Problem solver
Why your bathroom keeps getting mouldy, and how to fix it
Mould in a bathroom is almost always a moisture problem, not a cleaning problem. Scrubbing it off treats the symptom. This guide explains what actually causes it, what the NZ rules require, and how a renovation fixes it for good.
What actually causes it
Every hot shower puts a lot of water vapour into a small room. If that vapour is not pulled out quickly, it condenses on the cooler surfaces, the walls, the ceiling, the window and the grout, and sits there. Mould feeds on that damp, especially in the corners and along the silicone lines.
So the real question is never how to clean the mould off. It is why the moisture is not leaving the room fast enough. That comes down to ventilation.
What the rules require
The Building Code requires bathrooms to be ventilated. For rental properties, the Healthy Homes Standards go further and set a specific bar: kitchens and bathrooms must have an extractor fan that vents to the outside. At the time of writing that meant a fan of at least 120mm in diameter, or an exhaust capacity of at least 25 litres per second.
Two things matter more than the number itself. First, the fan has to actually clear the room, and the legal minimum is not always enough for real-world humidity, so sizing it to the room is worth doing. Second, it has to vent outside, not into the ceiling space. Always confirm the current standards, as they are updated from time to time.
How a renovation fixes it properly
When we strip a bathroom back, the ventilation gets done right as part of the job: an extractor sized for the room, ducted to the outside air, not the roof cavity. Combined with waterproofing to code and properly finished tiling and silicone, that removes the conditions mould needs rather than papering over them.
It is the difference between a bathroom that fogs up and stays damp, and one that clears in minutes. See what a proper job involves in a full bathroom renovation.
A note for landlords
If you own a Waikato rental, compliant bathroom ventilation is not optional, and a renovation is the natural moment to bring it up to standard rather than bolt on a cheap fan later. We can make sure the extraction meets the Healthy Homes requirement as part of the work.
FAQs
Ventilation questions, answered straight
Mould needs moisture, and a bathroom makes plenty of it. If that moisture is not extracted quickly, it settles on cold surfaces as condensation and feeds mould. The usual culprits are no extractor fan, a fan that is too weak, or a fan that vents into the ceiling cavity instead of outside.
Sick of a mouldy, damp bathroom?
Book a free measure and we will sort the ventilation and waterproofing properly as part of your renovation, for a fixed price in writing.