UFH fixing pipes to mesh ??

[albert]

Hi I have 150m2 GF of UFH to install  and I' d like to install it in the slab (125mm ) (100 mm PIR below) I have seen pipes cable tied to mesh on commercial jobs and wondered if there were any pit falls. The UFH company are after crazy money to install. We have done it  ourselves before but in flow screed and not to mesh. Any advice welcome.  A

[Jeremy Harris]

5 minutes ago, albert said:

Hi I have 150m2 GF of UFH to install  and I' d like to install it in the slab (125mm ) (100 mm PIR below) I have seen pipes cable tied to mesh on commercial jobs and wondered if there were any pit falls. The UFH company are after crazy money to install. We have done it  ourselves before but in flow screed and not to mesh. Any advice welcome.  A

 

Our UFH pipes are just cable tied to the reinforcing fabric:

 

[MikeSharp01]

Same with ours.

Edited August 30, 2019 by MikeSharp01

[Onoff]

I used Polypipe panels, video:

 

 

 

Then A142 mesh over the top:

 

 

Then 100mm of concrete:

 

 

[albert]

 Ok many thanks zip tie to mesh then. 

[mvincentd]

@albert maybe worth noting from the example images given above that Onoff has the advantage of the supportive red tray so his ufh pipes not following the line of the mesh is unimportant, whereas the others do as far as possible stick to the mesh lines.  The more instances of pipe spanning the middle of a 200mm square unsupported, the more vulnerability to a clumsy wellie etc' you have.

[mr-gobby]

What ufh system you using Albert and more interestingly what pipe, there seems to be a few options. My concern is damage or rather avoiding it on installing the concrete. I've seen mesh on little upstands to raise the pipe height in the slab but not sure how the size 10's are going to navigate it all on pouring the concrete which maybe barrowed in my case. Interested as have 30m to do (okay bit less than you) and contemplating going into concrete slab to save on costs of into a screed (quotes are around £1000) . Ours is a single storey extension  6x6m externals and I may have some levelling issues adjoining the existing floor of our 1950's house but think I could overcome that for less than the cost of installing a screed. Just had brickies in to build up to damp yesterday,  next bit is down to me to sort out before they return to build the shell. I've a couple things to address too including door thresholds and may have to nip out some inner skin bricks and backfill the cavity where the doors are going, I just needed them to get it built up to damp which they have done quickly and professionally.

Edited September 8, 2019 by mr-gobby

[Onoff]

I used Pex-Al-Pex 16mm pipe. 

 

It's as tough as old boots. @Nickfromwales quoted I think seeing labourers upending wheelbarrows on it without detriment to it.

 

 

However...

 

I am Mr Slow and then some. I laid the red tray, then the pipe but it was a long time before I poured the slab. My pipe suffered some abrasions from the rusty A142 mesh. This was simply where I'd been walking on the mesh for so long.

 

 

Tbh didn't seem to have done too much damage. I added some bits of conduit where it had rubbed.

 

 

Wouldn't have happened if I'd gotten my arse in gear and done the slab quicker.

[mr-gobby]

I was of the thinking of the mesh could be raised into the slab with meshmen but it makes navigating the mesh tricky

[Conor]

1 minute ago, mr-gobby said:

I was of the thinking of the mesh could be raised into the slab with meshmen but it makes navigating the mesh tricky

Mesh should be between 35 and 50mm from the finished surface of the slab anyway.

 

Just fire the mesh down and clip the ufh the day before the concrete arrives. If you are talking a 6x6m area, then I wouldn't expect too much foot traffic during the pour anyway. That's my plan... But I'm also going to use self compacting concrete (more for practicality reasons) that will drastically reduce foot traffic during the pour.

[Onoff]

1 minute ago, mr-gobby said:

I was of the thinking of the mesh could be raised into the slab with meshmen but it makes navigating the mesh tricky

 

Like what Jeremy did in his picture above.

 

Tbh it's what many do and it works. Chairs or stools are other terms used.

[mr-gobby]

4 minutes ago, Conor said:

Mesh should be between 35 and 50mm from the finished surface of the slab anyway.

 

Just fire the mesh down and clip the ufh the day before the concrete arrives. If you are talking a 6x6m area, then I wouldn't expect too much foot traffic during the pour anyway. That's my plan... But I'm also going to use self compacting concrete (more for practicality reasons) that will drastically reduce foot traffic during the pour.

May depend how deep are you pouring the concrete and thickness of mesh I suppose, I poured footings to 380/375mm off damp, pulled oversite off a touch below that to 400mm and allowed  100mm oversite, 10mm blinding, 100mm slab,.100mm celotex /insulation, 75 screed so I could just up the insulation with some 75mm XPS under the celotex on top of the sand blinding. Could put mesh down and space pipe off that rather than use mesh men. Pex al HDPE or pex al pex is another thing. I was looking at theunderfloorheatingstore.com and they list the pex al hdpe. I've put this extension on back of house but have also added 5mx3m to back of garage/workshop which is detached by about 30cm. Going to sink ufh pipe in that too while I'm at it but can't decide whether to use separate manifold for it and run flow & returns to it from house (quite a way from boiler, maybe 10-12m) or run the ufh pipes back to a manifold in the house along with the extension ufh pipework. Decisions decisions!

[Jeremy Harris]

There was no problem at all with heavy muddy boots tramping over the steel fabric and insulation whilst laying the pipes.  The fabric was stood on 50mm chairs, the pipes were clipped to it with cable ties, and the insulation underneath is 300mm deep EPS.  The slab is 100mm deep, so the pipes are just above the centre of the slab, which in practice works very well indeed.  We still get around 8% heat loss from the UFH to the ground through the 300mm insulation, but that's pretty typical for UFH; there's always an efficiency hit from increased heat loss to ground, just the price that has to be paid fro getting rid of radiators.

[gc100]

Not hijack the thread but a quick question - we have only 150mm of insulation due to certain constraints of our conversion. Is there anything we can do material wise to reduce the heat lose through the floor with UFH?

[Jeremy Harris]

18 minutes ago, gc100 said:

Not hijack the thread but a quick question - we have only 150mm of insulation due to certain constraints of our conversion. Is there anything we can do material wise to reduce the heat lose through the floor with UFH?

 

 

150mm of decent insulation is probably fine, there is a law of diminishing returns, where adding more insulation only makes a modest difference.  If the loss is under about 10% then realistically that's about as good as it's reasonable to expect.

 

Worth just doing a quick check to see how hot the floor is likely to run and how much heat will be lost.  I wrote a simple spreadsheet to do this that may help: Floor heat loss and UFH calculator.xls

 

To put our floor heat loss from the UFH into perspective, in very cold weather (as in -10°C outside), then that ~8% represents about 128 W, so about the same as us leaving most of the lights on in the house, which isn't a lot to pay for the convenience of not having radiators cluttering up the walls.

[SeanDean]

Sorry to highjack the thread guys but I want to check my last min plan for UFH is ok before I start laying the pipe.

I might not even use the UFH but thought it best to get it into the slab as I might regret not doing it down the line. Zone 01 is a workshop area and then a step up into zone 2 which is a bar/chill area. The entire space is open plan.

 

So I plan to zip tie 16mm PEX-AL-HDPE pipe to my lower layer of 142 mesh @ 200mm spacing, the base is 150mm thick.

I have a couple of questions below, if anyone can help me with them that would be greatly appreciated.

 

- Does anyone see any major issues with my design?

- What is the difference between PEX-AL-HDPE and PEX-AL-PEX and is one better than the other?

- Am I correct in not running UFH where I might have units/bar or machinery bolted into the ground?

- The pipes will not be hooked up to a manifold until later down the line but should I put water in the pipes when pouring the concrete base?

 

Any help with be greatly appreciated.

[Temp]

I have 80mm PIR in some rooms and if building again I would fit more. 

 

I assume your screed is 150mm thick in the workshop because you will be driving a car on it? Need not be that thick elsewhere.

[TonyT]

I would be concerned that the second layer of mesh during installation would damage the pipework?

[PeterW]

13 minutes ago, TonyT said:

I would be concerned that the second layer of mesh during installation would damage the pipework?

I hadn’t even clocked that ..!!

 

@SeanDean who has specified two layers of mesh in that slab ..? One is more than adequate,  you’re building a garage slab not a motorway bridge ... 

[SeanDean]

9 hours ago, Temp said:

I have 80mm PIR in some rooms and if building again I would fit more. 

 

I assume your screed is 150mm thick in the workshop because you will be driving a car on it? Need not be that thick elsewhere.

Yes, that is correct but also heavy workshop machinery might go in zone 2 as well so thought it best to over-spec the thickness there as well for future-proofing.

I guess I could reduce it to 100mm thick but other than saving a little bit of money I'm not sure what I would need to.

[SeanDean]

1 hour ago, TonyT said:

I would be concerned that the second layer of mesh during installation would damage the pipework?

I guess I could add bits of conduit over the points where the top layer of mesh comes into contact with the pipe like @Onoff has done in the images above.

[SeanDean]

56 minutes ago, PeterW said:

I hadn’t even clocked that ..!!

 

@SeanDean who has specified two layers of mesh in that slab ..? One is more than adequate,  you’re building a garage slab not a motorway bridge ... 

The original architect spec'ed it with two layers, if it's 100% not needed it could save us fathing about trying to protect the pipe from the top layer of mesh.

Is it possible the architect meant layered directly on top of each other rather than spaced apart? (long story short the architect is no longer working on the project)

 

If I was to remove the top layer of mesh am I correct in assuming I would move the single layer of mesh as close to the centre of the slab as possible while keeping the UFH pipe 50mm below the surface?

 

[PeterW]

Half way through is ideal. If you want belt and braces ask the concrete company to put fibres in the mix and it will be bombproof. 
 

 

[Onoff]

You could commission some snazzy, double ended, 3D printed stand offs to keep the two meshes 50mm apart... ?

 

Tbh I'd just cut some Celcon blocks into 50mm strips and CT1 lumps between the meshes here and there. 

[TonyT]

1 hour ago, Onoff said:

You could commission some snazzy, double ended, 3D printed stand offs to keep the two meshes 50mm apart... ?

 

Tbh I'd just cut some Celcon blocks into 50mm strips and CT1 lumps between the meshes here and there. 

Or just buy some off the shelf ‘chairs,stools’ and save the time?