it can be Svejk, there are two certificated barrier methods that put a barrier between the thatch and the rest of the house and also a fire retardant spray, but none of the options are cheap, the spray needs regular renewal and the barriers can only be applied when the thatch roof has been stripped off. Its suggested that the spray is re applied every 5 years and as its invisible, there is no way of seeing how much of the protective coating has worn away.