What Is Passivhaus? A Guide for Hampshire Homeowners
Passivhaus is the world's leading energy standard for buildings. Here's what it means in practice — and whether it's right for your project.
The word "Passivhaus" appears increasingly often in conversations about new build homes and ambitious extensions. It is sometimes presented as a niche, expensive, or technically complicated undertaking. In reality, Passivhaus is a rigorous but well-understood design and construction methodology that produces homes which are cheaper to run, more comfortable to live in, and significantly better for the environment than conventionally built equivalents.
What Is Passivhaus?
Passivhaus (German for "passive house") is an international energy performance standard developed in the late 1980s by physicist Wolfgang Feist and professor Bo Adamson. The standard is precise, measurable, and independently certified — which is what distinguishes it from loosely defined labels like "eco home" or "low-energy building."
A Passivhaus building meets three core performance criteria:
Heating demand. No more than 15 kWh per square metre per year for space heating and cooling (compared to a typical UK new build at 50–80 kWh/m²/year, and an older home at 200+ kWh/m²/year).
Primary energy demand. No more than 120 kWh/m²/year for all energy use, including heating, cooling, hot water, and all household electrical consumption.
Airtightness. No more than 0.6 air changes per hour at 50 Pascals pressure (n50). This is extremely airtight — roughly ten times more airtight than a typical UK new build.
These are not targets but thresholds. A building either meets them or it doesn't. Certification requires independent verification through an air pressure test and energy modelling using the Passive House Planning Package (PHPP) software.
The Five Principles
Passivhaus performance is achieved through five core design principles, applied together:
Superinsulation. Walls, floors, and roofs are insulated to a much higher standard than Building Regulations require — typically three to four times higher. In practice, this means external walls of 300–400mm total thickness, with insulation values (U-values) of around 0.10–0.15 W/m²K.
Thermal bridge-free construction. Heat losses at junctions — where insulation layers meet, at window reveals, at foundations — are carefully designed out. These "thermal bridges" are often overlooked in conventional construction but can account for 20–30% of a building's total heat loss.
High-performance windows and doors. Passivhaus windows are triple-glazed with thermally broken frames, achieving whole-window U-values of 0.8 W/m²K or lower. In Hampshire's climate, south-facing windows are net energy gainers — they admit more solar heat than they lose.
Airtightness and ventilation. The building envelope is sealed to the airtightness threshold above, and all ventilation is provided mechanically via a Mechanical Ventilation with Heat Recovery (MVHR) unit. The MVHR continuously supplies fresh air to the building while recovering 80–90% of the heat from the exhaust air — maintaining excellent air quality without heat loss.
Passive solar gain. Careful orientation and glazing design allows the building to capture solar energy in winter while managing summer overheating through shading, orientation, and thermal mass.
Does Passivhaus Mean No Heating System?
Not necessarily, though many Passivhaus homes in the UK can be adequately heated with very small heating systems — sometimes little more than an electric towel rail and an immersion heater. The MVHR system can also deliver small amounts of supplementary heating via a post-heater in the ventilation duct.
In practice, most of our Passivhaus-standard clients choose to install a small heat pump as a backup and for domestic hot water, combined with solar PV panels. The combination produces a home that has very low or even net-zero energy costs over the year.
Is Passivhaus Expensive?
Building to Passivhaus standard typically carries a construction cost premium of 5–15% over a well-specified conventional equivalent. This premium has reduced significantly over the past decade as UK contractors have become more experienced with the methodology and materials have become more readily available.
Against this premium, the savings in energy bills are substantial. A conventionally built four-bedroom house in Hampshire might spend £2,500–£4,000 per year on heating and energy. A Passivhaus equivalent might spend £300–£600. Over a twenty-five year mortgage term, the cumulative saving typically exceeds the additional build cost many times over.
There is also a growing body of evidence that Passivhaus homes command a price premium in the resale market, as buyers become more sophisticated about running costs and environmental impact.
Passivhaus for Extensions
While Passivhaus certification is primarily applied to whole buildings, the principles can — and should — be applied to extensions and renovations. Many of our clients choose to build to near-Passivhaus specification without seeking formal certification, achieving most of the performance benefits at reduced administrative cost.
This is particularly relevant for rear extensions, where a highly insulated, airtight addition can dramatically improve the thermal performance of the ground floor and provide an opportunity to upgrade the overall MVHR and heating strategy for the whole house.
Working with Us on Passivhaus
We have designed and delivered Passivhaus and near-Passivhaus projects in Hampshire and across the South. If you are considering a new build or extension and want to understand whether Passivhaus is appropriate for your project, we would be delighted to discuss it. Get in touch to arrange an initial conversation.
