A surprising number of internal damp and mould problems begin with something outside the house that takes twenty minutes to fix in September and becomes a decorating job in February. Autumn is the point in the year when the outside jobs are still comfortable to do and still worth doing.
Gutters and downpipes
Blocked or leaking guttering is one of the most common causes of a damp internal wall. Water that should be carried away instead runs down the same section of wall every time it rains, saturating it far beyond what the wall can dry out.
- clear leaves, moss and debris from gutter runs
- check that outlets and downpipes flow freely
- look for sagging sections and loose brackets
- check joints and seals for drips
- watch the house during the next heavy shower and look for overflow points
- check that downpipes discharge into a gully rather than onto paving or soil against the wall
If you can only do one outside job, this is it. An overflowing gutter on a north-facing wall reliably produces internal damp by midwinter.
Roof, flashings and chimneys
From ground level, look for:
- slipped, cracked or missing tiles and slates
- damaged or lifting flashing around chimneys, valleys and roof lights
- vegetation or heavy moss growth on the roof surface
- daylight visible in the loft when you check inside
- staining on loft timbers or on the underside of the roof
Roof work is not a DIY job for most people, but spotting a problem early and getting it looked at before winter is. There is more on the loft side of this in mould in lofts and roof spaces.
Walls, render and pointing
- look for cracked, hollow-sounding or blown render
- check pointing on brickwork, particularly on exposed elevations
- check sealant around window and door frames
- look at sills and drips, which should throw water clear of the wall
- check for staining patterns that show where water runs
Green or black growth on an outside wall is normal in shaded, damp spots and is not the same thing as internal mould. It does, however, tell you where the wall stays wet, which is useful information about the rooms behind it.
Ground level and drainage
- clear gullies, drains and channels of leaves and silt
- check that ground and paving levels are not bridging the damp proof course
- make sure soil, decking or raised beds are not piled against walls
- keep air bricks and vents clear and unobstructed
- check that paths fall away from the house rather than towards it
Blocked air bricks are an easy thing to miss and a common contributor to damp and musty smells at low level.
Vegetation
- cut back climbing plants, shrubs and branches touching walls or the roof
- clear vegetation from around gullies and air bricks
- keep growth off fences and boundary structures where it holds moisture
- remove leaf build-up in corners and against walls
Plants against a wall hold moisture there and stop it drying, which matters more in a wet autumn than a dry one.
Paving, driveways and steps
Green growth on paving, steps and driveways builds up quickly through autumn. Aside from the appearance, wet growth on a hard surface is a genuine slip hazard through winter, particularly on shaded steps and paths.
!Mould Solve Driveway and Patio Cleaner 5L
Autumn is a good time to deal with it, before the surface stays permanently wet. For exterior surfaces use a product intended for the job rather than an indoor mould treatment, as covered in Outdoor & Driveway Cleaning. There is more on when exterior treatment is the right choice in the patio and driveway cleaner guide.
Practical points:
- work on a dry day with a reasonable drying window afterwards
- clear leaves and loose debris first
- keep exterior products away from planting and check drainage routes
- follow the product instructions for the surface type
- take extra care on steps, which stay wet longest
Fences, sheds and garden structures
- clear growth from north-facing fence panels and shed walls
- check shed and garage roofs for standing water and leaks
- keep stored items off the floor in outbuildings
- make sure water butts and overflows discharge away from walls
What each job saves you indoors
Each job outside protects something specific inside:
- gutters and downpipes: damp patches and mould on the wall behind
- roof and flashings: ceiling stains, loft mould, damp in upper rooms
- render and pointing: penetrating damp on exposed walls
- drainage and ground levels: damp and musty smells at low level
- air bricks: poor underfloor ventilation and damp smells
- vegetation: persistently wet walls that never dry out
Autumn order of work
- Gutters, downpipes and drains first
- Roof and flashing check from ground and from inside the loft
- Render, pointing and sealant
- Ground levels, air bricks and vegetation
- Paving, steps and outdoor growth
- Then move indoors and check the rooms behind the worst walls
The last step matters. If you found a problem outside, look at the room on the other side of that wall before winter and treat any growth you find. Start with Mould Removal Sprays, or compare the Mould Treatment Kits for a full route.
FAQs
How often should gutters be cleared?
At least once a year for most homes, in autumn after the leaves have fallen. Properties near trees usually need it more often.
Can I use an indoor mould spray on the patio?
Use a product intended for exterior surfaces instead. Indoor and outdoor treatments are formulated for different surfaces and situations.
Does green growth on an outside wall mean the wall is failing?
Not necessarily. It usually means that part of the wall stays damp and shaded. It is worth noting because it shows where water sits, but it is not automatically a defect.
Is it worth pressure washing everything?
Pressure washing can damage pointing, render and some paving if used aggressively. Treating the growth is usually gentler on the surface than blasting it off.
