Construction defect · Defects & construction flaws
Insulation defects: thermal bridges, mineral wool settling in new-builds
Severity Moderate
Reporting deadline 90 days
Warranty Two-year + ten-year
Responsibility Contractor
How to detect an insulation defect?
Compliant insulation is verified through the EPC certificate issued at reception, on plans (thicknesses, lambda values, U-values), and on site (thermal camera in winter). Recurring defects: settled glass wool in attics (loses 30% of R), thermal bridge at wall/slab/roof junction, continuity defect (missing wool at corner, poorly jointed polyurethane panel), torn vapour barrier, ETICS installed on damp substrate. Run a blower-door test on recommendation: the n50 value must be below 6 vol/h in standard, below 0.6 in passive. Beyond that, reportable defect.
Before — compliant
continuous ETICS · no thermal bridge
EPC A · n50 < 1.5 · homogeneous thermal camera
⚠ After — defective
settled attic wool · visible thermal bridge
EPC B instead of A · to be regularised under warranty
Reporting procedure in 4 steps
Failed insulation can be invisible to the naked eye. Thermal camera and blower door are essential to prove the defect.
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1
Check the EPC certificate
The EPC certificate issued at reception details calculated performance. Keep it. Check actual insulation thicknesses in accessible spots (attics).
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2
Winter thermal camera
Use at outside temperature < 5 °C and inside/outside difference > 10 °C. Photograph abnormal cold zones (thermal bridges) with location.
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3
Blower door (air tightness)
Test recommended for air tightness. 50 Pa depression, leakage flow measurement. Cost €380-550. Covered by two-year warranty if EPC calculation not met.
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4
Formal notice
Registered letter to the contractor within 90 days of discovery. Attach thermal camera photos, blower-door report, comparison with EPC certificate.
Who pays for compliance? Responsibility table
The main contractor is responsible for compliance with the calculated EPC. Subcontractors are jointly liable.
Settled attic wool
✓ two-year warranty
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Major thermal bridge
✓ ten-year liability
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Torn vapour barrier
✓ two-year warranty
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Calculated EPC not achieved
✓ two-year warranty
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Overconsumption (usage mode)
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✓
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Get an inspection
Independent thermal camera + air-tightness audit
Admissible report · from €480 VAT incl. (audit + blower door)
FAQ
Common questions about insulation
My calculated EPC is A but I consume like a C. Abnormal?+
Yes, reportable. A gap of more than one EPC letter between calculated and actual suggests an execution defect (wool settling, thermal bridge, continuity failure). Run an audit with thermal camera to identify.
The blown-in wool in my attic is 35 cm thick instead of the 45 cm planned. What should I do?+
Reportable thickness defect. Demand a top-up by extra blowing under the two-year warranty. Keep photos with a visible rigid ruler and the manufacturer's delivery note.
How much does a thermal camera audit cost?+
Between €280 and €480 VAT incl. for a standard home. With blower door (air tightness): between €480 and €750 VAT incl. Cost recoverable if defect confirmed.
Can a thermal bridge cause condensation?+
Yes, frequently. The colder surface condenses ambient moisture. Over time: mould, paint deterioration, sanitary problems. Ten-year defect (unfitness for purpose).
Is the blower-door test mandatory in Wallonia?+
Mandatory in Wallonia for NEW builds since 2015 (EPC). In Brussels, mandatory for passive. Demand the blower-door report at reception. Absence = reportable defect.