How to lower 25cm thick concrete patio that's supporting house to adds damp. Patio is 25cm concrete

You don’t necessarily need to lower the patio, especially if the concrete is acting as structural support to the walls. If the patio level is above the damp proof course (DPC), the issue is more about moisture bridging rather than the slab itself. A more suitable solution would be: Install an ACO drainage channel around the perimeter of the property to intercept and redirect surface water away from the walls,Ensure the channel is installed below DPC level and connected to a suitable drainage outlet,Apply a waterproof bitumen coating (such as Black Jack) to the external wall to provide additional moisture protectio.Check that finished levels fall away from the property to prevent water sitting against the wall Breaking a 25cm reinforced concrete slab that may be supporting the structure could compromise the building if not properly engineered, so this should be avoided unless designed and approved by a structural engineer. This approach is commonly used to resolve damp issues without interfering with the structural integrity of the property.