Talk about an unsung source of cleanliness and health for us moderns! The noticed-only-when-its-leaking hard roof.
And yet, such roofs were rare until the industrial age. Before then, most persons lived beneath thatched roofs — which might look quaint when you see one pictured on a greeting card, but in reality they were nasty, filthy, and dangerous. Here’s a description from Frances and Joseph Gies, Life in a Medieval Village (Harper & Row, 1990), page 34:
Roofs were thatched [in medieval Europe], as from ancient times, with straw, broom or heather, or in marsh country reeds or rushes . . . . Thatched roofs had formidable drawbacks; they rotted from alternations of wet and dry, and harbored a menagerie of mice, rats, hornets, wasps, spiders, and birds; and above all they caught fire. Yet even in London they prevailed.