There is a particular smell that greets you when you step into a neglected period cottage: cold stone, old timber and something faintly musty underneath. It is the scent of a building that has lost its balance with the weather. The good news is that damp in an old cottage is rarely a mystery, and it is almost never a reason to walk away from a property you love. Once you understand what is happening inside the walls, the remedies are often simpler and gentler than the hard sell of injected chemicals might suggest.

Old cottages were built to breathe. Lime mortar, stone, brick, wattle and daub and unsealed timber all allow moisture to move through the fabric of the building and evaporate away. When that movement is blocked, water has nowhere to go but into the plaster, the timbers and the air you breathe.

Start by Finding the Source

Treating damp without diagnosing it is like painting over a crack. Before you spend a penny on repairs, work out which of the three main types you are dealing with.

• Rising damp creeps up from the ground through porous walls. Look for a tide mark no higher than a metre, often with salts blooming on the plaster and skirting boards rotting from the bottom. It is less common than people assume, and often turns out to be something else.
• Penetrating damp comes in sideways. A cracked render, a failed gutter, a slipped slate, a blocked drain or a high external ground level will all push water into the wall.
• Condensation is the modern intruder. It forms inside when warm, moist air meets a cold surface, and it leaves black spotty mould in corners, behind furniture and along north-facing walls.

A cheap hygrometer and a few days of observation will tell you a great deal. If the damp patches grow after heavy rain, you are looking at penetration. If they worsen after cooking, showering or drying laundry indoors, condensation is the culprit.

Ventilation Beats Sealing Every Time

The single most damaging change made to old cottages over the last fifty years has been the drive to seal them up. Draught-proofing, cement render, plastic paints and modern insulation all trap moisture. A period cottage needs air to move.

Open windows daily, even in winter, for ten minutes at a time rather than leaving a trickle vent all day. Keep trickle vents clear if they exist, and never block a chimney. An unused flue with a cowl on top still draws air up and out, which is why Victorian builders put a fireplace in almost every room.

• Fit extractor fans in bathrooms and kitchens that vent to the outside, not into the loft.
• Dry laundry outdoors or in a ventilated outbuilding, not on a radiator.
• Leave a gap between furniture and external walls so air can circulate.
• Keep gutters and downpipes clear twice a year; most penetrating damp starts at roof level.

Use Breathable Materials on Old Walls

Old walls need to release moisture, and that means choosing materials that let vapour pass through. This is where renovation often goes wrong. Cement render, gypsum plaster and vinyl silk paint are all but impermeable. Water trapped behind them will find the timber lintels and floor joists instead.

Repair with lime. Lime mortar, lime render, lime plaster and breathable clay or mineral paints are softer than the surrounding stone and brick, so they flex and let the wall dry. They also look right: a chalky, slightly uneven finish that sits naturally in a period room. If a wall is genuinely wet from the ground, a French drain or a gravel-filled trench outside, combined with a breathable internal finish, will usually do more good than an injected damp-proof course.

For floors, avoid sealing original stone flags or quarry tiles under a plastic membrane. Let them dry and they will stay sound for another two centuries.

Heating, Airflow and the Daily Routine

A cottage that is lived in warmly and ventilated well is far less likely to suffer than one left cold for weeks. Background heat keeps surfaces above the dew point, which is the temperature at which moisture condenses. Program your heating to come on gently in the morning and stay low rather than blasting in the evening.

• Aim for steady background warmth of around 16 to 18°C in unused rooms.
• Leave internal doors open when you can, so air moves through the whole house.
• Inspect the loft after stormy weather; a lifted tile is easier to fix than a sodden ceiling.
• Check external ground levels sit at least 150mm below the internal floor.

Health, Timbers and Knowing When to Call In Help

Persistent damp is not just a cosmetic problem. Mould spores aggravate asthma and allergies, and wet timber invites wet rot and, occasionally, dry rot. Watch for soft, crumbly skirting boards, a mushroomy smell, or fungal strands spreading across joists. These need professional attention quickly, but the first step is always the same: fix the water source.

If you have worked through the checklist and the damp persists, a surveyor who specialises in historic buildings will read the walls, the drainage and the materials in a way a general damp-proofing firm may not. Ask for a diagnosis rather than a quotation, and be wary of any remedy that involves covering the building in plastic or injecting a chemical barrier without explaining why.

Live with an old cottage for a full year and you will learn its moods. It will be damper after a wet winter and drier in a breezy spring. Treat it with breathable materials, keep the air moving, and stay on top of the gutters, and you will have a home that is warm, healthy and quietly doing what it has always done best: sheltering the people inside it.