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

[lineweight]

There are various beam & block systems which use polystyrene blocks instead of concrete blocks inbetween the beams. Then there's another layer of polystyrene and then a "structural topping".

 

Systems include Jetfloor or Warmfloor Pro.

 

Essentially they reduce the overall floor buildup thickness by moving some of the insulation layer thickness between the beams, as well as potentially using the "structural topping" to reduce the beam size necessary. If I have understood correctly.

 

This diagram is from Jetfloor literature:

 

 

Where they argue the Jetfloor system is more cost effective than a conventional B&B buildup. They compare a Jetfloor system with 150mm beams vs conventional using 175mm beams. They both achieve the same U-value.

 

It implies that you might save 100mm of ground excavation. However, if you only need 150mm beams in the first place, that's down to 75mm.

 

I'm wondering if anyone has any experience where using an insulated-block type system really did save any costs. Especially on small jobs, because usually it's best to stick with something that most builders are familiar with.

 

[Temp]

I wondered if it was possible to make your own insulated "blocks" from thick sheet insulation. 

[Canski]

check out litecast. Thats what I will be using. I'm not sure if they deliver to where you are.

[lineweight]

9 minutes ago, Canski said:

check out litecast. Thats what I will be using. I'm not sure if they deliver to where you are.

 

I'm assuming you are using their "Litecast GT" or "Litecast XT" systems?

 

For you, what swung the decision to use something like this, rather than conventional beam & block?

[nod]

The ones I’ve tilted with polystyrene always seam to have a lot of cracks on the screed 

[lineweight]

1 hour ago, nod said:

The ones I’ve tilted with polystyrene always seam to have a lot of cracks on the screed 

 

usually there is supposed to be some kind of reinforcement mesh in the screed, is that right?

[Canski]

2 hours ago, lineweight said:

 

I'm assuming you are using their "Litecast GT" or "Litecast XT" systems?

 

For you, what swung the decision to use something like this, rather than conventional beam & block?

yes the GT12. Those concrete blocks are heavy and then you need to add lots of insulation before screeding. I’ve used them on a few sites now and they are a doddle. Oh and you can get your UFH and floor screed in early and carry on with the build. 

Edited April 10, 2023 by Canski

[Iceverge]

I assume ground conditions not allow a slab?

[Canski]

2 hours ago, nod said:

The ones I’ve tilted with polystyrene always seam to have a lot of cracks on the screed 

The ones I fitted complete with metal fibre reinforced cemex had a couple of hairline cracks around some doorways but I intend to incorporate a movement joint at my 2 larger openings. 

[Canski]

46 minutes ago, lineweight said:

 

usually there is supposed to be some kind of reinforcement mesh in the screed, is that right?

Metal fibres

[saveasteading]

4 hours ago, lineweight said:

insulated-block type system really did save any costs. Especially on small jobs,

I have done many big projects with b and b, always dense blocks. Then a cement wash over the lot to fill any cracks, seen or unseen. Then brush in sand and cement to the bigger gaps.

Not only houses, but offices and assembly spaces, I think the biggest area was 800m2.

 

The eps blocks seem very expensive. 

Therefore over that area , any price difference can be  a lot of cash.

 

My belief is that housing developers use b and b for certainty.  The certainty that some subby of a subby isn't building on loose fill.

Do they use eps blocks? I don't know.

 

My default is always to build on the ground, which adds insulation in itself and doesn't have airflow under the slab, even though not fully acknowledged.

 

B and B only to overcome site conditions or on steep slopes.

 

I had not heard of using metal fibres  over eps blocks.  Is this for strength or crack control? It  is very expensive too.

 

 

[nod]

1 hour ago, lineweight said:

 

usually there is supposed to be some kind of reinforcement mesh in the screed, is that right?

No just fibers in the screed 

[lineweight]

1 hour ago, Iceverge said:

I assume ground conditions not allow a slab?

That's right yes, in this case.

[Rishard]

I have medium shrinkage clay and have been advised to use both heave protection in the trench wall and void formers under a suspended slab. I’ve read on here people dealing with poor ground conditions using block and beam and also the void formers. I’m about to cost out which is going to be best for us. I don’t like the idea of a void below the block and beam but wonder if the void former (cordek/Jablite) is also just creating an airspace below the slab by default. I know the suspended slab is designed to overcome this but is it likely to effect the insulation sandwich above the void former and below the slab? Does ground heave retract, or just heave and stay put? A bit off the original posters question but dealing with a similar issue. 

Edited April 10, 2023 by Rishard

[bassanclan]

Ive used Jetfloor.

Easier than traditional heavy dense blocks.

No fibres or screed, just 60mm "Tarmac Agilia" structural concrete topping.

 

I have no complaints, but it is more costly than a slab

[saveasteading]

My opinions:

Beam and lock preferable to void formers. Above void formers need a structural (ie expensive) slab. perhaps 200 thick and with 2 layers of heavy reinforcement.

If the ground heaves it crushes the former, but if it shrinks it then leaves a gap....so might as well have used B and B.

 

If you need fibres in the screed and it is only for crack control, then use plastic fibres, which add typically £100 to the job, as compared with very much more for metal fibres.

 

From my experience, Engineers (I am one) and Architects have been sold 'a solution'  by void former suppliers but don't always know the cost implications.

 

I am more used to severe shrinkage clay, so it should work for you with your lovely 'medium shrinkage'.

[Canski]

46 minutes ago, bassanclan said:

Ive used Jetfloor.

Easier than traditional heavy dense blocks.

No fibres or screed, just 60mm "Tarmac Agilia" structural concrete topping.

 

I have no complaints, but it is more costly than a slab

Out of interest Did the agila (now discontinued and renamed) not have fibres in it ? did it crack ?  I only ask because the last but one we did used Agila and that was the one that cracked. To be fair I’ve not seen the last one recently but the finish was awful. Thinking about it now I remember 2 previous builds with this system and the first was perfect the second was an absolute disaster with UFH pipes above FFL and blocks had been thrown in to weigh the pipes down. The site manager was nearly in tears and he was nearly all the way through the job due to the knock on effects. The contractor (against the site managers strong advice ) had hired a team of ‘experts’ in to lay the floor who were £1k cheaper for 4 plots.  This gives it a 50 - 50 success rate in my book. 😂 odds are far greater in our favour when we are self builders. It’s not rocket science. Your pipes are not allowed to float. 

 

Anyway Litecast deliver on time and are very helpful and are also specifying the concrete / flowscreed / Agilia ‘lookalikes’ for my builds  ( now with fibres added plus some concrete scientific techno sheet 😂 that I will post tomorrow if any SE’s would like to comment ? )  I hope this is not a signal of previous failures. Sorry for long post it’s been a long weekend 🍺🍺🍺

[Iceverge]

@lineweight

 

Often forgotten but a suspended timber floor is still an option. 

 

For instance a 240mm I-beam with 10mm hardboard below,  chipboard above and 50mm screed  full fill with mineral wool or cellulose will have a U value of 0.15 for a thickness of about 320mm. 

 

The screed is optional if you're really tight for space. 

 

 

 

[lineweight]

1 hour ago, bassanclan said:

Ive used Jetfloor.

Easier than traditional heavy dense blocks.

No fibres or screed, just 60mm "Tarmac Agilia" structural concrete topping.

 

I have no complaints, but it is more costly than a slab

What makes it more costly - the bits you buy from Jetfloor?

 

[lineweight]

35 minutes ago, Iceverge said:

@lineweight

 

Often forgotten but a suspended timber floor is still an option. 

 

For instance a 240mm I-beam with 10mm hardboard below,  chipboard above and 50mm screed  full fill with mineral wool or cellulose will have a U value of 0.15 for a thickness of about 320mm. 

 

The screed is optional if you're really tight for space. 

 

 

 

I suppose I am a bit wary of timber here because we have to have an internal floor level not much higher than the surrounding ground level, so to avoid those timbers getting wet would rely very much on various damp proof courses and membranes being done properly and carefully, and then ventilation not getting blocked in the future, and so on. I'd agree timber suspended is worth considering where you're well above ground level.

[Nickfromwales]

48 minutes ago, Iceverge said:

@lineweight

 

Often forgotten but a suspended timber floor is still an option. 

 

For instance a 240mm I-beam with 10mm hardboard below,  chipboard above and 50mm screed  full fill with mineral wool or cellulose will have a U value of 0.15 for a thickness of about 320mm. 

 

The screed is optional if you're really tight for space. 

 

 

 

Indeed, well said! How we forget. Less embodied carbon, and very DIY'able too.

[Nickfromwales]

10 minutes ago, lineweight said:

I suppose I am a bit wary of timber here because we have to have an internal floor level not much higher than the surrounding ground level, so to avoid those timbers getting wet would rely very much on various damp proof courses and membranes being done properly and carefully, and then ventilation not getting blocked in the future, and so on. I'd agree timber suspended is worth considering where you're well above ground level.

Yup, defo a choice when the circumstances allow.

 

I prefer products like Beam-shield, where the sections tuck under the beam and contact the preceding block. So when you look at the underside, you cannot see anything other than EPS.

[Rishard]

9 hours ago, saveasteading said:

My opinions:

Beam and lock preferable to void formers. Above void formers need a structural (ie expensive) slab. perhaps 200 thick and with 2 layers of heavy reinforcement.

If the ground heaves it crushes the former, but if it shrinks it then leaves a gap....so might as well have used B and B.

 

If you need fibres in the screed and it is only for crack control, then use plastic fibres, which add typically £100 to the job, as compared with very much more for metal fibres.

 

From my experience, Engineers (I am one) and Architects have been sold 'a solution'  by void former suppliers but don't always know the cost implications.

 

I am more used to severe shrinkage clay, so it should work for you with your lovely 'medium shrinkage'.

Thanks, my engineers spec is a 150mm reinforced slab with a single layer of a393 to the base. No spans greater than 4m for the slab so I would need to add another footing to help there. We may need to add some reinforcement to the top of the slab above these footings for ‘hogging’.  I imagine I would need to add an extra footing for b&b to break up larger spans. 
 

I originally planned on a ground baring slab to be used as our ff with underfloor heating within. With the added complexity of reinforcing the slab and potential hogging, does using the slab as a ff seem un realistic with the amount of crack potential. We have several dividing walls we can use crack control joints at but in the larger kitchen/diner it would be a shame to use control joints. My aim was to reduce the need for a screed buy polishing the slab (another discussion has already been had on this) 

 

Sounds like the options are:

Reinforced slab with void formers (potential crack issues).

Block and beam with screed.

Timber suspended floor.

[saveasteading]

Beam and block comfortably spans 4m.

Polishing the slab is ok, but a bit specialist for domestic. I prefer concrete screed, pir, screed with ufh. Control.

 

Or b and b, then pir and screed.

 

150 slab with 1 bottom layer of mesh is a surprise as a suspended slab. That will require great precision. 

 

 Crack control is simple enough. For later discussion.

[lineweight]

14 hours ago, Rishard said:

I have medium shrinkage clay and have been advised to use both heave protection in the trench wall and void formers under a suspended slab. I’ve read on here people dealing with poor ground conditions using block and beam and also the void formers. I’m about to cost out which is going to be best for us. I don’t like the idea of a void below the block and beam but wonder if the void former (cordek/Jablite) is also just creating an airspace below the slab by default. I know the suspended slab is designed to overcome this but is it likely to effect the insulation sandwich above the void former and below the slab? Does ground heave retract, or just heave and stay put? A bit off the original posters question but dealing with a similar issue. 

Presumably it depends whether the void formers are the type that are designed to disintegrate? If they are to deal with ground heave then presumably they are - in which case wouldn't you end up with an airspace of some kind under the slab?