0.6 air changes per hour is the airtightness number that defines a Passive House. On an exposed Cornish coast, hitting it isn't about better products — it's about discipline at every junction the Atlantic is going to test.

Airtightness is the part of high-performance building that's easiest to claim and hardest to fake.

You can't see it. You can't add it at the end. And on an exposed site, the weather will find every weakness you left behind. Wind doesn't read the specification — it pushes on every seal, every junction, every penetration, looking for a way through.

That's why 0.6 ACH matters as a target, and why it's so much harder to reach on an Atlantic-facing elevation than on a sheltered inland plot. The number is the same. The difficulty isn't.

→ Passive House Builder Cornwall → Airtight Homes Builder Cornwall

CH stands for air changes per hour — how many times the entire volume of air inside a building leaks out and is replaced through gaps in the fabric over an hour.

The Passive House standard sets the limit at 0.6 air changes per hour at 50 pascals of pressure. That second part matters: the building is artificially pressurised to 50 pascals during the test, roughly the load of a stiff wind, so the result reflects worst-case conditions rather than a calm day.

To put it in context: a typical new build in the UK leaks at five to ten times that rate. Reaching 0.6 isn't a marginal improvement on standard construction — it's a different category of building entirely.

Lower numbers mean a tighter envelope, which means less heat lost to uncontrolled leakage, lower running costs, and a more comfortable, stable interior. The airtightness layer is what makes everything else — the insulation, the heat recovery ventilation — actually work.

Coastal and elevated sites in Cornwall present unique challenges when trying to achieve airtightness targets. Strong winds, salt exposure, and changing weather conditions can affect building performance.

Common challenges include:

• Increased wind pressure on the building envelope
• Higher risk of air leakage through junctions
• Exposure to moisture and salt-laden air
• Complex structural detailing requirements

Addressing these challenges requires careful design and construction planning.

Achieving 0.6 ACH requires a clearly defined airtightness strategy from the early design stages. This includes identifying the airtight layer and ensuring continuity throughout the building envelope.

Key considerations include:

• Continuous airtight layer design
• Minimising penetrations through the envelope
• Sealing all junctions and connections
• Using appropriate airtight membranes and tapes

Consistency in execution is essential to achieving the target performance.

Precise construction detailing is critical in maintaining airtightness. Junctions between walls, roofs, floors, and openings must be carefully designed and executed.

Attention to detail ensures that there are no gaps or weak points where air leakage can occur.

Blower door testing is used to measure airtightness and verify that the building meets the required performance standards. Testing is often carried out at multiple stages during construction.

This allows issues to be identified and resolved before completion.

Warvena Construction delivers high-performance residential projects across Cornwall, combining architectural design with advanced construction techniques.

You can explore our completed homes on our projects page.

• The Ark – A coastal residence demonstrating precision construction and environmental performance.
• Kenwyn – A residential project highlighting careful design coordination and building performance.

Achieving 0.6 ACH in exposed locations requires careful planning, precise construction, and ongoing quality control. By maintaining strict standards and attention to detail, builders can deliver homes that perform efficiently in even the most challenging environments.

If you are planning a high-performance home in Cornwall, visit our About page or contact us to discuss your project.