Steel Framing and Condensation: A Balancing Act for Building Designers
January 24, 2024 By Anthony Broatch
Introduction
Attention, Architects, Builders and design specialists! Let's talk steel framing and it’s not-so-secret nemesis: condensation. This dynamic duo can spell big trouble for building longevity and occupant comfort. But fear not! With the right knowledge and design strategies, we can transform steel from a condensation culprit to a champion of structural integrity and healthy living.
Why Steel and Condensation Tango?
Steel's high thermal conductivity acts like a highway for cold, readily transferring cold, from the cooler exterior, to inside building constructions (walls, roofs, floors) and the warm and humid interior of a house. This temperature drop can cause water vapor to condense, leading to:
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Corrosion: Steel, unlike its timber counterpart, doesn't play nice with moisture. Rust weakens structural elements, compromising building safety.
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Mold and mildew: These unwelcome guests thrive in damp environments, posing health risks and reducing indoor air quality.
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Material degradation: Insulation loses its R-value when wet, impacting energy efficiency and comfort.
Interstitial Condensation: Steel vs. Timber
The battleground for condensation often lies within the wall cavity, known as interstitial condensation. Here's how steel and timber differ:
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Steel: Offers little to no moisture buffering capacity. Once condensation forms, it lingers, wreaking havoc.
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Timber: Can absorb and release moisture, acting as a natural buffer. However, excessive moisture can still lead to rot and mold growth.
Building Design Hacks for a Condensation-Free Future
Now, let's equip ourselves with the tools to outsmart condensation:
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Vapor barriers/control layers: These smart membranes installed on the warm side of the wall cavity prevent moisture from reaching the steel frame. Choose the right type and install it flawlessly for optimal effectiveness. This type of construction is covered in the BRANZ ER70 PHINZ High-performance construction details handbook (2022) and a detail provided below covering the four main control layers in a building’s enclosure.
Figure 1: Four main control layers in a building’s enclosure (Figure 5 in the handbook).
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Mechanical Ventilation
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Exhaust: Removing humid air is crucial. Strategically placed mechanical vents allow moisture to escape, preventing build-up. Think exhaust fans in kitchens and bathrooms and continuous whole-house ventilation systems.
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Outdoor Air Supply: In winter the cold air outside can only hold low amounts of moisture, therefore when heated inside the air becomes dry. Introducing dry air in winter also helps reduce internal humidity lowering the risk of condensation. Think continuous whole-house ventilation systems.
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These systems become even more critical when high-performance construction such as the above are not used as warm and humid air from the interior of a house can enter the wall cavity and condense on the cold structure.
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Façade Ventilation: Unobstructed ventilated cavities in walls and roof spaces are critical to allow moisture to escape from building systems.
Figure 2: Façade ventilation example.
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Thermal breaks: Provide thermal breaks between cold external surfaces and steel framing that joins to any area containing warm humid air.
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Insulation: The right insulation type and thickness play a vital role. Choose materials with good moisture resistance and ensure proper installation to avoid thermal bridges, which concentrate cold spots and promote condensation.
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Airtightness: Sealing air leaks is key. Gaps around windows, doors, and service penetrations can allow moisture-laden air to infiltrate the wall cavity.
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Building orientation and shading: Consider the sun's impact. Strategically designed buildings can help keep houses warm, but not too warm, allowing them to dry out quicker.
The tips above won’t guarantee the condensation risk will completely be resolved however they will reduce the risk as the risk depends on the design, the location, and usage.
So if you want to be more certain that your home won’t be leaky, at Reshape Consulting we offer Condensation Risk reports that include us simulating different design scenarios, predict potential moisture problems and optimize your strategies before breaking ground.
Conclusion
Remember, steel framing can be a fantastic choice for your next project. By understanding the condensation risks and implementing these smart design principles, you can create buildings that are both structurally sound and delightfully dry.
