How to build a shed roof over an existing roof

Constructing a shed roof over an existing one will help you protect your old roof and also insulate it against the elements. You will need to use sheet metal to build the roof. This is a simple job, just make sure that you respect the regulations.

Tools and materials

  • hammer
  • tape measure
  • screwdriver or screw gun
  • saw
  • metal cutters
  • sheet metal
  • roofing nails
  • rubber gasket tape
  • long screws
  • purlins

Attaching the purlins

The purlins represent the framework on which the shed roof will be installed. They need to be attached to the roof to provide a solid base. Line them up alongside the edge of the roof and press them tightly against one another. Make sure that they are even. The rest of the purlins will be installed up the roof. You can cut them to the right size by using a saw. On each side of the sheet metal you will want to install a purlin, for support. Screw them securely.

Attaching the sheet metal

Now it’s time for the sheet metal. Attach a strip of rubber gasket tape that stretches the entire length of the piece to the furthermost purlin. This will assure that water won’t get inside your house. After you have applied the tape and exposed the adhesive, then lay the piece of sheet metal. Make sure that it is completely even with the purlin. Now use roofing nails to attach the sheet metal to the purlin.

Finishing the layering

Now continue the process until the roof is entirely covered. You may need to use a metal cutter to trim the last pieces to the right size. If you want to be completely sure that no water will enter your house, then apply a thin bead of caulk where the pieces of sheet metal overlap.

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