What is a 4/12 roof pitch?

A 4/12 roof pitch (also written as 4:12) means the roof rises 4 inches for every 12 inches of horizontal run. This equals approximately 18.43 degrees. It's a common pitch for residential roofs with asphalt shingles.

What is the minimum roof pitch for shingles?

Most asphalt shingles require a minimum pitch of 2:12 (about 9.5 degrees) with special underlayment, or 4:12 (18.4 degrees) for standard installation. Below 2:12, you need a membrane roof system like TPO or EPDM.

How do I calculate rafter length?

Rafter length is calculated using the Pythagorean theorem: Rafter = √(Run² + Rise²). For a 12-foot run with a 4:12 pitch (4-foot rise), Rafter = √(144 + 16) = √160 = 12.65 feet. Add overhang if needed.

What pitch is considered a steep roof?

Roofs with a pitch steeper than 9:12 (about 37 degrees) are considered 'steep' and often require additional safety equipment for workers. They shed water and snow very efficiently but cost more to install.

Can I walk on a 12/12 pitch roof?

A 12:12 pitch (45 degrees) is very steep and difficult to walk on without fall protection. Most roofers use harnesses, toe boards, or roof jacks. DIYers should NOT attempt repairs on pitches steeper than 6:12 (26.5°) without proper safety gear.

🏠 Roof Pitch Calculator

Calculate Pitch, Angle & Rafter Length

Rise (inches)

Vertical height per 12" run

Run (feet)

Horizontal distance (half span)

OR Enter Angle (degrees)

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🏠 Understanding Roof Pitch

Roof pitch (also called slope) is the steepness of a roof expressed as a ratio of vertical rise to horizontal run. It determines water drainage, material choice, and construction difficulty.

Pitch vs Angle

Pitch is expressed as a ratio (e.g., 4:12), meaning 4 inches of rise for every 12 inches of run.
Angle is expressed in degrees (e.g., 18.43°).

Angle = arctan(Rise / 12) × (180 / π)

Common Roof Pitches

Pitch	Angle	Typical Use	Min. Material
1:12	4.76°	Flat roof (membrane)	TPO, EPDM
2:12	9.46°	Low slope	Special shingles
4:12	18.43°	Standard residential	Asphalt shingles
6:12	26.57°	Moderate slope	All materials
8:12	33.69°	Steep (Victorian)	Tile, slate
12:12	45°	Very steep (A-frame)	Any

💡 From Rick Martinez, Licensed Roofing Contractor (25 years):

"Most homeowners don't realize that roof pitch affects COST. A 12:12 pitch can cost 50% more to roof than a 4:12 because of safety equipment, ladders, and slower work. Also, don't trust 'flat roof' marketing—anything under 2:12 WILL pool water eventually. I always spec at least 1:12 for drainage, even on 'flat' commercial roofs."

⚠️ Common Mistakes

1. Confusing Rise with Height: Rise is per 12" of run, NOT the total roof height. A 24-foot wide house (12-foot run each side) with a 4:12 pitch has a 4-foot rise, not 8 feet.

2. Forgetting Overhang: Rafter length from ridge to wall is calculated from the run. If you have a 12" overhang, add that to your rafter length AFTER the calculation.

3. Using Wrong Material: Installing standard 3-tab shingles on a 2:12 pitch without special underlayment will cause leaks. Always check manufacturer's minimum pitch requirements.

Reviewed by Rick Martinez

Licensed Roofing Contractor, 25 years experience in residential and commercial roofing systems.

Visual Representation

🏠 Understanding Roof Pitch

Pitch vs Angle

Common Roof Pitches

⚠️ Common Mistakes

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