 Chestnut wood, though, loses much of its durability when the tree is more than 50 years old, and despite the local chestnut's quick growth rate, the timber used for these two buildings is considerably larger than a 50-year-old chestnut's girth.It has been proven that the roofs of these buildings are actually Durmast oak, which closely resembles chestnut in grain and color.It is therefore uncommon to find large pieces of chestnut in building structures, but it has always been highly valued for small outdoor furniture pieces, fencing, cladding (shingles) for covering buildings, and pit-props, for which durability is an important factor.