HAP Cut and Heel Height Calculator for Rafters

The HAP Cut and Heel Height Calculator determines the vertical heel height and HAP (Height Above Plate) based on the rafter's pitch, seat cut length, and thickness. HAP is a vital framing dimension indicating how far above the top plate the rafter extends, often used in pre-cut rafter design and layout.

• You will need to know the height above plate (HAP) measurement to calculate the height of the ridge above the plate. Subtracting the ridge beam's depth from the ridge height will give you the height of the post.
• You make the height above plate measurement from the wall's top plate to the top of the rafter along the plumb line.
• HAP height depends on rafter depth, the heel cut, and the roof's pitch.
• You must know the height above plate (HAP) measurement to calculate the ridge height above the plate. Subtracting the ridge beam's depth from the ridge height will give you the height of the post.
• You measure the height above the plate from the wall's top plate to the top of the rafter along the plumb line.
• HAP height depends on the rafter depth, the heel cut, and the roof's pitch.

To calculate a full birdsmouth cut including seat and vertical dimensions, try the Birdsmouth Cut and Heel Height Calculator.
For converting roof pitch to slope angle in degrees, use the Roof Pitch to Angle Calculator.
If you need to find the total rafter length from run and pitch, see the Common Rafter Length Calculator.

As the pitch of the roof increases, so will HAP. We are looking at it without a birdsmouth cut here;

If your rafter has an exact depth of 12 inches or lays flat (0/12 pitch), the height above the plate is 12 inches. At a 5 /12 pitch, HAP is increased to 13 inches. At a 12 /12 pitch, the height above the plate becomes 17 inches.

Adding a birdsmouth;

If your heel cut is one inch at a 5/12 pitch, HAP = 12 inches.
If your heel cut is one inch at a 12/12 pitch, HAP = 16 inches.

Roof Framing