90% of the original rafters still exist and are in pretty good condition although you can visibly see the new additions. The roof has been replaced several times over the years with new boards, before that it would have been crudepieces of wood that would have held the reeds and later the thatch in place.
The beams are attached to the wall supports using wooden pegs. Metal nails have existed since roman times but they were not used as they rusted easily especially with the Tannin from the Oak that eats through metal, having wooden pegs means they can last for hundreds of years.
Within the rafters you can usually see some Daubenton bats but more times you can spot their Guano on the floor rather than the bats themselves.
The bats access the castle through the many holes it has in the roof and also the various chimneys.
Daubenton Bats are very common throughout the castle