Porch and Sun porch

Porch noun - A covered structure adjoining an entrance to a building.

Sun porch and porch are semantically related. In some cases you can use "Sun porch" instead a noun "Porch".

Sun porch noun - A room enclosed largely with glass and affording exposure to the sun.

Porch and sun porch are semantically related. You can use "Porch" instead a noun phrase "Sun porch".