Almost every mould problem people deal with in January was set up months earlier. Late summer and early autumn are when surfaces are still warm, walls are as dry as they will be all year, and small jobs are easy. By the time black spotting appears on a bedroom reveal in the middle of winter, the room is cold, the wall is damp and the same job is much harder.
If you only do house maintenance once a year, this is the time of year to do it.
Why autumn is the turning point
Mould needs moisture, and in most homes the moisture arrives from two directions as the seasons change.
From outside, autumn brings more rain, shorter drying periods and higher outdoor humidity, so external walls stay wetter for longer and any defect that lets water in starts to matter.
From inside, the heating goes on, windows stay shut, laundry moves indoors and the amount of water vapour in the air rises just as surfaces are getting colder. The gap between warm, moist air and cold surfaces is what produces condensation.
The two arrive within a few weeks of each other, which is why problems appear so predictably from late October onward.
Outside jobs to do while it is still dry
These are the jobs that stop water reaching the building in the first place. They are far easier in dry weather and far more useful done early.
- clear gutters and check downpipes run freely
- look for overflowing or leaking joints during the next heavy shower
- check the roof from the ground for slipped or missing tiles
- clear debris from gullies and drains
- check that ground levels and paths are not bridging the damp proof course
- cut back vegetation touching walls
- look for cracked or hollow render, and failed pointing
- check window and door sealant lines
- make sure air bricks and vents are clear and unblocked
There is more detail on this in autumn outdoor jobs.
Inside jobs to do before the heating goes on
- check every extractor fan actually pulls air, and clean the grilles
- open and clear trickle vents on windows
- pull large furniture away from external walls and check behind it
- look at the top corners of external walls and around window reveals
- open wardrobes and cupboards on outside walls and check the back panels
- check under sinks and behind the bath panel for slow leaks
- look at loft insulation and make sure vents at the eaves are not covered
- treat any spotting you find now rather than leaving it until winter
Early spotting is much easier to deal with than an established patch, and treating it now means the room goes into winter clean.
Treat now, protect now
If you found growth during those checks, autumn is the right time to deal with it properly rather than patch it.
- Remove the visible growth with a product suited to the surface
- Let the surface dry fully, which is far quicker now than in December
- Protect the surface if you are redecorating
- Fix the conditions that let it grow
!Mould Solve Advanced Mould Treatment Kit with two sprays, air sanitiser, FFP3 mask and gloves
Start with Mould Removal Sprays for the removal stage. If you are redecorating a problem room before winter, Mould Prevention & Primers and Anti-Mould Paint cover the protective stage. For a complete route in one purchase, compare the Mould Treatment Kits.
Decorating in autumn also has a practical advantage: walls dry faster and rooms can be ventilated comfortably, which is much harder in midwinter. There is a full sequence in mould treatment checklist before painting.
Habits worth setting before October
The routines that prevent winter mould are easier to start before the weather forces them.
- run extractor fans during and after showering and cooking, not just when the room steams up
- ventilate briefly and widely each morning rather than leaving windows ajar all day
- keep background heating steadier rather than short bursts of high heat
- plan where laundry will dry, and vent or ventilate that space
- leave gaps behind large furniture on external walls
- wipe window condensation rather than letting it sit on sills
A simple autumn timetable
Late August to mid September: outside checks, gutters, roof, drains, vegetation, sealant.
Mid September to early October: inside checks, fans, vents, behind furniture, cupboards, loft.
October: treat any growth found, redecorate problem rooms if needed, set ventilation and heating habits.
November onward: monitor windows, reveals and corners monthly, and act on the first sign of spotting.
FAQs
Is it worth doing this if I had no mould last winter?
Yes, particularly the outside checks. Gutters and roof defects develop quietly, and the first sign is often damp on an internal wall.
When is the worst month for mould?
Problems are usually noticed from late autumn through to February, when surfaces are coldest and ventilation is lowest. The conditions that cause them start earlier.
Should I redecorate now or wait until spring?
If a room has a mould problem, treating and redecorating in autumn is usually better, because the surface dries faster and the room goes into winter protected.
What if the wall is still damp when I check it?
Do not decorate over it. A wall that is damp in late summer suggests something more than condensation and should be investigated. See when surface treatment is not enough.
