To French Drain or to not French Drain?

[LukesLog]

As part of a multipronged approach to tackling my interior damp problem. I am looking to tackle my exterior height issue(two inches higher externally compared to internally), at the same time as improving my overall rainwater control(downpipes that flow out to groundwater in places).


You can see from the pictures attached, that the downpipe on the front/gable end corner just puts out to ground.

My hope is to dig a French Drain which lowers the external height back to original(a drop of around 200mm based on the Drain to the front of the house pictured), and run the downpipe through the trench to the working drain at the front of the property.

My questions are many, but I'll ask the priorities. Is this a workable plan, or is there a more obvious solution I am missing?

Thank you.

 

[LukesLog]

Pictures attached.

 

[alexander]

its illegal to run rain water & foul water in the same drainage, has been for years

 

[LukesLog]

its illegal to run rain water & foul water in the same drainage, has been for years

Is that even to a privately handled septic tank? If not, I have no idea where my current downpipes connect to.

 

[RyanD]

its illegal to run rain water & foul water in the same drainage, has been for years

Many old properties have rain water connected into foul. Ours certainly has and it was stated so on the Thames Water report when we purchased the property.

 

[a twig]

Is that even to a privately handled septic tank? If not, I have no idea where my current downpipes connect to.

If you have a private septic tank then it’s preferable that you keep the rainwater seperate rather than overwhelm the septic system and potentially end up with a garden full of watery sewage whenever there is a heavy downpour.

Your rainwater goods should go to a soakaway - you can either have one big one and tie all your gutter downpipes to it, or have several smaller ones - even as far as one per downpipe if your layout makes running pipes around the garden tricky

Paying for a drain survey for both rainwater and waste drainage is always a good idea

 

[Stevers]

Surely the one place that rainwater should never ever go is a septic tank. It will just push even less adequately treated sewage into whatever watercourse or ground water that the septic tank drains to, and dilute the hard working good bacteria trying to digest waste. If you have a septic tank, soakaways are the answer unless you can pipe your rainwater direct to a watercourse.

Sadly any existing soakaway for an older building is likely to be blocked and be too close to buildings, 5m from any structure is I believe required, and can be difficult to achieve in the more crowded environments that will have mains drainage. We're edge of town with mains drainage, and our back roof drains into the culverted stream in the lane behind us, and the front roof under the pavement into the gutter in the road in front of us. Both required me to repair and enhance them to work as intended. We are on a slope with retaining walls around us, and being urban there is little scope for soakaways since the only bit of the garden far enough away from structures (mine and my neighbours) has some evil clay subsoil under it.

 

[LukesLog]

Thanks everyone. Going to be more complicated than first thought.

It does seem like a drain survey and professional opinion are the best next step.

 

[Kearn]

its illegal to run rain water & foul water in the same drainage, has been for years

Not true at all.

Ours is combined and we pay a charge each year for the privilege as stated on our bill.

 

[Kearn]

If you have a private septic tank then it’s preferable that you keep the rainwater seperate rather than overwhelm the septic system and potentially end up with a garden full of watery sewage whenever there is a heavy downpour.

Your rainwater goods should go to a soakaway - you can either have one big one and tie all your gutter downpipes to it, or have several smaller ones - even as far as one per downpipe if your layout makes running pipes around the garden tricky

Paying for a drain survey for both rainwater and waste drainage is always a good idea

You learn quite a lot by having a CCTV survey… ! Including any possible unseen issues from redundant historic pipes etc.

An aborted farmhouse purchase had some kind of large hole with a pipe leading away from it, slap bang under a large downstairs room now covered in concrete.

 

[Stevers]

its illegal to run rain water & foul water in the same drainage, has been for years

In saying this, I'm sure we'd have to distinguish between new builds and existing builds.

It's running rain water into foul water drains that causes our sewers to overflow into watercourses, there's simply too much water to be able to treat it all in times of heavy rainfall, and to provide the capacity to do so on mixed systems would be ruinously expensive. It's not particularly comforting that the sewage that escapes is heavily diluted by the excess rainwater. So whether legal or not, it's hardly a good thing, but can be difficult to avoid for some.

 

[alexander]

In saying this, I'm sure we'd have to distinguish between new builds and existing builds.

It's running rain water into foul water drains that causes our sewers to overflow into watercourses, there's simply too much water to be able to treat it all in times of heavy rainfall, and to provide the capacity to do so on mixed systems would be ruinously expensive. It's not particularly comforting that the sewage that escapes is heavily diluted by the excess rainwater. So whether legal or not, it's hardly a good thing, but can be difficult to avoid for some.

providing you are fixing existing pipes its not illegal, it only illegal to add extra pipe work / inlets to make things work