Will I need a retention wall ?? Quantity survey help needed !!

mrbungle

Hi All,

We are very interested in this house but have not signed contracts yet. I visited the house a couple of times over the last couple of weeks, 1 day it was really lashing, extreme rain and I noticed some channels of water streaming down the mound of dirt/hill behind the house.

After all the rain had subsided last week I noticed that a load of muck was washed down onto the gravel at the back of the house and also around the side of the house where the cars would be parked.

According to the selling agent, the builder has said that he would dig out whatever we want from the hill in case we want more car space or a shed, etc.

Do I need some form of drainage here where the dirt meets the gravel or do I need a retention wall ? I'm a bit wary that under prolonged rain that water will pool and potentially flood the gaff !!

Should I get the placed surveyed by a professional, when I search the web all I'm getting is house snaggers.

Some pictures:

De_man

This is a common problem, don't worry about it, try and get a couple of quotes before commencing work


I'd recommend you dig out say another 5/6 feet of the hill or even more to give that bit of space at the back and to let more light into the house

1. Build a retention wall where you removed the soil (ensure Block on Flat)
use the following site to give you an estimation of the amount of blocks
required. see www.crescentbs.com/calculator.htm

2. Throughout the retention wall include drains mid way and down towards
the bottom of the wall (2inch pipe), these should be spaced every
10 feet.
Don't forget to create steps to your garden mid-way through the retention
wall or convenient position to back/patio door.

3. Looking again at the picture you might be better to go back about 15feet
as otherwise the steps would be very steep, especially after having
a pint or two of plain.

3. Create a soakway on the hilly side of the wall with clean hardcore
80/100mm from the base of the wall to the top then backfill with soil.

4. On the house side of the wall, dig a new drain, and insert a drain every
10 feet this depends on the levels, and what type of surface are you
going to use.
Connect these drains to your storm water drain on the far corner side of
the house, or divert to new soakaway





a pint of plain is yer only man

muffler

Works very well described by De_man.

if the builder is prepared to do more excavation works then by all means go for it. I doubt if he will build a retaining wall though but it shouldnt cost that much. A good blocklayer will tell you exactly what you need but from looking at the pics I think a 12" block might be safer.

2 other things I would consider. Form a stone drain up at the fence as this will take away a lot of your top water and put less pressure on your retaining wall.
Also I would consider putting heavy gauge polythene behind the wall prior to filling with stone. This will ensure that your wall remains relatively dry (visually). just make sure not to cover any of the pipe drains at the base of the wall

mrbungle

Sound advice so far, men, Thanks.

The majority of the garden is at the front of the house, .8 acre. I reckon there won't be much of a garden at the back for the time being.

Just to give you an idea, if you picture the top of that mound in the pictures as the top of the hill on our site, there is a gradient starting from there that continues down to the base of the site where our gate is. The house foundation is cut out at the top of the site and the base of the front door intercepts the gradient.

So basically, I'm initially only worries about drainage and greenery at the back can wait.

Thanks again.

De_man

Muffler is 100% correct,

apologies, i had forgot about the "heavy gauge polythene behind the wall prior to filling with stone" it also helps if you coat the inside of the wall with a bitumen or similar sealer.

from looking at the photograph again, you'll have no problem with regard
to flooding provided you put in adequate drainage at the back of the house
as previously described, you have plenty of room to build a soakaway at
the front of the house


a quick question though, which way is the house orientated?
and will you want to have a patio area at the rear of the house?

Just a suggestion, personally, from looking at the photo the slope could make your rooms at the back dark, i'd take away another couple of feet to give you adequate room i.e. to have a patio or deck area also to enable you to drive the car around the back if needed.


a pint of plain is yer only man

mrbungle

From the photo, that is the back of the house. The house is dormer style and it oriented towards the front. Not overly concerned about light on this side.

I was actually standing on the patio, which the builder has laid and is already conveniently sloping away from the house.

mrbungle

Will I need to direct the drainage to a soakaway or could I lead the drain toward the drive way and let it pee down the hill !!

I noticed the rain nicely running down the driveway last week during the heavy downpours.

The driveway currently is coarse aggregate and was told that it would be gravelled.

De_man

there's no way i'd let it "pee down the hill",

the easiest option imho would be to connect up to your existing
storm water drain on the side of your house.

Personally, i'd dig another soakaway at the side of your house and
use this instead to deal specifically with the back, a JCB only costs 35Euro per hour and hardcore is cheap.

The site is .8 Acre, with this, your driveway will be quite long,
from looking at the gradient, it not just the water on the back of the
house you have to worry about, its the entire footprint of the driveway.

As the gravel will be washed away & channels will appear where the flow
of water occurs, you'll be wasting your time with gravel unless this is sorted i'm afraid

(Our family homeplace had this exact problem, except the other way 'round
water flowing down the driveway towards the house but that's another story )

What i reckon you should do is

1. build the wall at the back of the house as per muffler and myself
suggestions (get plenty of quotes)

2. On your driveway, have two maybe three channels installed across
your drive, leading to a soakway in your garden (they don't have to be too big) because (a) your gravel driveway won't be there for too long & (b) your neighbours across the road won't thank you for the deluge of water coming across the road.
If you get the builder to do it, don't go for precast channels that would be inserted across the drive!!! (these fill up with gravel & dirt too easily) use Steel boxing/grid available cheaply at any builders providers.

3. It's a new house, I reckon the Planners have studied this, my guess if you read the planning application, the planners would have made specific reference with regard to surface water, i reckon you should check this one thoroughly!!!!

If there's no reference to surface water i'd still take care of the driveway
afterall, you don't want excess surface water ruining your driveway or being a contributory factor in a road accident due excess surface water.

Have a word with your builder i'm sure they'll sort it otherwise you could have it done yourself in a weekend

If this is the only problem with your house purchase..go for it..enjoy


A pint of plain is yer only man

muffler

De_man wrote:

It's a new house, I reckon the Planners have studied this, my guess if you read the planning application, the planners would have made specific reference with regard to surface water, i reckon you should check this one thoroughly!!!!

On that point there will be (or should be) a condition that states that no surface water from the site to discharge to road. Again there may well be a condition that any roadside drain to be piped or even new piped drain to be provided with gulley at lowest point along site frontage. Check out the planning conditions. Most likely there will be a storm water pipe along the site frontage. If there is connect all your rainwater to that.

Soakaways/soakpits are fine if on well drained ground but if you are using a septic tank make sure that any soakaways are kept well away from and downhill from the tank and percolation area otherwise you will flood your system.

De_man is right about the gravel drive. Get the surface water off it otherwise you will need a tractor in no time at all to navigate your driveway because your driveway will end up as one big vennel/drain.

And yes you dont have too much to worry about overall if its only surface water drainage. Personally I would ask the guy on the JCB about it as he would probably have a lot of "hands on" experience in that area.