Dampness is one of the most common complaints in buildings — butNot all humidity is a hidden defect, And Not every technical report is useful in court.
The difference between a successful claim and a dismissal is:
✅ Thehidden natureof the defect (Art. 1,591 CC),
✅ Thecausal relationship with the work or its materials,
✅ And, above all, inhow it is expertly demonstrated.
As an Official Judicial Expert in construction with more than 30 years of experience in building pathologies, I explain what the courts require — and how to structure an opinion that stands up to contrast.
1. What does the law say? The hidden defect in humidity
The Art. 1,591 of the Civil Codeestablishes that the seller is responsible for thehidden viceslet them do the thingunfit for use or decrease their valuesubstantially —as long as they are not easily detectable.
⚠️Eye:
- Visible moisture (stains, mold on surface)It is not “hidden”.
- But oneleak in embedded pipeA defective vapor barrier or one waterproofing absent under slab Yes they are— even if its effects appear years later.
STS 345/2023 (May 17):
"Moisture due to the absence of a waterproofing layer on a flat roof, not visible without demolition, constitutes a hidden defect. The period of 6 months begins from its discovery through technical inspection."
STS 112/2022 (February 3):
"The presence of chlorides in reinforced concrete, without external manifestation at the time of delivery, is a hidden defect. Its detection requires non-destructive testing (corrosion potential, chlorimetry)."
Legal conclusion:
It is not the humidity that is judged, but rather its origin and its technical concealment.
2. Forensic expertise: how to demonstrate it so that a judge will admit it
A technical reportIt is not an expert opinion. to haveprocedural validity(Art. 335.2 LEC), must comply:
| Origin identification | “Capillary humidity” is not enough. It must be:“absence of anti-humidity barrier on the perimeter wall (DB-HS-1 not met), with rising humidity measured >8% in a witness taken 30 cm from the slab” | Generic reports without exact physical location |
| Relationship with the work | Compare with executive plans, work book and technical specifications. Ex:“The plans show SBS membrane, but endoscopy inspection (photo #7) does not detect any waterproofing layer” | Do not contrast with contractual documentation |
| forensic method | Numbered photography, chain of custody sampling, non-destructive testing (thermography, resistance hygrometer, endoscopy) | Only photos without georeference or verifiable date |
| Concealment criterion | Show that the defectwas not detectable by a diligent buyerupon delivery (e.g. wall behind false ceiling, pipe under floor) | Assume that “everyone sees humidity” |
Key tools in my practice:
- Infrared thermography + surface/subsurface thermohygrometry
- Endoscopy in walls and slabs
- Analysis of salts (nitrates, chlorides, sulfates) to differentiate origin
- Correlation with maintenance history (were there leaks reported before the sale?)
3. Real case (anonymous, with real technical data)
Situation: Community of 12 homes. Dampness in ground floor baseboards since 2021. The builder alleged “condensation due to misuse.”
Expert opinion:
- Thermography: thermal differences >3.5 °C at 1.2 m height → rules out condensation.
- Plinth endoscopy: absence of anti-moisture layer (DB-HS-1 requires 2 layers in contact with ground).
- Capillary absorption test: 12.4 kg/m²·h (regulatory limit: 0.5).
- Work book: membrane certification does not appear.
Result: Favorable ruling. It condemns the developer to carry out perimeter drainage + chemical barrier + restoration.Repair cost: €186,000.
Scan this situation in 3 minutes:
- Did the humidity appearafter delivery/sale?
- Do you requiredemolition or non-visual techniquesto locate the origin?
- There istechnical documentation(plans, work book) that does not match what was executed?
→ If you answerYES to 2 or more, you probably have a hidden defect with a legal basis.
Write me a WhatsApp at 662 221 582or send photos and plans toclients@aureliotamarit.es.
I will tell you without obligation if the case has expert and judicial feasibility.
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