Detailed Drainage Design Condition on Planning Acceptance

[acurachris]

Hi

I have had plans for a two storey side extension accepted which was great until i saw two conditions appear. The conditions are:

Condition 4 - No development shall take place unless and until details of the full detailed drainage and sustainable urban drainage design including all relevant documents to limit the proposed peak discharge rate of storm water from the development to meet the requirements of the Councils Level 2 Hybrid Strategic Flood Risk Assessment (SFRA) have been submitted and approved in writing by the Local Planning Authority. The development shall not be brought into use until such works, as approved, are implemented in full and they shall be retained and maintained to a standard capable of limiting the peak discharge rate as set out in the SFRA and FRA thereafter.

Condition 5 - No development shall take place until details of flood resilient measures are to be submitted to and approved in writing by the Local Planning Authority. The development shall then be constructed in accordance with the appproved details and retained thereafter.

I feel like i am going around in circles with this as I don't know exactly what the council are expecting. I have spoken to and emailed the planning officer but he says it's not his area of expertise! I have spoken with the guy who drew the basic house plans and he said "google companies that do it"; which i did.

I have had varying responses from, that seems excessive for a small extension to £1650 + vat to draw plans not including any site visits, tests, requests for info. £1650 + vat for someone to draw something to say the water from your new roof goes here or there!

I get that i need to show the extension will not increase storm water into the mains drains and will need to show if i can use a soak away (doing infiltration test next week) or if i need rain water harvesting but how "detailed" do these drawings need to be to satisfy the conditions?

Has anyone experienced these conditions and what exactly is required? Is it detailed like CAD drawings or a simple diagram? Should the guy doing the building regs do this? Basically what will satisfy the conditions?

Cheers, Chris.

 

[Nakajo]

Welcome to my world. It's all bonkers.

 

[noseall]

The hilarious part is that you may spend £££'s on the accurate drawings only for the excavations to start and find that the original proposals are unworkable and get completely changed.

Chance your arm and send something in on the back of a fag packet. Invent the invert levels and generally make it up as you go along. You need to use words like inspection chamber.. granular material... falls to 1:40....invert level....percolation test....5m from any structure....roddable access....etc.

 

[Ian H]

Also say, Dye was introduced into the system, this proved the existing surface water runs to ..... via .......

Do you know your existing drain layout and where abouts in Lancashire are you?

 

[acurachris]

Ian H - A ground/drain survey that was done on our property in 2010 before we bought it (included in the paperwork from the solicitor) shows a rough layout of the storm drains and I know where the foul drains go as the sewer grid is at the back of the house about 3 metres from where the soil pipe comes down (had blockage a year ago and lanes for drains opened the grid). To me it all seems rather straightforward to be honest, it seems that some people over complicate things! I'm in Urmston, Manchester which i think is classed as Greater Manchester/Lancashire.

Noseall - I have been thinking of doing some kind of drawing myself although i'm concerned it won't be "professional" enough to satisfy the decision makers at the council, even though they can't advise what i need to show! I am going to do an infiltration test (that's genuine) so i will have some basic test results.

Another guy i spoke to yesterday said he could prepare a report to aid the designing of the drains for £650 + vat (haha - not even the drawings) and that my building regs drawer guy should include drawings to conform with part h.

 

[Ian H]

The professional drawings are pretty crap anyway, mine look like this and the ones I've seen from DynoRod and others are not much different. Just symbols for gullys, soil stacks and manholes and basic info on depth and size of pipe within the manholes.

That all does sound massively over complicated, I can't imagine Urmston is a flood risk.

Once you have done you percolation tests I can't see why the design needs to be anything more than a gully, 5mtr run of 110mm pipe then a square labelled soakaway. I'd have a go yourself.

 

[^woody^]

Whoever did your plans should have done this as part of his design work.

Anyway, its a very basic drawing showing the drain runs and connections (new and old) and you say what amount is going down the new drains.

You state that rain water from your new roofs is going into a soakaway (1m3) and thats it. No ground tests required. You then just add a sentence or two about the water perculating the ground and dispersing.

Read the council's flood risk policies, pick out key phrases and items, and just refer to these and how your work complies. Nothing lengthy or involved.

 

[^woody^]

Welcome to my world. It's all bonkers.

True, and that's got nothing to do with this post.

 

[wessex101]

We had a thread about flood risk assessments recently.

From the sounds of it the area has got a problem with flooding from the surface water drains so they want a design to show the quantity of rainwater run off from the extension and that it will not discharge straight into the existing surface water sewer during heavy rain thereby overloading the sewer, so as Woody said discharge to a soakaway or perhaps some kind of holding tank/cistern. Although I suspect if the run off is below a certain limit you can discharge direct to the sewer.

As for the flood resilient measures, pretty standard stuff and reasonably easy to find online.

Your designer has been a bit of a plonker, you would think if he works in the area he should already know about the policy and if it is a new policy or the first time he has encountered it he would be interested in following it through so he has it covered next time. That's what I do, how else do you learn? Maybe I should just tell my clients to "Google it".

 

[acurachris]

Those drawings do look quite basic (i'm sure even i could do that ). Urmston a flood risk; i know right! We had to have a flood risk assesment done as a part of the planning process because we are in flood risk zone 2 mainly due to us being "close" (not that close, maybe 3/4 mile-1mile!) to the Manchester Ship Canal. These were the drawings from that survey in 2010 - i've added the red comments.

wessex101 - i've been a bit of plonker really for hiring him in the first place, i don't think he's a proper architect just a guy who draws up basic plans. Why would I not need to test the ground for soakaway suitability? People i have spoke to (a lot and still none the wiser!) say the ground may not be suitable to have a soakaway unless the water can disperse at a certain rate. The ground here is clay based and i don't think it's suitable before i even do the test, but they're not going to take "my word" so i'll have to prove it one way or the other i guess. Maybe i'm mis-informed.

Thanks for your repsonses people.

 

[tony1851]

Just make it up by cutting and pasting stuff from the internet. Nobody in the council will actually sit down and read it - they just want to make sure youu spend £££s. It's one of the perks of their miserable little jobs.

 

[wessex101]

Just make it up by cutting and pasting stuff from the internet. Nobody in the council will actually sit down and read it - they just want to make sure youu spend £££s. It's one of the perks of their miserable little jobs.

At least they only applied it as a condition on the approval. Here you have to produce all this stuff including flood risk assessments, bat surveys and heritage statements and a whole load of other paperwork before they will even accept the application, then it could be refused.

 

[wessex101]

Why would I not need to test the ground for soakaway suitability? People i have spoke to (a lot and still none the wiser!) say the ground may not be suitable to have a soakaway unless the water can disperse at a certain rate. The ground here is clay based and i don't think it's suitable before i even do the test, but they're not going to take "my word" so i'll have to prove it one way or the other i guess. Maybe i'm mis-informed.

Thanks for your repsonses people.

That will depend on local conditions, if you are on clay it may not be an option. We have some areas here where they are just not allowed but that is more to do with unstable sandy ground conditions. Check local guidelines and if in doubt you'll have to do a percolation test. Ah that brings back memories as office junior looking into muddy holes and timing how long it takes for the water level to drop, or not dropping if it was on clay. Once I seem to recall we had a high water table and a wet winter and the water level actually rose. Happy days.

As I said before you'll have to read the Council's policy and do the peak discharge rate calculation, probably just new roof area multiplied by notional peak rainfall rate per hour and then see where that takes you. And don't forget to deduct any existing roofs or drained hard paving areas that are being demolished to make the results more favourable.

 

[tony1851]

At least they only applied it as a condition on the approval. Here you have to produce all this stuff including flood risk assessments, bat surveys and heritage statements and a whole load of other paperwork before they will even accept the application, then it could be refused.

Agree about that 100%. We have the same demand up here for reports which could be affixed as conditions; the system is peverse and can lead to applicants spending into four figures, and then ending up with a refusal.

 

[tony1851]

Increasingly, council Planning departments are asking for details which should really be in the Building Regs domain (eg drainage/gas membranes/land remediation/energy efficiency/security etc). The irony is that most planning officers are not even competent to assess these reports.