Hi Tim,

Some thatched roofs still have smoke blackening on the underside of the thatch from the days when the open hall fire was burning on the hall floor with the building open all the way to the rafters and apex of the roof. This practice ceased about 1550 - 1600. That is what happened inside this building but unfortunately we cannot see the underside of the thatch due to the plaster ceilings. Ideally thatch should just be raked down to remove any mouldy or composted crud and then a new dress top coat applied. In time this builds up to form quite a thickness. A long straw roof like this will need to be recoated every 25 years or so thus your guess as to overall age is probably quite a good estimate. It is now quite frowned upon to remove all of the thatch but eventually the weight of the thatch can become quite overpowering for slender rafters and breakage of same and / or localised collapse of sections of the roof is not unknown.

Regards

Ken Hume