Condensation & ventilation failure

The problem

Condensation and ventilation failure drive mould growth, timber decay and building-related health complaints. Causation often involves retrofit insulation, changed occupancy patterns or mechanical ventilation system failure.

Since the push for energy efficiency and retrofit insulation, condensation problems have become epidemic. Airtightness improvements without adequate ventilation create environments where relative humidity exceeds safe limits. Mould growth follows. Landlord-tenant disputes frequently turn on whether condensation is caused by a building defect (the landlord's responsibility) or occupant behaviour (lifestyle condensation). Without quantified environmental data, this question cannot be answered defensively.

The risk

Disputes turn on whether condensation or construction defect is the primary cause. Ventilation performance, air exchange rates and dew point conditions must be quantified — not estimated.

In Housing Act disrepair claims, landlords face significant liability if condensation is attributable to inadequate ventilation provision. Conversely, tenants may be responsible if ventilation is adequate but unused. Our forensic approach quantifies ventilation performance and environmental loading to answer this question with data.

Our investigation

We deploy CO₂ and humidity data loggers, measure air exchange rates, conduct psychrometric analysis and model dew point conditions. We assess mechanical ventilation system performance where installed.

1. CO₂ monitoring to quantify actual ventilation rates and occupancy patterns
2. Temperature and relative humidity data logging over 7–28 days
3. Dew point modelling across wall, window and ceiling surfaces
4. Mechanical ventilation system assessment (MVHR, extract fans, trickle vents)
5. Building fabric assessment for thermal bridging and insulation defects
6. FLIR thermal imaging to identify cold bridges and condensation risk zones
7. Psychrometric analysis and air exchange rate calculation

Findings

Environmental loading, ventilation shortfalls and condensation risk are quantified with recorded data. Dew point modelling identifies which surfaces are at risk and under what conditions. Causation is attributed with confidence.

Who commissions this investigation?

Frequently asked questions

What causes condensation in a well-insulated home?

Insulation reduces heat loss but also reduces air exchange if not paired with adequate ventilation. Moisture from cooking, bathing and breathing accumulates, relative humidity rises, and condensation forms on cold surfaces — typically windows, external wall corners and behind furniture.

Can you prove whether condensation is the landlord's or tenant's fault?

We quantify ventilation performance, environmental conditions and building fabric performance. If ventilation provision is inadequate or the building has thermal defects, the cause is attributable to the building. If ventilation is adequate and conditions are driven by occupancy, the data shows that too.

How long do data loggers need to be in place?

Typically 7–14 days for a clear picture. In some cases, 28 days captures a wider range of weather conditions and occupancy patterns. Loggers record continuously and are non-invasive.

Related investigations

• Damp & moisture forensics
• Indoor air quality & health investigation
• Insurance & dispute reports