Stop Mould in Your House During Heavy Rain: 7 Easy Fixes

When rain falls for days and the air never dries, black spots appear on walls, clothes smell sour and shoes turn green in the cupboard. Mould needs only three things: moisture, still air and something to feed on, like wood, cloth or dust. You cannot stop the rain, but you can take away the still air and some of the moisture. These seven fixes help you stop mould in house rooms using common materials and simple tools. Houses differ across Southeast Asia, from raised wooden houses in Laos and Cambodia to concrete row houses in Thailand, Vietnam, Malaysia and the Philippines. Pick the fixes that suit your home, and check local building rules before you cut new openings.

Fix 1: Find Where the Damp Comes From

Before you fight mould, find the water. Cleaning a wall that is still getting wet only buys you a few days. Walk around the house during a heavy shower and again after it stops. Look for:

• Drips or stains on the ceiling, which point to a roof leak or a blocked gutter.
• Wet patches low on walls, often from rain splashing back off the ground or water rising up from wet soil.
• Damp under windows, where seals or sills have failed.
• Steam from cooking, bathing or drying clothes indoors with the windows shut.

Some causes are quick to fix. Clear leaves from gutters and downpipes, and point the downpipe outlets at least a metre away from the wall. Lay a strip of gravel or a few bricks under the eaves so rain does not splash mud onto the wall. Hang a lid on boiling pots and open a window while you cook. A large roof leak, cracked walls or water coming through the floor are bigger jobs. Ask an experienced local builder to look at them.

Fixes 2 and 3: Let Air Move Through the House

Moving air carries moisture out. Still air lets it settle on cold walls and in corners. Even when it rains every day, the air outside during a break is often drier than the air trapped inside a closed room.

Fix 2: Open Ventilation Gaps

Cross ventilation works best: air comes in one side of the house and leaves on the other. During breaks in the rain, open windows or doors on opposite sides for an hour or two. Keep internal doors open so air can pass between rooms.

Many older houses in the region have gaps above doors and windows, or patterned vent blocks near the top of walls. If yours are blocked with cardboard, plastic or dust, clear them. If a room has no high openings, a carpenter can fit a vent panel or slatted grille above a door frame. Cover every gap with fine insect mesh to keep out mosquitoes, and fit a small hood or angled slats on outside walls so rain does not blow in. Wear gloves and eye protection when cutting mesh or sawing wood. Do not cut openings into concrete or brick walls yourself; that can weaken the wall and should be planned by a builder.

High gaps matter because warm, wet air rises. A vent near the ceiling lets it escape, while a low gap on the other side brings fresher air in.

Fix 3: Add or Clear Roof Vents

The space under a metal or tile roof traps hot, wet air. That moisture drips back as condensation, which looks like a leak and feeds mould on ceilings and roof timbers. Gable vents, ridge vents or open gaps under the eaves let that air out. A simple gable vent is a slatted wooden or metal grille with insect mesh behind it, set into the triangle of wall at the end of the roof.

This is height work, so treat it seriously. Only do it on a dry, calm day, never in rain or wind and never on a wet roof. Use a sturdy ladder on firm, level ground, tie or hold it secure at the top, and have a second person at the base the whole time. Wear rubber-soled shoes, gloves and eye protection. If the job means walking on the roof or working high above the ground, use a harness or hire a roofer. Rough costs for a basic gable vent grille run from about 5 to 30 US dollars, but prices vary by country and material.

Once roof vents are in, check the roof space after the next storm. If ceiling drips stop, condensation was the cause. If they continue, you likely have a real leak to repair.

Fixes 4 to 6: Stop Mould in House Corners and Cupboards

Mould loves hidden places: behind wardrobes, under beds and inside closed cupboards. These fixes cost little and take an afternoon.

Fix 4: Move Furniture Off the Walls

Pull wardrobes, beds, sofas and shelves away from outside walls, leaving a gap of about 5 to 10 centimetres so air can flow behind them. Outside walls are often the coldest and dampest in the house. Lift heavy furniture with two people, bend your knees, empty drawers first and wear sturdy shoes. Raise items off a damp floor on bricks, wooden blocks or plastic feet, and keep storage boxes on shelves rather than on the floor.

Wipe the wall and the back of the furniture before you push it back. If you find mould there, clean it using Fix 7 first.

Fix 5: Use Fans to Keep Air Moving

A simple electric fan helps a lot. Point it at the dampest corner or place it near a window to push wet air outside. A small exhaust fan in a bathroom or kitchen is even better. Keep fans and plugs away from water, never use wet hands on switches, and do not run extension cords across wet floors. If wiring, sockets or the fuse box get wet or show marks of water, switch off at the main supply if it is safe and call a qualified electrician. Do not fit new wiring yourself.

Fix 6: Try Simple Moisture Absorbers

In closed spaces like wardrobes and shoe cupboards, moisture absorbers can help. Be honest about their limits: they work only in small, closed spaces, not open rooms. Common options include:

• Calcium chloride tubs, sold in many shops for a few US dollars. They fill with water that you pour away. Keep them away from children and pets, and wear gloves when emptying them.
• Silica gel packets, which can often be dried in the sun or a low oven and reused.
• Lumps of plain wood charcoal in a cloth bag. They absorb some moisture and smells but much less than the options above.

Rice and salt bowls are popular tips but do little. If you own an electric dehumidifier, run it with doors and windows closed and empty the tank daily. Also dry clothes fully before putting them away, and leave cupboard doors open for a while each day.

Fix 7: Clean Mould Safely

Mould spores can irritate the eyes, nose and lungs, especially for children, older people and anyone with asthma. Protect yourself before you start: rubber gloves, eye protection and a dust mask, with long sleeves and the windows open. Keep children out of the room.

• Mist the mould lightly with water first so spores do not fly into the air.
• Scrub hard surfaces with water and dish soap, or a mix of white vinegar and water.
• For stubborn stains on tiles or painted concrete, a weak bleach solution can help. Follow the bottle directions and never mix bleach with vinegar, ammonia or other cleaners, as this releases dangerous gas.
• Wipe surfaces dry with a clean cloth and run a fan afterwards.
• Bag and throw away cloths, and wash your clothes after the job.

Soft items like mattresses, ceiling boards or cardboard that are deeply mouldy usually cannot be saved. Remove them rather than cleaning them again and again.

Know When to Call for Help

These fixes handle everyday damp. Call a professional if mould covers a large area, keeps returning within days, grows inside walls or ceilings, or if floodwater has entered the house. Timber that feels soft, cracking walls and wet electrics are signs of bigger problems. Conditions, materials, building rules and prices differ by country and even by village, so ask an experienced local builder or your local housing or extension office before major work. Start with the simple steps today: clear the gutters, open the vents, pull the wardrobe off the wall, and let the air move.