Ground-Level Damp Ingress and Mould in a Converted Garage
The Problem
An occupier reported persistent mould growth and damp conditions within a ground-floor converted garage room. Despite repeated cleaning, mould returned within days, and during periods of wet weather there were instances of visible water pooling on the floor surface.
Due to the recurring nature of the issue and concern around the condition of the space, a full inspection was requested.
Our Investigation
Our inspection identified several critical factors contributing to the problem:
External ground levels were significantly higher than the internal floor level
The converted garage floor lacked an effective damp proof membrane (DPM)
The rear elevation of the conversion sat below surrounding garden ground levels
Existing floor finishes had trapped moisture beneath the surface
Ventilation within the converted space and bathroom was limited
These findings indicated that the issue extended beyond surface condensation and required structural intervention.
Diagnosis
The damp and mould were caused by ground moisture ingress combined with inadequate floor construction and insufficient ventilation. While the space may have performed adequately as a garage, the conversion to a habitable room without appropriate damp protection had created an environment prone to ongoing moisture problems.
Remedial Approach
Two approaches were discussed with the client:
A mitigation-based option, focusing on external drainage improvements and drying, with the understanding that results may be gradual and dependent on weather conditions
A full remedial solution, addressing the problem at source through floor reconstruction, improved drainage and ventilation
The client elected to proceed with the full remedial solution to ensure a robust, long-term outcome.
Works Undertaken
We delivered a fully managed, end-to-end remedial programme, including:
Reducing external ground levels around the affected elevation
Installing a drainage trench with membrane and gravel backfill
Removing the existing floor structure and drying the subfloor using dehumidification
Applying both liquid and sheet damp proof membranes
Constructing a new insulated floating floor with PIR insulation and moisture-resistant floorboards
Installing new floor finishes and adjusting doorways and thresholds
Repairing and repointing external brickwork around window openings
Replacing defective rainwater goods to improve water management
Installing passive ventilation to the converted space
Installing a new inline extractor to the bathroom, vented externally
Treating mould-affected areas and redecorating where required
Managing the temporary removal, storage and reinstatement of the occupier’s belongings
All works were documented photographically throughout the process.
The Outcome
The remedial works successfully resolved the damp and mould issues by addressing the underlying causes. The space was returned to full use, with improved moisture control, ventilation and long-term resilience against future damp problems.
The occupiers confirmed they were satisfied with the completed works and the overall outcome.
Key Takeaway
This project demonstrates the importance of addressing the root cause of damp rather than relying on surface-level treatments. By combining external drainage improvements, correct floor construction and ventilation, a long-term solution was achieved.