Visti

UFH Screed Depth?

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How thick of a screed layer did you install to fit the UFH?

 

We've planned for 75mm but have been warned that this may be insufficient by MBC. So are considering an increase to 100mm.

 

Current composition (above EPS) is:

  • up to 24mm reinforcing mesh (2x12mm diameter steel)
  • 16mm UFH piping
  • 35mm concrete cover

 

Key question is whether the 35mm is enough? and what margins of error should we accept? ~/-5mm?

 

 

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Is this sand & cement screed over insulation over a concrete oversite or slab..?

 

whats the floor make up as that will affect the thickness needed 

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Because of problems during the initial build we were unable to go with 100mm concrete floor with UFH and have just laid 70mm flow screed for the UFH ( we were told they don’t do more than 70mm with this particular product).

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It is indeed Peter, though it's a suspended Beam & Block rather than a slab. Composition below.

 

I should note that the power-floated screed will be the finished floor. Nothing is going on top of that.

 

Quote

Ground Floor:

 - Reinforced Sand-Cement power-floated screed with integral underfloor heating as floor finish. 

 - 2 layers of 150mm jablite 70 EPS @ 0.11w/m2k

 - DPM lapped & double taped @ perimiter

 - Beam & Block

 - 150mm ventilated void

 

5a589edbdde6f_20180112-UFHScreedDepth.thumb.png.e5131743f4b8b65943a12d6fbdd66d87.png

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@Visti

A couple of points:

- in the situation you’ve described s/c screed is normally a minimum depth of 50mm so you’d need that much over the top of the pipes.

- check that the beams of your beam & block floor aren’t pre-cambered. If they are then this will affect your set-out and screed thickness calculations.

- you’ve said that you’ll be power floating the sand cement screed but I didn’t know you could do this. I’ve only ever seen concrete floors being power floated.

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2 hours ago, Visti said:

 

 

Current composition (above EPS) is:

  • up to 24mm reinforcing mesh (2x12mm diameter steel)
  • 16mm UFH piping
  • 35mm concrete cover

 

Key question is whether the 35mm is enough? and what margins of error should we accept? ~/-5mm?

 

 

You’ve forgotten that the rebar will need to be held off the top of your EPS layer on small plastic or concrete spacers

Edited by Ian

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So....

 

I would ditch the EPS and go 150mm of PIR which gives you 0.1 on the uValue. 

 

Then it’s 100mm of concrete on top - Agila or similar flowing / self compacting and that gives you 35mm chairs for the mesh, 16mm pipes and 50mm over. 

 

Quick and cheap. 

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Generally for liquid screed the minimum coverage of UFH pipes is 40-50mm so you are looking at a minimum depth of around 60mm screed, some people will say 55, some say 65. For sand cement you are looking at around 75mm minimum depth.

 

However this is an unusual floor build up, why is the screed reinforced? The beam and block floor should be load bearing. Are there load bearing interior walls sitting on the screed with the insulation below them rather than all the way down to the beam and block? Otherwise I do not see why it would be reinforced.

 

I must admit I am not sure the thickness of the screed once it is reinforced, but I could imagine it being nearer 100mm. If so I would just make theEPS thinner. The lost insulation value would be negligible. PIR will be much more expensive.

 

I can't imagine that they have reinforced the screed for no reason as obviously a thinner screed and no rebar would be a lot cheaper.

Edited by AliG

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6 hours ago, AliG said:

However this is an unusual floor build up, why is the screed reinforced? The beam and block floor should be load bearing. Are there load bearing interior walls sitting on the screed with the insulation below them rather than all the way down to the beam and block? Otherwise I do not see why it would be reinforced.

 

The reason is exactly what you suspected; we have internal lead bearing walls that'll be resting on the screed.

 

9 hours ago, Ian said:

- check that the beams of your beam & block floor aren’t pre-cambered. If they are then this will affect your set-out and screed thickness calculations.

 

That's a good point and not one I'd known/considered. I'll ensure to bring it up with the engineer!

 

 

7 hours ago, PeterW said:

So....

 

I would ditch the EPS and go 150mm of PIR which gives you 0.1 on the uValue. 

 

Then it’s 100mm of concrete on top - Agila or similar flowing / self compacting and that gives you 35mm chairs for the mesh, 16mm pipes and 50mm over. 

 

Quick and cheap. 

 

 

The best PIR I can find is Kingspans Kooltherm K103, which is at 0.018 W/mK. That's a u-value of 0.12 @ 150mm for £43/m2 (2x75mm)

Two layers of 150mm Jablite EPS at 0.035 W/mK gives an equivalent u-value of 0.117 but for only £19/m2. 

 

As we're not struggera 150mm, we'll stick with the EPS.

 

Also, there also appears o be a nationwide PI0mmR shortage. Anyone clued up on that?!

 

 

I think we'll be going with 100mm thickness overall. To be safe and account for the spacers too. That'll give us 5-10mm of 'headroom'.

 

 

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9 hours ago, Ian said:

@Visti

 

- check that the beams of your beam & block floor aren’t pre-cambered. If they are then this will affect your set-out and screed thickness calculations.

 

 

I thought all beams would be pre-cambered??

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9 hours ago, Visti said:

 

The reason is exactly what you suspected; we have internal lead bearing walls that'll be resting on the screed.

 

 

That's a good point and not one I'd known/considered. I'll ensure to bring it up with the engineer!

 

 

 

 

The best PIR I can find is Kingspans Kooltherm K103, which is at 0.018 W/mK. That's a u-value of 0.12 @ 150mm for £43/m2 (2x75mm)

Two layers of 150mm Jablite EPS at 0.035 W/mK gives an equivalent u-value of 0.117 but for only £19/m2. 

 

As we're not struggera 150mm, we'll stick with the EPS.

 

Also, there also appears o be a nationwide PI0mmR shortage. Anyone clued up on that?!

 

 

I think we'll be going with 100mm thickness overall. To be safe and account for the spacers too. That'll give us 5-10mm of 'headroom'.

 

 

Big fire in European factory apparently. Strange how there's a massive shortage but they've got as much as you want if you pay more! Suppose it's economics

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I'd go with a self compacting concrete too just for ease of use and can work off it. Is this your finished floor as in no covering on top?

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42 minutes ago, Oz07 said:

I'd go with a self compacting concrete too just for ease of use and can work off it. Is this your finished floor as in no covering on top?

 

Correct! Nothingis going on top of this concrete surface. We're being quite stingey on the budget and both like the idea.

 

Speaking of which, anyone else with bare screed / concrete able to share some pictures of the surface? The SO is worried about the potential size of divets etc...

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1 minute ago, Visti said:

We're being quite stingey on the budget and both like the idea.

 

So are you not looking to polish the floor..? Just a pure powerfloated finish ..?

 

It will need protecting whilst you’re working as otherwise plaster, adhesive etc will get into it.  Once you’ve done then it will have to be sealed otherwise it will continually scuff dust up so that’s an additional expense. This will need to be maintained too. 

 

If you are considering polished concrete where the aggregate is exposed by grinding then you are talking about a fairly substantial cost on top of the laying. The concrete pour also needs to be done carefully and not over worked and has to be as flat as possible as you can’t fill troughs you have to grind down. 

 

I’m pretty sure someone on here had polished concrete and the costs are around £60-70sqm, which is far from being a budget item ..! 

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We also (against all sensible advice) did a powerfloated finish on our concrete slab. MBC just powerfloated it for a good bit longer than they would have normally and I think it looks great, but I am by no means fussy about obtaining a "perfect" finish. It is definitely not perfect, although no massive holes. The small holes and cracks that are there, we are thinking about filling with a brightly coloured resin to avoid them filling up with toast crumbs and dust and to make a feature of their "imperfect" nature. 

 

It is also not reflective - just smooth, but this is a plus point for me, as I hate shiny finishes. We bought a LOT of cheap hardboard (like the back of IKEA kitchen cabinets) and taped it all together to cover the floor. The bits (near window/door thresholds) where grit and muck have got in are noticeably scratched up and look rough. We may try and finish these bits off with a thin wood trim when the build is finished, depending how much they annoy us to look at. One unexpected bonus of having the hardboard down is that it got wet before the roof went in, and the dampness has slowed down the concrete curing, much reducing cracking over some of the larger areas. 

 

Good luck with whatever you choose!

dj 

 

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I must admit I powerfloated my last garage floor and it left a really good finish, non dusty and quite resilient to fluids. I am just a little knarked that I was too late to powerfloat my current garage floor so ended up with a rougher finish but painted it to avoid dust and stains ( it is only a garage after all).

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@divorcingjack Excellent, that we're glad to hear! We're thinking of a resin too to deal with the cracks, though the contrasting colour sounds like a great idea... just have to sell the SO on it. 

 

Did you have to specify the concrete mix, or did MBC have a standard mix that you chose to use?

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Is it going to be shoes left at the front door house ?

 

I have thin vinyl pre-tend wood tiles over my screeded ufh with 200 PIR under that. And even then it is cold to walk on in socks only in the summer, in autumn I found myself putting the ufh on just to remove this chill even though the room was not cold.  

 

I guess I could buy some fluffy slippers like my partner though.

Edited by readiescards
Clarification

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