In the 18th Century builders were not totally confident about brick and in houses, churches, Guildhalls, used timber lintels to spread the load.All Brindleys locks (Droitwich, Staffs and Worcs, Chesterfield ) were totally timber framed, bridges stood on elm tree abutments instead of stone for cheapness. I placed a copy of a contemporary engineers drawings with the Waterways Museum, Gloucester.Elm was used as it doesnt rot in wet conditions.