this work underway and fast.
Building Magazine on 8th February reported Encraft's recent study, which showed that the costs of the upgrading 'hard to treat' homes has been woefully underestimated.The effective cost per ton of carbon saved they estimate to be £180 compared with the government's £80, a difference we will all have to bear through increases to our fuel bills.
So it is more than ever important that the technical solutions employed do actually work.
Neil's overriding point was that we do not yet have robust, widely applicable, whole building solutions based on sound science: inappropriate and partial solutions seriously risk causing a new generation of moisture-related problems, from mould growth and ill-health, to fabric degradation and premature decay.
To meet this challenge we need the pace of research and dissemination to accelerate.
In the meantime, we need some good rules of thumb to guide us. In this debate the five 'principles for building' still stand up*. What are they? Two overriding constraints, two overarching objectives, and the fifth a guiding caution.
- 'High to low' restates what should be obvious, that gravity generally makes water flow downhill, that temperature goes from hot to cold, that vapour diffuses from high to low vapour pressure.
- 'Separate lives' reminds us that buildings are assembled in a process and that different materials move and decay at different rates, processes which if ignored cause premature failure.
- 'Continuity' of performance is an implicit objective for the building envelope. The increased performance we now expect from our building envelopes, where internal conditions are held further apart from the external environment, means design has to be more rigorous to achieve this. Continuity of the measures to achieve continuity of performance has become more critical, whether at the air tightness line or thermal insulation. This might be obvious but it is only the Passivhaus standard that appears to recognise that continuity (by truly avoiding cold bridges and demanding a demonstrable air tightness performance) is an essential rather than a nice-to-have. By its nature, 'continuity' is often in conflict with 'separate lives'.
- 'Balance' is the objective that encompasses the equilibrium of environmental conditions, of structural forces, and distribution of resources. Achieving balance is often in conflict with the constraint of 'high to low'.
- The fifth, cautionary principle can be called 'creative pessimism' - accepting that in the world of building what can go wrong at some point will, and creatively anticipating it. I enjoyed Neil's restating this as the 'principle of forgiveness'.
The relevance of all this is that accepting and working with these principles by following some rules of thumb - 'going with the flow' - rather than fighting them against does reduce the risk of failure. Increasing thermal resistance towards the cold side and increasing vapour resistance towards the moist side is one such rule. External wall insulation still needs to be continuous but is inherently less risky than internal linings. Fighting against the principles always requires more highly stressed solutions, such as 100% vapour barriers. That is why we should all be concerned about the prospect of 'hard to treat' homes being internally lined with insulation.
Colin Rice, Cullinan Studio
*Addleson and Rice, Performance of Materials in Buildings, 1991
Richard Griffiths from Parity Projects.
Q&A session following the three presentations.
The 'Healthy Retrofit' talk was presented by ASBP (Alliance for Sustainable Building Products) which is a cross sector, not for profit organisation, comprising building product manufacturers and distributors, specifiers, designers, architects, contractors, public interest and sustainability organisations, academics and other building practitioners.
The ASBP are committed to accelerating the transition to a high performance, healthy and low carbon built environment by championing the increased understanding and use of building products that meet demonstrably high standards of sustainability.
