Sanity check: Relocating soakaway installed against foundations of house

grassylawn · 03-05-2021 9:16am #1

The drain under one of the gutters for my house has a soakaway installed right there. About 40 sq metres of patio also drains into this drain. I have installed a large rain butt on the downpipe for the gutter but need to do more to deal with the patio water draining into it. The patio is on a concrete slab.

I have sketched the problem and my conceived solution in mspaint in two images below.

The soakaway appear to have been constructed when the patio was put in in around January of last year. The pipe from the patio connects to the drain lower down than the outflow pipe. However I dug up the outflow pipe and it goes as far as the other side of the concrete apron and it is just normal [clay] soil on the other side.

My idea is to cut the pipe from the patio and connect it to a corrugated land pipe with the perforations facing upwards. Then run that along the side of the house in a French drain and connect it to a new soakaway in an appropriate location at the front of the house. I have tried to communicate this in the second picture below.

The lawn on the side of the house it is on gets pretty waterlogged itself during wet seasons. The ot

Does this idea make sense? I don't work in construction so it is possible I am missing something important or could be creating a problem somewhere.

Am I right in thinking that I should fill the existing soakaway with something as soon as the water has somewhere else to go? Sand? Cement? Something else

I'll need to go across water mains, a gas line and I think power cables to get the drain to a feasible location for a soakaway. They are all at the front corner of the house. I'm assuming all of these will be deep enough that that won't be too difficult to achieve. Am I right?

chooseusername · 03-05-2021 10:10am

Quote;
My idea is to cut the pipe from the patio and connect it to a corrugated land pipe with the perforations facing upwards. Then run that along the side of the house in a French drain and connect it to a new soakaway in an appropriate location at the front of the house.

I believe those pipes are perforated all round.
Maybe get non-perforated and make your own perforations.

mickdw · 03-05-2021 10:18am

Just make sure you place any drainage pipes well above foundation level of the house.
If you were to successfully drain below foundation level, you could cause all sorts of structural problems.

grassylawn · 03-05-2021 10:24am

chooseusername wrote: »

Quote;
My idea is to cut the pipe from the patio and connect it to a corrugated land pipe with the perforations facing upwards. Then run that along the side of the house in a French drain and connect it to a new soakaway in an appropriate location at the front of the house.

I believe those pipes are perforated all round.
Maybe get non-perforated and make your own perforations.

You can get semi-perforated ones as well as fully-perforated ones. The lower left panel of page three of this brochure gives an example of what I would be looking for:

https://www.coopsuperstores.ie/files/Co-Op_Farm_-_lowering_Prices.PDF

grassylawn · 03-05-2021 10:30am

mickdw wrote: »

Just make sure you place any drainage pipes well above foundation level of the house.
If you were to successfully drain below foundation level, you could cause all sorts of structural problems.

How deep would the foundations be? It is a 90 sq m 1979 block-built bungalow on floating slab.

I plan to only go as deep as I needed to create a gradient. I'll need to dig the trench manually and it will be an awkward and hard enough job. The pipe I plan to connect the french drain to is barely below the surface.

I'll need to go across water mains, a gas line and I think power cables to get the drain to a feasible location for a soakaway. I'm assuming all of these will be deep enough that that won't be too difficult to achieve. Am I right?
...I will add that to the original post actually.

Calahonda52 · 03-05-2021 10:37am

Depending on the space to the right of the house, and if u have access fo a small digger and a dumper/skip
I would dig an intercepter soak hole/drain about 1.5m away from the concrete apron, starting at the patio and then turn around the corner and out toward the front of the house, finishing with a larger soak hole well way from the house.
The drain could be 500/600/750 wide, string at 300mm deep,depending on the scale of the runoff and filled with crushed stone, with layer of geo textile membrane on top and then re-lay the lawn.
the bottom on the drain could have a slight slope with a land drain pipe in the bottom.

Penn · 03-05-2021 11:12am

Soakaways should typically be 3m from boundaries and 5m from structures (house/shed etc).

There's no issue having a french drain around the side of the house, but the pipe must be perforated and direct water into the soakaway.

I'd also be inclined to get perforated pipes which are perforated the full way around, or to have the perforations facing down. You're not trying to catch the rainwater as it soaks through the french drain, you're trying to disperse it once it rises to a certain level. If the perforations were facing upwards most of the water would have to rise to over half the height of the pipe in the french drain before it enters it. With the perforations facing down, once the water reaches the bottom third of the pipe it should enter the perforations and flow thorugh the pipe until it reaches a point where the water is lower.

grassylawn · 03-05-2021 11:14am

Calahonda52 wrote: »

Depending on the space to the right of the house, and if u have access fo a small digger and a dumper/skip
I would dig an intercepter soak hole/drain about 1.5m away from the concrete apron, starting at the patio and then turn around the corner and out toward the front of the house, finishing with a larger soak hole well way from the house.
The drain could be 500/600/750 wide, string at 300mm deep,depending on the scale of the runoff and filled with crushed stone, with layer of geo textile membrane on top and then re-lay the lawn.
the bottom on the drain could have a slight slope with a land drain pipe in the bottom.

There's not much space at all to the right of the house. It slopes up pretty sharply and there are dense and established shrubs along the whole of that side, with a gap for steps near the back. I plan to hire a digger to make the soakaway itself but there is not space for one along the side.

500mm is wider than I imagined but should be possible in the space that is there. There isn't room to put it far from the concrete apron though because of the slope and shrubs. I imagine the awkwardness of the layout is why it wasn't done properly before.

The existing drain on the patio is under rubber play tiles that are enclosed at the side by the concrete. Connecting to a different point on that drain would be outside my capabilities and would need to go through deeper ground in the slope beside it. We walk a lot on that slope as it is a main access point to the lawn. I'd much prefer to connect to the pipe from the existing connection unless this is a bad idea for some reason. The existing connection is 2m from the house (the concrete apron is wider at the back).

grassylawn · 03-05-2021 11:19am

Penn wrote: »

Soakaways should typically be 3m from boundaries and 5m from structures (house/shed etc).

There's no issue having a french drain around the side of the house, but the pipe must be perforated and direct water into the soakaway.

I'd also be inclined to get perforated pipes which are perforated the full way around, or to have the perforations facing down. You're not trying to catch the rainwater as it soaks through the french drain, you're trying to disperse it once it rises to a certain level. If the perforations were facing upwards most of the water would have to rise to over half the height of the pipe in the french drain before it enters it. With the perforations facing down, once the water reaches the bottom third of the pipe it should enter the perforations and flow thorugh the pipe until it reaches a point where the water is lower.

I had read that perforations should be on the bottom alright in normal setups. The reason I was thinking of placing it the other way up in this case was that I want it to carry the water from the patio as well and imagined it soaking into the ground on the way to the soakpit if I had the perforations on the bottom. I don't know if that is something that would actually happen or not, outside of water being spilt on the patio in dry conditions. The solid area that drains into is large enough (40 sq m iirc).

There's plenty of space for a soakaway in the front - it's just connecting from the back that might be an issues

Penn · 03-05-2021 11:29am

grassylawn wrote: »

I had read that perforations should be on the bottom alright in normal setups. The reason I was thinking of placing it the other way up in this case was that I want it to carry the water from the patio as well and imagined it soaking into the ground on the way to the soakpit if I had the perforations on the bottom. I don't know if that is something that would actually happen or not, outside of water being spilt on the patio in dry conditions. The solid area that drains into is large enough (40 sq m iirc).

There's plenty of space for a soakaway in the front - it's just connecting from the back that might be an issues

The perforations on the pipes aren't so big that they'll catch all the water that way. Not to mention the pipe won't be the full width of the drainage channel as you'll still have gravel both sides of the pipe, plus the gravel will disperse the water throughout the drain.

If you lay geotextile around the drain and have the perforations in the pipe on the bottom, once the water gets to the bottom of the drain and builds up, the perforations on the bottom of the pipe will allow the water into the pipe and out to the soakway quicker.

grassylawn · 03-05-2021 11:41am

Another thing is that the solid pipe from the patio is near the surface of the ground - so the pipe in the French drain would be starting at a much shallower depth than in a regular French drain setup. I suppose I should put a slab or something over it at the start where it might be walked on to protect it.

The main thing is carrying the water from the patio to a soakaway. The land drainage is probably secondary to that. I'm concerned that if the perforations are in the bottom of the pipe it might compromise the crriage of the water from the patio to the soakaway.

grassylawn · 03-05-2021 11:45am

Any thoughts on how/whether to fill the existing soakaway at the corner of the house?

Penn · 03-05-2021 11:47am

grassylawn wrote: »

Another thing is that the solid pipe from the patio is near the surface of the ground - so the pipe in the French drain would be starting at a much shallower depth than in a regular French drain setup. I suppose I should put a slab or something over it at the start where it might be walked on to protect it.

The main thing is carrying the water from the patio to a soakaway. The land drainage is probably secondary to that. I'm concerned that if the perforations are in the bottom of the pipe it might compromise the crriage of the water from the patio to the soakaway.

Well then what you need instead is an aco drain along the edge of the patio.

https://www.aco.co.uk/products/raindrain

grassylawn · 03-05-2021 11:49am

Penn wrote: »

Well then what you need instead is an aco drain along the edge of the patio.

https://www.aco.co.uk/products/raindrain

There already is an aco drain along the edge of the patio (under rubber tiles). That's what the solid pipe in the sketch above connects to. However it connects to a soakaway that is directly against the edge of my house. I am looking at how to relocate the soakway. I'm asking if using a perforated pipe in the way I've described is a good idea.

Penn · 03-05-2021 11:55am

grassylawn wrote: »

There already is an aco drain along the edge of the patio (under rubber tiles). That's what the solid pipe in the sketch above connects to. However it connects to a soakaway that is directly against the edge of my house. I am looking at how to relocate the soakway. I'm asking if using a perforated pipe in the way I've described is a good idea.

You can keep the aco drain and just redirect it to a new soakaway.

But no, using a perforated pipe in the way you've described is not a good idea for the reasons I've already stated. Again, you wrap the drain in geotextile, use drainage gravel, and have the perforated pipe with perforations pointing down (unless pipe is perforated the whole way around). You can switch to a solid pipe between the drainage channel and the soakaway, but in the drainage channel, perforations point downwards.

mickdw · 03-05-2021 11:59am

grassylawn wrote: »

How deep would the foundations be? It is a 90 sq m 1979 block-built bungalow on floating slab.

I plan to only go as deep as I needed to create a gradient. I'll need to dig the trench manually and it will be an awkward and hard enough job. The pipe I plan to connect the french drain to is barely below the surface.

I'll need to go across water mains, a gas line and I think power cables to get the drain to a feasible location for a soakaway. I'm assuming all of these will be deep enough that that won't be too difficult to achieve. Am I right?
...I will add that to the original post actually.

If its on a raft as you say, you should be able to identify the side of the raft by digging a small hole against the wall of the house.
Id imagine not very deep at all. Todays rafts are typically built sewer pipes coming out near the bottom of the raft.

grassylawn · 03-05-2021 12:09pm

The ground gets waterlogged too though in the area to the right of the patio. There is a need for land drainage there as well. I don't know if there is the same need the whole length of the side of the house though

Perhaps put a French drain in the lawn and join it to the solid pipe from the patio at the corner?

grassylawn · 03-05-2021 12:30pm

I think I need to connect the orginal outflow pipe from the gutter drain to the new solid pipe as well, and change the drain under the gutter to connect to that. The water butt is helping but it is almost full after a day of heavy rain and the diverter on the downpipe is letting some water past. Not sure how easy any of that will be.

Calahonda52 · 03-05-2021 2:19pm

grassylawn wrote: »

There's not much space at all to the right of the house. It slopes up pretty sharply and there are dense and established shrubs along the whole of that side, with a gap for steps near the back. I plan to hire a digger to make the soakaway itself but there is not space for one along the side.

500mm is wider than I imagined but should be possible in the space that is there. There isn't room to put it far from the concrete apron though because of the slope and shrubs. I imagine the awkwardness of the layout is why it wasn't done properly before.

The existing drain on the patio is under rubber play tiles that are enclosed at the side by the concrete. Connecting to a different point on that drain would be outside my capabilities and would need to go through deeper ground in the slope beside it. We walk a lot on that slope as it is a main access point to the lawn. I'd much prefer to connect to the pipe from the existing connection unless this is a bad idea for some reason. The existing connection is 2m from the house (the concrete apron is wider at the back).

I was just giving ideas that others, such as Penn, more qualified than I, to explore.

Are there drainage holes in the retaining wall?

grassylawn · 03-05-2021 2:22pm

Calahonda52 wrote: »

I was just giving ideas that others, such as Penn, more qualified than I, to explore.

Are there drainage holes in the retaining wall?

No drainage holes in the retaining wall. On the left side I have dug a trench in the lawn that drains into the side of the aco drain on that side. Before I did this the septic system flooded because surface water was going in. The trench basically follows the line of the sewage pipes so the access points and the treatment tank do not have surface water entering them. That trench will be a French drain when I complete it. That alleviates the water logging on that side.

Sanity check: Relocating soakaway installed against foundations of house

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