Any recommendations for tanking this plant room?

[Great_scot_selfbuild]

We've a very airtight build (timber frame) and the plant room has a dry screed floor.

 

I want to tank the plant room so the if the DHW cylinder leaked / flooded, then the plant room could hold the 300 L long enough for me to pull the plug out of the drain (before laying the floor I installed a pipe that it could drain through); the floor of the house is suspended off the ground, so there's no issue with where the water then drains to btw.

 

The photo shows the plant room floor with the various ducting and airtight tape. I need the tanking area to be 150mm deep to hold 300L, and was going to batten off the bottom of the door area to create a step-over into the plant room.

 

What would you recommend for tanking the plant room floor and up the sides of the walls to the 150mm height?

 

Any other comments / advice welcome (is this overkill? I'm perhaps being over-precautious about having a timber framed house and not wanting to risk anything significant).

 

TIA

 

[JohnMo]

51 minutes ago, Great_scot_selfbuild said:

create a step-over into the plant room.

Nice trip hazard!

 

If you need to it in the plant room, do you need to do it to every wet room, a fitting may leak while you out for the day?

 

Do you have a floor drain? That maybe all you need. If not your hot swimming area will be difficult to empty anyway.

 

Maybe over thinking it, our cylinder is above the kitchen, is it bunded area no, have I had leaks yes, were they an issue, no.

 

 

[Great_scot_selfbuild]

1 hour ago, JohnMo said:

Do you have a floor drain?

Yes (mentioned in first post) - there's a drain, but it will be plugged to retain the airtightness.

 

Valid point about any connection could spring a leak, but only one room has a tank ready-filled with 300L. Good to hear I'm over-thinking it, but a sodden ground floor with timber walls was my worry.

[Russdl]

3 hours ago, Great_scot_selfbuild said:

if the DHW cylinder leaked / flooded, then the plant room could hold the 300 L long enough for me to pull the plug out of the drain

If you were home. 
 

If the DHW cylinder sprung a leak why would it only loose 300L, wouldn’t the supply of water be endless until you isolated it?

 

I reckon you are massively over thinking this, get a flood sensor (Shelly do one, I’m sure many others exist)

 

If you spring a leak, unless it is some kind of catastrophic failure, then it’ll take a long time to empty that tank.
 

A flood sensor will tell you the floor is getting wet whilst you’re miles away, you send the neighbours round to isolate the leaking component and continue your holiday. Small leak, dries relatively quickly, zero damage to the timber frame but the plasterboard may need some attention. 
 

[crispy_wafer]

Would it still need to be plugged if there is a water seal in the drain trap?

[dpmiller]

^ or even better a waterless trap

[Russell griffiths]

Use a waterless trap then you don’t need to be home. 
im as crazy as you, see pic. 

[torre]

Personally I'd worry at least as much about leaks around the rest of the home. Drain with a waterless trap sounds good here but there are smart leak detectors and remote shut off valves that are probably a better fit in most cases

[Nickfromwales]

15 hours ago, Russell griffiths said:

Use a waterless trap then you don’t need to be home. 
im as crazy as you, see pic. 

And a fire extinguisher in case the water catches fire as it leaks out? 
 

That’s a new level of belt & braces lol    

[Nickfromwales]

18 hours ago, Great_scot_selfbuild said:

Yes (mentioned in first post) - there's a drain, but it will be plugged to retain the airtightness.

 

No, it doesn’t get left plugged! What would be the situation at each basin / sink / shower / bath?

 

This is what the water in the throat of the trap does, so you need to chill out sir!

 

If you’re considering bunding a room to accept 300L of flood water, forget it. Typical leaks are slow, progressive ones which often go unnoticed for days / weeks / months or even years. 

[Nickfromwales]

For completeness, I have always managed risk pragmatically, wherever a client has expressed any such concerns. 

 

For one current project I spec’d all the ‘wet plant’ to be housed within a newly created GF plant area, and in that footprint I specified a recessed area in the concrete of 30mm.

 

In the middle of the recess, back to back with the utility wall, sink and washing machine, I installed a trapped gulley with a back inlet for 50mm waste to feed in.

 

Note: the white self-adhesive stuff is Radon rated peel & stick barrier, as there was a very high Radon risk here. PITA to do but very necessary.

 

 

 

 

Here is where the washing machine up-stand will eventually connect via 50mm waste. 

 

 

 

Then I shuttered it with EPS / tape / foam (mummified it) before the pour. The idea being that this can be easily moved / removed after the pour if needs be (for fine tuning height of gulley etc / wiggle room).

 

 

 

The finished article, post pour. Note the sand shuttering around the UFH pipes, cheap and simple / effective; just hoover it out after the pour, final fix the manifold / pipes in their forever positions, and backfill with cementitious SLC LINK

 

 

This was an MBC raft, so they pour the SCC concrete and then return the following morning to cut / scabble the recesses out very accurately, so in that area we now have a 30mm L-shaped recess as a bund for management of any leaks.

 

The plan is to use moisture resistant cement board for all of the wet plant room walls and ceilings, caulking joints etc with intumescent acrylic sealant to attain A1 fire rating too.
 

These bottom of the cement boards will go down past the DPC under the stud walls to meet the concrete in the recess (eg TOC -27mm) where I’ll use 3mm packers to hold the boards just above the rough concrete to create a void for the SLC; this is to ensure the SLC will completely envelop the boards to arrest any future movement / feck any waterproofing up. The boards will effectively be ‘submerged’ in the (~5mm layer of) SLC, and the SLC will naturally run back under them to fully close the purpose made gap. Belt and 500 braces for £2 worth of packers. This will also detail airtightness at the external wall, where the tapes are meant to meet the slab at TOC; plenty of CT1 behind the cement boards at DPC level +/- 15-20mm. 
 

Then I will self-level the whole recess, banking it up at the far ends of the room by just 1 or 2mm max, to create a smooth graded surface which arrives at the gulley pot from all corners; The walls will all get smothered with liquid tanking solution, and left to cure fully for a couple of days. No need for steep falls like a shower tray, as gravity and a 25/30mm bund means water can only go into the gulley. Aim is for a burst pipe or failed EV etc to be nothing this room cannot handle. 

 

It’ll all get painted with heavy duty 2-part garage floor paint, white on the walls and grey on the floor to make my OCD happy, and lots of it, to create a fully maintainable and presentable, watertight finish.

 

The trap in the 100mm gulley will need to be maintained (kept ‘wet’) to prevent stench; in this instance this will be topped up routinely by the washing machine output. Note: the utility sink will NOT discharge into that 50mm up-stand and into the same gulley, but instead into the adjacent foul pipe rising to the FF, which will also collect the kitchen sink from the adjacent room. This means zero food solids or other stinky stuff will ever sit in the gulley in the plant room floor and create a stink; the only thing the plant room will ever give off a whiff of will be laundry / washing powder. The fact that folk use their WM’s every day, or every few days minimum, means the trap will be wet year-round. If the topology doesn’t lend itself, then you can run the water softener regen discharge into it instead; as a source of daily, clean water. 
 

I prefer to not rely on a self-sealing trap in the slab, as I will always want the full flow potential of an uninterrupted 110mm arrangement, vs water squeezing through these socks. Such units are available from decent manufacturers if a retrofit is your only option LINK. Avoid cheap / unbranded units as they’ll let you down eventually.

 

[Gus Potter]

11 hours ago, Nickfromwales said:

For completeness, I have always managed risk pragmatically, wherever a client has expressed any such concerns. 

But the photo shows you have happily cut the rebar without reinforcing not least diagonally to prevent cracking. 

 

You've dropped a bollock there!

 

 

[Nickfromwales]

45 minutes ago, Gus Potter said:

But the photo shows you have happily cut the rebar without reinforcing not least diagonally to prevent cracking. 

 

You've dropped a bollock there!

 

 

MBC guys tidied all that up the following morning, and inspected before the pour .
 

My bollocks are both accounted for  

[Gus Potter]

I'll take you word for it that they turned up with some lose rebar and made it all good. 

 

That requires diagonal bars to transfer the shrinkage loads around the service penetrations and supplementary bars to compensate for the cut ones. 

 

My experience tells me other wise. I doubt this happened, forgive my old school sceptesism, rafts and so on are not my first "rodeo!"