How to Measure the Square Foot of a Hip Roof

A roof with hips, or diagonally sloping edges, is slightly more complex to measure than a roof that has rectangular faces only. However, it is easy if you have the right tools, are methodical, and take neat notes. You will proceed one roof face at a time and add up the area of all the faces at the end. The simplest way to measure a hipped roof face is to use two plumb lines to divide it into three sections: a rectangle and two triangles.

Things You'll Need

• Two plumb lines
• Tape measure
• Carpenter's square
• Calculator
• Pen and paper

Instructions

1. Drop a plumb line from the top left corner or "ridge cap" of one hipped face of the roof all the way to the bottom edge of the hipped roof face. Pull the line taut and use a carpenter's square to ensure the line meets the bottom edge of the roof face at a 90-degree angle.

2. Repeat Step 1 for the top right ridge cap of the hipped roof face.

3. Calculate the square footage of the rectangle defined by the two plumb lines and the top and bottom edges of the hipped roof face. To do this, multiply the length of one plumb line by the length of the top ridge. Call this number "Sum A" and write it down on a sheet of paper. Do not remove the plumb lines yet.

4. Calculate the square footage of the left triangle defined by the left plumb line, the left hip and the bottom edge of the roof from the left plumb line to the bottom left corner. To do this, multiply the length of the left plumb line by the length of the bottom edge of the triangle, and then divide by two. Call this number "Sum B" and write it underneath Sum A on the tally sheet.

5. Repeat Step 4 for the right triangle defined by the right plumb line, the right hip, and the bottom edge of the roof from the right plumb line to the bottom right corner. Call this "Sum C" and write it underneath Sum B on the tally sheet.

6. Add Sums A, B and C to determine the square footage of the hipped roof face. Call this number "Face A" and write it on a new tally sheet.

7. Remove the plumb lines and repeat Steps 1 through 6 for each hipped roof face, naming each face's square footage "Face B," "Face C" and so on on the tally sheet.

8. If there are any rectangular roof faces, measure the bottom edge and a side edge of each rectangular roof face and multiply those two lengths to determine the square footage of the face. Continue naming the square footages of the roof faces--"Face D," "Face E" and so on--and writing them down in a single column on the tally sheet.

9. Add all faces together to determine the total square footage of the roof.

References

• Roof Help: Measuring Your Roof

Resources

• Builder Bill: Roof Glossary