Extension drainage and patio

[Maatz123]

Hi all,

I need a lot of guidance and hand holding, finishing off the drainage outside new extension and patio prep.

We want to build a patio, side fence to fence to finish just below the bottom of the air bricks, its around 300mm from current soil level to desired finish level.

I understand I need to build a retaining wall (red lines) to build up to this level - first bit of guidance needed for this please.

I have a lot of hardcore as well as a lot of soil, however my understanding is I cannot use the soil to back fill as it will sink over time?

What do I need to do with the drainage, as you can see the guttering down pipe is not connected to the soak away drainage yet? (soak away is in place further down garden and pipe to meet downpipe is in place).

You can also see that the drainage from the kitchen hasnt been completed yet.

Do I need a threshold drain running across the back of the extension (blue line) and if so how do I complete the kitchen drainage and downpipe to soak away as it will be sitting right in the way?

Sorry for stupid questions, this was a 50% DIY build, hence the in completion.


https://freeimage.host/i/JE4yFaI

 

[23vc]

Assuming dpc level is at bottom of patio doors, you’d be better finishing the patio 2 courses of bricks below that, to satisfy the general requirement of 150mm below dpc. That also lines up with where the kitchen gulley has been been set. also means less filling to build the level up.

Patio can drain and slope to another gulley set at the right height into which the downpipe discharges.

You could retain the sides with decent thickness concrete slabs set vertical in concrete as a lightweight and easier alternative to building a retaining wall. Not sure why the whole thing needs to end up higher than adjacent ground on both sides though

 

[noseall]

Hi all,

I need a lot of guidance and hand holding, finishing off the drainage outside new extension and patio prep.

We want to build a patio, side fence to fence to finish just below the bottom of the air bricks, its around 300mm from current soil level to desired finish level.

I understand I need to build a retaining wall (red lines) to build up to this level - first bit of guidance needed for this please.

I have a lot of hardcore as well as a lot of soil, however my understanding is I cannot use the soil to back fill as it will sink over time?

What do I need to do with the drainage, as you can see the guttering down pipe is not connected to the soak away drainage yet? (soak away is in place further down garden and pipe to meet downpipe is in place).

You can also see that the drainage from the kitchen hasnt been completed yet.

Do I need a threshold drain running across the back of the extension (blue line) and if so how do I complete the kitchen drainage and downpipe to soak away as it will be sitting right in the way?

Sorry for stupid questions, this was a 50% DIY build, hence the in completion.


https://freeimage.host/i/JE4yFaI

Hardcore ok - soil not ok.

If the patio has to fall to the house - fit an Aco or similar. Or just run it away from the house if you can gain the falls.

Patio height - 150mm below DPC (Regulations).

Fence with gravel boards - fine to slab against. You need to build this prior to slabbing.

Kitchen waste - sewer/foul drain. Storm (Aco) - soakaway etc.

 

[Maatz123]

Thanks for the replies.

My understanding is that the rule of 150mm below DPC is a 'should' and not a 'must'......is this not correct?

As per this image, the red line is the DPC level.

The reason I want to have finish patio level higher (blue line) is obviously because it will look nice and I wont have to have a step down from the kitchen.

Is this possible???

 

[noseall]

My understanding is that the rule of 150mm below DPC is a 'should' and not a 'must'......is this not correct?

As per this image, the red line is the DPC level.

The reason I want to have finish patio level higher (blue line) is obviously because it will look nice and I wont have to have a step down from the kitchen.

Is this possible???

It's frowned upon, as well as contravening the rules. Surveyors love to fluff out their home-buyer reports with the dread of raised patios. The reality with modern construction is that there is unlikely to be issues with damp breach. However, you may have an absorbent brick that is susceptible to frost etc, so you still need to be wary.

What is the issue with having a step down?

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• noseall
• 20 Dec 2023

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• noseall
• 20 Dec 2023

 

[Maatz123]

Thanks for the replies and help noseall, really appreciate it.

Your right, a step looks OK.

I think my previous image was completely wrong as well. I believe DPC is the red line in this image, so If I was following advice my finish patio would be around the blue line.

If I was to follow advice and build below DPC, would I still need any Aco drainage running across, a long the blue line?

 

[23vc]

That’s what I originally said, yeah. And although an aco may be a better idea, if the fall is right, you can drain it into a gulley against the house.

 

[Maatz123]

Thanks 23vc I know you originally advised this, but I really wanted to go ahead with my desired outcome of having a high enough patio level where a step is not needed as in my opinion it looks perfect.

 

[Maatz123]

Hi Noseall, your advise to slab against gravel boards, I guess would work fine on my side of the fence, however couldn't I run into issues on the other neighbors side if they ever wanted to replace their fence?

 

[noseall]

Hi Noseall, your advise to slab against gravel boards, I guess would work fine on my side of the fence, however couldn't I run into issues on the other neighbors side if they ever wanted to replace their fence?

Not sure what you mean? Surely your fence is effectively their fence. Panels sat above gb's are interchangeable.

 

[Maatz123]

Sorry I didn't mean to fence, but the fence posts and gravel boards.

Say I go with your idea and have a mortar bed and slabs butted up to gravel boards, IF my neighbor ever decided they wanted to remove/replace the gravel boards or fence posts my patio would be in trouble as it would lose its structure on the side

 

[23vc]

You could retain the sides with decent thickness concrete slabs set vertical in concrete as a lightweight and easier alternative to building a retaining wall

With a small gap between that and the fence. Done that on mine, works fine. Occasionally pull the odd weed out that grows in the gap.