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Flashing & Ridge/Hip Calculator

Calculates linear footage of flashing needed for valleys, hips, and ridges. Determines ridge cap shingle bundles and metal flashing quantities.

Results

Ridge Length
--
linear feet
Hip Length (total)
--
linear feet
Valley Length (total)
--
linear feet
Penetration Flashing
--
linear feet
Total Flashing
--
linear feet
Ridge Cap Bundles
--
35 ft/bundle

Exact measurements should be verified on the roof. Hip/valley factors are based on simplified geometry. This is an estimate for material ordering purposes.

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How to Use This Calculator

1. Enter building dimensions. Length is the longer side of the building. Width/depth is the shorter side (the direction the roof slopes down).

2. Select the roof pitch. The pitch affects the hip and valley rafter lengths. Steeper pitches mean longer hip and valley runs.

3. Choose the roof type. Gable roofs have a ridge but no hips. Hip roofs have both a ridge and 4 hip rafters.

4. Add valleys and penetrations. Each valley adds a diagonal run of flashing. Vent pipes, chimneys, and skylights each require their own flashing kits.

How the Flashing Formula Works

The calculator uses hip/valley factors based on pitch to estimate diagonal rafter lengths from the building dimensions.

Hip_Factor = sqrt((Rise^2 + 144) / 144)

Hip_Run = Building_Depth / 2

Hip_Rafter_Length = Hip_Run x Hip_Factor

Valley_Length = Hip_Rafter_Length (same calc)

Ridge_Cap_Bundles = ceil((Ridge + Hips) / 35)

Penetration flashing is estimated at 8 linear feet per vent pipe, 15 feet per chimney, and 20 feet per skylight. These are standard industry allowances for material ordering.

Frequently Asked Questions

How do I calculate flashing for a hip roof?
For hip roofs, calculate hip rafter length using the hip factor for your pitch. Multiply the building depth divided by 2 by the hip factor. For an 8/12 pitch, the hip factor is 1.1744. A 50-foot deep building has a hip run of 25 feet, so each hip rafter is about 29.4 feet long. Multiply by the number of hips (typically 4) for total hip flashing.
How many ridge cap bundles do I need?
One bundle of ridge cap shingles covers approximately 35 linear feet of ridge or hip. Measure the total ridge and hip length, then divide by 35 and round up. A roof with 30 feet of ridge and 60 feet of hip needs 90 feet total, or 3 bundles of ridge cap.
How much flashing do I need per penetration?
Standard allowances: vent pipe boots need about 8 linear feet of flashing each, chimneys need about 15 feet (step + counter flashing), and skylights need about 20 feet each. These are estimates — actual measurements should be verified on-site.

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