Water, water all around ...

[Emanresu]

Similar issue to this one https://forum.buildhub.org.uk/topic/39497-patio-issue/

 

Our late 70's house is built below a road and two levels of garden. There are retaining walls and steps up to the garden. Around the house is a slab patio which is in need to replacement. We have been reluctant to replace the patios due to the amount of silt laden water that comes off the garden each winter/spring. So the question is how to improve the drainage before we press the button and get the patio guys back in. The job they did on our driveway was first class but a lot easier to drain as it has a slight slope. The patios area are flat.

 

Main issue is how to deal with the block drain holes embedded in the retaining walls. Can they be re-drilled or replaced. Secondly there is a small drainage area that is no connected to any drain and gets swamped with water when there is anything heavier than a light shower. Suggestions where to start looking to understand how to solve the issue.

 

 

[TerryE]

  On 29/01/2025 at 13:10, Emanresu said:

Main issue is how to deal with the block drain holes embedded in the retaining walls.

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These are a feature not an issue.  Sorry.  Excess rain. typically in winter, has to go somewhere, and where it goes depends on your subsoil profile, e.g. 

a high chalk content will be free draining; a clay layer will tend to keep water near the surface.  Without adequate drainage the upper lawn area could saturate and become fluid, leading to your retention walls collapsing.  The water coming out of the drains simply means that they are doing their job.   You need to get the water away before it floods the patio.  Once on the patio where it gathers depends on the fall-away design. Having truly level patios is a mistake. They should really have a few % gradient to allow drainage

 

We have a  similar raised area with wall retention, but I put in a soak-away for the upper area linked to our main soak-away, so I didn't need extra in-wall drainage.  Where our patio meets the house, I have a 75×75 drainage gutter filled with 5mm pea shingle and linked to the rainwater down-pipe traps.   We have one small area where the gradients run counter leading to rainwater pooling, but because our patio was laid on 50mm MOT 1 over 300mm MOT3 drainage that is again linked to main soak-away, it was again simple to use a 110mm circular cutter to cut a hole in the patio at the low point, dig out the sand and MOT1, them insert a but of 110mm downpipe as a sub-layer retainer with a slot in cover to create an instant drain point. 

 

You and your builder need to discuss similar remediation if you find the pooling runoff unacceptable, but also realise that the builder won;t regard this as a free-remediation, so you will need to do this work yourself or pay to have it done.   

 

 

 

Edited January 29 by TerryE

[Emanresu]

Thanks for the heads up on the alternatives/

 

About 15% of the patio area is currently gravel on clay. We want to put slabs on this area which will further reduce the chances of the runoff draining. A suggestion from our usual builder (not the driveway guys) is to connect the current small (concrete?) gutter/soakaway which runs the length of the supporting walls with the main drains. Should the pooling/groundwater be sent to the drains or should it drain away to the sublayers using new 110mm holes? 

[TerryE]

BRegs for new builds state that it shouldn't go to the drain, but I think you can be pragmatic when tweaking an existing patio area.  You need to do one of the two: feed to soakaway or to the drain.  My inclination would be to do whatever is the simplest / least disruptive. 

Your "usual builder" seems to be suggesting what we did.  

 

Edited February 1 by TerryE