Patio higher than DPC and new foundations

11 Sep 2022
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United Kingdom
Hi, this is my first post, I hope the below will make sense. We have been doing some research online but still in a bit of a quandary about what to do!

We have had a small new extension put in with bifold doors in place however the foundations and new DPC are below the patio. Unfortunately the patio slopes slightly towards the house, and so does the foundation, meaning we have seen water running under the dpc in the recent down pours we've had. This is also exacerbated by the fact that there are two different levels of foundation and the base of steel post interfering (see photos).

One solution would be to lower the ground outside below DPC and perhaps install an aco drain? This would likely mean chasing out some of the concrete foundations, something we're concerned may compromise the steel.. the main piece of concrete that the steel post is bolted to is 1mx1mx1m. This would still leave the foundations higher than the patio so we have thought about adding a full length step to cover this.

Essentially we'd like to find the easiest and best looking solution if possible but struggling as to what this could be.

Any advice would be greatly appreciated.


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What is the lump of concrete with the pink chalk on? Is it covering a pipe?

Normally, you'd have foundation, trench/brick/block then DPC, then carry on up, your DPC seems to be at ground level sat on the foundation, have a check to see if there is another DPC sat on top of air vent (under bifold) do you remember one being put it there?

Normally you'd allow two course of brick (150mm) below DPC to the ground level.

Is water getting inside?
Frustratingly a considerable amount of water this week..

The lump of concrete with the pink chalk is the foundation for the vertical steel beam (1mx1mx1m - we hope). For some reason the builder built the 1m3 foundation and the strip foundation for the bifolds at slightly different levels... Very frustrating to deal with as the dpc also follows this line and there is a route for water to pass through the weak hardcore/mortar mix between the two concrete foundations.

There is no additional dpm above the air vent, however I have installed a second one in the cavity yesterday (builder had partially backfilled with concrete, I've now dug back out to avoid thermal bridge) as there was a lot of water ingress recently and noticeable perforations in the dpm..

We had quite a bit of water coming in over the last week, the slope on the foundations sending it right under the dpm and inside... first time I've seen ACTUAL rising damp in action wicking right up the concrete blocks (presumably due to the perforations in the dpm?)!

I wish the builder had allowed 150mm before hitting ground level, however due to the floor height indoors and the patio height, I can see why he's done it (sort of), but there was clearly not a lot of joined up thinking on his part.

Can we grind off some of the concrete so it slopes away at the very least? I can't see how we're going to get 150mm below the dpm..
Surely the patio etc needs lowering now? Digging it all out to the correct depth and allowing the water to drain away from the house.
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Put in an aco threshold drain for doorway and maybe a o drain around walls.

then finish paving flush with inside floor level.

can you put in sub floor ventilation elsewhere?
Thanks for all your responses. I've lifted the paving and cement today. I'm thinking to run a step around the base of all doors (in an L shape below all doors) and extend the air bricks as we can't place the ventilation anywhere else. Unfortunately we can't get away with a neat flush threshold as there's no where else to put the air bricks. Perhaps put a threshold/aco drain at the base of the step? Would putting a step around the base of the cill/doors (bridging the dpm) be an issue if it was slightly pitched and the ground below it was sloping away? Whatever way you look to solve the issue, the concrete foundations still run towards the house - do you think I'm OK to grind away some of the foundations so the they don't run back into the house?


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There is a constant supply of idiot "builders" making this stupid mistake

Presumably they know no better, or hope to get away with the money before the homeowner realises

I suppose it would be possible to grind a slot in the patio and excavate a French Drain, but it might cost thousands.

Have you got rid of the builders yet? What language do they speak?
Yes agreed JohnD. We're rid of the builder now, caused too many problems before even realising this one.

We're hoping to just grind a slope on the concrete footing slabs away from the house then re-lay the patio at a lower level (level tbc) and sloping away from the house. This would mean we'd then need to put some paving slabs in as a step over the concrete footings as the heights are mis-matched.
We're not going to be able to get the foundations 150mm below the DPC so we are thinking grinding a slope away is the first point of call then I guess the questions we have are:

1) Do you think we'd still need to put in some sort of drainage system and if so where placed? Between the step and the patio? Ideally we don't want to run a channel though the concrete but maybe needed in front of it?

2) Would we get away with lower the rest of the patio 75mm? Or is this only with a drainage system in place? Otherwise would we need to go 150mm lower? The concrete footings under the doors will still be at DPC level of course.

Many thanks

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