Learn & Understand

The Oldest Job in Building: A History of the Roof

Every roof does one ancient job — keep the rain out — and the materials used to do it trace the whole history of building. From bundles of reed to machine-made asphalt shingles, roofing has always been a contest between the weather above and the shelter below, won by whatever material could shed water reliably and last.

Why Roofs Are Pitched

The pitched roof is a near-universal answer to rain. A slope sheds water quickly, so it runs off rather than pooling and seeping through. The steeper the roof, the faster it drains — which is why rainy and snowy regions favor steep pitches, while dry climates tolerate flatter ones. The angle of a roof is a direct response to how much water it must shed.

From Thatch to Slate

Early roofs used whatever shed water locally: bundled thatch of reed or straw, layered so water ran off the surface; wooden shakes split from logs; and, where it could be quarried, slate — thin stone that lasts generations. Each material worked by overlapping small units so that water always ran onto the piece below, never into a seam. Overlap is the enduring principle of every roof.

The Asphalt Shingle

The dominant modern roofing — the asphalt shingle — won on cost, weight, and ease. A mat saturated with asphalt and surfaced with mineral granules is cheap to make, light to carry, and simple to nail down in overlapping courses. It brought durable, weatherproof roofing within reach of ordinary homes, which is why it now covers so many of them.

Squares, Bundles, and Overlap

Because shingles overlap, more material is needed than the bare roof area, and the trade measures it in its own units — the “square” covering a hundred square feet, sold in bundles. Complex roofs with many hips, valleys, and dormers demand extra for all the cutting and fitting those features require. The overlap that keeps water out is the same feature that drives the material count up.

Estimating the Shingles

To convert roof area into squares and bundles, use the Roof Shingle Calculator. Plan the drainage below with the Gutter Length Calculator, and the attic beneath with the Attic Ventilation Calculator.