What is a plumb cut in roofing?

A plumb cut is a cut made at a vertical angle on the rafter, allowing it to fit snugly against the ridge board or peak of the roof.

How do I calculate the multiplier for a 10/12 pitch?

To calculate the multiplier for a 10/12 pitch, divide the rise (10) by the run (12), which gives you approximately 1.25. This multiplier can be used for various calculations related to the roof's dimensions.

Why is snow load not sized in this explanation?

Snow load sizing is dependent on local climate conditions and building codes, which vary widely. It is important to consult local regulations to determine the appropriate snow load for your specific area.

10/12 gable rafter on a 20 ft span

Explore the essentials of gable roof construction, including pitch multipliers, plumb cuts, and considerations for snow load sizing. Learn how to effectively design your roof.

Formula SSC-2026.1

10.00 / 12 · 39.81°

Pitch angle

39.81°

Multiplier 1.3017

Common rafter

14 ft 2 7/8 in

Tail 1 ft 3 5/8 in

Cuts

39.81° plumb

50.19° seat

Roof area

740 ft²

7.40 squares

Shingle bundles

3 bundles per square + 10% waste

Sheathing / felt

26 sheets

3 underlayment rolls

Delivery weight

3,030 lb

1,374 kg · 70 lb bundles, 46 lb sheets, 28 lb rolls

Gable truss triangleLive scaled blueprint

Rise and run are scaled from the span, overhang, and pitch. The small triangle is the pitch ratio.

Bill of materials and shopping list
Item	Net	Waste	Order	Unit price	Line total	Source Spec Material / Tool
Architectural shingle bundles	7.40 squares	10%	25 bundles	USD	$1,050.00	Source Spec Material / Tool
4x8 CDX sheathing	23.1 sheets	10%	26 sheets	USD	$728.00	Source Spec Material / Tool
Underlayment rolls	740 ft²	overlap allowance	3 rolls	USD	$165.00	Source Spec Material / Tool
Ridge cap bundles	26.0 ft ridge	—	2 bundles	25 ft per bundle	—	Source Spec Material / Tool

Source links open a product search on the Amazon storefront for the selected currency. SiteSpecCalc may earn a commission. The link does not change the quantities above.

Side-by-side pitch comparison
Pitch	Degrees	Multiplier	Rafter	Squares	Bundles	Sheets
10.0/12	39.81°	1.302	14 ft 2 7/8 in	7.40	25	26
12.0/12	45.00°	1.414	15 ft 5 5/8 in	8.04	27	28

Show the deterministic formula

Angle = arctan(rise ÷ 12). Multiplier = √(1 + (rise ÷ 12)²). Gable run = span ÷ 2 − ridge thickness ÷ 2. Rafter length = (run + horizontal overhang) × multiplier.

Plumb cut = pitch angle. Seat cut = 90° − pitch angle. Area uses both slopes on a gable and one slope on a shed, and it includes a rake overhang equal to the eave overhang.

Bundles = ceiling of squares × 3 × 1.10. Sheets = ceiling of area × 1.10 ÷ 32. Rolls use 360 ft² effective coverage. Delivery weight plans 70 lb per bundle, 46 lb per sheet, and 28 lb per roll, then the header converts that pound total at 1 lb = 0.45359237 kg.

Contractor sign-off

Project: 10/12 gable rafter on a 20 ft span

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Date

Verified by (PE / electrician / inspector)

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This sheet is an estimate for ordering and layout discussion. It is not a sealed design. Confirm the quantities with a licensed local professional and the authority having jurisdiction before you buy or build.

Engineering notes

A gable roof with a 10/12 pitch means that for every 12 horizontal units, the roof rises 10 vertical units. This pitch can be used to calculate the roof's slope and determine the appropriate materials and structural support needed.

The multiplier for a 10/12 pitch is approximately 1.25, which is used to convert horizontal spans to vertical rises. When making plumb cuts, it’s essential to ensure that the cuts are accurate to maintain the integrity of the roof structure. Additionally, snow load considerations should be factored in based on local building codes, but specific sizing is not provided in this context.

Code reference

Refer to local building codes for specific requirements regarding snow load and structural integrity.

Field questions

What is a plumb cut in roofing?: A plumb cut is a cut made at a vertical angle on the rafter, allowing it to fit snugly against the ridge board or peak of the roof.
How do I calculate the multiplier for a 10/12 pitch?: To calculate the multiplier for a 10/12 pitch, divide the rise (10) by the run (12), which gives you approximately 1.25. This multiplier can be used for various calculations related to the roof's dimensions.
Why is snow load not sized in this explanation?: Snow load sizing is dependent on local climate conditions and building codes, which vary widely. It is important to consult local regulations to determine the appropriate snow load for your specific area.