The Minimum Roof Pitch for Regular Shingles

Roof pitch refers to the steepness of a roof as a ratio relative to absolute flatness. In North America we express this as a fraction of 12. Hence a roof pitch of 2/12 is a gentler gradient that say 4/12.

These measures tell a roofer those roofs rise 2 inches (or 4 inches) for every 12 inches of depth. We interpret this in terms of climbing precautions, and how well rain, sleet and snow will drain away.

Why Roof Pitch Varies for a Variety of Reasons

Thatched roofs have a steep pitch in order to drain properly. This characteristic knocked through into the Gothic architecture common on medieval European cathedrals. However roof pitch became shallower during the Renaissance period as architects turned to Greek and Roman styles for inspiration.

Nowadays roof pitch is more a matter of taste, unless the design must blend into the surrounding vernacular. However, the choice of roofing material may have the final say, as is the case with regular shingles.

Asphalt Shingles Require a Minimum Pitch of Roof

measure roof pitch in calgaryCanadians love their asphalt shingles for their great value and weather resistance. They are readily available in a variety of colours and styles too. However, the overlapping nature of their installation does have implications for roof slope.

That’s because very-low-sloped roofs drain relatively gradually compared to steeper pitched ones. While we may get away with a 1/12 slope with corrugated sheets, this is not the case with shingles owing to capillary action.

This natural phenomenon allows water to flow uphill against gravity, through narrow spaces because of intermolecular forces between the liquid and surrounding solid surfaces. In other words moisture can creep up behind shingles, and seep onto the surface below.

There is only one way to prevent this happening and that’s to have a roof pitch that’s steep enough to overpower the force of capillary action. The industry standard for regular shingles is a roof slope of at least 2/12. This incorporates a safety factor to allow for stormy conditions.

How Best to Determine the Pitch of Your Roof

If you want to know if your Calgary roof slope is safe for shingles, you could climb into your attic with a tape measure and dust off your geometry. It could be simpler to ask Valiant Exteriors to calculate your roof angle using their Eagle View software. You can call them on (403)829-1661 during business hours.

More Reading

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How to Walk on Concrete Roof Tiles Carefully

Low Pitch Shingle Roof: Fastily BY CC 4.0

Display of Roof Pitches: Enoctis BY CC 3.0