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Damp Proofing

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

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.

4 Answers from MyBuilder Damp Proofing Specialists

Best Answer

Hello my name is Patrick
I would definitely move the channel 1 or 2 bricks out away from house this will take the water away from the wall.
What I would recommend is to then dig down about 12 inches put in some clean 20mm stone, leave down about about 4 inches and put a breathable membrane down and cover with coloured stone, this will make a feature of it and take any water away but keep below the air bricks and Dpc hopefully this helps.


Answered 17th Apr 2020

Stick with the Telescopic / periscope vents as you call them
Then you can just leave as is
Sounds like he’s done a fairly decent job overall despite the obvious air brick height
The fact it runs into an already connected drain system is very good news
& should funnel away most everything
I use these vents regularly there not to hard to install but are so so important
Good luck


Answered 19th Apr 2020

1) The chappie that laid the patio didn’t know is job
2) When laying a patio you never have water running towards a property
3) If you move the Top Water Chanel about a meter away from the property with a run of towards the top water chanell slope this should solve the problem & will keep the air vents clear
Sorting the problem of top water

Regards Chris


Answered 19th Apr 2020

Remove the aco drain a cut out one brick below top of channel install cavity tray put bricks back and channels this will extend any wash up the wall by 150mm which is regs using a 300mm wide tray regards Steve


Answered 18th Apr 2020

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