Beam & Block systems with insulative blocks - when do or don't they make sense?

[lineweight]

36 minutes ago, Dave Jones said:

 

still wouldn't bother with them with the massive built in thermal bridging, double/treble the price of a standard floor and only benefit is saving a couple muck always.

 

Here are you talking about a b&b floor with insulative blocks, vs a b&b floor with concrete blocks?

 

And when you talk about thermal bridging, do you mean the result of having to build sleeper walls underneath all of the internal wall locations?

[Dave Jones]

8 minutes ago, lineweight said:

 

Here are you talking about a b&b floor with insulative blocks, vs a b&b floor with concrete blocks?

 

And when you talk about thermal bridging, do you mean the result of having to build sleeper walls underneath all of the internal wall locations?

 

yes.

[saveasteading]

I've looked at litecast and see it is a pretty standard beam system to support concrete blocks. 

As such the screed isn't crucial to floor strength and bounce. 

(It would be crucial  with a plank ststem).

 

As such, if I had done this on my own house I'd fill the cracks with cement paste. 

[lineweight]

Litecast G12 appears to be a system with polystyrene infill blocks, not concrete infill blocks.

 

Therefore as I understand it, the screed does have a structural function.

 

https://www.litecast.co.uk/media/1357/kiwa-bda-gt-agrément-certificate.pdf

[saveasteading]

Search for litecast g12 and I see eps blocks. Search for litecast and I see concrete blocks...which did surprise me, as obv not light.

@Canski please advise.

[Canski]

On 27/08/2023 at 17:48, saveasteading said:

First I'd ask the contactor what they think about it. Prediction....its normal.

Then see thd delivery tickets.

 

What's underneath determines whether this is a problem or inconvenience.

The contractor admitted that they added water. I’m still waiting for the delivery notes which ‘they say’ are with the concrete supplier that they engaged. They asked what I’d like as an outcome from this. Well 🙄🙄 supply and fit ditra to the whole ground floor and some sort of finish to my garage maybe ?

[Canski]

On 28/08/2023 at 18:23, saveasteading said:

Search for litecast g12 and I see eps blocks. Search for litecast and I see concrete blocks...which did surprise me, as obv not light.

@Canski please advise.

Hi sorry I missed this. This is the system that I used. I have used it several times before with no issues. 

[saveasteading]

OK so the blocks are eps and the topping is said to be structural. 

In that case we, here, can't dabble. The cracks may be unacceptable,  and your Architect or Engineer or the manufacturer must examine and advise.

[lineweight]

On 01/09/2023 at 07:53, Canski said:

They asked what I’d like as an outcome from this. Well 🙄🙄 supply and fit ditra to the whole ground floor and some sort of finish to my garage maybe ?

 

The outcome, surely, needs to be some kind of assurance that the structural slab is structurally sound, and will be able to take the loads that will be imposed on it, and if that can't happen, then it has to be redone.

[lineweight]

On 28/08/2023 at 09:27, Dave Jones said:

 

yes.

 

It looks to me like the system illustrated above (litecast GT12) is designed so that you don't need sleeper walls underneath loadbearing partitions - it has what it calls "EPS load-bearing rails" that fit above the concrete beams where loadbearing walls need to sit. So there doesn't have to be thermal bridges. But maybe I have misunderstood something.

[Gus Potter]

On 28/08/2023 at 17:56, lineweight said:

Therefore as I understand it, the screed does have a structural function.

Yes you are correct.

 

The load bearing rails are there to transfer direct loads from walls above.

 

The EPS has no load bearing capacity as it relies on the small lip on the edge of the beams for support.

 

Therefore the screed has to span between the beams.. this makes it a structural slab according to the design codes (rectangular section in solid slabs see below table 3.25 below ). A structural slab needs a minimum percentage of steel. The same rules apply in the Eurocodes in very much the same way.

 

Reinforcement in both directions which is 0.13% based on gross section area. Sometimes folk sell stuff and gloss over the other bits that may have an impact on the overall cost of the design.

 

Ok how does that translate into real life?

 

Say you have a screed 100mm thick. A 1000mm wide strip x 100 mm deep has a gross section area of 1000 x 100 = 100,000 mm ^2

 

0.13% of that = 0.13* 100,000 /100 = 130 mm^2 of reinforcement per metre run of width of slab. Thus an A142 mesh will do the job in terms of minimum percentage steel.

 

But now we need to check what loads we are putting on the slab as it needs to span between the beams and be strong enough in bending. You also need to work out how you are going to design what is now a structural slab.. is it continuous over the supporting beams or do you treat the slab as simply supported over each beam. This is a dilemma as the design codes don't cover UF heating say in domestic slabs.

 

Now once you do this you just may find that the mesh is not heavy enough as you need some cover to the mesh, you have lots of laps and maybe some UF pipes. At the end of the day you could be putting in A193 or at the top end A252 mesh as self builder.

 

if you want to be really pedantic we can look at the ductility of the steel.. but that is a story for another day and usually we are ok with an A type mesh in this application.

 

If you go for a screed less than 100mm thick it just aint going to fly in terms of practical installation and cost with UF and EPS between the beams.

 

 

 

 

 

 

 

 

Edited September 6, 2023 by Gus Potter

[Dave Jones]

adds more hassle and cost.

 

does it have any positives over normal block and beam, insulation and screed ?

[lineweight]

1 hour ago, Dave Jones said:

adds more hassle and cost.

 

does it have any positives over normal block and beam, insulation and screed ?

Well, that's essentially the question I started this thread asking. As explained in my OP, the claim (from one manufacturer of this kind of system) is that it reduces the thickness of the overall buildup and this can mean less digging out of ground, which can mean a cost saving.

[lineweight]

5 hours ago, Gus Potter said:

Yes you are correct.

 

The load bearing rails are there to transfer direct loads from walls above.

 

The EPS has no load bearing capacity as it relies on the small lip on the edge of the beams for support.

 

Therefore the screed has to span between the beams.. this makes it a structural slab according to the design codes (rectangular section in solid slabs see below table 3.25 below ). A structural slab needs a minimum percentage of steel. The same rules apply in the Eurocodes in very much the same way.

 

Reinforcement in both directions which is 0.13% based on gross section area. Sometimes folk sell stuff and gloss over the other bits that may have an impact on the overall cost of the design.

 

Ok how does that translate into real life?

 

Say you have a screed 100mm thick. A 1000mm wide strip x 100 mm deep has a gross section area of 1000 x 100 = 100,000 mm ^2

 

0.13% of that = 0.13* 100,000 /100 = 130 mm^2 of reinforcement per metre run of width of slab. Thus an A142 mesh will do the job in terms of minimum percentage steel.

 

But now we need to check what loads we are putting on the slab as it needs to span between the beams and be strong enough in bending. You also need to work out how you are going to design what is now a structural slab.. is it continuous over the supporting beams or do you treat the slab as simply supported over each beam. This is a dilemma as the design codes don't cover UF heating say in domestic slabs.

 

Now once you do this you just may find that the mesh is not heavy enough as you need some cover to the mesh, you have lots of laps and maybe some UF pipes. At the end of the day you could be putting in A193 or at the top end A252 mesh as self builder.

 

if you want to be really pedantic we can look at the ductility of the steel.. but that is a story for another day and usually we are ok with an A type mesh in this application.

 

If you go for a screed less than 100mm thick it just aint going to fly in terms of practical installation and cost with UF and EPS between the beams.

 

 

 

 

 

 

 

 

 

Thanks for this clear explanation - exactly what the slab does, and who exactly designs it, in many cases seems to be obfuscated when I look at information provided by manufacturers of this kind of system. I wonder how often they just get installed with a non structural screed.

Edited September 6, 2023 by lineweight

[Dave Jones]

6 hours ago, lineweight said:

Well, that's essentially the question I started this thread asking. As explained in my OP, the claim (from one manufacturer of this kind of system) is that it reduces the thickness of the overall buildup and this can mean less digging out of ground, which can mean a cost saving.

much away costs will need to be very significant to outway all the negatives and extra ££££