Damp Proofing

Patio slopes towards back of house with drainage channel 1 brick below DPC and level with air brick

Anonymous user 09/03/2024 - 3.08 PM

I have a 1970's semi and the garden slopes to the back of the house. All the floors are suspended timber. When I bought it 18 months ago it had a pre-existing lean-to which went across most of the back wall. It was on a raised brick base which was on top of an existing concrete base. The concrete is like a patio and goes along the back of the house and round the side to the back wall of the attached garage and is below the DPC. The base for the lean-to was built above the DPC and covered both air-bricks. My builder checked under the floor and said despite the lean-to being in place for around 30 years, it all looked in good condition with no damp or rot. The lean-to has gone and he laid a patio on top of the existing concrete base. The patio slops towards the back of the house and he installed a drainage channel that goes along the back wall to an existing drain (laid in July 2019). My problem is the top of the channel is 1 brick below the DPC and the air-bricks are directly below the DPC and so the bottom hole of the air-bricks are at the same level of the top of the drain channels. Any water that might miss the drains or might pool against the house will go directly through the bottom holes of the air bricks and cause damp over a period of time. I can't afford to rip up the patio and the concrete base to slope it away from the house but I need to find a solution before it becomes a major problem with damp. I was thinking of moving the drainage channel out from the wall and sinking them down another 1/2" so that I can fill in the gap from the house with cement that can slope towards the drains. I have also looked at periscope air vents but I haven't really got a clue whether either of these will work. Any advice would be much appreciated.