Only 75mm for Underfloor heating, insulation and screed

Zagato

I'm installing UFH too and find myself in a situation where the concrete subfloor is in, but has only left me with 75mm to my floor height instead of the planned 150mm or so. The 75mm has to cover my insulation, UFH screed, and tiles which are supposed to be 20mm, but can get at 15mm if I need. I can either get the concrete removed -sounds painful and expensive, or use a 7mm multifoil insulation [product snip]. My concern with this apart from how thin it is, is that as you will see from the link -it doesn't provide a U-value. I'm not sure how worrisome that is as I suspect that the standard tests for determining insulation properties probably undervalues the radiation insulation. Would I also be right in thinking that most of the heat going down from the UFH is going to be radiant heat anyway?

Mellor

Zagato, I've moved your question into tis own thread. It was similar to the original thread but a few differences. Just feel its best to avoid any confusion between your self and the other question. I also snipped out the product. We don't allow products to be posted as it leads to spam.

As for you problem, how did you end up with only 75mm? Even 150mm was tight.
How much insulation was specified originally, were BER calculatios done?

First of all, the 7mm multifoil is useless. They are mostly based on the wrong principal. THey work best are reflecting heat. This works best with higher temperatures. They are commonly used in hot climates to keep heat out of roofs. They provide "some" insulation due to the foam layers but its next to nothing. No where near enough for a new build. The fact that they don't quote a u-value should say a lot (at 7mm it would have to be at the level of aerogels used by nasa to work in a floor).
You will notice on their website that they refer to the product as supplementary insulation. This is there get out of jail card. It means the product is not to be used as a stand alone insulation. They are aiming for renovation work where the floor is already in place. The fact that this isb't clear should also tell you a thing of two about them.

Not use this. Simply avoid them and anyone who recomends them.

As for you problem ay hand. I can't see any other solution but to raise the floor level or kango out the floor. if the builder put the floor in to high its his expense to remove it.

If you go with the option of raise the floor slightly, then there are ways you can minimise total height. Choose the best proforming rigid insulation, this keeps the totalt thickness down. Go for an easi-screed or similar. These are screed designed for UFH and are much thinner, c.35mm. 15mm tiles also. You are still looking at 150mm total at least

Beware of ceiling height and the stairs (first step etc)

sinnerboy

Reminder - min U Value with UFH is 0.15 .

sydthebeat

Zagato wrote: »

I'm installing UFH too and find myself in a situation where the concrete subfloor is in, but has only left me with 75mm to my floor height instead of the planned 150mm or so.

how did that happen? what F-C height are you left with?


you can use an easi-screed type floor, check with your manufacturer for suitability.

and also as SB has said, min u value for UFH is 0.15
this usually amounts to about 120-140 high density insulation.

methinks a jack hammer may be called in

mickdw

Id be interested to know how this happened too. Im sure the build was undertaken without working drawings and by a builder totally unaware of regulations and final spec.
I dont see how taking the whole floor out is an option. If its a raft its certainly not an option. If its a concrete subfloor, it would need to come out completely, remove some hardcore and replace concrete. This is not something I would consider doing if it could be avoided.
How are your door and ceiling heights? Could you move away from UFH to reduce floor insulation requirement.

martin46585

If the sub floor is of a fairly decent depth , you could try using a road saw set to a constant depth of approx 3", with cuts every 6" inch or so, then it would be easier to kango out the strips, it's would be a hellish amount of work, though not as much or as costly, as complete removal of all the floor, radon????, and hardcore, only to have to do it all in reverse again,

AckwelFoley

75mm is too thin for effective underfloor heating as their isnt the optimum storage of heat available in that amount. 100mm is best.

However as syd said you do have the option of easyscreed, because it is more dense, you require less of it

Mellor

martin46585 wrote: »

If the sub floor is of a fairly decent depth , you could try using a road saw set to a constant depth of approx 3", with cuts every 6" inch or so, then it would be easier to kango out the strips, it's would be a hellish amount of work, though not as much or as costly, as complete removal of all the floor, radon????, and hardcore, only to have to do it all in reverse again,

I'd consider living in a house with 2250 high ceilings far more hellish that re-doing a floor.
The cost of re doing the floor is less than the value you'll lsoe from the house based on 2250 high ceings.

*2250 is made up, but prob not too far off.

snyper wrote: »

However as syd said you do have the option of easyscreed, because it is more dense, you require less of it

It's not significantly more dense (slightly but not the reason for the being thinner). Its a different material. It's not a cementitious product, differently structurally and basically has far stonger bonds. costs more per sq.m, as you imagine

martin46585

Nobody mentioned raising the floor levels, In most new builds the f/c height is 2700mm give or take, so the ceiling height will be not near as important as the height of your door heads which will rule out any change in ffl,

sydthebeat

martin46585 wrote: »

Nobody mentioned raising the floor levels, In most new builds the f/c height is 2700mm give or take, so the ceiling height will be not near as important as the height of your door heads which will rule out any change in ffl,

as the op says the only has 75mm to deal with, i think its a safer assumption to consider that they only have minimums to work with, as a reduction in floor to ceiling heigh as far as the minimum is always an option.

OP can you clarify what the F-C is at the moment

Mike2006

Personally, if I was faced with this, I would seriously consider not installing the UFH.
From the facts, if you want UFH you need a min of 100mm poly-iso insulation, UFH pipes on that is 16mm and 30mm of easi-screed on that min. That takes you up to 146mm at a very min.
That means that if you want to keep your UFH, then you HAVE to root out the concrete. If you don't root it out then you WILL have a very inefficient heating system where your UFH will be heating the everywhere except your home....

If you go with radiators at least downstairs, then you possibly could make it work for you...

You are probably set on the UFH but this decision will affect the performance of your home for the rest of your life so do not take the easy out here.

Either bite the bullet and dig or compromise with the radiators.

Mike.

RKQ

If this is a new build, which I assume it is, then ytou must comply fully with the current Building Regulations. I agree with Mellor, Syd & Mike2006.

martin46585 makes a good point. There is a swedish UFH product that works in a very thin screed - 10mm to 20mm. Its usually used over timber joists and it wouldn't resolve the lack of insulation that would be required.

I'm afraid Mike2006 is right "Either bite the bullet and dig or compromise with the radiators."

YouTookMyName

Is it a raft or strip foundation?

The insulation might be in the foundation already if its a strip.

Poor Uncle Tom

YouTookMyName wrote: »

Is it a raft or strip foundation?

The insulation might be in the foundation already if its a strip.

Any insulation in a foundation (usually ICF type to stop cold bridging) does not replace the need for insulation in the floors.

TheAnswer

Interesting thread, I'm putting on an extension and the subfloor is only 140mm below level of existing house floor, I'm not doing UFH but is 140mm enough depth allowing for insulation and screed etc?

Poor Uncle Tom

Interesting thread, I'm putting on an extension and the subfloor is only 140mm below level of existing house floor, I'm not doing UFH but is 140mm enough depth allowing for insulation and screed etc?

It depends on the thickness of insulation specified for your floor (shouldn't normally be below 100mm thick) then add a 125mm thick reinforced floor slab. This gives a total thickness of 225mm or 275mm if you are using 150mm insulation. Assuming you already have the radon barrier/DPM in place.

TheAnswer

Poor Uncle Tom wrote: »

It depends on the thickness of insulation specified for your floor (shouldn't normally be below 100mm thick) then add a 125mm thick reinforced floor slab. This gives a total thickness of 225mm or 275mm if you are using 150mm insulation. Assuming you already have the radon barrier/DPM in place.

So basically you're saying I don't have enough with 140mm? DPM is only a few mils so not an issue. will I get away with 50-70mm of insulation and 70-90mm screed?

Poor Uncle Tom

TheAnswer wrote: »

So basically you're saying I don't have enough with 140mm? DPM is only a few mils so not an issue. will I get away with 50-70mm of insulation and 70-90mm screed?

Why do you have to get away with anything? why not do it right?

Yes, you can get 100mm insulation and 40mm fibre cement screed but whether the 100mm insulation is enough or not can only be answered by an assesor, and the fibre screed costs more than concrete.

TheAnswer

Poor Uncle Tom wrote: »

Why do you have to get away with anything? why not do it right?

Yes, you can get 100mm insulation and 40mm fibre cement screed but whether the 100mm insulation is enough or not can only be answered by an assesor, and the fibre screed costs more than concrete.

Because, like OP, I'm faced with digging out a 200mm concrete subfloor and repouring just to get 225-250mm for insulation and screed, i'm not trying to "get away" with anything, just exploring alternative possibilities.
Thanks very much for your comments, most helpful, and I mean that, I'm not being sarcastic just in case you think I am:)

Slig

TheAnswer wrote: »

Because, like OP, I'm faced with digging out a 200mm concrete subfloor and repouring just to get 225-250mm for insulation and screed, i'm not trying to "get away" with anything, just exploring alternative possibilities.
Thanks very much for your comments, most helpful, and I mean that, I'm not being sarcastic just in case you think I am:)

I dont want to be dismissive but can I just ask where this 140mm came from. Did you get a specified finished floor level and floor build up from your drawings or was the sub floor put in by a builder as they saw fit?

Again I'm not trying to prove a point or critisise your methods I'm just curious as to how this potentially costly and time consuming situation came about.

TheAnswer

Slig wrote: »

I dont want to be dismissive but can I just ask where this 140mm came from. Did you get a specified finished floor level and floor build up from your drawings or was the sub floor put in by a builder as they saw fit?

Again I'm not trying to prove a point or critisise your methods I'm just curious as to how this potentially costly and time consuming situation came about.

Slab was already there from the previous owners endeavours (I think he started on the project, then either ran out of funds or just decided it was easier to move house:D), various builders who looked at the job reckoned the slab was fine to use as a subfloor (though one lad did say it was a bit tight for insulation/screed). New foundation trenches for walls were cut tru the slab so depth of slab and hardcore underneath checked out ok.

Slig

TheAnswer wrote: »

Slab was already there from the previous owners endeavours (I think he started on the project, then either ran out of funds or just decided it was easier to move house:D), various builders who looked at the job reckoned the slab was fine to use as a subfloor (though one lad did say it was a bit tight for insulation/screed). New foundation trenches for walls were cut tru the slab so depth of slab and hardcore underneath checked out ok.

What stage are you at with the blockwork? are the lintels in above doors and windows?
I take it that this is a project you bought on and as such arent really interrested in peoples critisism for the previous builders mistakes and are only interrested in solutions. I will ,however, say that you should probably get some official specification and details from an Architectural professional as to how the build up is to comply with the relevant building regulations.
Putting in the cheap option now that doesnt comply with the regs could end up costing you alot more if the building control officer insists that there isnt sufficent insulation in the floor never mind the extra heating costs that could accumilate from poor insulation levels.

TheAnswer

^^^^^^^^
Walls are up, ready for roof and windows, I could chop out the slab but not really into it, seems like a huge amount of work for no real gain. OP seems to have a bit of work on his hands only having 75mm to play with and he wants to install UFH. I've 140mm and am not installing UFH. Is it the unknown spec of the existing slab thats the problem or the 140mm that I'm left with? Builder seems happy enough to proceed with his DPM, insulation and screed.
This thread caught my eye though which is why I asked the question.

Carlow52

TheAnswer wrote: »

Slab was already there from the previous owners endeavours (I think he started on the project, then either ran out of funds or just decided it was easier to move house:D), various builders who looked at the job reckoned the slab was fine to use as a subfloor (though one lad did say it was a bit tight for insulation/screed). New foundation trenches for walls were cut tru the slab so depth of slab and hardcore underneath checked out ok.

Re

New foundation trenches for walls were cut tru the slab so depth of slab and hardcore underneath checked out ok.

The plot thickens:)

How did this tie in with the radon barrier or whats the plan?

TheAnswer

Carlow52 wrote: »

Re

The plot thickens:)

How did this tie in with the radon barrier or whats the plan?

Slab is there at least 15yrs, possibly 20! no radon barrier, I don't live in a high risk area anyways (I personally think the whole "Radon" thing is over egged).
Can't a radon barrier be laid between slab and insulation? It'll also act as a DPM which afaik is perfectly acceptable.

Carlow52

TheAnswer wrote: »

Slab is there at least 15yrs, possibly 20! no radon barrier, I don't live in a high risk area anyways (I personally think the whole "Radon" thing is over egged).
Can't a radon barrier be laid between slab and insulation? It'll also act as a DPM which afaik is perfectly acceptable.

Over egged on Easter Sunday, I suppose is a common complaint:D.

Apart from being the regs, the way the Radon data
http://www.rpii.ie/radon-map.aspx

was produced is as follows: a certain number of data samples were taken per grid square.

AFAIK the geology that creates concentrations of radon was formed a tad before the grid references so the only way you can be sure is have samples taken at your location

YouTookMyName

Poor Uncle Tom wrote: »

Any insulation in a foundation (usually ICF type to stop cold bridging) does not replace the need for insulation in the floors.

I seen a job once 2007 it was where they put in 60mm kingspan on top of the sand binding in the strip foundation, they said it would save the hassle of putting it in the screed. The screed went into the kitchen/bathroom, rest all solid timber joisting.

The same house isn't a cold house now. Would another 60mm kingspan in the screed have been better?

Whats ICF type BTW?

Poor Uncle Tom

YouTookMyName wrote: »

I seen a job once 2007 it was where they put in 60mm kingspan on top of the sand binding in the strip foundation, they said it would save the hassle of putting it in the screed. The screed went into the kitchen/bathroom, rest all solid timber joisting.

The same house isn't a cold house now. Would another 60mm kingspan in the screed have been better?

I suppose the simple answer is that if you put floor insulation beneath your foundations then it isn't floor insulation anymore, therefore your house doesn't have floor insulation and is non compliant with Part L of the Building Regulations.

Generally, there is a specification for every house which includes the floors and incorporates the insulation element. Deviating from the specification may make your house non compliant.

YouTookMyName wrote: »

Whats ICF type BTW?

ICF is Insulated Concrete Formwork and for the foundations this is like a mould of insulation into which the concrete foundations are poured.

No6

In regard to the OP, I have come across a product which replaced the floor screed, its a gypsm based tile about 10mm thick with rasied circular studs, you can then lay your UFH pipes between the studs and its finished with a gypsum based screed over all about 25mm thick I think. This still leaves on 50mm for insulation which is way too little for a new build and not enough for an extension either. I am of course also ignoring the tile finish as this will also have to change to get any insulation in. Does the op know if there is insulation under the floor slab, it is allowable there too but normally only done with strip foundations.

In relation to the answer's post he has 140mm, and no UFH. Its a little tight but 70 or 80mm of insulation should achieve the U value for an extension, it depends on the floor area / floor perimiter ratio, 75mm of sand and cement screed is current best practice to avoid cracking in the screed but you could use slightly thinner and accecpt some cracking or use some of the flo screed type products which can get thinner again but cost more.