Grass on Sand Dunes?

[Alcuin]

Roofing material around the world is traditionally grass or reed. In English, the word for this stuff and the verb for using it is thatch. (Anglo-Saxon þæc, same word pronounced approximately the same way for “roof� or “thatch,� and the verb þeccan, “to [put a] roof [on]� or “to thatch.� It’s related to the modern word deck, which still retains its old meaning “cover.� “To deck� someone is to put them on the floor by hitting them; the “deck� of a ship; “Deck the halls with boughs of holly,� &c.) Thatched roofing is excellent stuff, and a well-thatched roof with good-quality reed can last several decades. The stuff burns, of course, which is a drawback; but the main reason it is only used in more rural countries is that it is time-consuming and expensive to hire someone to thatch a roof: in the less-developed and more rural regions of the world, people’s time is less expensive. (That sounds terrible, but I suppose it must be true.) A well-thatched roof does not readily burn, however (most fires in thatched roofs start around the chimneys, where the embers get stuck and overheat the roofing material nearby); and thatch is warmer in the winter than asphalt or wooden shingling, and certainly warmer than tiles, metal or slate!

Not only were houses thatched, but so were barns, outbuildings, and so forth: it was by necessity the roofing material of choice in the medieval world. On some low-lying buildings, so the story goes, cats and dogs, which were not always welcomed into the house (particularly cats during the Middle Ages), would climb onto the roof because it was warmer there. (Heat rises, and it rose through the roof...) When it rained, however, the thatch would become slippery, and the animals would slide off – hence the turn of phrase.

I’ve seen other versions of the source of the phrase, and attempts to debunk this one. For now, I don’t know the truth of the matter; but I do know that the phrase was used in England in the 1300s, so I think there’s a better chance that this source of the saying is true rather than some of the other explanations offered. I know that some websites and internet pundits claim that this explanation is specious and of recent minting; however, one of my college English professors, himself a medievalist (with a masterful command of Anglo-Saxon), offered us that explanation one afternoon during an autumn downpour in 1978.