Understanding moisture conditions in warm roofs during summer

Understanding moisture conditions in warm roofs is essential for maintaining the longevity and performance of your building. During the summer, high temperatures and humidity can cause moisture to migrate, leading to condensation that may be mistaken for leaks. In this blog, we explore how Tector’s moisture monitoring system helps you accurately assess and manage these conditions, ensuring your roof remains in optimal condition year-round.

Why Moisture Monitoring Matters

In a warm roof setup, maintaining low moisture levels is essential. When insulation becomes too wet, it loses its effectiveness and increases the risk of condensation. Even small imperfections in the vapour barrier or roof structure can allow moisture to migrate and settle at the bottom of the roof, leading to issues that could be mistaken for active leaks.

Understanding these dynamics is key to making informed decisions — especially during the summer when moisture behaviour changes significantly.

How Summer Conditions Influence Moisture

Moisture Migration

During summer, solar radiation can heat the surface of a roof up to 70°C. This intense heat drives moisture downwards towards the cooler bottom layers. Between June and August, condensation at the base of warm roofs can become particularly pronounced, with relative humidity levels nearing 100%.

Roofs already carrying higher levels of built-in moisture are especially vulnerable. Condensation can appear more severe, increasing the risk of misdiagnosing the situation as an active leak.

Built-In Moisture: A Hidden Risk

Built-in moisture refers to moisture trapped in the roof during or after construction — and it’s a stable condition, unlike an ongoing leak. Common causes include:

• Delayed Leak Response: Water damage isn't addressed quickly, allowing moisture to saturate the insulation.
  
  
• Partial Insulation Replacement: Only the visibly damaged insulation is replaced, leaving hidden wet areas.
  
  
• Poor Night Sealing: Water enters during construction phases and gets trapped when the roof is sealed.
  
  
• Ingress During Installation: Weather exposure during build-up phases introduces moisture into the roof.
  
  

Tector’s system uses a moisture-sensitive element embedded within the roof structure to track moisture levels. In summer, it absorbs moisture from the surrounding insulation, resulting in naturally higher readings that remain until conditions shift.

It's important to note: built-in moisture is not the same as a leak. While leaks continue to allow water ingress, built-in moisture is stable.

What Tector’s Data Tells Us

Across thousands of sensors installed in flat roofs, Tector has identified clear patterns:

• The 10% wettest roofs in Denmark consistently show moisture readings above 40% WMC (Wood Moisture Content) each summer. That also means that 90% of roofs are below 40% and only minor increases should be seen on the majority of sensors.
  
  
• High solar radiation and low rainfall create ideal conditions for moisture migration within roof structures, as seen in Tector’s long-term data since 2022.
  
  

Additionally, in controlled environments, Tector monitors two roofs:

• One with 0.01% built-in moisture.
  
  
• Another with 0.93% built-in moisture.
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The 0.93% roof currently shows sensor values around the median of all roofs measured — a strong indicator that many real-world roofs are carrying higher built-in moisture levels than recommended.

(Note: These detailed calibration results are internal and not published externally.)

How to Accurately Assess Roof Moisture with Tector

Tector’s risk score system simplifies complex moisture data, helping you act faster and smarter:

• Risk score 0–1: No action needed. Moisture levels are stable, with no signs of leaks or problematic summer condensation.
  
  
• Risk score 2–3: Moderate risk. Elevated moisture levels detected. The system will highlight if summer condensation is a likely cause, based on nearby sensors and weather conditions. It's a good time to inspect the area, especially on new roofs.
  
  
• Risk score above 4: Immediate attention required. The presence of liquid water is highly likely, and you will receive an alert recommending action to prevent further ingress.
  
  

By combining Tector's risk scores, raw data, and roof analysis, you get a complete picture — helping you distinguish between harmless seasonal behaviour and real problems that need intervention.