Bathroom Ventilation

Every shower is a litre-class humidity event in the house's smallest room — and bathroom ventilation is mould prevention, paint preservation and respiratory housekeeping in one switch.

The wet room, dried properly.

The Moisture Event

The physics: hot showers vaporise water that condenses on every cool surface — mirrors announce what walls absorb; without extraction, the room cycles damp-dry-damp daily, and the mould chapter's futures open on silicone lines, grout and ceilings. Adjacent rooms inherit the overflow humidity through open doors.

Fan Sizing and Run-Time Rules

The specification: extraction capacity matched to room volume (regulations-and-rules of thumb put small bathrooms at ~50+ L/s or 8+ air changes hourly — undersized builder-grade fans explain many mouldy ceilings); the RUN-TIME rule — fans work mostly AFTER the shower: 15–20 minutes post-steam (timer or humidistat models automate the discipline nobody sustains manually); and the door-gap detail — extraction needs makeup air (a door cracked or undercut lets the fan actually pull).

Prevention Economics

The cost-benefit: a timer-fan upgrade and silicone squeegee cost little against repainting cycles, regrout jobs and the respiratory tenancy of chronic mould; the daily two-minute protocol — squeegee the glass, crack the window or run the fan's timer, door ajar after — cancels most bathroom mould futures outright. Towel-and-mat rotation (dry textiles, not permanent dampness) finishes the moisture audit.

Renter Workarounds

The no-renovation toolkit: window-and-door draught discipline after showers, portable dehumidifier service for extraction-less bathrooms, shorter-cooler showers in problem rooms, squeegee religion, and documentation habits where building-grade damp exceeds tenant control — the mould chapter's escalation lines apply. Landlord conversations go better with hygrometer readings attached.

Bathroom verdict: fifteen fan-minutes after every shower is the cheapest mould policy ever written.