If you're building a new home, you need to know about condensation. Left unmanaged, it leads to mould and structural damage. This guide explains condensation in simple terms, what causes it, and what to check on your build.

What is Condensation?

Condensation happens when warm, moist air touches a cold surface and the moisture in the air turns into water droplets. You've seen it on windows in winter. The same thing can happen inside walls, ceilings, roofs and floors, where you can't see it.

Causes of Condensation

Condensation depends on the outdoor climate, how much moisture you generate inside, and ventilation:

  • Outdoor climate: In colder climates, warm indoor air meets cold walls and windows. In hot, humid climates like Queensland, it often works the other way: humid outdoor air reaches the cold side of an air-conditioned room, so condensation forms inside walls and roofs behind the plasterboard.
  • Indoor Moisture Generation: Cooking, bathing, and drying clothes release moisture. Without proper ventilation, this excess moisture can contribute to condensation.

Ventilation removes that excess moisture, which matters most in bathrooms, laundries and kitchens.

Methods to Reduce Condensation

Here are practical ways to reduce condensation in your new home:

Proper insulation: Insulating walls, ceilings and floors keeps internal surfaces warmer (or, in Queensland summers, keeps the cold inside), which reduces the cold spots where condensation forms. Get the insulation and wall wrap specified together, not separately.

Ventilation Strategies: Good ventilation is critical to reducing condensation. Here are a few strategies you can use:

  • Use exhaust fans: Install exhaust fans in bathrooms, kitchens and laundries, ducted to outside. They remove humid air before it spreads through the house.
  • Open windows when the weather permits to let fresh air circulate and bring humidity down.
  • Use Dehumidifiers: Dehumidifiers can help control moisture levels, especially in areas with high humidity.
  • Use heating and cooling sensibly: Keeping a consistent temperature helps. Some tips:
  • Avoid overcooling: In warmer months, avoid pre-chilling an empty home. Set the air conditioner to a comfortable temperature instead.
  • Seek Informed Advice: When choosing an air conditioning system, consult professionals who can help you select a system that can effectively control both temperature and humidity.

The Building Envelope's Four Control Functions

To avoid excessive relative humidity (RH) and condensation, the building envelope (walls, roof and floor) needs four control functions:

Thermal insulation: Keeps internal surfaces closer to room temperature so moisture doesn't condense on them.

Vapour retarders: Vapour retarders slow water vapour diffusing through materials. Placed on the wrong side of the wall in a hot, humid climate like Queensland, they can trap moisture, so follow your designer's condensation advice.

Air barriers: Air barriers stop moisture-laden air leaking into the wall and roof cavities, where it can condense. They also improve energy efficiency.

Ventilation: Removes excess moisture from inside the home. Balanced ventilation with heat recovery suits colder climates, where it brings in fresh air without losing heat.

What the NCC Requires

NCC 2022 added condensation management provisions for new homes (ABCB Housing Provisions Part 10.8). Exhaust from kitchens, bathrooms and laundries must discharge to outside, not into the roof space. There are also rules for pliable building membranes (wall wraps) and roof-space ventilation, which mainly apply in cooler climate zones. For Queensland homes, the biggest checks are exhaust fans ducted outside and a wall system designed for humid conditions.

Strategies to Reduce Condensation Risk During Construction

During construction, these steps reduce the risk of moisture problems:

  • Controlling moisture sources: Seal plumbing fixtures, use moisture-resistant materials, and use temporary ventilation to help remove moisture during construction.
  • Monitoring Indoor Humidity: Regular monitoring of indoor humidity levels can provide valuable insights into potential condensation issues. If elevated humidity levels are detected, prompt action can be taken to mitigate the risk.
  • Proper Ventilation: Temporary ventilation systems, such as portable fans or dehumidifiers, can maintain adequate air circulation and control moisture levels during construction.
  • Building Envelope Design: Optimising the design of the building envelope, including insulation, vapour retarders, and air barriers, can significantly reduce the likelihood of condensation issues.

Conclusion

Condensation is influenced by many factors, but it can be managed with the right envelope design, ventilation and construction practices.

Ask your builder how the insulation, wall wrap and ventilation work together on your home, and check exhaust fans are ducted outside at the enclosed and fixing stages.

References

Further Reading

A Guide to Managing Home Condensation in AustraliaExplore the concept of managing condensation in Australian homes. Understand the challenges, implications, and effective strategies for maintaining a healthy, energy-efficient living environment.Why a Condensation Risk Analysis is Crucial to Home HealthWondering why some new homes develop damp or mould issues? The culprit is often avoidable condensation. This article delves into why every builder should conduct a Condensation Risk Analysis to ensure the home’s longevity and efficiency.Why Rainscreens are Essential for New HomesDiscover the crucial role of rainscreens in new home construction. This exterior cladding system not only wards off rot, mold, and water damage but also boosts energy efficiency. Despite the upfront cost, the long-term benefits make it an essential investment. Learn why you can’t afford to skip it.Optimizing the 4 Control Layers for High-Performance HomesBuilding an energy-efficient home requires a deep understanding of the four control layers: water, air, vapour, and thermal. This guide delves into how project builders optimize these layers, ensuring homes are comfortable, sustainable, and cost-effective.