New kitchen island sink on existing concrete slab - drainage and water supply

[infaddict]

So glad I found this amazing forum!

 

I'm remodelling a kitchen in a 10yr old bungalow which has a conrete slab floor.  I want to create a new island with a sink so need hot, cold and drainage fed to the middle of the concrete slab.  All hot and cold pipes run through the loft and down the dot-and-dab walls, so new pipes can easily be fed off in the loft, down a nearby wall and then along a gully cut in the concrete slab to the island.

 

For the hot and cold, a few places I need help/guidance/confirmation:

 

1) I was planning to use a conduit (like a wider waste pipe or simiar) to run each of the hot and cold pipes.  2 conduits to keep hot and cold separate (this might be overkill but thought hot would need insulating but not cold and don't want hot heating cold).  Does this sound ok or unnecessary?  
 

2) How deep into the slab do I need to bury the conduits/pipes and do I need to protect plastic conduit from the cement?

 

 

Then for the waste situation, I have a private foul sewer that runs under unused (soil) last to the side of this kitchen, so was hoping to route a waste pipe in a new gully in the slab, to that side of the kitchen.  With suitable fall built in of course.  Over the weekend, I will open the inspection chamber to see how deep that sewer is and if there are any spare connection points I could use.  

 

For the waste, again some things I'm wondering about:

 

1) Can I use standard 42mm white plastic waste pipe to bury in the new gulley I've cut, or is that a bad idea and there's another way (conduit, different kind of pipe, wider etc)?

 

2) How deep into the slab should I bury any waste pipe?

 

3) What is best practice to connect to the private foul sewer buried outside my wall?  Does this have to be done underground, meaning I have to drill/cut/dig very deep and potentially hit foundations, DPC, ironwork etc.  Or can it come out at ground level and go down into this sewer.

 

 

Sorry for all the questions and thanks in advance.

[infaddict]

Bump, anybody got any pointers for running hot, cold and draining in a concrete slab, thanks.

[PeterW]

Use 50mm waste for the ducts with 20mm concrete or self levelling over the top and will be fine. All the bends need to be pairs of 45° at the ends or into boxes that you can get push fit fittings in to. 
 

Waste wants to be in 40mm solvent weld but put a Y branch into it and flow the waste into the branch from above using a long bend to bring it up out of the slab. Then on the run add a 45° bend and then an access cap above slab level in case you ever want to run a jet or small rod down it. 

[Conor]

If you are burying a waste pipe it has to be underground rated, and rod-able, I.e. 110mm brown PVC. Sorry, but there is no shortcut for this. It'll be a lot of work.

 

The water supply is simpler, run the 15mm feeds inside some 25mm blue MDPE. 

 

You want at as much cover as you can get over the pipes.

[infaddict]

18 hours ago, PeterW said:

Use 50mm waste for the ducts with 20mm concrete or self levelling over the top and will be fine. All the bends need to be pairs of 45° at the ends or into boxes that you can get push fit fittings in to. 
 

Waste wants to be in 40mm solvent weld but put a Y branch into it and flow the waste into the branch from above using a long bend to bring it up out of the slab. Then on the run add a 45° bend and then an access cap above slab level in case you ever want to run a jet or small rod down it. 

 

Thanks Peter, makes sense.  I need to work out my exact distances to see if ventilation becomes an issue and have to use certain pipe size.  Option 1 is a short 1.7m run to an existing gully but I might end up too low (as I need the required fall) and can't remove that gully or replace it without damaging a lovely new patio laid only last year.  Option 2 is a much longer run (approx 4m) to side of house where my private foul sewer runs with several inspection chamber (and not patio to worry about).  But longer run means more fall required and potentially bigger diameter pipe and/or syphon proof trap etc.  With this option I will likely end up below the DPC and therefore have to be careful to repair that as necessary.

[infaddict]

8 hours ago, Conor said:

If you are burying a waste pipe it has to be underground rated, and rod-able, I.e. 110mm brown PVC. Sorry, but there is no shortcut for this. It'll be a lot of work.

 

The water supply is simpler, run the 15mm feeds inside some 25mm blue MDPE. 

 

You want at as much cover as you can get over the pipes.

 

Thanks Conor.  Local building control did suggest 110mm as first choice, but also seem happy with narrower than that depending on the distances involved. But advised protecting it with PVC protection tape.

 

But I like to do a "proper job" so if it needs to be 110mm I'd rather bite the bullet and get it done.  The 110mm option clearly means a deeper trench to run the pipe with required fall, which will certainly mean breaking the DPC.  Again building control seem fine as long as thats repaired properly, either using liquid DPC or patch and seal.

In terms of making it rod-able, any recommendations please?  I would likely convert from 110mm down to smaller white under sink size immediately so unsure where to put a rodding point.

[Carrerahill]

Remember to add some power to your island!

[infaddict]

6 minutes ago, Carrerahill said:

Remember to add some power to your island!

 

Absolutely, I need drainage, cold water (for tap and dishwasher), hot water (for tap) and power (for dishwasher - and potentially a phone charger hidden somewhere.

Ideally all in the same trench!!

[infaddict]

I have no idea what depth of concrete pad I have either.  House was built 10 years ago.  The deepest hand held saw cuts around 120mm, the deepest floor saw cuts around 165mm, but found the one below which cuts much deeper (400mm) if required.  I quite like the idea of nibbling little bits away at a time but unsure if it would be more efficient in the long term.

 

https://www.husqvarna.com/uk/power-cutters/k760-cut-n-break/

 

 

[Carrerahill]

If it was me, I would hire a diamond floor saw and cut a decent channel, dig out, lay conduits, waste pipes etc... plumb it all up, test it, replace concrete. 

 

I'd go for continuous runs of plastic pipe (although I hate it and won't use it) laid in conduit in such a way you can pull through new lengths if needed in the future.

 

Allow spare conduits too. I'd put in some 63mm smooth bore twin-wall ducting for water pipe and power: https://skyplastics.co.uk/63-50mm-black-twinwall-electric-duct-x-50-metre.html

 

 

Edited October 16, 2023 by Carrerahill

[infaddict]

26 minutes ago, Carrerahill said:

If it was me, I would hire a diamond floor saw and cut a decent channel, dig out, lay conduits, waste pipes etc... plumb it all up, test it, replace concrete. 

 

I'd go for continuous runs of plastic pipe (although I hate it and won't use it) laid in conduit in such a way you can pull through new lengths if needed in the future.

 

Allow spare conduits too. I'd put in some 63mm smooth bore twin-wall ducting for water pipe and power: https://skyplastics.co.uk/63-50mm-black-twinwall-electric-duct-x-50-metre.html

 

 

 

Been looking at floor cutters and more than willing to hire one for the job.  Unsure if 165mm depth of cut is enough, as I don't know how deep my pad is.  Maybe I could drill a test hole or something. 

And perhaps 165mm is enough even if concrete is a bit deeper, as likely an impact breaker might do the rest.

Wondering if its possible to dig a decent channel, but not damage the DPC too much allowing me to repair it fairly easily.

Thanks for advice on conduit, I definitely need to use it to future proof, including some spare mousing lines etc.

[goodbyegti]

I would guess the slab is approx 150mmm