It was originally built with a very steep pitch and the turves laid on it were about 12 inches (30 cm) thick in places with little drainage. As they got wet, the weight of the roof grew until it pressed down hard enough to break one of the windows!
The first task was stripping the roof back to the underlying timbers. We discovered that the original builders had built it with slab wood overlying the ash rafters, then carpet, then straw, then damp proof membrane gaffer (aka duct) taped together, then another layer of carpet then finally turves dug up from around the site.
The turves came off fairly easily by just sliding them off on the underlying carpet. Digging the resulting piles up and moving them about the site was a lot harder!
We then stripped the black plastic damp proof membrane off and saw it had ripped in a few places. We will replace it with EPDM pondliner, as this is more durable although more expensive. Under the plastic was the straw and then more carpet. These both acted as insulation and will be replaced when relaying the roof.