How *Not* to Build a Passivhaus: 2 Costly Lessons [and How to Avoid Them]

Passivhaus reduces the amount of energy your home needs to run by integrating five core building principles:

• Generous amounts of high-performance insulation: 
  Keeps you comfortable and reduces energy demand.
   
• Airtight construction: 
  Taping and sealing gaps in the building fabric minimises heat loss, eliminates cold draughts and maximises longevity.
   
• Triple-glazed windows with effective shading: 
  For year-round comfort and efficiency.
   
• Mechanical ventilation with heat recovery [MVHR]: 
  The lungs of your home, delivering fresh, filtered air 24/7 quietly and efficiently.
   
• Minimal thermal bridges: 
  Prevents cold spots and mould growth.

These alone don't reliably deliver Passivhaus performance. Three approach principles are also essential.

• Strict performance and comfort criteria: 
  Measurable targets for your home's space‑heating/peak heating load, overall energy demand, summer temperatures, airtightness, ventilation and acoustic performance.
   
• Accurate PHPP modelling: 
  The Passivhaus Planning Package is the software that a certified Passivhaus designer will use to calculate and optimise your home's year‑round energy use and comfort.
   
• Quality Assurance/Passivhaus Certification: 
  An independent Passivhaus certifier checks your design, PHPP calculations and construction information at key stages of the build. When satisfied, they award your home an official Passivhaus plaque.

It's the combination of all these principles [building and approach] that delivers the Passivhaus Standard. Skip one and you undermine the lot. 

Two projects in Wales serve as a cautionary tale.

• 13-home social housing scheme in Wales
• Aim: lower residents' energy bills and operational carbon
• Contract vaguely referenced "Passivhaus principles" / "inspired by Passivhaus" but did not require Passivhaus certification
• Mention of "meeting Passivhaus Standards" without defining what that meant
• No PHPP modelling in design phase
• No Certified Passivhaus Designer appointed

• Residents immediately experienced comfort issues
• Homes were cold in winter and overheated in summer
• Energy bills became unaffordable as residents cranked heating and bought portable cooling systems
• A retrospective 'as built' PHPP model exposed design issues that would've been cheap and easy to fix early but were carried into construction
• Vague quality-assurance requirements led to inconsistent airtight construction and no reliable audit trail to demonstrate build quality

• Resident's energy bills had to be subsidised on an ongoing basis
• Huge rectification costs, far exceeding the uplift needed [4-8%] to build certified Passivhaus homes
• Severe reputational damage

If you want Passivhaus results, use the whole recipe. Choosing to build a certified Passivhaus from the outset typically adds 4-8% to your project costs, but it's an investment that saves money, hassle and comfort issues later.

Which wouldn't have been required if the client had required a certified Passivhaus at the outset:

• 16-home social housing scheme in Wales
• Aim: lower residents' energy bills and operational carbon
• Big focus on using "low carbon technologies"
• No PHPP modelling

• High-tech, low-carbon systems added 18% to capital costs versus the 4–8% needed to build certified Passivhaus homes
• Promises of generating 80% of required energy on site and cutting bills by up to 50% [vs residents' previous homes] didn't materialise
• Overreliance on manufacturers offering innovative but unproven tech solutions
• Limited technical support for the products installed
   

• Residents in brand-new "low-energy" homes were effectively pushed into fuel poverty
• Homes did not perform as intended
• Avoidable overspend on tech with higher maintenance needs and shorter lifespans
• Significant reputational damage and substantial rectification cost

Loading a home with high-tech components won't guarantee results. Passivhaus may cost a little more than a standard build, but bolt-on tech usually costs more, needs more maintenance, and has shorter lifespans without guaranteeing lower bills, lower carbon, or better comfort.

Which wouldn't have been required if the client had required a certified Passivhaus at the outset:

Passivhaus isn't a shopping list, it's a recipe. When every ingredient works together, the result is a home that feels brilliant: cosy in winter, comfortable in summer, fresh air always, bills you barely notice.

At Coldwells Build, we model our Passivhaus homes using the Passivhaus Planning Package. We design and build with Passivhaus certified architects and tradespeople. We prove the results with independent Passivhaus certification.