If you are planning a hip to gable roof conversion, one important factor to calculate is the change in attic volume. Converting a hip roof into a gable roof often increases usable attic space and improves headroom.

A Hip to Gable Roof Volume Calculator helps you estimate:

• Existing hip roof volume
• New gable roof volume
• Added attic space
• New ridge height

In this guide, we’ll explain the formulas used in the calculator and provide a step-by-step example.

Step 1: Understanding Roof Pitch

Roof pitch is usually expressed as Rise / Run, such as 6/12.

This means:

• Roof rises 6 inches
• For every 12 inches of horizontal run

To calculate roof height (H):

$H=\frac{\text{Rise}}{\text{Run}}\times \frac{W}{2}$

Step 2: Volume of a Gable Roof

A gable roof forms a triangular prism.

Formula for triangular prism volume:

$V_{gable}=\frac{1}{2}\times W\times H\times L$

Where:

• W = House width
• H = Roof height
• L = House length

Step 3: Volume of a Hip Roof

A hip roof volume can be estimated as:

$V_{hip}=\frac{1}{3}\times W\times H\times L$

(Approximation assuming four sloped sides reducing attic space.)

Step 4: Added Volume After Conversion

To find additional attic space:

$V_{added}=V_{gable}-V_{hip}$

Full Example Calculation

Let’s assume:

• House Length (L) = 40 ft
• House Width (W) = 24 ft
• Roof Pitch = 6/12

Step 1: Calculate Roof Height

$H=\frac{6}{12}\times \frac{24}{2}$

$H=0.5\times 12=6$

Step 2: Gable Roof Volume

$V_{gable}=\frac{1}{2}\times 24\times 6\times 40$

$V_{gable}=0.5\times 24\times 6\times 40$

$V_{gable}=2880$

Step 3: Hip Roof Volume

$V_{hip}=\frac{1}{3}\times 24\times 6\times 40$

$V_{hip}=1920$

Step 4: Added Volume

$V_{added}=2880-1920$

$V_{added}=960$

Final Result

After converting from a hip roof to a gable roof:

• Existing Volume = 1920 cubic feet
• New Volume = 2880 cubic feet
• Added Attic Space = 960 cubic feet

This means you gain 960 cubic feet of usable attic volume.

Why This Calculator Is Useful

A Hip to Gable Roof Volume Calculator helps you:

• Estimate new attic space
• Plan loft conversions
• Calculate insulation needs
• Estimate construction cost impact
• Understand structural benefits

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