A louvered roof weighs typically between 400-500kg per structure dependent on final size and specification. This load is spread evenly over the post uprights, creating a load per post of around 100-125kg and therefore it is possible to install a louvered roof on all ground types, with little or even no groundworks.
For an existing patio, subject to the patio being in good condition with the patio intact, solid and no cracks in the slabs/tiles, the louvered roof can sit directly on top of the patio, with the posts attached down to the patio slab/tile through concealed base plates using resin bonded anchors (threaded steel rods), which provide a stress-free anchorage which is usually stronger than the base material itself. Commonly used for the anchoring of structural steel such as columns, beams, safety barriers and railings, resin bonded anchors provide a premium anchoring solution with maximum load capabilities, with the fixings never coming loose as they have formed a stress-free bond.
This is the same fixing method we use for attaching lean-to louvered roofs (with no rear posts) to façades along with patio awnings to facades that create much higher loads (stresses and strains) due to their cantilever effect.
Where the ground surface is not solid including timber decking and grass a small concrete pad is required beneath each post, which depending on the ground surface will be between 400-500mm square x up to 250mm high (thick), with the post uprights attached to these concrete pads using the same resin bonded anchor method details above.