Soakway Cost and Water Consumption

[Ed_MK]

1 hour ago, Ian said:

Just an educated guess but I’m assuming your build is in Scotland?

 

The system there can be a nightmare and is very different to the one operating in Wales & England.

 

nope

Buckinghamshire 

[Ian]

19 minutes ago, Ed_MK said:

 

nope

Buckinghamshire 

Wow!!....and Local Authorities wonder why they are losing business to private Approved Inspectors!

 

It's not often that I'm surprised by something to do with Building Regs but your description of what they want from you reminded me of the old days when I first started work as an architect in the late 80's. (and the system that still operates now in Scotland)

Edited April 24, 2018 by Ian

[PeterW]

On 18/04/2018 at 18:18, Ed_MK said:

 

I have re-jigged the footprint to move it slightly more AWAY from the fence (and hence the bushes)

 

Errr that’s a planning change ..!! Can’t just move a footprint as that could be a very expensive mistake ...!

[Ed_MK]

Hi Peter,

 

When i say "move" ...I wish i COULD
I have already had the initial plans "shrunk" across the width to fit.

I am working off the external masonry dimensions, as thats all i have until the foundation guys finalise the drawing for base

 

I know along one edge (where the trees (bushes) are i have 1.8m from external masonry finish to the fence) and so about 2.5m from the closes actual bush,
on the other edge i have 2 "corners" that are actually 1.2m from the boundary fences on each end. the land is an oblique diamond shape so i cannot move the
house left or right at ALL

So I dont really have anywhere to go ..If i move the house closer to the fence, I may "tickle" the RPZ of the hawthorns and if i move it further away then I am not leaving 
enough "gap" at the corners

 

I originally was trying to keep a border of 1.5m all around ...which is possible...but with all the talk of roots and stuff i was considering asking groundworkers
to shift it about so that i could grab literally a few INCHES at the tree side 

 

So as you can see move is a strong word for this situation ...I think

 

 

[Ed_MK]

19 hours ago, Ian said:

Wow!!....and Local Authorities wonder why they are losing business to private Approved Inspectors!

 

It's not often that I'm surprised by something to do with Building Regs but your description of what they want from you reminded me of the old days when I first started work as an architect in the late 80's. (and the system that still operates now in Scotland)

 

Actually Ian, yesterday I actually spoke to the lady at BC ...she is VERY nice!
Some of the things they have asked, they are going to "conditionalise" them so work can continue.

 

I am not making excuses for them, but they are VERY busy around here and every 100 yards houses are literally going up.
It was timescales that irked me ....and the fact that my groundworkers got nervous and pulled off due to the letter i got .
But its all back on now !

 

I have been told it is NOT easy around here though, so at least now i know...Firm but Fair is the term that i would use (from my experience so far)
But if anyone is thinking they can "wing" it, cut corners, put in a few fudgy bits and hope that it will just get stamped  on a Friday afternoon by a tired clerk
back from a pub lunch ....then FORGET IT. Milton Keynes is not the place to start

[Ferdinand]

@Ed_MK

 

Quote

 did think that the incline may add to the volume per second ...or something,

but i understand what you are saying.

 

It may add to the speed with which it runs off the roof (drag of the surface vs gravity) but that would affect eg the size of gutter you have along the bottom edge to prevent water running over etc.

 

Volume would not change, since that would be the same as they amount of rain landing per unit time. Perhaps there may transient effects eg when the rainstorm starts, but those should be minor.

 

F

Edited April 25, 2018 by Ferdinand

[epsilonGreedy]

On 17/04/2018 at 17:35, Ed_MK said:

So I was thinking Polystorm ...but by god ....it will cost an arm and a leg ...Is there any other way ?

 

 

The structural plastic crate thingys? I need 4.5 m3 of these and I was surprised how cheap they were, something like £200 all in. Even the variant that can cope with the weight of a vehicle were only 40% more.

 

I fear I have overlooked something in my budget. 

[Ed_MK]

1 hour ago, epsilonGreedy said:

 

The structural plastic crate thingys? I need 4.5 m3 of these and I was surprised how cheap they were, something like £200 all in. Even the variant that can cope with the weight of a vehicle were only 40% more.

 

I fear I have overlooked something in my budget. 

at that price PLEASE PLEASE tell me ...I am looking at close to £800 including the Vodka

[Ed_MK]

PLEASE PLEASE I AM GOING INSANE !! (well Ok not really, but close)

I am trying to do this soakaway calc and stuff to tie in with the first calculation LEGIT
As i would like to understand it rather than copy or guess ...am i mad ?

 

Well i will tell you where I am 

 

The roof area is 135m2 (vertical area, as you guys pointed out)

I have been advised that a good calc for this is 

 

Roof Area * (50/3000)

 

*the 50mm is hourly peak rainfall (apparently)
not sure what the 3,000 means perhaps getting it to seconds ..i think ?? 

 

but then i get the figure of 

 

135*0.0166

2.241

 

Which I think equates to 2.241 Litres or  (2.24m3)
For ease of working ...lets say i make this 2400

 

OK then in i plug this 2400 into the trench calculation as 2.4

and i get the following presumptive of a 1m square hole

2.4 / (3.142*r Sq)
2.4 / (3.142*0.5 Sq)

2.4 / (3.142*0.25)
2.4 / 0.7855
=3.055 Deep

 

So basically 3m2 of Crates will cover it ?

 

Does all or any of that make sense to you guys ?

and if it does 

 

then i hope i have done the porosity test right too !?

this damn F number 

 

apparently F= Volume of Hole from 25% to 75%  / (half internal area of hole inc base )x seconds from 75% to 25% full

 

My trench is 0.5m x 1.5m and it is 2m deep

 

So this comes out as:
0.75 / (4.75 x 2880 seconds)
0.75 / 13,680

0.00005.48

 

or 5.48 x 10(to the power of -5) m/sec

 

So what is my F rate represented as 5.48 ?

 

and if this is the case ..what do i see things online saying the number should be between 15 and 75 ?

 

PS 

 

i got the equations from here
http://www.polypipe.com/sites/default/files/percolation_test_datatsheet.pdf

 

 

Edited April 25, 2018 by Ed_MK

[Ed_MK]

Actually reading up online .,.i think this value is the "Soil Infiltration Rate"

I wonder is there a correlation between this and the mystical ""Soil Percolation Value"

 

?

 

 

[Ed_MK]

Actually ..i MIGHT have got it !

 

apparently the SP Value is calculated by the amount of time it takes to lower the level by 1mm

So mine was 2880 Seconds over 1000mm (or there about)

so thats 2.8 seconds per mm ?? (does that make sense) ..value for V

 

Area (A) = V X P X 0.20

 

So if i presume they will expect my house to be capable of living 4 people (P value)

then the above comes to

 

2.24m3

 

2.8 x 4 x 0.20

 

 

####

 

I mean it ties in with the above  ...2.4m2 (ish)

not so sure of the relevance of the "F" number though

 

Do these figures look good to you guys ?

 

 

[Ed_MK]

Coming to think of it

why is there a P value at all ??

 

why would the number of people in a house be relevant to a rainwater Soakaway 

[ProDave]

Rainwater and sewage soakaways are calculated differently.

 

Fior sewage soakaways the calculations are in the link I gave you on the last page, which I will repeat here https://www.wte-ltd.co.uk/percolation_test.html

 

V is the percolation rate in seconds per mm

P is the number of people the house can accommodate, based on the number of bedrooms. This is determined by BC e,g, my 3 bedroom house is deemed to have an occupancy of 5 people, irrespective of the fact there will only be 3 of us living there.

 

And the formula is Area (A) = V X P X 0.20  for sewage treatment units

 

This gives the AREA in square metres of land that is required of a soakaway.  You cannot use crates for sewage disposal this is a layer of rocks or stone, a herringbone of perforated drain pipes, more stones then a membrane then soil put back

 

You seem to have got confused and arrived at a cubic metre figure not a square metre figure.

 

What was your V figure in seconds per mm and how many bedrooms?

[Ed_MK]

Thanks Dave

 

Well the trench is 1.5m long x 0.5m wide by 2m deep

i had to fill it for ages as it was draining away quick ...but it finally slowed

 

I put 2 sticks in at 25% and 75% height and filled to first stick

and waited until i could see the second stick

 

it took about 45 mins ..to be exact 47.5

so 2850 seconds

 

So what do you make of it 

 

PS

 

there are only the 2 of us.

but i suppose the house could take 4/5

 

..but i am still struggling to see how it affects a rainwater soakaway 

Edited April 26, 2018 by Ed_MK

[ProDave]

So 2850 seconds to drop 1 metre?  You are only supposed to fill a smaller 300mm deep hole and time that to go down.

 

So 2850 seconds to drop 1000mm is 28 seconds per mm.  Do the official 300mm test and the result may be different.

 

You say it "could" accomodate 5 so lets assume it is 3 bedrooms and the occupancy for building regs is 5 people

 

So Area = 28 *5 *0.2

 

=28 square metres

 

This is for the soakaway for the treatment plant only. DO check the V figure by doing the percolation test properly with just a 300mm dole in the bottom so you are timing how long it takes to drain down 150mm

 

I don't know how to calculate the rainwater soakaway, I have never had to do that but I would expect that o be based on the roof area and as you say not the number of people.

[Ed_MK]

Another one ...

 

concerning the Waste/Sewage pipework .

 

the depth of the first (highest) wastewater inlet will be from a pipe just under the block and beam .

Now it runs around the property, picking up the various outlets and then ends in a manhole near my border

 

i always hear talk about sewage pipes being a MINIMUM depth ..something like 700mm down.

But can this also apply to the pipes around the house feeding he manhole or is it just AFTER the manhole toward the main drain ?

 

Looking at plans my Block and beam TOP  is about level with the outer brick DPC
So the BOTTOM of the Block and beam will be 160 lower ..almost at ground level

If i presume the waste pipe comes through this and them turns to the next junction then this first invert
will be about 110mm-150mm BELOW the Beam and Block Bottom

 

So will start its run at 150mm below the ground level (technically) ??

With various falls at 1:60 and 1:50 it eventually should be at almost 700 when it enters the last manhole.

 

Is this fine ?

 

 

 

 

 

 

Edited April 26, 2018 by Ed_MK

[ProDave]

That's about right then. Most treatment plants have an inlet level of about 700mm below ground and outlet a little lower.  Then add in a sample chamber and your outlet is probably about 1 metre down which is about right for a soakaway.