Mold & Moisture — Identify Causes and Renovate Properly
Why mold is a symptom, not a cause — and how proper renovation solves the problem permanently.
Mold Is Not Inevitable
Mold spots on walls, black corners in the bedroom, musty smell in the basement — many homeowners know the problem. The common reaction: mold spray, paint over it, ventilate more. But that only fights the symptoms.
Mold is always the result of a building physics problem. The cause lies in the building envelope, the ventilation situation, or a combination of both. Understanding the cause is the key to solving it permanently.
The Most Common Causes
Thermal Bridges
Points in the building envelope where heat flows outward faster: window reveals, exterior corners, roller shutter boxes, balcony connections. The surface cools down, moisture condenses.
Insufficient Ventilation
Too much moisture with too little air exchange. Especially critical after installing new windows: the building envelope becomes tighter, but moisture transport outward is reduced.
Leaky Building Envelope
Penetrating rainwater through damaged facade, leaking roof, or rising damp in the base area. Mainly affects older buildings without horizontal barriers.
Poorly Planned Insulation
Interior insulation without vapor barrier, external insulation systems with gaps, or insulation that ends at thermal bridges — all of this can trap moisture and promote mold.
Understanding Thermal Bridges
A thermal bridge is a point in the building envelope where thermal protection is weakened. Here, a disproportionate amount of heat flows outward, the interior surface cools down — and becomes a condensation point for humidity.
Typical thermal bridges in old buildings:
- •Window reveals — especially when windows sit flush in the exterior wall
- •Exterior room corners — two exterior walls meet, surface cools more
- •Roller shutter boxes — often uninsulated and directly connected to outside air
- •Radiator niches — thinner wall behind recessed radiators
- •Balcony connections — concrete slabs penetrate the insulation layer
- •Base area — transition from basement wall to exterior wall often uninsulated
The Dew Point: Why Physics Decides
Air can only hold a limited amount of moisture. The warmer the air, the more water it can hold. When humid air cools at a cold surface, it reaches the dew point — and water condenses.
💡 Example: At 20°C room temperature and 50% relative humidity, the dew point is 9.3°C. Any wall surface below 9.3°C gets wet — and provides optimal growth conditions for mold. The risk already begins at 12.6°C (80% relative surface humidity).
That's why it's so important that interior wall surfaces stay warm. This is achieved through good external insulation, elimination of thermal bridges, and sufficient heating.
Proper Renovation Instead of Treating Symptoms
Anti-mold paint, mold spray, or simply painting over it — these are not solutions. Mold returns as long as the cause persists. Permanent elimination requires structural measures:
Apply External Insulation
Increases interior wall surface temperatures and eliminates thermal bridges. The most effective single measure against condensation mold.
Target Thermal Bridges
Insulate window reveals, isolate roller shutter boxes, close radiator niches. Often targeted measures at critical points are sufficient.
Implement Ventilation Concept
After window replacement or insulation, air exchange must be ensured — ideally through mechanical ventilation with heat recovery.
Eliminate Moisture Sources
Seal leaky spots, retrofit horizontal barriers against rising damp, repair defective downpipes and gutters.
When Energy Consulting Helps
When mold keeps recurring or the cause is unclear, a professional analysis helps. As energy consultants, we use various diagnostic methods:
- ThermographyThermal imaging camera makes thermal bridges visible — inside and outside. Shows exactly where the weak points are.
- Blower Door TestMeasures the airtightness of the building. Reveals leaky spots where moist air enters the construction.
- Moisture MeasurementCapacitive and microwave instruments determine moisture content in walls, ceilings, and floors — non-destructively.
- U-Value CalculationCalculation of thermal transmittance shows how well or poorly individual building components insulate.
Prevention: How to Avoid Mold
Until renovation or in addition to it, these practical measures help:
Heat Properly
No room below 16°C — including bedrooms or rarely used rooms. Maintain even temperatures rather than letting them fluctuate.
Ventilate Properly
Burst ventilate 3–4 times daily for 5–10 minutes. Open windows wide rather than tilting. In winter, 5 minutes is enough — walls barely cool down.
Move Furniture from Exterior Walls
Leave at least 5–10 cm gap between large furniture and exterior walls. Otherwise, humid air accumulates behind cabinets.
Monitor Humidity
A hygrometer (from €10) shows relative humidity. Ideal: 40–60%. Above 65%, mold risk increases significantly.
Find the Cause of Mold and Solve It Permanently?
We analyze your building with thermography and moisture measurement and create a renovation concept that eliminates the cause — not just the symptoms.
Request analysis