Waberthwaite Local History Group recently got grant funding for a tree-ring analysis of the roof timbers of St John's. This is done by cross matching the growth rings of samples from the roof beams with other locally grown timber. The width of each ring is pretty much determined by the weather conditions of each year.
These investigations don't always produce results as it depends on whether the timbers are suitable for analysis, but we've been lucky. The conclusion is that the roof timbers have two different felling dates with those at the west end felled in 1537. The two trusses at the east end date to 1675-1700, suggesting it was a later extension.
Thank you to all those involved, including Cumberland and Westmorland Archaeological and Antiquarian Society and the Nottingham Tree Ring-dating Laboratory. It all adds to our understanding of this building.