What happened

A new bathroom in a loft conversion had its mechanical extract fan ducted to the loft void rather than to an external grille.

How it was discovered

Condensation on roof timbers within months. Independent inspection traced the duct.

The consequences

Duct extended to external grille, condensation treated, timbers monitored. Modest cost, but discovered before timber damage.

What homeowners can learn

Mechanical ventilation needs to terminate outside. 'Into the loft' is never a compliant solution.