Complex sentence: The original chancel arch was demolished in about 1440 and a replacement was built about 2ft further east which is mis-shaped owing to the clerestory being raised at the end of the 15th century and a new low-pitched roof being installed above it.
Split into simpler sentences: The original chancel arch was demolished in about 1440 and a mis-shaped replacement was built about 2ft further east. The clerestory was raised at the end of the 15th century and a new low-pitched roof was installed above it.