We want to build a wooden deck over a concrete patio. How do we ensure water drainage?
It’s not recommended that you rely on a concrete slab to support a sundeck. The deck should have its own structural system for support (footings, beams, etc.). You could break-up the patio with a chipping or hydraulic demolition hammer. This will allow water drainage through holes and cracks. But if you get to the point of using a demolition hammer, you may as well just remove the concrete spoils and grade the soil away from the house.