Chase concrete or raise floor?

[Pocster]

BUM!

 

My insulated reinforced concrete floor doesn't have drainage channels at the perimeter ; which are needed!

To chase is out (!!!) would be a nightmare (100mm x 50mm) around 30m of it 

 

Can I cheat?. Could I bolt wood around the edge and then simply pour concrete in the middle? i.e. make a channel effectively by raising my floor?

 

The reason for all this is as I'm below ground I have the dimpled membrane on the walls for drainage; but I'm guessing I should have a dimpled membrane on the floor that runs into the perimeter channels i.e. has to be higher than the channels.

 

Also if I 'chase' these channels there's no way they are going to be level and neat!. Is this a good plan?

 

Although my concrete slab is insulated I did wonder rather than put concrete in the middle why not just put an extra 100mm insulation down and then the membrane on top? (followed by UFH and screed)

 

Advice welcome! (so dumb!; on pouring the slab I could of allowed for this with ease! )

[MikeSharp01]

You might be able to raise the floor but there are things to consider. First the ceiling height will reduce and you may hit building control issues. Second the heights of everything else will need adjusting, doors. Windows, plug sockets, light switches etc. Finally any related inside and outside levels will need to be reconciled - steps etc.

[Pocster]

Thanks 

I've got the height 

no wiring or plumbing is in yet ; so no issue there

 

should I pour concrete though or pad up with insulation? Does it matter ??

[PeterW]

Questions

 

was the concrete as poured supposed to be your finished floor ..?

 

you say UFH - you're still going to need an insulation layer unless your slab is going to get heated too ..??

 

If UFH is needed and you have a decent insulation layer below the slab, why not just lay UFH on the slab and put a 50x75 up stand around and top with concrete - so two jobs with one ..? 

[Pocster]

Hey PeterW!

 

Concrete pour was meant to be finished slab i.e. UFH + tiles on top

 

My assumption was the UFH heats the slab also to act as a thermal store.

 

"If  UFH is needed and you have a decent insulation layer below the slab, why not just lay UFH on the slab and put a 50x75 up stand around and top with concrete - so two jobs with one ..? "

 

Not sure exactly what you mean by this?. My issue is the perimeter drain would currently be above the floor rather than below it. Can you explain please?

 

Cheers

[IanR]

16 hours ago, pocster said:

My insulated reinforced concrete floor doesn't have drainage channels at the perimeter ; which are needed!

 

To be honest, I'm not clear on what you mean by this. Do you have a section that shows how it should be, preferably showing the floor/wall junction.

[PeterW]

Is this Wet UFH or electric ..??

 

[Pocster]

WET UFH

 

Will put some drawings up to help explain 

[Pocster]

There!

 

Hope that helps. I called a few of the membrane suppliers and most suggested it had to (unsurprisingly) have the channel below the floor level.

But some definitely had it sat on the floor! 

Is my suggestion ok?. Majority of any water ingress is via the walls; but I have to assume it's possible I may get some up through the slab.

 

Thanks

 

p.s. forgive quality artwork!

Edited February 3, 2017 by pocster

[Pocster]

Right!

 

Finally got to talk to someone who seemed to understand!

Easiest solution seems to be battens around the perimeter and a sacrificial screed in the centre thereby creating my 'channels'.

Presumably then floor membrane ontop ; UFH and final screed.

 

Just one question if this is the best method. The existing slab; does it need 'treating' before the sacrificial screed is applied or will that just stick anyway (obviously will jet/clean slab first)?

Edited February 3, 2017 by pocster

[IanR]

Neither of your sections show (for me) a viable floor.

 

Are you expecting moisture to breach your slab and insulation (or is insulation between slab and screed) and therefore require draining from between the slap top and screed?

 

Have you got the original engineering drawings of the "suggested" slab. Are you sure your "drainage channel" should not be running within the sub-base below the slab?

[Pocster]

The slab is insulated to 250mm.

 

Whats wrong with the drawings? i.e. no viable floor???????

 

here's a manufacturers info; you can see the 4 suggested methods

 

http://static.safeguardeurope.com/downloads/datasheets/aquadrain-perimeter-drainage-channel-datasheet.pdf#_ga=1.192104355.866109518.1486119729

 

So example 2) is what I'd end up with by adding a sacrificial screed.

 

Actually floor spec; is just this!!!

 

Floor Structure

 

50mm screed on;

cast in situ reinforced concrete slab to

Structural Engineer's details on;

polythene on;

100mm thickness insulation on;

tanking membrane on;

blinded hardcore

Edited February 3, 2017 by pocster

[IanR]

I did caveat my comment with "for me". I'd not seen this sort of detail before.

 

In the OP you mention insulated slab, and to me if water is breaching the insulation it's going to negate it. ie. water at ground temp will get passed the the insulation and on to the underside of your screed with the UFH pipes in, so you end up warming up the ground water.

 

 

[Pocster]

6 minutes ago, IanR said:

I did caveat my comment with "for me". I'd not seen this sort of detail before.

 

In the OP you mention insulated slab, and to me if water is breaching the insulation it's going to negate it. ie. water at ground temp will get passed the the insulation and on to the underside of your screed with the UFH pipes in, so you end up warming up the ground water.

 

 

:-) I know when you said "for me" I assume I've done it wrong !

 

Yes. My assumption was the UFH could end of heating 'ground water'. So with the floor membrane beneath the UFH this should be avoided.

 

Beneath the insulation in the slab is plastic sheeting ; but I guess this can only reduce the chance of water coming up through the slab. After-all it only takes 1 hole somewhere!. Perhaps I'm going belts 'n' braces on this - but better safe than sorry!

Edited February 3, 2017 by pocster

[IanR]

Just now, pocster said:

Yes. My assumption was the UFH could end of heating 'ground water'. So with the floor membrane beneath the UFH this should be avoided.

 

No, with membrane beneath the insulation, the insulation would avoid you heating up the ground water and sub-base.

 

If the slab is already in then I would have thought you need to insulate above the slab, on top of the membrane.

[Pocster]

So *more* insulation on top the slab??

 

Insulated Slab

Screed to make height for drainage channel

Floor membrane for drainage

Insulation

UFH

Screed

 

That correct??

Edited February 3, 2017 by pocster

[IanR]

No, more like no. 1 on the sheet you linked to.

 

Slab

Membrane (tanking)

Insulation (120mm - 200mm PIR) and form the channel at perimeter

75mm screed with UFH over the top of insulation and channel.

 

Then male sure the channel drains well to a sump and keep the sump clear. I think I'd want a couple of pumps for redundancy to protect from pump failure.

[Pocster]

Ah I see.

So you are saying use the insulation in the centre to form my channels (rather than sacrificial screed).

One company did suggest this; but said I had to use foam glass for the insulation - now I know; this stuff is MEGA expensive! - it would be cost ineffective.

I think the problem was walking on the floor membrane would simply dent the insulation .

 

I'll have 2 or 3 sump pumps with battery backup; don't worry about that!!

 

p.s should I 'stick' the insulation to the slab????

Edited February 3, 2017 by pocster

[IanR]

Slab with insulation above and and then screed on top is pretty standard. I assume the advice you had for using foam glass would be relating to a sole plate for any load bearing walls. The PIR insulation under the screed is non-load bearing, so can't go underneath any load bearing walls. If you have load bearing walls then you could use foam glass to reduce the cold bridge at the floor junction.

 

No need to "stick" the insulation to the slab.

 

I'm concerned something is being missed. Who specified the insulation under the slab, but tanking and drain channels above/within the slab? Is there any other drainage specified under the slab insulation, within the sub-base? Is it possible the drainage within the slab is belt and braces and will only be called into effect if there is a failure somewhere?

[Pocster]

No load bearing walls.

 

The architect's original slab was a 'raft' ; so effectively had a 'gap' underside in the middle ; he suggested to make this 'form' to put insulation in there (non load bearing). The edge of the slab (load bearing) has foam-glass equivalent insulation.

There is zero specification for drainage below or in the slab ; this is what has concerned me and hence my post.

 

BTW you've been super helpful!

 

Here's a link to a 'suggested' floor insulator I've been sent  i.e. expensive! 

 

https://www.permagard.co.uk/newton-fibran-xps-500-c-closed-cell-insulation

Edited February 3, 2017 by pocster

[IanR]

I'm thinking you need some professional support. A bit of basic googling suggests your planned internal drainage should be part of a multi-system approach to protecting the structure from water ingress.

 

On its own it may be insufficient for building control.

 

If other systems have been specified and employed then the risk of water ingress may be so low that there may be a better position for the membrane.

[Pocster]

Yeah. I'm probably over thinking this and maybe confusing you 

 

The problem also is different manufactures / resellers give different advice.

That newton link did seem the correct stuff (for example it deals with any 'floating issues' ; something one of the sales guys mentioned ; hence his suggestion of sticking insulation to the floor).

TBH as my slab is 250mm thick it's going to take some serious water pressure to come up through that. I also have an external land drain around the base. The general ideal was that it could/would fail some day. The plastic sheet membrane externally on the walls also could/would fail one day. The internal dimpled membrane (floor and walls) into drainage channels theoretically  (!!!!) can't fail ....