Why Passivhaus? Why *Certified* Passivhaus?

The design for the house is now very nearly complete and it’s time to get a Passivhaus Certifier involved to check the PHPP model and review the thermal bridging details.

People sometimes ask why I want to go “all the way” to Passivhaus. Here’s my rationale:

  • Insulation is A Good Thing, so more insulation is better, right? The question is, how much insulation is “optimal”? UK Building Regulations have a view on this and specify the minimum acceptable standard, but as we’ve seen that changes (rather dramatically) over time: my previous house, built in 1995, had no wall insulation when originally built but that would be unthinkable now, just 20 years on. Since a new house is expected to have a long life it needs to be designed to cater for future conditions, but those are hard to predict.
    • I really like the way the Passivhaus standard looks at the physics of building performance and declares that the “optimal” point is where you no longer need a regular central heating system. There’s no reliance on speculative pay-back times based on predictions for future energy prices.
  • Energy costs are increasing all the time, and whether or not you believe that global warming is a result of carbon emissions it’s almost certain that government policies will continue to reward energy efficiency and penalise energy consumption.
    • In all likelihood, any investment in improving the quality of the building fabric will pay dividends. People building at or close to current Building Regulations today will soon wish they had done more.
  • It’s not just about energy consumption; it’s also about comfort. One reason that the Building Regulations have specified increasing levels of insulation over the years is that people’s expectations have changed. These days most people expect a constant 20 degrees (or more) all over the house without draughts or hot or cold spots, and the research shows that most people feel comfortable at a lower temperature when that temperature is consistent throughout a room.
    • One of the big benefits of triple glazing over double glazing is not the basic energy performance but rather the impact on the temperature of the inner pane of glass. That stays warmer so it feels more comfortable.

So what’s not to like? Good insulation, good air-tightness to stop warm air escaping in an uncontrolled fashion, mechanical ventilation with heat recovery to provide adequate ventilation in a controlled manner and a sufficiently low heat demand that the ventilation system can deliver the necessary heat without a conventional heating system.

There’s a good 90-second video with an overview of the key features of a Passivhaus here.

OK, so why Certified Passivhaus? My thinking:

  • The design details and construction techniques required to meet the Passivhaus standard are not yet mainstream in the UK, and the level of understanding varies considerably. In such cases it’s good to get an expert opinion from a qualified professional.
    • Having an independent Passivhaus Certifier review the design produced by a qualified Passivhaus Designer provides a second opinion which helps to ensure that nothing is missed.
  • One of the demonstrable benefits of Passihvaus construction is that the performance of the final building closely matches the predictions generated by the Passivhaus Planning Package (PHPP), which is not always the case with other approaches. This is generally because the property is actually built in accordance with the design.
    • While it’s not strictly essential to obtain Passivhaus certification in order to ensure that the design is closely followed, the validation performed in order to achieve certification does ensure this is the case.
  • There are a lot of informal variations on the Passivhaus theme: some people follow Passivhaus principles; some aim for zero carbon etc. You can’t claim to have a Passivhaus unless you have a certified Passivhaus, and the experience from my day job is that the standards which require formal certification are the ones which offer the best value.
    • My hunch is that some buildings which are being constructed to “Passivhaus principles” will deliver disappointing performance and certified Passivhaus buildings will attract a premium as a result.

There’s a more expert summary of the benefits of certification at: I want a Passivhaus; why bother with certification?