A couple of building questions ?

[stuart45]

Normally you should do the drainage first. Can you put on a diagram of what you are doing with the drainage system.

 

[hammerswinger]

Hi,
sorry I don't think I made it clear, I haven't done the drains or the oversite yet.

Below is a diagram of the proposed drainage layout.

I posted a thread in the Plumbing section about the drain layout, you can find it here:
http://www.diynot.com/forums/plumbing/drain-layout-advice-views-please.293658/

Thanks.

 

[stuart45]

You can have the oversite concrete lower than the external ground levels and run the pipework on top, but the concrete would need to be laid to fall to a drainage system to stop any ponding.
You don't have to put a DPM under oversite concrete, it's only an option.
Have you checked for sure that you can't get the fall going under the oversite?
Pity you can't run the pipework externally as it's usually better to avoid going under the property if possible.

 

[hammerswinger]

Hi, thanks for your advice & help.

You can have the oversite concrete lower than the external ground levels and run the pipework on top, but the concrete would need to be laid to fall to a drainage system to stop any ponding.

What sort of drain, how would it be constructed?

Yeah I could miss out the DPM if it would help the situation.

I haven't checked for sure if I can get the fall with the pipes under the oversite but it doesn't look like it.
If the pipes were under there would have to be a gap between the top of the pipe & the bottom of the oversite so this wouldn't help either.
What happens if the drains start on top of the oversite then disappear into it as they go, can you do that?

No real option of running the drains outside of the property I'm afraid.

I was going to put the oversite at the same height as it is under the timber floor of the house, but the joists in the house are only 4" x 2" and they sit directly on top of 2 course of bricks (no wood sole plate) as the joists for the extension have to be 6" x 2" that means that I wouldn't be able to keep a 150mm air gap between the oversite & the bottom of the joists.

I'm a bit stuck with this lot, I really need to get it figured out so I can get on with the drains & get the oversite in before we get snow.

Cheers.

 

[stuart45]

Hi, thanks for your advice & help.

You can have the oversite concrete lower than the external ground levels and run the pipework on top, but the concrete would need to be laid to fall to a drainage system to stop any ponding.

What sort of drain, how would it be constructed?

Either a gulley going to a storm drain or a pit and sump pump doing the same.

I haven't checked for sure if I can get the fall with the pipes under the oversite but it doesn't look like it.
If the pipes were under there would have to be a gap between the top of the pipe & the bottom of the oversite so this wouldn't help either.
What happens if the drains start on top of the oversite then disappear into it as they go, can you do that?

You need to talk to the BCO about that one.



Cheers.

[code:1][/code:1]

 

[hammerswinger]

Hi,
Yeah before I do anything I'm going to check the the BCO approves of my design as I want it right first time.

Good news anyway, I've been out measuring and I think the drains will be able to go under the oversite ok and I've been worrying unnecessarily.
Where the WC & kitchen sink drains start, if the pipe is 50mm below the bottom of the oversite this will give me about 230mm of available fall over a 4.1m run, that's over 50mm per metre which from what I've read is more than enough, so I can probably adjust the depth of the drain to be under the oversite more.
My measurements were taken assuming the oversite being about 1 inch lower than the outside ground level, this is to give me the required 150mm minimum air gap under the floor.

With only having 150mm between the top of the oversite and the bottom of the joists I'm going to be struggling to get 2 course of bricks in for the sleeper walls, what would be the best way to do this? any ideas?

Cheers.

 

[stuart45]

Don't put too much fall on the drains or the solids can get left behind.
With 150mm you can only have one course of honeycomb brickwork and a wall plate on top.

 

[hammerswinger]

Yeah I've read that too much fall isn't a good thing so I'll read up on the subject and go with the flow!

I'll run my plans for the drains / oversite past the BCO in the next few days to see if he has any input but hopefully he'll ok my proposals

Thank you for your help and advice.

Cheers.