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

The Passivhaus Standard takes a 'fabric first' approach to energy efficiency. This means your home’s materials and components [the building fabric] do the hard work to reduce the amount of heating and cooling required to keep your home comfortable. It achieves this by using 5 complementary building principles:  

• Continuous amounts of high-performance insulation: 
  Keeps you comfortable all year round and reduces energy demand.
   
• Airtight construction: 
  A continuous, high-performance airtight layer is formed around your home. Then any gaps around doors, windows, electrical outlets, pipes and lights are taped and sealed. This stops heat escaping, cuts down on energy use and keeps your home comfortable with no draughts. Two airtightness tests are performed both during and after construction to make sure your home hits the strict Passivhaus airtightness target. 
   
• Triple-glazed windows: 
  These provide optimum comfort and efficiency in summer and winter. Triple glazing doesn't feel cold to touch and also helps reduce outdoor noise, keeping your home quiet.
   
• Mechanical ventilation with heat recovery [MVHR]: 
  The lungs of your home, quietly delivering fresh, filtered air 24/7 while recovering heat from outgoing air. Continuous air circulation means your bathroom doesn't steam up, cooking smells vanish and laundry dries faster. If you've got allergies or asthma, the MVHR's filters remove dust, pollen and pollutants, keeping your home healthy.
   
• Eliminate thermal bridges: 
  These are weak spots in a building envelope. They often occur around corners, junctions and where materials meet (ie- a steel beam passing through insultation). The problem is, these areas become cold spots, which can lead to condensation, damp, mould or structural decay. The Passivhaus Standard requires that any junctions, corners, connections and penetrations are carefully planned in the design phase to avoid thermal bridging. This is cheaper and easier to address early, rather than on the building site.

Certified Passivhaus designers and tradespeople will ensure these 5 building principles are integrated into your home. However, these alone don't reliably deliver Passivhaus performance. Three approach principles are also essential.

• Strict Performance and Comfort Criteria: 
  Your home must meet strict targets for space‑heating/peak heating load, overall energy demand, summer temperatures, airtightness, ventilation and acoustic performance.
   
• Passivhaus Planning Package Modelling: 
  The Passivhaus Planning Package [PHPP] is powerful, physics-based design software. A certified Passivhaus designer uses it to calculate and optimise your home's year‑round energy use and comfort. It tests design options instantly and flags risks such as poor energy performance, occupant discomfort and high bills. PHPP clarifies the impact of each design choice and helps maximise your value for money, highlighting when design ideas work against energy efficiency.
   
• Quality Assurance/Passivhaus Certification: 
  Passivhaus Certification is an independent, third-party quality-assurance process that protects your interests. A qualified Passivhaus Certifier reviews the technical drawings and the PHPP energy model, checks detailed construction evidence at key stages of the build and verifies test results [eg - airtightness]. When all criteria are met, your home is certified and it receives the official Passivhaus plaque. Certification gives you confidence that you’re living in a genuinely low-energy, high-comfort home. The quality assurance process also ensures the design and build teams are trained in the Passivhaus Standard.

It's the combination of all these principles [building AND approach] that delivers the Passivhaus Standard. Skip one and overall performance can be compromised.

Two housing projects in Wales serve as a cautionary tale.

• 13-home social housing scheme in Wales
• Aim: lower residents' energy bills and operational carbon
• The design and build contract vaguely referred to "Passivhaus principles" / "design inspired by Passivhaus" but didn't require third-party Passivhaus certification
• Mention of "meeting Passivhaus Standards" without any definition of what was meant by this. Such terms are unenforceable in a contract.
• No PHPP models were prepared during the design phase
• No Certified Passivhaus Designer appointed

• After moving in, residents immediately experienced comfort issues
• Several homes were very cold in winter and resorted to using portable electric radiators
• Other homes experienced overheating in summer
• Energy bills were much higher than expected, with many residents unable to pay and officially in fuel poverty
• A retrospective 'as built' PHPP model exposed design issues that would've been cheap and easy to fix early, but instead were carried into construction
• The absence of clear quality-assurance requirements during construction led to inconsistent airtightness results 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

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 (often less), but it's an investment that saves money, hassle and comfort issues later. Case Study A's partial adoption of Passivhaus principles resulted in hefty rectification costs to address performance shortcomings.

Which wouldn’t have been needed if the client had required Passivhaus-certified homes from the start:

• 16-home social housing scheme in Wales
• Aim: lower residents' energy bills and operational carbon
• Big focus on using "low carbon technologies" such as solar PV panels with battery storage, domestic hot water from individual Air Source Heat Pumps [ASHPs], preheated by Transpired Solar Collectors [TSCs] and Mechanical Ventilation with Heat Recovery Systems [MVHRs]
• 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
• Substantial rectification cost

While Case Study B wasn't claiming to follow Passivhaus principles, it's been included to highlight the risks of loading a home with high-tech components without a strong 'fabric first' approach. Passivhaus certification may cost a little more than a standard build, but bolt-on tech typically costs more again, needs more maintenance, has shorter lifespans and still doesn’t guarantee lower bills, lower carbon, or better comfort.
 

Which wouldn’t have been needed if the client had required Passivhaus-certified homes from the start:

As awareness of Passivhaus has grown, some of the fundamental building principles (for example, continuous insulation, airtight construction and MVHR systems) have also spread throughout the industry. That must be seen as a positive. 

However, this has led to projects that have declared they're following “Passivhaus principles” because they incorporate some or all those characteristics, while neglecting to follow the principles of accurate PHPP modelling, quality assurance and meeting performance and comfort criteria, which are central to all certified Passivhaus homes and deliver so many of the health, comfort and energy benefits for occupants. 

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.