Vapour control in facades

How Moisture Really Gets into Façade Walls, and Why Polythene Is No Longer a Safe Default

About This CPD

This technical CPD looks at the most misunderstood form of moisture in the building envelope: water vapour. Most condensation problems are not caused by vapour diffusing through materials, but by humid air leaking through gaps no wider than a millimetre, and this session explains why that changes how walls should be designed, detailed and built.

Presented by Eugene Korch (IAST) in conversation with John Straube, building scientist at RDH Building Science and the University of Waterloo, and author, with Eric Burnett, of Building Science for Building Enclosures, this CPD takes the familiar UK steel stud wall and the brick-faced precast façade and asks what really happens to moisture inside them, now that summers are hotter and more buildings are air conditioned.

This session covers:

  • Why the textbook teaches heat, then vapour, then rain, and why the precision of our calculations runs opposite to their real-world impact

  • The two ways vapour moves, diffusion and air leakage, and why air leakage delivers most of the moisture behind condensation problems

  • Where condensation actually does damage, and why a wet brick outer leaf is not a problem while wet paper-faced gypsum is

  • Sun on wet brick and fibre cement, and what happens to the traditional UK stud wall once the building is air conditioned

  • The history of polythene, and why it only ever worked because it stopped air

  • Breather membranes, and why air, water and vapour control layers need different joint rules

  • Brick-faced precast concrete walls, hidden mould, and how to find it without opening the wall

  • What to use instead of polythene, from continuous airtightness to smart vapour control membranes and warm-side insulation

Drawing on decades of forensic investigations and clear visuals, this CPD answers a question every façade designer should be able to face: where is the moisture in this wall really coming from, and can the wall dry out again?

Target Audience

This session is designed for anyone who designs, specifies, builds or investigates external walls on residential, commercial and mixed-use buildings, and especially for those working with steel stud backing walls and brick-faced precast concrete.

This Short Course is designed for:

  • Architects

  • Architectural Technologists

  • Envelope Designers

  • Façade Engineers

  • Façade Specialist Contractors

  • Building Envelope Consultants

  • Building Physics and Sustainability Consultants

  • Precast Concrete Specialists

  • Building Control Professionals

  • Project Managers

  • Design Managers

Speakers

Eugene Korch

Programme Director, IAST

Eugene is a façade engineer and educator who leads educational initiatives through the Institute for Architectural Science and Technology (IAST) and Facade Intelligence, delivering training to construction professionals.

Principal, RDH Building Science; Associate Professor, University of Waterloo

John Straube

John is a building scientist, a principal at RDH Building Science and an associate professor at the University of Waterloo. He wrote the textbook Building Science for Building Enclosures with Eric Burnett and is an internationally recognised expert in moisture-related durability of building enclosures.

Course Objectives

By the end of this CPD course, learners are expected to be able to:

  • Explain the difference between vapour diffusion and air leakage, and why air leakage carries far more moisture

  • Recognise why a vapour control layer does not stop air unless it is continuous and its joints are sealed

  • Identify the two conditions condensation needs to cause damage: a cold enough surface and a vulnerable material

  • Explain how sun on wet absorbent cladding drives vapour inward, and why air conditioning makes the inner layers of a wall the cold surface

  • Describe the risks of the traditional UK steel stud wall with polythene, including stud corrosion and timber decay

  • Distinguish the air, water and vapour functions of a membrane, and see why “breather membrane” is a misleading name

  • Recognise why brick-faced precast with mineral wool and polythene traps moisture, and the early signs of hidden mould

  • Evaluate alternatives to polythene, including smart vapour control membranes and warm-side insulation

  • Understand why a one-dimensional model can show a wall as safe when real air leakage makes it fail

Course Details

  • Format: On-demand CPD, the interview with supporting visuals and an interactive 3D detail of a precast concrete façade

  • Duration: Approximately 45 minutes of video

  • CPD Points: 1 hour structured CPD / 1 Learning UnitCertificate: CPD certificate issued on passing the multiple-choice test

  • Recording: Available on demand on the IAST learning platform

C032

Vapour control in facades

Free for IAST FI PRO Members.

TAKE THE COURSE
BECOME A MEMBER

Pricing Options

Take advantage of exclusive savings with IAST Corporate Membership. If you are booking multiple places or using your IAST Corporate Member discount, please email corporate@iast.uk with the number of places required, your IAST Membership number (if applicable), and company details for invoicing. Alternatively, complete our group reservation form below. We aim to provide quotations within two working days after receiving the form.

Interested in becoming an IAST Corporate Member? Access exclusive discounts and benefits—visit our Membership Page to apply today.

Enhance your expertise with a Façade Intelligence Professional (FI Pro) subscription. Subscribe now at facadeintelligence.com. If you are already an FI Pro member and would like to use your discount, simply email our team at info@iast.uk to claim your benefits.