ROUND TABLE REVIEW 27
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.”
MYTH BUSTING Misconceptions around the cost of Passivhaus were tackled and debunked
The cost of Passivhaus design – and the 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, Lorna Taverner noted that sometimes good aspirations rapidly change 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 Rishad 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.”
Joel Callow said that PHPP, the well-regarded Passivhaus design software, was, despite its 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, warning: “Those are risks that should be built into projects, and driven down over time.” 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
Delegates agreed PHPP was a useful predictive design tool, not just a tick-box, 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 rising temperatures and protect residents, particularly resonant in this heatwave summer, with heat a “silent killer” in the words of Joel Callow, versus the much more visible deaths at Grenfell Tower. He said there was “no natural ventilation solution to high-density housing.” In terms of MVHR delivery, Cundey said that ‘design-only’ software layouts for MVHR are often wrong;, but site surveys and close supplier–installer collaboration can avoid oversizing and over-engineering. Hugh Franklin of Aeroseal UK (who specialise in air-tightness solutions) also homed in on perceptions of construction risk in Passivhaus, in his question. He asked: “Of the fi ve core Passivhaus
ADF SEPTEMBER 2026
WWW.ARCHITECTSDATAFILE.CO.UK
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78
