Main structural timbers were usually of oak and sometimes elm. Elm was generally used for floorboards. Oak is long grained, strong, and durable, making it an excellent timber for construction purposes. After it is first felled it is easy to work, but with time the wood hardens, making it difficult to saw or axe across the grain. For building purposes it was therefore used in its 'green', unseasoned state, a short time after felling (normally done in the autumn or winter when the leaves had been shed and there was no sap rising).