Condensation is a key challenge for an enthusiast contemplating their classic car storage. The key to storing a classic car is the control of the storage environment. Contrary to common understanding, a heated garage is not necessarily be the answer. A bit of warmth is great for you as you enjoy a glass of wine whilst admiring your pride and joy as the elements hammer down outside, but the real key for your car is humidity control.

As the seasons change we are aware of colder temperatures and increased rain, but how the relative humidity of the atmosphere changes is more subtle and less obvious. We keep records of temperature and humidity outdoors and in our classic car storage unit, and the results at this time of year are interesting. Here’s a chart for late October 2017.

Temperature and humidity

In fact for us this chart is very reassuring, but for anyone ¬†keeping a cherished classic car over the winter in less than perfect conditions it could be alarming. What it shows is the large variation of atmospheric relative humidity (the green line) present outside our buildings in Andover in late October and early November and just how high the unseen humidity can be – over 90% on the 23rd October. Compare this with the red line, external temperature and look how they vary. It is this variation that will cause condensation and damp on surfaces that can’t change temperature as fast as the surrounding air does – like a car, for example.

Condensation may not always be obvious to the eye, but it will be there, hidden away in engine bays or interiors, or keeping hidden mud and grime nice and damp . . . and where there’s damp there’s the risk of corrosion and rot.

Now look at the yellow line on the chart – that’s the relative humidity inside the building, maintained at a consistently lower level and controlled to prevent, so far as possible, the big changes in gradient that lead to condensation. And then look at the blue line, that’s internal temperature and because our building is hugely insulated, there’s barely any change.

So the air in the building has had harmful humidity removed, and the lack of temperature gradient removes any danger of condensation forming, ensuring the cars stay dry. The average internal relative humidity over the period was 55.6%, which is reflects museum quality and perfect conditions for a classic car to slumber through the winter.

We can sleep easy!