Passivhaus: What it is and why it matters for windows and doors

What is Passivhaus?

Passivhaus is a performance standard created in Germany and used worldwide. It focuses on lowering a building’s heating and cooling demand by combining:

Very high insulation
Excellent airtightness, with controlled fresh air via MVHR
Thermal‑bridge‑free construction
High‑performance windows and doors
Good solar design, so you get useful winter gains without summer overheating

The aim is comfort, healthy air and energy efficiency all year, not just hitting a number on paper.

Key targets

Space‑heating demand: about 15 kWh per m² per year.
Airtightness: about 0.6 air changes per hour at 50 Pa (blower‑door test).
Windows: whole‑window U‑values around 0.80 W/m²K or better, with low frame losses and good solar gain where appropriate.

Benefits

Comfort
Rooms feel even in temperature. Cold spots near glass are minimised. Draughts are rare because openings seal properly and the install is airtight.

Low energy bills
Needing very little heat saves money. Smaller heating systems are common.

Quiet interiors
Triple glazing and deeper frames cut traffic noise and wind noise.

Healthy air
With an MVHR system, stale air is extracted, fresh air is filtered, and heat is kept indoors.

Durability
Dry, consistent internal conditions help the building fabric last.

UK considerations

Climate and solar gain
The UK has mild winters and variable sun. South and west elevations may benefit from higher g‑value glass. North elevations often prioritise the lowest U‑value.
Regulations vs Passivhaus
Building Regulations set minimums. Passivhaus targets are stricter and focus on the whole building. Windows that meet Building Regs may not be suitable for a Passivhaus.
Overheating
Consider shading, opening lights for purge ventilation, and careful glass choice, especially in the south of England and urban sites.

Retrofit
For existing homes, look into the EnerPHit approach. It applies the same principles with targets suited to retrofit constraints

Passivhaus windows explained

What makes a window “Passivhaus level”

Triple glazing with warm‑edge spacers, argon n gas fill and low‑e coatings.
Thermally broken, insulated frames, alu‑clad timber and alu-clad uPVC.
Whole‑window performance: focus on Uw (frame plus glass), not just centre‑of‑glass.
Airtight gaskets and quality hardware so sashes seal properly.
Installation that keeps the insulation line continuous, avoids thermal bridges and uses airtight tapes and membranes.

The numbers to look for

Uw (whole‑window U‑value): around 0.80 W/m²K or better is typical for Passivhaus projects.
g‑value (solar factor): usually between 0.5 and 0.6 for glazing that brings useful winter sun.
Linear thermal bridge (Ψ‑install): keep it low with insulated frames, correct packers and reveal insulation.
Air leakage: very low, verified through test standards.

Certification

Some windows are PHI‑certified components. Certification confirms performance under a standard method. Many projects also use windows tested to equivalent levels even when the component itself is not certified. Ask for test reports that state whole‑window values, sizes tested and the glazing used.

Our Passivhaus rated windows

Below are the specific product ranges that we offer that are Passivhaus compliant.

Manufacturers & models

Internorm: KF410, KF50, HF410, HF510, HV450, KV440
Rationel: AuraPlus, FormaPlus
VELFAC: V200E

Opening types and options

Internorm: tilt‑turn, fixed, side entrance doors, entrance doors and lift‑slide options available.
Rationel: side‑hung, top‑guided, fixed lights; glazed doors.
VELFAC: casement, top‑guided, tilt‑turn (project dependent), fixed; curtain wall/frames to match.

If a model is PHI‑certified, add the component class and certificate ID. If it’s tested to an equivalent standard without formal PHI certification, add the report reference and test house.

Passivhaus UNO Project Feature

Bowerley Gardens Project

A unique and highly ambitious PASSIVHAUS new build tucked into the Yorkshire landscape. This stunning subterranean home is built into the hillside and finished with local Yorkshire stone, blending beautifully into its surroundings while meeting some of the highest standards in energy efficiency and building performance.

View Project

Detailing and installation

Set windows in the insulation layer to align with the thermal envelope.
Use airtight tapes and membranes on the warm side, and weather‑resistant tapes outside.
Insulate the reveals and sills to cut Ψ‑values.
Commission a blower‑door test before finishes, fix leaks while access is easy.

FAQs

Do I need Passivhaus certified windows to build a Passivhaus?

Certification helps, but the building can meet Passivhaus with non‑certified windows if they truly achieve the required performance and the installation is correct.

Are triple glazed windows hard to live with?

They open, close and clean like modern double glazing. They are heavier, so good hardware and installation matter.

Will my home overheat with large south facing windows?

Use the right glass, external shading and summer ventilation. Passivhaus design tools help set safe window sizes and specs.

What about cost?

Passivhaus‑level windows cost more than standard units, but they can allow a smaller heating system and bring better comfort. Many clients see this as a long‑term value choice.