ARCHITECTURE & CONSTRUCTION Technical solutions for interior insulation without humidity or mold
Key Points
- • Heating savings: 25 to 50% with well-executed interior insulation
- • Costs: €20 to €90/m² compared to €150/m² for exterior insulation
- • Return on investment: 4 to 8 years with public subsidies
- • Success condition: absolute control of humidity and condensation
Interior wall insulation represents an economical solution for improving a home's thermal performance, with costs of €20 to €90/m² compared to €150/m² for exterior insulation. However, its success depends entirely on controlling humidity and preventing condensation, which can quickly turn an energy renovation into a health disaster.
Five available interior insulation techniques
Adhesive-bonded lining
The most economical solution. Composite panels combining insulation and plasterboard, bonded directly to the wall.
- • Cost: €20-35/m² including installation
- • Performance: R = 2.95 to 4.50 m².K/W
- • Requires flat surface (2 cm tolerance)
Metal frame system
More technical flexibility, allows correction of significant unevenness.
- • Cost: €35-55/m²
- • Thickness: 60 to 200 mm
- • Elimination of thermal bridges
Sprayed polyurethane foam
Premium solution for complex surfaces. Expanding foam with exceptional performance.
- • Cost: €40-60/m²
- • Performance: R = 4.50 m².K/W for 100 mm
- • Perfect continuity and optimal sealing
Masonry counter-wall
Most effective but expensive solution. Secondary wall with intercalated insulation.
- • Cost: €60-90/m²
- • Excellent thermal inertia
- • Reduces living space
⚠️ Beware of thin reflective insulation
Often presented as revolutionary, they remain supplementary solutions with low intrinsic thermal resistance (R = 0.1 to 1.0 m².K/W). Their effectiveness depends on still air layers, which complicates their implementation.
Diagnosis and preparation: crucial steps
🔍 Mandatory thorough diagnosis
A complete diagnosis costs €500 to €1,500 but avoids errors that can generate claims of €20,000 or more.
- • Assessment of existing building (composition, thickness, condition)
- • Identification of moisture sources
- • Measurement of current thermal performance
- • Dew point calculation with hygrothermal simulation
Checklist for flawless insulation
1. Surface preparation
- • Treatment of existing pathologies
- • Drying of damp walls
- • Moisture content < 5% before installation
- • Drying time up to 6 months
2. Implementation
- • Continuous installation without compression
- • Perfectly adjusted joints
- • PU foam to improve sealing
- • Insulation returns of 30 cm minimum
3. Sealing
- • Continuous membrane without folds
- • Overlaps of 10 cm minimum
- • Dedicated accessories for penetrations
- • Intermediate airtightness test
Ventilation adaptation
Ventilation adaptation to new requirements follows directly from the diagnosis. An old house naturally ventilated will require the installation of an efficient CMV system after insulation.
Old house
Installation of efficient CMV necessary
Recent housing
Optimization of existing system possible
Conclusion
Efficient and durable interior insulation rests on three inseparable pillars: choosing materials adapted to the existing substrate, rigorous implementation following best practices, and effective ventilation to evacuate produced humidity.
Benefits
- • Energy savings: 25-50%
- • Improved comfort
- • Property value increase
- • ROI: 4-8 years with public subsidies
Success conditions
- • Compliance with DTU standards
- • Adaptation to specificities
- • Control of hygrothermal transfers
- • Strict adherence to recommendations