Adding Pitch to a Flat Roof

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  • 12-40 hours
  • Intermediate
  • 750-2,500
What You'll Need
Measuring tape
Roof trusses (pre-manufactured)
OSB or plywood
Bridging material
Tar paper
Roofing material
Roofing nails

If you have a flat roof, you may decide to add pitch for more attic space or maybe just to enhance your home's look. The flat roof already has a slight pitch as it is required by law. Various styles of a pitched roof can be built or you can purchase pre-manufactured trusses. You will need to ensure that you are in standards with your local building codes and have the permits required. Most people view pitching a flat roof as a tedious job. This does not have to be the case with the right step-by-step guide to guide you along. However, it requires certain tools and good knowledge to be done.

Step 1 - Calculate the Roof Span

Calculate how much the roof span is going to be by measuring from one top plate to the other top plate. An overhang that is measured from the face board needs to be added. This is how you will know where the roof’s ridge will be.

Step 2 - Calculate Material Prices

making calculations

Find out about the pitch and make estimates on the cost of materials. Roof trusses are manufactured with a pre-estimated pitch and delivered to the construction building site. If you will want a roof pitch that is not standard, it is best to build own roof pitch. When you have found the pitch, you will need to calculate the area of the surface for your new roof. Make a list of the materials too.

Step 3 - Prepare the Materials

Have the roof material removed and tie the trusses onto the current lumber using a Sawzall and a crowbar. Wood will be exposed. Therefore, be sure that it is not raining. If it is, you can use construction tarps to cover the area of work. Cut out the rot, if there is any, and determine if your current flat roof lumber can handle the new roofing load.

Step 4 - Re-Sheath Roof

sheathing a rooftop

Use OSB or plywood to re-sheath the roof. This will depend on your area’s building code. You can use the old sheath to sheath your new one if the old sheath used on the current flat roof does not show signs of rotting. In order to do this, twice the material is needed. Galvanized nails can be used to connect the sheathing.

Step 5 - Replace Roofing Material

Replace roofing material with tile, rubber composite, shingle, slate, or cedar shake. Set the tar paper under the roof material. Use the fasteners that are recommended for your roof type.

Once the roofing is complete, you can add a new attic space or a room to store the items that you cannot keep in the garage or closets, such as Christmas decorations. Another advantage of pitching your roof is that the rain will now run down the roof instead of sitting there creating a pool.