Raising rear yard/garden

partyguinness

Hi Guys,

Currently at the end stages of a house extension. As you can see from the pic there is a approx 10 inch drop from the top of the manhole to the existing ground level. The pic is just a small sample of the area. I took measurements to a local building merchants and I will need about 15 ton of hardcore. I ordered 6 to begin with and shifted 3 ton myself from the front to the back of the house over the weekend.

Unfortunately I am not getting much clear help or advice from anyone. The builder didn't offer much guidance.

1. I presume I will have to get a compactor to level it. How thinly do I need to spread it before starting that?
2. Do I need to protect the drainage pipes?
3. The material is quite nice and small/sandy with small pebbles. https://ehsmith.co.uk/product/bag-mot-type-1-sub-base/
4. Is it okay to keep using this product to bring it up 10 inches or so before putting done slabs (kept back as they were there already) or is there another type of gravel needed in due course?

I haven't got a clue what I am doing after spending £100k already I am loathe to pay out for a landscaper if I can manage 90% of it myself.

Cheers.



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listermint

Better off on the construction forum.you will be hard pressed to get relatable advice in here for this.

Car99

Is that a rain water pipe and a sink drain pipe going into the same drain pipe?

You need to set your levels first 6 inches below your dpc level . Ideally you need a laser level for that .That black manhole cover can be cut down to lower it a few rings if needed.

Are you putting footpath around the base of the new extention?

recedite

partyguinness wrote: »

1. I presume I will have to get a compactor to level it. How thinly do I need to spread it before starting that?

About once every course of blocks, which is 225mm, or near enough your 10 inches. So you will get away with hiring a wacker for only one day at the end of the job.

2. Do I need to protect the drainage pipes?

Not really just keep any rocks away and backfill around them with fine sandy stuff.

3. The material is quite nice and small/sandy with small pebbles. https://ehsmith.co.uk/product/bag-mot-type-1-sub-base/
4. Is it okay to keep using this product to bring it up 10 inches or so before putting done slabs (kept back as they were there already) or is there another type of gravel needed in due course?

If you're buying this stuff in bags it will be way too expensive. You'd be better to get stone delivered by a tipper lorry. I'd have used "3 inch down" for backfilling that amount, and only use a layer of the finer stuff on the very top layer.
Its not critical what you use though, as long as its some kind of stone (no soil or bits of timber) and you compact it afterwards.
Finally rake some coarse sand or grit to a level surface, and lay your slabs on that.

partyguinness

recedite wrote: »

About once every course of blocks, which is 225mm, or near enough your 10 inches. So you will get away with hiring a wacker for only one day at the end of the job.

Oh right ok. I thought I would have to rack it out to say 2-3 inches- compact it, another 2-3 inches- compact it and so on. That's better.

recedite wrote: »

Not really just keep any rocks away and backfill around them with fine sandy stuff.

Cheers. I read somewhere about using pea pebbles.

recedite wrote: »

If you're buying this stuff in bags it will be way too expensive. You'd be better to get stone delivered by a tipper lorry. I'd have used "3 inch down" for backfilling that amount, and only use a layer of the finer stuff on the very top layer.

Yes it is about £10.00 per tonne cheaper to buy it loose which I was aware of but my problem is that I would have to tip it on the front drive which has been recently cleaned and resanded and it would severally impact on parking. The house is off a busy road. The supplier is not charging extra and it was they suggested breaking up the delivery into 2-3 runs to make sure I didn't order too much.

recedite

Well it will be easier to shift round the back in bags anyway.
Pea gravel is more for when the backfilled gravel itself is making a drain.

partyguinness

Car99 wrote: »

Is that a rain water pipe and a sink drain pipe going into the same drain pipe?

No. The drain water pipe empties into the drain pipe sitting on the ground which you see running off to the right of the picture. This carries on and another rain water pipe drains into it and then there is a (sorry can't think of the technical term) run off tank about 8-10 feet away from the property buried in the garden which the builder installed underneath the soil.

The sink drain empties into a separate pipe which which runs underground to the inspection chamber you see to the left of the picture.

Car99 wrote: »

You need to set your levels first 6 inches below your dpc level . Ideally you need a laser level for that .That black manhole cover can be cut down to lower it a few rings if needed.

Are you putting footpath around the base of the new extension?

On the first point it looks like the rain water and sink drain pipe are 2.5 bricks below the internal floor level.

Would it be a good starting point to use the top of the plastic grating as the absolute top level including the slabs so that I should bring the soil within say 2 inches of the top to allow for the slabs and fine sand- then I can cut down the man hole as you mention.

We had not planned on a footpath but rather relaying the stone slabs that came with the property. I take it we need to allow for a drainage channel of sorts?

recedite

partyguinness wrote: »

On the first point it looks like the rain water and sink drain pipe are 2.5 bricks below the internal floor level.

Would it be a good starting point to use the top of the plastic grating as the absolute top level including the slabs so that I should bring the soil within say 2 inches of the top to allow for the slabs and fine sand- then I can cut down the man hole as you mention.

We had not planned on a footpath but rather relaying the stone slabs that came with the property. I take it we need to allow for a drainage channel of sorts?

Yes, you are on the right track now. 2 brick courses = 1 block course = 225mm, so your drain covers are slightly deeper than the minimum requirement now, which is good.
The finished level should be minimum 150mm below the dpc, but if you set it at the 2 brick courses (225mm below) you will have a lot less stone to shift. It just means the step outside your back door will be bigger, or else you can have 2 steps down to the slabs.
Sharpen up some wooden pegs now and bang them into the ground around the place to mark this level. That level will be the 275mm (including the 50mm for the slabs) below the dpc and is called your datum. Use a laser level (or else a spirit level on top of a long straight edge) when setting the height of the pegs. Use the top of the pegs as a guide when bringing in the stone. Try not to trip over the pegs, and remove them at the end when all the stone is in place.
Also bear in mind its going to compact down a bit more after you use the wacker on it, so you'll need to be slightly above the top of the pegs with the loose stone.