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Advice on drainage and gradients for multi level patio

Posted: Wed Feb 22, 2023 7:44 am
by tvrulesme
We're in the process of planning an extension and part of the building works will be to sort out some landscaping issues as well as some internal damp problems caused by high exterior ground levels.

The site is complicated, overall it slopes quite a lot and the detached garage is 465mm above the house.

We are trying to achieve:
  • Lower the patio ground levels. I've dug a trial trench around the property and the internal damp now seems to be under control
  • Have a multi level patio as the whole site slopes downwards but we want the areas to be usable for a seating area
  • Finished surface to be yorkstone pavers which will finish a minimum of 150mm below DPC and floor levels
  • All existing rainwater connects to combined waste and BCO has agreed that future rainwater can also join to this as there is no place for a soakaway or any other alternative
  • The building is grade II listed and they are very fussy about changing anything in the existing structure but have agreed to allow channel or french drainage


Plan is to make every effort to move the water away from the house and garage.

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Looking for advice on drainage and gradients to take the water away from the foundations as much as possible.

Some pictures to help visualise

Trial trench around property to reduce damp
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Looking towards where the new extention between the two buildings will be
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Upper Patio with gates
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