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UFH Screeds


sheepie

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Hi Folks,

 

I have had a look at some plans for a house + land that has PP and founds in place.

 

The Construction of the sub floor is 100m concrete then goes the DPM then Insulation 100mm poly but the cut away shows a further 100mm screed

 

But say I wanted to put UFH in does this add further to the 100mm screed or do I skip this and put in a lower 60+mm screed. 

 

The second wee question is there a difference between Liquid Screed (That seems to be laid over UFH) vs Sand and Cement mix?

 

Cheers

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The additional screed described is the one in which your pipework will be installed. If they have it down as a 100mm they probably have done so referencing a standard sand and cement screed, they are usually thicker to allow for strenght and to avoid shrinkage cracking. Liquid screed will do the same job and better at alot thinner circa 50-60mm and fill around the UFH pipework better allowing them to be more efficient.  Also the thinner floor screed will dry faster helping your programme.

Edited by Ronan 1
Because i cant spell
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You will need to up that insulation level as 100mm is a very low spec and in keeping with the time your foundation was put in, you need to allow at least 150mm plus 50-80mm of screed depending on type of screed, then finish floor. 

 

So that means your finished floor will be 250mm higher than the concrete you have in your pics. 

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Thanks folks,  I haven't bought the site yet as the Estate Agent is closed and I want to see Building Control regs for the existing founds but I think its best I have all my ducks in a row so that I if I meet the owner of the site I don't look like a complete idiot not having a clue what I am buying.

 

@Russell griffiths

I am still on the fence about UFH as the pro for it is that it keeps the house warm all the time but the con is that it requires more pokery installing it (As I want to do a lot of the plumbing myself) to keep costs down buying ebay bulk loads for a basic 'Homerun' e.g. 1 pipe for each utility.

 

A house I lived in before my current one had a DPM that was cut with copper pipes running from below it.  All burred in a slab so of course after 2 years of wondering why I had rising damp in the bathroom we found 'boxed' pipes below a thin layer of screed which were leaking into the subfloor.  I have also had several plumbers do wee jobs in my current house only to find that there are always the occasional leak.

 

So this has put me off plumbers touching anything,  I can run a very long pipe end to end and bring it out of a wall and put connectors on each end,  I've fitted god knows how many Ethernet cables in conduit / pattress so pipework is very similar.

 

Because the house is a bungalow im thinking of using metal webbed joists to the attic so I can run individual pex runs to each outlet rather than drilling a chunky joist which has a heck of alot of regs associated with that.

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UFH is very much in the realms of DIY, many of us have done it ourselves.   Use at least 150mm of PIR / PUR type insulation and a thinner screed. 

 

But would it even matter if you fitted more insulation and ended up with a slightly higher finished floor level?  Unless there is a very srict planning condition on floor or building height, nobody is going to notice another 50 oe 100mm.

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Running the pipe in the screed is the easy bit, individual continuous pipes, a nice DIY job, enjoyed doing mine very much.

 

You pressure test it all before laying the screed.

 

Plan for your main supply to/from manifolds to be above the floor. Mine are buried under the floor and I used the wrong pipe supports, consequently they creak with expansion/contraction. I'm now planning another accessable route overhead so I can remedy my error. 

 

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@sheepie you say the founds are in, does that include the slab, if not put yours in lower to accommodate more insulation. DIY UFH is easier than radiator plumbing IMO. loads of advise here.

Edited by joe90
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Knocked out 57m2 of the old concrete, excavated the sub floor then sand, dpm, 100mm of PIR and more dpm. Then approx 400m of UFH pipe. 25mm of PIR upstand along with expansion strip foam and 75mm of free flow screed (laid by contractor)....... kept me fit over the summer doing the project and is now keeping us toasty warm over Christmas..... probably the most enjoyed end product ive ever done!! i echo the above comment in that it is easier to install than radiators etc. one thing to remember- keep the pipes under pressure when you have the screed laid. You dont need to hire or buy an expensive pressure tester, i bought one from ebay for £11 and it works fine.

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DIY UFH is dead easy - if you can run a cable you can run UFH pipe. Plenty of options with the tray systems, rails or just clipped to the insulation. You can DIY the design using LoopCAD or get one of the suppliers such as Wunda to do it for you. Pressurising is as simple as connecting the hose pipe to flush the loops and then capping off the manifold and keeping an eye on things. 

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1 hour ago, johnbarleycorn01 said:

Knocked out 57m2 of the old concrete, excavated the sub floor then sand, dpm, 100mm of PIR and more dpm. Then approx 400m of UFH pipe. 25mm of PIR upstand along with expansion strip foam and 75mm of free flow screed (laid by contractor)....... kept me fit over the summer doing the project and is now keeping us toasty warm over Christmas..... probably the most enjoyed end product ive ever done!! i echo the above comment in that it is easier to install than radiators etc. one thing to remember- keep the pipes under pressure when you have the screed laid. You dont need to hire or buy an expensive pressure tester, i bought one from ebay for £11 and it works fine.

 
can I be a nuisance and ask you to roughly draw this in a diagram With dimensions on? I’ve seen so many different methods and am looking for a definite method to copy. As soon as I get the keys I want to get digging and don’t want to get it wrong 

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Something to check...

 

Is the CIL mentioned in the Planning Grant and if so has it been paid? If not be aware that you probably can't claim the exemption because work has started.

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7 minutes ago, Temp said:

Something to check...

 

Is the CIL mentioned in the Planning Grant and if so has it been paid? If not be aware that you probably can't claim the exemption because work has started.

We don't have anything like that in NI.

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3 minutes ago, Gareththesparky said:

 
can I be a nuisance and ask you to roughly draw this in a diagram With dimensions on? I’ve seen so many different methods and am looking for a definite method to copy. As soon as I get the keys I want to get digging and don’t want to get it wrong 

Ill try my best Gareth- what dimensions is it you want, the section of the UFH and insulation etc or the plan of the room ?

If its the former its very similar to Wozzas diagram above. If its the latter i downloaded the trial version of loopcad and uploaded my cad drawings to it and spent a weekend drawing pretty shapes to design the pipe layout. I ended up with 115mm approx centres on the pipes with 4 circuits in the room. 

Ill get scribblin.......

 

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1 hour ago, johnbarleycorn01 said:

20210102_195635.jpg

Thank you very much John, this is exactly what I was after. I’m guess img that’s liquid screed? Did you so that yourself or use a company to do it for you?
ive about 1/3 of an acre of swampland to lose the concrete I excavate in luckily/unfortunately 

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  • 1 month later...
On 02/01/2021 at 22:03, Temp said:

Avoid Anhydrite screeds if you are planning on tiling. They can form a Laitance on the top which is hard to bond to. Avoid aerated screed for obvious reasons.

 

What about using a calcium based tile adhesive (unlike cement based), like Anhyfix?

 

 

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Still have to remove the laitance (according to the instructions) because its a weak layer. It's not recommended for wet rooms either but perhaps that doesn't matter.

 

https://www.tilemasteradhesives.co.uk/file/TDS-AnhyFix.pdf

 

Calcium Sulphate Screeds:  Calcium sulphate screeds dry with laitance on  the surface.  The laitance must be removed before the tiling commences by mechanically sanding and/or abrading the surface of the screed.

 

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On 02/01/2021 at 22:03, Temp said:

Avoid Anhydrite screeds if you are planning on tiling. They can form a Laitance on the top which is hard to bond to. Avoid aerated screed for obvious reasons.

 

1 hour ago, Temp said:

Still have to remove the laitance (according to the instructions) because its a weak layer. It's not recommended for wet rooms either but perhaps that doesn't matter.

 

seems to be a bit contradictory here @Temp. sounds likes you can use Anhydrite screeds if you want to tile then, you just have to ensure that the laitance has been removed, which should be part of the service for installing the screed.

 

plus, it seems to be recommended to use a decoupling mat under floor tiles so, in theory, the tiles aren't being laid on to the screed but to a mat on top of the screed. 

 

so does the "avoid anhydrite screeds if you are planning on tiling" quote still stand if the laitance is removed and you're using a decoupling mat?

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