Potential damage to outdoor wood. (a) Initial and final relative humidity at Heathrow 1949–2011 for changes likely to cause irreversible deformation in lime wood. Inset (i): seasonal distribution as the number of days with irreversible deformation each month. Inset (ii) The initial daily relative humidity for events which cause irreversible deformation in lime wood. (b) The annual estimates of days likely to cause irreversible deformation to lime wood at Gatwick (diamonds) and Heathrow (squares).