Grades K–2 · Everyday Life
Why does a roof have overlapping shingles?
Look at a roof covered with shingles. The pieces overlap, a little like the scales on a fish. Each upper piece covers the uphill edge of the piece below it.
In the diagramUpper shingles overlap the ones belowEnlarged side view of a sloping roofRoof deckUnderlaymentRain movesdown and outThe upper piece covers the uphill edge below.A roof has more protective layers underneath.
Rain lands on the outside. Gravity pulls the water down the slope. It can run over one shingle and onto the next, instead of finding an uncovered uphill edge to slip beneath.
Shingles are one part of the roof. A protective layer underneath helps manage water too, and the roof deck supports the covering. These parts work together. The little drawing follows ordinary rain moving downhill; real roofs also meet wind, snow and ice.
About this explanation
Starting knowledge: Recognize rain, above and below, and a slope.
Sources
- US Department of Energy · Pacific Northwest National Laboratory — Flashing of Penetrations in Existing Roofs: Water Management
- US Department of Energy · Pacific Northwest National Laboratory — Asphalt Shingle Roofs