Ufh solid floor build up

[Tommyt01]

Hi all. 
I’ve been searching the forum and the internet to see what the best solid floor build up would be for Ufh, from what I have found, I’m thinking of going with 

type 1 

sand binding 

dpm

150mm pir 

dpm

Ufh stapled

100mm fibre reinforced concrete 

 

I’ve suggested this to a couple of companies and they have advised against it and it’s not the correct way it’s done and needs a concrete under the pir and a screed above. 
 

is what I’m suggesting correct or is there a better way? If it is, what spec of concrete would be needed? 
 

Cheers 

[JohnMo]

What do your structural drawings say?

[Tommyt01]

I don’t have any drawings, this is to replace a uninsulated slab in the kitchen and wooden floors throughout downstairs 

[nod]

As above SE drawing should really dictate this 

Also Why only 150 insulation If your putting it into a slab without any restrictions 

 

[nod]

2 minutes ago, Tommyt01 said:

I don’t have any drawings, this is to replace a uninsulated slab in the kitchen and wooden floors throughout downstairs 

Then I would definitely update the insulation Even 50 mil can make a massive difference 

[Tommyt01]

I can put the 200mm in if it would make a difference.

 

i didn’t know if a se would make a set of drawings just for a floor build up? I will contact some locally to advise and purchase the drawings 

[Andehh]

How's the rest of the house? 150mm to 200mm is a big step, for disproportionate improvement.... Especially if rest of the house is lacking!

[Iceverge]

I assume you mean something like a light grade of polythene between the UFH pipes and the PIR rather than another DPM? Alternatively you could forgo this and just tape the joints in the boards. All it's doing is stopping the juice from the concrete going between the boards and floating them. 

 

 

Otherwise it looks fine to me. With insulation more is always better. It might be as cheap to get 200mm of Seconds&Co PIR as 150mm of new stuff. Beware you will need to do more digging however. 

 

 

 

Edited January 16 by Iceverge

[Iceverge]

On the pipes in 100mm of concrete. This will be obviously slower to heat up or cool down than a thinner screed.

 

Not an issue if you run your house at a constant temp 24/7 but it will require some extra heating if you have a very high heat loss building and only intermittently heat the house. 

 

If this is the case I would just use extra large rads. 

[Tommyt01]

All of the downstairs floor will be coming out, so it’s pretty flexible on what we can do as the new slab will run throughout downstairs with regards to depths 

 

If it doesn’t need to be as thick as a dpm, Ill use polythene to keep the concrete off the pir boards

[JamesP]

My floor build up has 100mm of concrete below the 150mm insulation. I set the UFH in 60mm screed. 

1 hour ago, Tommyt01 said:

I’ve suggested this to a couple of companies and they have advised against it and it’s not the correct way it’s done and needs a concrete under the pir and a screed above. 

 

[Roger440]

2 hours ago, Tommyt01 said:

I don’t have any drawings, this is to replace a uninsulated slab in the kitchen and wooden floors throughout downstairs 

 

I did foamed glass with concrete over. Total depth 240mm.

 

Didnt meet current regs, but light years better than what you have, and avoids any risks of excavating too deep next to existing foundations.

[HughF]

This is exactly my floor build up in the extension. Except we’re on 200pir and about 120mm conc.

 

works perfect, crack on.

 

 

 

 

[Nickfromwales]

24 minutes ago, HughF said:

works perfect, crack on.

Yup, +1.

 

I've done plenty of these types of installs and with exactly the methodology described by the OP, never an issue.

 

IMO the underlaying concrete (that most builders knee-jerk to without any thought) is a waste of money. This is absolutely reliant on the preparation works and that having been done meticulously without divots or voids in the sub ground / earth.

 

Last one I did was 200mm of PIR then 85mm or so of dry screed with 16mm UFH pipes stapled to the insulation.

 

I don't really bother with the top 'membrane' and I've never had any issues. I once had to do an insurance job where I had to take an Everest conservatory floor up (tiles were cracking and floor screed caving in) and they had done this methodology, just very poorly prepped and loads of undulation in the ground prep. The screed was laid directly onto the PIR and all that happened was the foil had tarnished a little, over 5 years or so.

 

I'd only go with the upper membrane if going for a true liquid screed.

[saveasteading]

19 minutes ago, Nickfromwales said:

IMO the underlaying concrete is a waste of money

I agree that it technically isn't essential for strength,  but i would  do it, even in my own building with my own supervision. A marginal decision though.

This is because it is close to impossiblle to lay and compact stone level and smoothly enough. Even the best laid Type 1 will have undulations, and then need sand blinding to be properly flat.

Blinding needs to be ultra-thin or it gets footprints and other indents.

So i would lay at least 50mm of concrete with fibre addditive as long as the labour is skilled enough to make it flat and smooth.

 

In real life the loads in a domestic situation are tiny enough that pir does not crush, and will probably bridge small dips in concrete or hardcore.

In theory i might accept pir straight onto stone if the method and skill levels guarantee a level surface. 

Blinding smoothed and membrane on it, planks for movement, pir laid immeduately and progressively, planks on top again.

Top membrane is essential with liquid screed over pir. Not with dry screed, but the cost is tiny.

[HughF]

What's this mythical screed you talk of, we used readymix straight off the truck 😀 Tiny bit of self leveller at a transition where we knocked through and LVT straight over the top.

 

 

[saveasteading]

12 minutes ago, HughF said:

readymix straight off the truck

Absolutely fine, and about a third of the cost per m3.

Also a cost advantage in labour when the area is quite small. such as an extension. 

The downside is that it isn't so easy to lay to a very thin layer of say 60mm, and won't find its way tight to every surface of the UFH pipes.

 

It's also very bold to do that so early, in the open, as the weather and oncoming trades will do their best to damage the surface.

 

@HughF what thickness is that?  What mix of concrete and did it have plasticiser?

 

If you have stuck vinyl straight onto that, then you've done remarkably well with the finishing.... and controlled the weather and workers well.

[JohnMo]

30 minutes ago, saveasteading said:

and won't find its way tight to every surface of the UFH pipes

That really depends on the slump you ask for, when requesting the concrete. We used a structural grade concrete (forget which) but quite high slump with fibre reinforced. But we have the structural ground bearing slab below the insulation. 

 

We did ours prior to walls going up, very exposed site.

 

Disadvantages, in cold weather if ice foams on the slab, because it's very well insulated, it stays covered in ice for days. If you have water in UFH pipes you also need antifreeze. Due to the slab size 192m² there were a few dips and high spots, ground down high areas, self leveling on low spots.

 

Damage during build none 

Edited yesterday at 17:59 by JohnMo

[saveasteading]

11 minutes ago, JohnMo said:

high slump with fibre reinforced

They cancel out to some extent.   How thick was it?

 

The current family project will have 350m2 of UFH with screed.  350m2 x 60mm = 21m3.    I fancy avoiding paying £350/m3 for the material, but would be nervous about the self levelling and time involved.

I've used fibre and love it, but never less than 125mm thick and with power floating.

How did you level it? Screed board then a trowel?  Did you use the triffid-like level control things?

[HughF]

1 hour ago, saveasteading said:

Absolutely fine, and about a third of the cost per m3.

Also a cost advantage in labour when the area is quite small. such as an extension. 

The downside is that it isn't so easy to lay to a very thin layer of say 60mm, and won't find its way tight to every surface of the UFH pipes.

 

It's also very bold to do that so early, in the open, as the weather and oncoming trades will do their best to damage the surface.

 

@HughF what thickness is that?  What mix of concrete and did it have plasticiser?

 

If you have stuck vinyl straight onto that, then you've done remarkably well with the finishing.... and controlled the weather and workers well.

It’s was just ‘concrete’ off the truck, laid by my builders (father and son team) with me on hand labouring. 120mm if memory serves. Pipes at 150 centers.

 

click down lvt with the integrated foam backing - not glued.

Edited yesterday at 18:31 by HughF

[JohnMo]

28 minutes ago, saveasteading said:

How thick was it?

100mm