MBC slab and land drains

[Weebles]

We are looking for some help from anyone with experience of MBC slabs.  Its the order of doing things that is confusing us.

We believe we need a land drain.  We will also have surface water drainage.

We have been advised by a drainage contractor to do the drainage (foul and surface inc soakaways) after MBC put the frame up, so probably after the roof is on and the rainwater pipes in place?  Maybe before the render because of dirt?

So is the best order broadly as follows?

 

Dig foundations, compact hardcore 

MBC slab

MBC frame

Roof / windows

Drainage (foul, surface, soakaways) plus other service trenches 

Render / cladding

 

Where does the land drain fit into all this?  It seemingly is supposed to go where the hardcore is around the slab.  So do we dig that out again (when we do the other drainage) or do we put it in at the same time as compacting the hardcore.

 

Opinions please.  And thank you.

Edited May 29, 2018 by Weebles
forgot the timber frame!

[lizzie]

We have an mbc slab and put a french drain around our perimeter. I think it was dug at the same time as the rest of the drainage channels were done which was after frame was up roof on and windows in.  Before cladding and render as you say. Due to various delays we didnt do our sevice trenches until a few months later and render and cladding  was on  by then but by that time all we needed to do was come down the drive from our gate to the house and along the back alleyway where all the services entered the plant room.

[Mr Punter]

I am keen on getting all service trenches, ducting and pipework in as early on if it is possible. It means you get all the excavation done and backfilled and a clean, safe, level site.  The main issues are protection from vehicles and scaffolding, and making sure any ducting is suitably sized for the subsequent service to be pulled / pushed through.

[Mr Punter]

Also, bear in mind that gas and electric cos will not work when you have scaffold, so it is either soon or very much later.  I also like to connect temporary downpipes to the drainage to keep the site tidy.

[nod]

11 hours ago, Weebles said:

We are looking for some help from anyone with experience of MBC slabs.  Its the order of doing things that is confusing us.

We believe we need a land drain.  We will also have surface water drainage.

We have been advised by a drainage contractor to do the drainage (foul and surface inc soakaways) after MBC put the frame up, so probably after the roof is on and the rainwater pipes in place?  Maybe before the render because of dirt?

So is the best order broadly as follows?

 

Dig foundations, compact hardcore 

MBC slab

MBC frame

Roof / windows

Drainage (foul, surface, soakaways) plus other service trenches 

Render / cladding

 

Where does the land drain fit into all this?  It seemingly is supposed to go where the hardcore is around the slab.  So do we dig that out again (when we do the other drainage) or do we put it in at the same time as compacting the hardcore.

 

Opinions please.  And thank you.

I would do it at the same time as the foundations One lot of mess

Itherwise you will stone up around your slab for scaffold Only to dig it all up once the scaffold comes down 

[dogman]

Re land drain.  You need to check as we did not need one.  MBC will advise you on this.  Also if you do remember that you have already dug out 1m past the foundation so unless you are on some horribly draining land then the land drain sits in the 1m strip 

[JanetE]

We are on pretty impermeable clay and we dug out the trench for the land drain in readiness for the MBC slab. As @dogman says, 1m out all the way round the house.  The MBC guys then laid down the impermeable membrane then the land drain and filled with fine gravel. Then Iaid out the hardcore etc in preparation for laying the slab.  We now have no problem with standing water around the house.  Prior to the slab going down there was always a mini lake which was a great attraction to all the local birds.