You might think that the area would run out of redundant agricultural buildings to convert but they seem to keep appearing and still hold charm for many people.

This is no scholarly research (see below for that) but just my observations from many years of working on barn conversions.

The barns of the central Lake District may appear all quite similar but in fact are seldom so. Stone for construction is heavy and difficult to transport and so will normally come from the nearest quarry, sometimes mixed with field 'cobbles' - rounded stones from a beck (stream) or cleared from the land. The higher the proportion of cobbles the greater the likelihood of instability over the centuries as rain washes out any earth packing within the wall, until the weight of the slate roof is all that provides sufficient friction to stop the whole wall tumbling down (something to bear in mind when propping a barn roof).

In some areas the local stone has no strata and can only be smashed into jagged pieces - not ideal for walling but needs must. You tend to see more mortar around such stones rather than a true drystone walling technique.

You also have to remember that the function of a barn has some bearing on the arrangement of the plan, height, construction and any openings. The barn and farm cottage were often part of the same structure.

The oldest barns I see in the central Lake District seem to date from 1646 onwards - i.e. that is the earliest date stone I have come across in a barn. However the roof timbers I would think are frequently much older. I have read that the permission of the Lord of the Manor was required to cut down construction timber and so old timbers were commonly recycled. You can occasionally find cruck frames from earlier buildings which may have stood on the ground, reused at higher level to support roof beams (purlins).

Stone was also reused - indeed it still is. It is a very flexible material although care needs to be taken when demolishing old walls for reuse that the clean outer stone is kept apart from any inner stone which has lime wash or mortar adhering.

Quoin (corner) stones seem to be largest in the oldest barns for a reason that I have never worked out.

'Barn' is often a misnomer, at times being used to describe stables, hay stores, accommodation, cow sheds, sheep sheds, kennels and all manner of outbuildings.

It is very common to find a barn with openings modified, moved or just blocked up as needs changed over the years - there are clues in straight joints in the otherwise random rubble stonework or an oak lintel (the beam above an opening) left in place.