Levelling hollowcore slab

[Conalmcn]

At the stage of my build now where the insulation will need to be put down for the first floor, my issue is the slab has some variance and I'm not 100% on the best way to deal with it. What have others done to level the slab?

[Adam2]

42 minutes ago, Conalmcn said:

What have others done to level the slab?

We used dry sand to level the precast planks under the insulation sheets

[Conor]

Forget the PIR and use TLA. We had loads of variation and had steel beams to deal with as well. Didn't work out that much more and saved a load of labour.

[ETC]

5 hours ago, Conor said:

Forget the PIR and use TLA. We had loads of variation and had steel beams to deal with as well. Didn't work out that much more and saved a load of labour.

Don’t forget that with TLA you’ll need a bit more to get the same thermal resistance as PIR. Otherwise a great way of dealing with floor variances in the sub-structure.

[Conalmcn]

On 01/05/2022 at 15:59, Adam2 said:

We used dry sand to level the precast planks under the insulation sheets

I had heard of that being done, its really only one room with ~20mm difference due to need to use a mix of precast and prestressed slabs. Does it work alright?

 

On 01/05/2022 at 16:35, Conor said:

Forget the PIR and use TLA. We had loads of variation and had steel beams to deal with as well. Didn't work out that much more and saved a load of labour.

Debating TLA but they're charging over double what pir would be. Who supplied your TLA Conor?

On 01/05/2022 at 21:54, ETC said:

Don’t forget that with TLA you’ll need a bit more to get the same thermal resistance as PIR. Otherwise a great way of dealing with floor variances in the sub-structure.

Wouldn't be as concerned about the insulation aspect as long as it was level for the underfloor

[Conor]

@Conalmcn alpha flow screeds in Armagh. We dealt with Alan and Kirsty.

 

Once you factor in two days labour for levelling and laying PIR boards, there's not much difference in price. 

[Adam2]

12 hours ago, Conalmcn said:

Does it work alright?

Well I hope so 🙂 We had 2 floors in our build with precast planks that had both the usual camber and of course the gaps where they join each other. We just used the dry sand and placed boards on top then plastic then UFH pipes then screeded it - no issues that I can tell. The PIR boards were not rocking around and no obvious hollows. With the screed 55-75mm thick I can't see any small voids which we may have missed causing any issues.

[Iceverge]

On 01/05/2022 at 15:16, Conalmcn said:

At the stage of my build now where the insulation will need to be put down for the first floor

 

Why the insulation on the first floor? 

[Conalmcn]

On 04/05/2022 at 06:53, Conor said:

@Conalmcn alpha flow screeds in Armagh. We dealt with Alan and Kirsty.

 

Once you factor in two days labour for levelling and laying PIR boards, there's not much difference in price. 

That's who I was dealing with. Works out around £1k more than doing pir for me

On 04/05/2022 at 19:07, Adam2 said:

Well I hope so 🙂 We had 2 floors in our build with precast planks that had both the usual camber and of course the gaps where they join each other. We just used the dry sand and placed boards on top then plastic then UFH pipes then screeded it - no issues that I can tell. The PIR boards were not rocking around and no obvious hollows. With the screed 55-75mm thick I can't see any small voids which we may have missed causing any issues.

Maybe worth going down that route then. Had debated using plasterboard washers and screwing it into the slab to keep it tight 

22 hours ago, Iceverge said:

 

Why the insulation on the first floor? 

For the underfloor heating pipes

[Iceverge]

3 hours ago, Conalmcn said:

For the underfloor heating pipes

 

Unless your house demands very rapid heat response because of high heat losses via poor insulation and airtightness I suspect the insulation won't achieve anything.

 

For clarity we're talking about a floor above a heated room? If so just use the money and put more insulation elsewhere.  

[Conalmcn]

11 hours ago, Iceverge said:

 

Unless your house demands very rapid heat response because of high heat losses via poor insulation and airtightness I suspect the insulation won't achieve anything.

 

For clarity we're talking about a floor above a heated room? If so just use the money and put more insulation elsewhere.  

I need it to clip the underfloor pipes onto. I dont need it for insulation as such. Its a 200mm concrete slab. Do you mean I shouldn't have any heat source on the first floor?

[Iceverge]

What's your heat source? 

 

What are your airtightness levels and insulation like?

 

You can use rails to clip UFH pipes to. 

[Adam2]

I did question the real benefit of having pir on upper floors and was advised to keep it to make hearing more responsive. 25mm PIR is not that expensive so just carried on even though I feel it has little benefit as the aim is for the whole house to be same temp anyway inc floor structure but at least is something to clip ufh to!

[Nickfromwales]

On 06/05/2022 at 11:53, Conalmcn said:

I need it to clip the underfloor pipes onto. I dont need it for insulation as such. Its a 200mm concrete slab. Do you mean I shouldn't have any heat source on the first floor?

 

Gas nailed onto concrete, with clip rails.

[Trw144]

On 01/05/2022 at 16:35, Conor said:

Forget the PIR and use TLA. We had loads of variation and had steel beams to deal with as well. Didn't work out that much more and saved a load of labour.

Hi @Conor, can I ask who you used for supply of the hollowcore slabs?

[Conor]

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