42 DELIVERING COST-EFFECTIVE PASSIVHAUS PROJECTS AT SCALE IN RESIDENTIAL & DOMESTIC SECTORS ENGINEERING THE VALUE
Dr Joel Callow of Beyond Carbon gave the fresh insight that might be counterintuitive: “Passivhaus is in some ways the best value engineering tool”
as in the words of Serenity Projects’ MD, housebuilder Daniel Levey, “proper education on the benefi ts.” In terms of the ‘carrot versus stick’ debate for increasing uptake, several in the group favoured incentives and outcome-based rules over simple prescriptive approaches Mike Roe, Passivhaus Certifi er at WARM, said that mandating Passivhaus was “dangerous; if we keep on mandating it, we’re always going to get pushback.” Instead he wondered whether there were “ways of incentivising Passivhaus, i.e. if you did Passivhaus, it smoothed the way.” Lorna Taverner from Willmott Dixon however reckoned that the industry had to pursue “the carrot and the stick” to make developers take up the approach: “If they don’t want to, they will fi nd a way not to do it.” One potential ‘planning incentive’ mooted was the idea of faster approvals granted if teams delivered Certifi ed Passivhaus. Cundey argued for mandating “sensible ventilation,” saying “if we are going to mandate things, let’s look at mandating a sensible ventilation solution rather than a four-inch bathroom fan. If we put MVHR in as the baseline, then people will start saying, ‘What’s the next solution after that?’”
Aaron McCarthy of Hive said that the Passivhaus community was growing, but Government incentives were needed to grow it further, and that each new project “becomes a new benchmark.”
The cost of Passivhaus design; and debunking myths The delegates discussed the perception versus reality of the cost of Passivhaus, which has traditionally been seen as ‘higher end’ in UK residential projects, but where at-scale projects are demonstrating new levels of cost-effectiveness. However, Willmott Dixon’s Lorna Taverner noted that good aspirations can rapidly shift as clients discover the investment required: “many clients began with Passivhaus as an ambition but drop it as soon as cost advisors say it’s 30% more.” Attzaz Rashid described the journey that Barratt London had taken to Passivhaus adoption, a large part of which was proving viability, meaning “a year of building physics and work with a cost planner.” This was followed by a presentation to the board which was “framed around customer value, repeat business, and future resale, not just capex.” He added: “Once you put all the puzzle together and you present it right, it becomes very diffi cult to ignore.” Dr Joel Callow said that PHPP, the well-regarded Passivhaus design software was, despite some limitations, also a worthy, but underappreciated value engineering tool. He said: “We regularly save the contractors money because we know they don’t need X, Y, or Z.”
Delegates discussed how at-scale schemes were able to further reduce costs, but the incentives for developers to do this were less in private residential than in commercial projects. The pricing of risk, and the ‘de-risking’ of Passivhaus, was fundamental to increasing its uptake, said delegates including Hugh Franklin, as is the presence of QS’ in the early decision-making around projects’ feasibility. However, Ann-Marie Fallon of the Passivhaus Trust counselled against ‘double counting’ in cost plans – “they often double count or mis-assume, such as double counting wall insulation. She cited a school project where a cost plan reportedly priced an air test at £250K. She warned: “Those are risks that should be built into projects, and driven down over time.” Aeroseal UK’s Hugh Franklin commented: “The person that should be in this conversation is the QS, otherwise there will be a red light in the middle. It will stop.” Lorna Taverner said while Passivhaus Designers should be engaged early, getting clarity on the project that will lead to realistic risk pricing and other certainties was “the difference between a Certifi ed Designer and a good Passivhaus Certifi ed Designer – they will give you really good starting points.” Evette Prout from Kind & Co builders, said that they “love early engagement,” and had been able to spot and fi x overengineering with a particular social housing client as a result.
The conversation also looked at the need for dynamic modelling to cover the fl uctuations in living behaviours and climate in large-scale, complex Passivhaus schemes, but also how PHPP could be the engine for the crucial collaboration that was needed in design teams. Aaron McCarthy of Hive Group said from his experience in large-scale schemes, “collaboration is really driven through the PHPP; no-one I have come across knows the ins and outs of every single aspect.” Delegates agreed that PHPP was a useful predictive design tool, not just a set of tick boxes. On the other hand, SAP and Future Homes Standard modelling was heavily criticised for “baked-in errors” (e.g. not valuing permeability higher than 3 m³/h·m²).
The debate looked at the possibility that designers and contractors could be over-engineering Passivhaus, particularly in terms of the design of services, such as HVAC and MVHR in particular, and this could be one factor contributing unnecessary cost to projects. Instead, a more streamlined approach was possible, emphasised by our co-sponsor, Ubbink, at the debate.
Solutions: airtightness, MVHR & overheating As ever, the second half of the debate began with our sponsors posing realistic, and often searching questions to the group. Ubbink’s Craig Cundey asked, based on experiences of several prospective Passivhaus domestic clients deciding against going the ‘whole hog,’ “What constraints are stopping them achieving Passivhaus? We know there’s a fi nancial element, but is the void as big as we think? Is it planning issues? Is it product availability, a lack of skilled supply chain? Michael Brett of Milestone said that the biggest issue was “knowledge and education; people were either being told the wrong thing, so it’s putting them off, or the homeowner themselves isn’t educated on the benefi ts.” Cundey suggested that even the term “Passivhaus” could put people off, and wondered if something more like Barratt London’s ‘Low E’ branding would be more helpful with consumers.
The conversation around ventilation solutions was enmeshed with a continuing debate around Passivhaus’ ability to tackle
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