
The Physics of Fresh Air: Natural Ventilation Still Works in 2025 - Ben Jones #115
Air Quality MattersShow Notes
This week, we sit down with Ben Jones, Associate Professor at the University of Nottingham and one of the lead authors of AM10, CIBSE's guide to natural ventilation in non-domestic buildings, to explore a question that fundamentally challenges how we think about ventilation strategy: What if the oldest approach to ventilation—natural airflow—still has a critical role to play in some of the most advanced buildings we're designing today, and what if we've been making the same mistakes for decades because we never really understood the fundamentals?
After a decade in development, AM10 has been completely rewritten for 2026—not just to update the maths, but to make natural ventilation accessible, understandable, and practical for everyone from salespeople to architects to engineers who need to know whether natural ventilation is even feasible for their project before they waste time and money chasing the wrong solution.
Key Topics Discussed:
Why AM10 Needed Rewriting: The 2005 version was intimidating, dense, and assumed too much prior knowledge. The 2026 version is structured in layers—chapter two is designed so that anyone, from a student to a salesperson, can understand the basic physics. If you want the deep maths, it's there. If you just need to know whether natural ventilation will work for your building, you can get that answer quickly.
The Physics Made Simple: Warm air rises. Pressure differences drive flow. Wind complicates everything. But somewhere on every facade, there's a neutral pressure level where the sign flips—where air stops coming in and starts going out. Controlling that point is the essence of natural ventilation design. Get it wrong, and your building doesn't breathe.
Effective Area vs Free Area: One of the biggest changes in AM10 is how openings are measured. Combining free area with discharge coefficients into a single effective area metric forces window manufacturers to actually test their products aerodynamically and gives engineers a real number they can design with. No more fudging the geometry.
Single-Sided Ventilation Gets Smarter: The old equations were too simplistic. The new version accounts for recirculation zones in large openings—where air comes in at the bottom, goes out at the top, and mixes in the middle. It accounts for wind-driven turbulent mixing. The result: better-sized openings that won't leave buildings overheating in summer
GUEST:
Ben Jones
Associate Professor, University of Nottingham | Lead Author, CIBSE AM10
https://www.linkedin.com/in/benjamin-jones-0686a214/
CIBSE AM10: Natural Ventilation in Non-Domestic Buildings
The Air Quality Matters Podcast in Partnership with
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Lindab (https://www.lindab.ie/) - Eurovent (https://www.eurovent.eu/) - Aico (https://www.aico.co.uk/)
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Chapters
00:00:00 Introduction: The Return of Air Quality Matters 00:02:14 The Genesis of AM10: A 20-Year Evolution 00:06:03 From PhD to Practice: Ben's Natural Ventilation Journey 00:08:34 The Philosophy Behind AM10: Making Physics Accessible 00:10:14 Why Ventilate: Sizing for Summer, Surviving Winter 00:11:19 The Physics of Buoyancy: When Hot Air Actually Rises 00:13:09 When Design Meets Reality: The Complexity Challenge 00:14:41 The Feasibility Question: Is Natural Ventilation Right for Your Building? 00:15:48 The Neutral Pressure Level: Where Physics Flips Sign 00:16:50
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