Uneven wideslab flooring

[Moggaman]

Hi.

I have just got my wideslab precast laid on my ground floor blockwork. I wasn’t around when it was dropped in. Bottom line is it is not very level. Maybe 15mm difference in level in some places . My drawings show a 50mm layer of insulation on the wideslab and then the floor screed with UF pipes in it.  It’s clear to me that I won’t be able to lay 50mm insulation across the floors without leaving voids under it. Is there a fix for this ?

thanks 

[saveasteading]

If it is prestressed (with the hollow cores) then there is always a hump in the middle. This is a pain, but you have to work with it.

[tonyshouse]

Are we talking steps or slopes?  50mm sounds like very insufficient insulation to me 

Edited August 7, 2021 by tonyshouse

[Conor]

I was told to spread out a layer of sand before laying the boards down. That sounds like a lot of work over 115m². I've found a local company that does an insulated liquid screed (similar R value to EPS). Think I'm going to put 50mm of that down, ufh, then 50mm liquid screed 

[Moggaman]

4 hours ago, tonyshouse said:

Are we talking steps or slopes?  50mm sounds like very insufficient insulation to me 

Steps!..10mm in places 

[Moggaman]

11 hours ago, saveasteading said:

If it is prestressed (with the hollow cores) then there is always a hump in the middle. This is a pain, but you have to work with it.

No that’s not it.. steps between slabs I’m afraid 

[Moggaman]

3 hours ago, Conor said:

I was told to spread out a layer of sand before laying the boards down. That sounds like a lot of work over 115m². I've found a local company that does an insulated liquid screed (similar R value to EPS). Think I'm going to put 50mm of that down, ufh, then 50mm liquid screed 

The sand might work.. if not option 2 with the insulated liquid screed seems to be an option…

[saveasteading]

Can you lay the insulation to follow the slab shape, with cuts in the insulation so that there are no voids, and the  same steps are then showing on top of the insulation? Then the floor screed will simply be thicker in places and take up the level. Extra screed but barely any extra labour.

 

Unless the area is one open plan area, there will be division walls and changes in level may be of less importance than it seems.

 

What is the logic of only 50mm insulation? Presumably this is not a suspended ground floor, and so it is only to keep the heated floor from convecting downwards to a lower floor.

Small gaps and changes in thickness are then also much less significant, with a warm room below.

 

[tonyshouse]

I would use dry sand mixed with cement. How are you getting away with only 50mm of insulation? 
 

 

[Moggaman]

1 hour ago, tonyshouse said:

I would use dry sand mixed with cement. How are you getting away with only 50mm of insulation? 
 

 

It’s detailed in the dwgs… rep of Ireland .. not uk.. maybe that’s the diff ?. 150 wideslab first floor , 50mm insulation, then 75mm screed!…

[dpmiller]

it's a first floor then, not a GF?

[tonyshouse]

Thanks but then I would wonder why first floor even needs heating if g/f is heated, is it an upside down house? 

[Mr Punter]

Yes, for first floor you could bin the 50mm insulation, UFH and 75mm screed.  40mm flow screed would get you nice and level.

 

Towel radiator are all many on here have for first floor heating.

[Moggaman]

7 hours ago, dpmiller said:

it's a first floor then, not a GF?

Yes first floor.. sorry for bad description 

[Moggaman]

6 hours ago, tonyshouse said:

Thanks but then I would wonder why first floor even needs heating if g/f is heated, is it an upside down house? 

It’s my second time building.. this time it’s for good.. building it to A2 rating but am putting in UFH upstairs .. if I never use it, so be it… but I can’t put it in after …

[Moggaman]

6 hours ago, Mr Punter said:

Yes, for first floor you could bin the 50mm insulation, UFH and 75mm screed.  40mm flow screed would get you nice and level.

 

Towel radiator are all many on here have for first floor heating.

Sorry, you mean get rid of heating upstairs ?… bit of a gamble on the west coast of Ireland for me!.. thing is, even tho I will try hard, I know the quality is not going to be top end so I need the back up of having the heating system upstairs …I am self building 

[Moggaman]

11 hours ago, saveasteading said:

Can you lay the insulation to follow the slab shape, with cuts in the insulation so that there are no voids, and the  same steps are then showing on top of the insulation? Then the floor screed will simply be thicker in places and take up the level. Extra screed but barely any extra labour.

 

Unless the area is one open plan area, there will be division walls and changes in level may be of less importance than it seems.

 

What is the logic of only 50mm insulation? Presumably this is not a suspended ground floor, and so it is only to keep the heated floor from convecting downwards to a lower floor.

Small gaps and changes in thickness are then also much less significant, with a warm room below.

 

Thanks for this.. you may be right about increase the screed…

in terms of why I am putting in the insulation….well…. I think it’s to 1.help the slab respond better to heating up 2. Not to lose heat downwards 3. Not to take heat from downstairs?…

but maybe it’s overkill???

[tonyshouse]

If you go steps in the insulation then use anti cracking mesh ot it will crack above the steps 

[MikeSharp01]

6 hours ago, Moggaman said:

Sorry, you mean get rid of heating upstairs ?… bit of a gamble on the west coast of Ireland for me!.. thing is, even tho I will try hard, I know the quality is not going to be top end so I need the back up of having the heating system upstairs …I am self building 

Perhaps you could put the UFH in the liquid screed so avoid the voids and get the UFH in as well, unless building control where you are insists on it the insulation it will do very little thermally, might have an acoustic effect, so might usefully be dropped. If you try and fill back up to the same level with screed however the extra 50mm of concrete might be too great a load so that would be worth checking if going that route.

[Iceverge]

On 08/08/2021 at 00:12, Moggaman said:

Thanks for this.. you may be right about increase the screed…

in terms of why I am putting in the insulation….well…. I think it’s to 1.help the slab respond better to heating up 2. Not to lose heat downwards 3. Not to take heat from downstairs?…

but maybe it’s overkill???

 

Your engineer/architect sounds like they’re still designing houses for the days of minimal insulation, no airtightness, uncontrolled ventilation, and oil boilers. 

 

If you’re off gas you’re pretty much tied into an air to water heat pump in Ireland. The argument about response times is a bit mute as they work best at low temperatures and longer run times unlike the old oil boiler in a drafty house which needed hard firing whenever the occupants were home and shutting off afterwards to spare energy.

 

Our hollow core (ducon) had a 75mm 35N concrete screed with concrete mesh. This was a structural requirement.

 

In your case get rid of the UFH pipes and insulation and wait until as late as possible in the build ( after interior plastering) and pour a pumped screed as thin as the supplier will stand over. This will leave you an immaculately level floor that won’t be covered in lumps of plaster etc.

 

Spend your time now filling the ends of the hollow core slab if it’s not wrapped already for airtighness.

 

By the way we’re not a million miles from the west coast and have no central heating, just a single electric rad in the hall. 

[Ian]

@Moggaman

the insulation layer is there for acoustic reasons - it’s there to prevent impact noise like footsteps transmitting directly through to the rooms below.

[Moggaman]

On 21/08/2021 at 01:05, Iceverge said:

 

Your engineer/architect sounds like they’re still designing houses for the days of minimal insulation, no airtightness, uncontrolled ventilation, and oil boilers. 

 

If you’re off gas you’re pretty much tied into an air to water heat pump in Ireland. The argument about response times is a bit mute as they work best at low temperatures and longer run times unlike the old oil boiler in a drafty house which needed hard firing whenever the occupants were home and shutting off afterwards to spare energy.

 

Our hollow core (ducon) had a 75mm 35N concrete screed with concrete mesh. This was a structural requirement.

 

In your case get rid of the UFH pipes and insulation and wait until as late as possible in the build ( after interior plastering) and pour a pumped screed as thin as the supplier will stand over. This will leave you an immaculately level floor that won’t be covered in lumps of plaster etc.

 

Spend your time now filling the ends of the hollow core slab if it’s not wrapped already for airtighness.

 

By the way we’re not a million miles from the west coast and have no central heating, just a single electric rad in the hall. 

 

Im off electric!, You are suggesting no heating upstairs?..my missus might have something to say about it.. i am trying to make it as airtight as possible, have mvhr also. Perhaps i will never turn it on but id prefer to be looking at it than looking for it!

 

[Iceverge]

What is your heating going to be powered from? 

 

MVHR is very good but needs to be installed correctly to not be annoying. 

 

If you're happy with the extra cost of the UFH drive on with it upstairs but its not needed in my opinion in a well insulated house.