What low humidity does

Timber gives up moisture and shrinks. In a frame, that means joints that were tight become slightly loose, and over several dry winters the cumulative effect is a frame that rattles and eventually racks.

Rooms with underfloor heating or aggressive forced-air heating are the common culprits, sometimes dropping below 25% relative humidity for months.

What high humidity does

Springs and steel hardware corrode, and corrosion changes spring behavior before it becomes visible. Upholstery foam holds moisture, which produces odour and eventually degrades the foam. Hardwood swells, which can bind moving parts.

Coastal locations are worse again, because salt in the air accelerates corrosion substantially. Spring replacement cycles are genuinely shorter near the sea.

Environmental effects by material
ConditionHardwood frameAluminum frameSprings & hardware
Below 30% RHJoints loosenUnaffectedUnaffected
40–60% RHIdealIdealIdeal
Above 70% RHSwelling, bindingUnaffectedCorrosion risk
Coastal airAs aboveUnaffectedAccelerated corrosion

Practical management

A cheap hygrometer in the room tells you whether there is a problem at all, and most rooms are fine. Where they are not, a humidifier in winter or a dehumidifier in summer solves it for a modest cost.

Position matters too: keeping a machine away from radiators, vents and direct sunlight avoids the localized extremes that do most of the damage.

Choosing equipment for a difficult environment

If the room genuinely cannot be climate-controlled — a garage, a coastal outbuilding, a converted barn — an aluminum-framed machine removes most of the risk. It is dimensionally unaffected by humidity and needs no corrosion protection.

Springs remain the vulnerable component in any humid environment, and shorter replacement cycles should be planned for rather than treated as a surprise.