Clothes Drying In Apartments And Where The Moisture Goes

Drying clothes indoors puts a surprising amount of water into the air. A single load releases roughly two litres of it.

In an apartment with a closed drying area and no ventilation, that water condenses on the coldest surface it can find, and then mould grows there.

Why it is worse in newer buildings

Modern buildings are sealed much better than older ones, which is good for energy and removes the incidental ventilation that used to carry moisture away.

An older apartment leaked air constantly through gaps and old windows. A newer one does not, so moisture produced indoors stays indoors unless something removes it deliberately.

Add a balcony that cannot be used for drying, either because of a by-law or because it faces the wrong way, and the washing goes inside.

The three sources and the one mechanism

Drying clothes, showering and cooking all add moisture. The mechanism is the same: warm moist air meets a cold surface and the water comes out of it.

The cold surfaces in an apartment are predictable. Window reveals and frames. The wall behind a wardrobe on an external wall. The corner of a room on two external walls. Behind furniture pushed against an outside wall. A ceiling under an uninsulated roof.

Which is why mould appears in those exact places, and why cleaning it without dealing with the moisture means it returns in a season. The same diagnosis applies as in [bathroom condensation and the exhaust fan](/blog/bathroom-condensation-mould-and-the-exhaust-fan).

Dryers, and the difference between them

A vented dryer pushes hot moist air out of a duct. Excellent, provided the duct actually goes outside. A vented dryer discharging into a laundry cupboard or into a ceiling space is worse than no dryer at all, because it delivers the entire moisture load into the building fabric in concentrated form. We find this regularly and it is the cause of some of the worst mould we see.

A condenser dryer collects the water in a tank or drains it. No duct needed, so it suits an apartment where there is nowhere to vent. It still releases some heat and moisture into the room, and far less than line drying.

A heat pump dryer is the same principle, more efficient, and it runs cooler.

For an apartment with no external wall available in the laundry, a condenser or heat pump unit is usually the right answer, and the plumbing for the drain is a small job.

What has to work

A mechanical exhaust in the drying area, ducted outside, on a timer or a humidity sensor. Not a fan discharging into the ceiling void.

Somewhere for makeup air to come from, because an exhaust fan in a sealed room with the door closed moves very little. A gap under the door is enough.

A drying line outside where the building allows it, which is the cheapest answer and is frequently prohibited by a by-law that was written for appearance reasons.

A drying room, in buildings that have the space. A small room with heat and a ducted exhaust serves a whole building and is far more efficient than every apartment drying separately.

The building manager view

Mould complaints in a building follow a pattern.

They concentrate in the units with the least ventilation, the coldest external walls and the most occupants. They peak in winter. And they get reported as a building defect when the immediate cause is moisture production with no extraction.

Both things are usually true at once. The tenant is producing moisture and the building is not removing it, and the argument about which one is at fault does not fix anything.

What fixes it is extraction that works, insulation where the cold spot is, and a practical drying option. In a building where the same three units complain every winter, it is worth checking the exhaust ducts in those units before anything else, because a disconnected duct in the ceiling is common and invisible.

The cheap checks first

Confirm every exhaust actually discharges outside, not into a ceiling. Confirm the dryer duct does the same. Check the fan actually moves air, with a tissue rather than by listening to it. Check the windows have working seals, which ties into [window and door seals](/blog/window-and-door-seals-draughts-and-noise).

Those four checks resolve a large share of mould complaints and none of them require a specialist report.

Ample handles ventilation, exhaust ducting and the electrical and building work around it across apartments in the eastern suburbs and inner city.