Humidity and guitars

The UK has been gripped by the first cold weather of the year, with snow covering much of the country and it is bitterly cold . The cold weather looks set to continue for a while yet. In global terms Britain's weather is not extreme but it is the rarity of freezing conditions that can take guitarists and guitar makers unaware.
Yesterday I got a call from a local guitarist who had discovered a top split on one of his guitars, and this is almost certainly as a result of the very low humidity that the UK is experiencing at the moment. Fortunately it was not one of my guitars that had split, but it can happen to any instrument that isn't properly cared for.
The air around us contains moisture and the amount of moisture varies according to natural influences such as the weather, but can also be affected by heating systems in buildings and so on. Wood is a material that will take in or give up moisture and will respond to the environment it is in. A guitar therefore will expand and contract with changes in humidity, and it is this movement in the materials and structure of the guitar that can lead to problems. The main danger is from excessive dryness and rapid fluctuations in humidity, and the commonest problem encountered is the guitar drying out, shrinking and then splitting.
When I make a guitar I firstly ensure that the timber I use is dimensionally stable - dry and seasoned in other words. Secondly I build in a controlled environment, with a dehumidifier keeping the relative humidity in the workshop at around 45%. Once the instrument leaves the workshop however it is down to the player to look after it but with care it should be possible to avoid too many problems. I would recommend that all players invest in a digital hygrometer (this is a device that will measure relative humidity) Costing about the same as a set of strings, the hygrometer will give you a pretty good indication of the humidity of your surroundings. When you detect the humidity getting low, say 50% or below, then you can take steps to humidify the guitars environment. This can be as simple as putting a wet cloth over a hot radiator, or by using an electrical humidifier. One of my clients stores his guitars in a specially built cabinet with its own climate control system. This is not a practical solution for everyone, but keeping the guitar in its case along with a commercially available humidification system and a hygrometer to monitor humidity levels is a sensible measure.
It is worth contacting the maker of your instrument and asking their advice as to how they would recommend you to look after the guitar they have made for you. I am always very happy to help as much as I can with this as I hate seeing instruments I have made needlessly damaged.

(Photographs of David Whiteman 2010 Cedar/rosewood guitar taken by Malcolm Maxwell at Crisplitho Ltd)