Slab Insulation, UFH and Mesh

[MarkH]

Here's our floor construction. I'd appreciate any opinions on it and in particular on a couple of details currently in decision limbo:

 

1) I'd assumed the DPM would go as pictured in this diagram - under the insulation - as it seems to make sense to have it contained within the waterproof envelope. A couple of people have suggested that the membrane goes OVER the insulation though.

 

2) slab reinforcement & UFH... am I overkilling by adding reinforcement mesh mainly to give me something to attach the UFH pipes to? Would it be easier to clip the UFH to the insulation (I saw a handy clip gun thing) and leave out the steel?

 

 

By the way, the EWI isn't shown on the diagram above but is (probably) 200mm of EPS extending down 200mm below the slab insulation.

Edited September 24, 2016 by MarkH

[jfb]

I had a very similar build up with the dpm as you have it and used mesh for slab strength and, as you say, something to attach UFH to. Not sure how easy it would be to clip the UFH pipes to EPS (might be easier with other types of insulation board). The pipes will be under a fair bit of tension especially at tight corners and EPS isn't the firmest/strongest material to fix to.

[joe90]

I am having UFH pipes cable tied to steel mesh within the concrete slab and that slab is going on top of the internal wall so there is no potential weakness in doorways. Our DPC is going under the insulation like this:-

 

[PeterW]

@joe90 are you using the extruded insulation as the former for the slab ..?? 

[Nickfromwales]

The mesh reinforces the slab, adding immensely to the integrity for one. I'd not even think about not fitting it tbh as it's cheap as chips and gives you a grid to attach the pipes to. 

Has your engineer / BCO specified no re-bar ( mesh ) ? I'd have thought it would be a given. 

[TerryE]

Here is the lads pouring our slab.  We have a passive slab hence the rebar box ring and 2 load-bearing internal walls.  Note how the UFH piping is snappied to the rebar mesh.  We also have extra 200×200mm bracing sections every 2m on the slab areas.  (The funny T that Danny on the left is holding is the laser target -- the slab was levelled end-to-end within a few mm.)

 

As Nick says, I am surprised that your BCO would be happy with 100mm unreinforced concrete.

[MarkH]

3 hours ago, Nickfromwales said:

 

Has your engineer / BCO specified no re-bar ( mesh ) ? I'd have thought it would be a given. 

 

Our garage has a 150mm slab with reinforcement specced by planning but the house is just 100mm, no reinforcement (the architect mentioned having a couple of movement joints recently). Since getting prices for mesh and taking into account the convenience of mesh acting as a suitable spacing for the UFH pipes I can see your point - why not use it... 

 

Thanks! I'll order some steel on Monday.

 

 

[MarkH]

25 minutes ago, TerryE said:

 Note how the UFH piping is snappied to the rebar mesh. 

 

What method of attachment did you use? 'Snappied'?

[IanR]

Just to mention an alternative option for fixing UFH.

 

On mine UFH clip rails fitted to EPS, pipes into clip rails, mesh over the top.

 

 

I'm having a heart attack with every hole drilled into the slab (mostly to bolt down sole plates), so am grateful of having the pipe generally 75mm deep into the concrete.

 

Pipe was also protected by the mesh while being walked over during the pour.

[TerryE]

@MarkH cable ties. 

 

We were pretty conservative about our UFH footprint and stayed well clear of walls, units, etc. and stuck to the floor areas where there is no chance of having to drill into the slab or use fixings. Our house is essentially to passive standard, so the number is heating days is pretty small and the total demand will typically be a couple of kW tops, so didn't have to push the UFH area hard.

 

This is the MBC system and quite a few of the members here have got it without any problems.

Edited September 24, 2016 by TerryE

[MarkH]

Ok thanks folks. 

 

We'll stick with the mesh - can't see a good reason not too - and probably attach the pipes to it. 

[Onoff]

I used Polypipe panels atop the 150mm of PIR then 4" of concrete:

 

 

 

Doesn't need a membrane between the foil of the PIR & makes it super quick to lay as the video shows:

 

 

Mesh sits atop the top of the Polypanel "peaks":

 

 

Of course I'm just playing at this doing one room. More of a test bed for the rest of the house. I think I'd use the Polypanels again. Might thought remove them from the wet room corner to get more concrete in there.

 

 

[joe90]

16 hours ago, PeterW said:

@joe90 are you using the extruded insulation as the former for the slab ..?? 

In effect yes, not sure what my builder is going to do exactly but it will be built as per the diagram above. He did mention making wooden formers to support the concrete. Anyway, I am meeting him on site tomorrow to mark out the site, founds being dug on Tuesday and concrete strips being poured soon after, so after a two and a half year battle we finally are getting started. We just have to wait for our Secretary of State appeal to find if the top floor is cottage ( as we want) or room in roof that the LPA are insisting on.

[PeterW]

On 25/09/2016 at 10:29, joe90 said:

He did mention making wooden formers to support the concrete. Anyway, I am meeting him on site tomorrow to mark out the site, founds being dug on Tuesday and concrete strips being poured soon after, so after a two and a half year battle we finally are getting started.

 

Just to check - has this now started and have you got any photos ..?? May need a similar approach for my garage so would be keen to see the detail. 

[joe90]

Hi peter, this will be done in a few weeks ( hopefully) and I will post photos and let you all know how it goes.

[SteamyTea]

1 hour ago, joe90 said:

this will be done in a few weeks ( hopefully)

Can I come and watch

[MarkH]

Slab poured, four miles of UFH pipe and a million cable ties buried forever. 

 

Thanks for the help.

[PeterW]

4 minutes ago, MarkH said:

Slab poured, four miles of UFH pipe and a million cable ties buried forever. 

 

Thanks for the help.

 

I'm not sure those pipe tails are long enough ....... 

 

That is a very linear build - what's the room width and overall floor area..?

[MarkH]

3 minutes ago, PeterW said:

 

I'm not sure those pipe tails are long enough ....... 

 

That is a very linear build - what's the room width and overall floor area..?

 

Ha. We had a last-minute dither about putting the manifold in the loft space and having included extra pipe length in case of mishap thought we'd leave that option open.

 

It is somewhat linear. The planning permission was granted based on the new building sitting on the footprint of the 18th century cottage which was a traditional 'rectangle with small lean-too attached' (there is a name for it, I forget...) hence the layout. Room width is 4.8M in the large section, 3.4 in the small bit. Overall area - 70.5m2. P/A = 0.67

 

Anyone want 100m of UFH pipe? 

[volcane]

Just resurrecting this thread, rather than start a new one,

 

My Kore passive slab is nearing completion and I have a query regarding the ring beam and the radon barrier. The ring was tied and then lifted into the EPS, in doing so made multiple punctures in the DPM/radon barrier. Is this a problem? how successful is patching likely to be? Are all ring beams in slabs lifted in after tying or are some tied insitu?

I'll never build another house!!!!!

[Jeremy Harris]

25 minutes ago, volcane said:

Just resurrecting this thread, rather than start a new one,

 

My Kore passive slab is nearing completion and I have a query regarding the ring beam and the radon barrier. The ring was tied and then lifted into the EPS, in doing so made multiple punctures in the DPM/radon barrier. Is this a problem? how successful is patching likely to be? Are all ring beams in slabs lifted in after tying or are some tied insitu?

I'll never build another house!!!!!

 

Why was the steel not tied in situ?  That would be the normal way to do this, as there is a high risk (as you've found) of the DPM being damaged if you try to lift the pre-tied steels into place. 

 

All I can suggest is that the steels be taken out and all the wire ties undone, a new DPM laid, and the steels then assembled and tied in situ, to reduce the risk of damaging the DPM again.

 

AFAIK, there's no good, long term, solution to patching holes in DPM, as nothing much sticks to it.  You may get away with lifting the steels partially, then fitting large areas of overlapping DPM, but it would be a bit of a bodge.

[Barney12]

19 minutes ago, JSHarris said:

 

AFAIK, there's no good, long term, solution to patching holes in DPM, as nothing much sticks to it.  You may get away with lifting the steels partially, then fitting large areas of overlapping DPM, but it would be a bit of a bodge.

 

If you are going to do that then stick the overlap with radon tape. Its sticks like sh*t to a blanket and once joined wont come apart (as long as it was applied to clean and dry DPM).

Its like a thick sticky tar. https://www.toolstation.com/shop/p43717?table=no

 

A dare say you could use it to patch the holes but its even more of a bodge really. 

 

[Alexphd1]

That's what we used to join the dpm with big overlaps, I can't see why it wouldn't work with patching . 

[volcane]

Thanks for all the replies, I favour the solution offered by @JSHarris but unfortunately that was a non-runner so patching with the sticky tape will be used. We are in a low risk radon area and MVHR should further lower the risk.