mortise joints in the tie beams. It is these mortise joints that provide
ideal 'cavities' that prove to be so attractive to bats.
How many other bats have gone unnoticed and maybe become
entombed? Not everyone realises that the bat roosts (even when the
bats are not there) and the access points are protected as well as all
bats under The Wildlife and Countryside Act 1981. There is a legal
requirement for advice to be taken from the Statutory Nature
Conservation Organisation before any work" is carried out that might
affect a bat roost.
This is a report of a small scale survey carried out over the last 18
months in Hertfordshire and Essex targeting barns that appeared on
planning application lists with the occasional extra barn if owners were
amenable. The aim of the survey was to establish whether or not barns
were used by significant numbers of bats.
There are three main types of barn construction
1. The simple Cruck frame
2. The more complex Box frame
3. The Post and Truss type of barn
The majority of the barns in this area are the post and truss type of
construction. These barns, especially the aisled type, proliferated in the
south and south-east, from Portland Bill to the Fens, between the 12th
and 19th centuries. Prefabrication was the rule from early times. The
weight of the larger timbers was enormous and the value of the unused
wood considerable. It was for these reasons that the timber
construction was prepared in the wood where the trees were cut. Each
piece of wood was jointed into its neighbour, numbered and transported
to the building site for assembly there.
The type of wood used for construction varied from Oak, Chestnut, Elm
and Ash. In Essex, Black Poplar was often used where grain was going
to be for sale: it was said that rats disliked Black Poplar. Softwood
only started to be used after 1870. The wooden frames were usually
assembled laid flat on the ground and then hoisted into a vertical
position. This method ensured that the mortise joints at the top of the
frame were really tight. There would be no space for air around the
socket. Where a mortise is too big for the tenon fitted into it, the
implication is not only poor workmanship, but assembly may have been
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