How green is green? Like many others active in cohousing, members of Still Green aspire to building and living in high-sustainability homes. That pointed towards Passivhaus, a sort of gold standard for eco-builders. But is it or should it be the benchmark for sustainability? Anyone familiar with the debates in architectural circles will know that some full-on environmentalists are concerned that it is arbitrary, in some respects and settings inappropriate, procedurally quite expensive, and that it does not address some important environmental issues. But if not Passivhaus, and given the demise of the Code for Sustainable Building, then what?
The AECB offer an alternative marque the Silver Standard. This also involves MVHR, and whilst levels of air tightness and thermal insulation are lower, they still greatly exceed current Building Regulations. In consequence, it seems to offer greater cost effectiveness, in the sense that it there is a noticeably lower build cost for a modest reduction in environmental performance. Or at least that was the finding from financial modelling carried out by our Quantity Surveyor, Keith Broadhurst, based on the designs Potter & Holmes prepared for us, and the selling price constraints we had set.
These are complicated matters, but in brief here is what we found: built to building regulation standards, the scheme generated something like the surplus the industry would normally expect; but with passivhaus designs it barely broke even, and it would not have carried credibility with our members, let alone our partners. At this point, one of our members suggested the AECB Silver Standard as an alternative. This turned in the sort of result we needed: the additional cost, above the costs of meeting Building Regulations, was around half of that required by Passivhaus.
Whether the Silver Standard is green enough remains an open question. The results from this exercise are only forecasts and may not be achieved elsewhere with different designs. Clearly, compared to not being able to afford the scheme at all, Silver Standard is very positive indeed. Nevertheless, compared to Passivhaus, that ‘modest reduction’ in environmental performance (and higher fuel bills) will go on and on for years. We would be interested to hear from other groups who have explored this issue
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