At Bradley Van Der Straeten Architects, we believe the best homes aren’t just beautiful — they’re comfortable, healthy, and built to stand the test of time. That’s why we design using natural, low-energy principles that go beyond insulation and double glazing. In this post, we explain three key ingredients we integrate into our projects: airtightness, breathability, and thermal mass.

Airtightness: Locking In Comfort, Not Air

It’s a common misconception that airtight homes are stuffy or sealed shut. In fact, airtightness is one of the most important parts of making a home energy efficient and comfortable — especially if you’re investing in improved insulation and low-carbon heating.

Warm air can escape through the smallest gaps and cracks. Without good airtightness, up to 40% of a building’s heat can leak out — a huge waste of energy and money. This is one of the main reasons behind the so-called “performance gap”, where a home’s real-world energy use doesn’t live up to predictions.

We design to minimise uncontrolled air leakage while ensuring your home still has plenty of fresh air, delivered through carefully considered, controlled ventilation. That’s how we create homes that are warm in winter, cool in summer, and feel great to live in.

Breathability: A Natural Approach to Moisture Control

Airtightness and breathability go hand in hand. While airtightness controls air movement, breathability is all about moisture — and it’s particularly important in older buildings or retrofit projects.

Traditional homes were built using breathable materials like lime plaster and solid masonry, which allowed moisture to move through the fabric and evaporate naturally. This helped prevent condensation and mould.

Modern materials like cement render, vinyl paints, and gypsum plaster are far less forgiving — they trap moisture inside walls, which can lead to mould, poor air quality, and damage to the building fabric over time.

That’s why we recommend using breathable, natural materials wherever possible. Not only do they help regulate internal humidity and improve occupant health, but they also protect the building for the long term.

Thermal Mass and Overheating: Designing for a Changing Climate

With better insulation and warmer summers, overheating is becoming one of the biggest risks in modern homes — especially in loft conversions or homes with large roof areas.

Standard foam-based insulations may perform well on paper, but they have very little ability to absorb and slow down heat. That means once heat gets in, it quickly builds up inside.

We prefer to use natural insulation materials like wood fibre or cork, which have a higher thermal mass. This allows them to delay internal heat build-up, helping homes stay cooler for longer — particularly important during summer heatwaves. These materials also tend to have lower embodied carbon and are naturally breathable, making them an all-round better choice.

Future-Proofing Your Home with Intelligent Design

Every home is different. But whether we’re transforming a Victorian terrace or building from the ground up, we always design with a deep understanding of how homes actually perform — not just how they should perform on paper.

If you’re planning a renovation and want a home that looks amazing, works naturally, and feels as good as it looks, we’d love to hear from you.

Get in touch to talk about how we can help bring your vision to life. contact us by clicking here.