Building a reverse gable roof

A gable roof is a type of roof with a high pitch. They are very popular in areas with high quantities of rain and snow, because they allow the water to slide down quickly. A reverse gable roof is also known as a dormer window roof.

This one sits perpendicular to the main roof line.

Some of the tools and materials needed for the job are:

  • Paper
  • Pencil
  • Calculator
  • Compass
  • Circular saw
  • Hammer or nail gun

Roof pitch

Before you begin the construction, you will need to determine the pitch of your mainn roof, so that they will match. You can do this by dividing the rise by the run (length of the roof from peak to eaves). You can then calculate the pitch of the dormer gable roof.


Measure the pieces of wood and then cut them to the right size. Also be careful to cut the beams at the right angles.

Assembling the trusses

You will need to first lay the roof base. Then you can set the diagonals and secure them to the base and at the peak per local building codes. Do this for the rest of the trusses.

Roof assembling

Now assemble the trusses on the roof. You should start at the outed edge and work your way inward. Maintain the spacing between the trusses and joists. Secure the trusses using nails. You will need to trim the trusses so that they can fit between the dormer and the main roof. Also you will need to remove some roofing materials from the main roof. Now you will need to install the ridge.

Roofing underlayment

Cover the roof with plywood. Secure it in the roof trusses using screws or nails. After you have done this, lay the water barrier tar impregnatd felt on the roof. This will protect it against water. Start from the bottom of the roof and then continue your way upwards. Use staples to secure it. Overlap the layer by about 3 inches. You can now cover the roof with the material of your choice.

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