Book 3, Question 55
Why Do Houses Have Sloped Roofs?
A sloped roof is a slide for rain and snow. Water runs off, instead of pooling and leaking through the ceiling. Slopes keep our houses dry!
From the book
Page from A Million Whys Book 3
More fun facts
- Roof slope is measured by how many inches the roof rises for every 12 inches across. A 4 in 12 roof climbs 4 inches every foot.
- Asphalt shingles should never go on a roof that rises less than 2 inches per foot.
- On gentle slopes, water drains more slowly, so it is more likely to back up and cause damage from ice dams.
- Gentle slopes also let wind driven rain sneak in more easily during storms.
- Even roofs that look flat usually slope a little. Building codes often require at least a quarter inch per foot.
- If a long roof beam sags just three quarters of an inch in the middle, water can pool in that low spot. This is called ponding.
- Engineers design nearly flat roofs to hold the deepest pond possible, imagining that all the main drains are blocked.
Sources: asphaltroofing.org, woodworks.org
Questions kids ask
Why are shingle roofs steep instead of flat?
Water drains slowly on gentle slopes and can back up and leak. Shingles should never go on roofs that rise less than 2 inches per foot.