Improving ventilation in modern airtight homes

Why airtight homes need a different approach

If you live in a modern home in Edinburgh, East Lothian, Midlothian or West Lothian, you may already have noticed the upside of tight construction: your heating bills are lower, the house holds its warmth, and draughts are rare. Homes built to current Scottish standards are sealed far more effectively than the villas and tenements of a century ago. That is a genuine benefit, especially when the wind comes off the Forth in February.

But there is a trade-off. Older properties leaked air through chimneys, sash windows, floorboards and imperfect plaster, which meant moisture and everyday pollutants found their way out whether you wanted them to or not. A modern airtight home has no such escape routes. Without deliberate ventilation, cooking steam, shower moisture, laundry drying, cleaning products and carbon dioxide all build up indoors. In practice, that shows up as condensation on north-facing windows, a faint musty smell in wardrobes, black spotting around silicone seals, and sometimes a heavy, stuffy feeling in bedrooms overnight.

The answer is not to cut holes in your insulation. It is to ventilate on purpose while keeping the heat you have paid for.

Mechanical ventilation with heat recovery, explained simply

MVHR is the system you will hear about most in new-build properties around Livingston, Dunfermline and the Edinburgh urban extension sites. A central unit sits in a loft, cupboard or utility space, connected by ducting to ceiling valves in wet rooms and living spaces. It extracts warm, moist air from kitchens and bathrooms, passes it across a heat exchanger, and uses that recovered warmth to temper fresh air drawn in from outside.

In a well-commissioned system, you can expect to recover somewhere between 70% and 90% of the heat that would otherwise be lost. The incoming air is filtered, so pollen and particulates from busy roads are reduced, and the house stays at a steady, comfortable humidity. Because the system runs continuously at low speed, it does the job quietly and without anyone needing to remember to open anything.

What matters more than the brand or the spec sheet is the commissioning. A system balanced properly will deliver the right airflow to each room. One that has never been set up will either under-ventilate the bedrooms or overcook the kitchen. Ask for the commissioning report, check that filters are changed every six to twelve months, and have the ducting checked occasionally. Filters are inexpensive and easy to swap yourself.

• Boost settings should run automatically when a bathroom light is switched on or humidity rises.
• Summer bypass should be enabled so the unit does not push warm air into an already warm house.
• Never block intake or extract valves with furniture, curtains or storage boxes.
• Keep a spare set of filters so you are not tempted to skip a change.

Trickle vents, extractor fans and the systems you already have

Plenty of homes in the Lothians fall between the old and the very new. These usually rely on trickle vents in window frames, background wall vents, and intermittent extract fans in the kitchen and bathroom. It is a perfectly workable approach, provided the components actually work.

Trickle vents are easy to forget. They are the small slotted openings at the top of a window frame, usually operated by a plastic slider. Many people close them because they assume they cause heat loss. In reality, a correctly set trickle vent passes a small, controlled amount of air and saves far more in moisture damage than it costs in heat. If yours are painted shut, broken, or missing their internal baffle, replacing them is a modest job with a real return.

Extract fans deserve the same attention. A fan that hums but moves almost no air is common, particularly in older flats where ducting is long or has collapsed. Test it with a sheet of tissue paper held against the grille. If it will not hold the tissue, it is not extracting. Humidistat and timer models are worth the extra few pounds, because they keep running after you leave the room and clear the moisture properly. In tenement flats, shared ducts need to be clear at the roof terminal as well as inside the flat.

Using windows well, not just often

There is a technique to ventilating with windows, and it matters more in a well-sealed house. The aim is a short, sharp air change rather than a window left ajar all day.

Open two openings on opposite sides of the house, or a low and a high opening in the same room, for ten to fifteen minutes. That cross-flow replaces the air quickly with minimal cooling of the building fabric. A bedroom window cracked open for eight hours on a January night wastes far more heat than a fifteen-minute purge before bed. In warmer months, overnight purging is excellent for cooling a home that has absorbed heat all day.

Bathrooms and kitchens benefit most. Run the extract fan or open the window during and for at least ten minutes after showering or cooking, and keep internal doors closed so moisture does not drift into bedrooms and hallways.

Small habits that make a real difference

Ventilation works best when it is matched by how you actually live in the house. A few adjustments go a long way, particularly in winter when windows stay shut.

• Dry laundry outdoors or in a ventilated, door-closed room with an extract fan running. A single load of washing can release several litres of water into the air.
• Keep lids on pans while cooking and use the extract hood every time.
• Leave internal doors open for at least part of the day so air can move to where it is extracted.
• Do not block airbricks, vents or under-door gaps with carpets, draught excluders or furniture.
• Watch for early warning signs — misted windows, damp patches on external walls, or a musty smell in cupboards.
• Keep humidity roughly between 40% and 60%. A cheap hygrometer will tell you far more than guesswork.

If condensation persists despite all of this, the cause is usually a system that needs balancing, a fan that needs replacing, or a room that never had adequate ventilation designed in. Getting that assessed early is far cheaper than dealing with damp plaster and timber later. A warm, airtight home should feel fresh as well as economical, and with the right setup it genuinely can.