How much rebar in a Nudura building?

[Andrewb]

Good evening,

I understand that all scenarios will be different, but I wondered what people's different experiences with rebar quantities were for builds with Nudura.

 

I will have the standard 6 inch core blocks and am building a two storey 7.5m x 5m extension on strip foundations. My structural design currently only has rebar in the lintels etc. My engineer is experienced with ICF, and I know the Nudura guidance is that reinforcement design is by the structural designer, but my expectation after the nudura training day was that all walls would have horizontals at each course and verticals at regular spacings too. Hence my question to the forum?

 

Any information on people's experiences would be much appreciated.

 

thanks 

[freshy]

Not Nudura, but I have rebar every 450mm vertical & every 600mm horizontal on my Jackon Thermomur ICF.

 

I also remember from the Nudura course they were saying horizontal every course i.e. 300mm.

[Jenki]

My PolySteel is ridiculous, having this reviewed by my certifier of design. My spec is two rows every 300 horizontal, and 2 vertical on 150mm ctrs🙈

[ToughButterCup]

Hmmm, a common ICF 'worry'.  And it needn't be. I built in one particular ICF, sent the design to an SE: his response was (can't remember the detail) - but in essence, you'll need to fetch enough from your local steel mill.

 

Asking colleagues on BH , one response was - ask the ICF producer's  own SE: and what does the ICF's published guidance say? The reason for that (apart from the obvious) is that the BCO may well not know. S/he'll want access to the formal documentation about it

 

I rang Durisol's (spits quietly) SE up and had a chat.

He listened to what had been specified, and when he'd finished blowing his breakfast out of his nose with laughter,  sent me a prpperly certified design.  

Including his fee, we saved several thousand.  In places, I doubled up on his recommendation - a few quid extra.

• Get the official documentation
• Ask for Ndura's own SE to specify for your design.

[Conor]

13 hours ago, Jenki said:

My PolySteel is ridiculous, having this reviewed by my certifier of design. My spec is two rows every 300 horizontal, and 2 vertical on 150mm ctrs🙈

Very similar to our basement, two rows every 200mm.

 

On thing to point out that the SE may not be considering is the practicality of some rebar specs. E.g. for our master bedroom cantilever head, ours had specced two rows of 32mm, horizontal, with something like a single 25mm running below. If we'd done that, there's no way we would have got the concrete in to the cavity.

[Tosh]

Lintels only on our Nudura 8''

[Jenki]

20 hours ago, Conor said:

Very similar to our basement, two rows every 200mm.

 

On thing to point out that the SE may not be considering is the practicality of some rebar specs. E.g. for our master bedroom cantilever head, ours had specced two rows of 32mm, horizontal, with something like a single 25mm running below. If we'd done that, there's no way we would have got the concrete in to the cavity.

 

 

22 hours ago, ToughButterCup said:

Hmmm, a common ICF 'worry'.  And it needn't be. I built in one particular ICF, sent the design to an SE: his response was (can't remember the detail) - but in essence, you'll need to fetch enough from your local steel mill.

 

Asking colleagues on BH , one response was - ask the ICF producer's  own SE: and what does the ICF's published guidance say? The reason for that (apart from the obvious) is that the BCO may well not know. S/he'll want access to the formal documentation about it

 

I rang Durisol's (spits quietly) SE up and had a chat.

He listened to what had been specified, and when he'd finished blowing his breakfast out of his nose with laughter,  sent me a prpperly certified design.  

Including his fee, we saved several thousand.  In places, I doubled up on his recommendation - a few quid extra.

• Get the official documentation
• Ask for Ndura's own SE to specify for your design.

The crazy thing about this is:

1, poly steel blocks have a steel mesh on 150mm ctrs  to form the cavity. so have lots of reinforcement in them , granted only 3mm bars on a 50mm SQ. but that's a lot.

2, This was the SE for Poly steel - he mentioned the BS for reinforcement blah blah 

[Nickfromwales]

11 hours ago, Tosh said:

Lintels only on our Nudura 8''

XR35?

[Andrewb]

Thanks for this feedback, quite a lot of variation!

 

20 hours ago, Conor said:

On thing to point out that the SE may not be considering is the practicality of some rebar specs. E.g. for our master bedroom cantilever head, ours had specced two rows of 32mm, horizontal, with something like a single 25mm running below. If we'd done that, there's no way we would have got the concrete in to the cavity.

Thanks for this point - I'll have a think through this, just to check, but I don't expect the design to be too difficult to implement from that perspective.

 

I have the supplier and SE lined up to talk, so any of my concerns should hopefully be settled after that.

 

I've got some steel prices coming in now and the rebar for my 7 lintels and beams is coming in at just £300.

My quick calc is that rebar throughout would be very roughly an additional 2-3x that. Not the biggest cost in the scheme of things, but will avoid if the consensus is that it is pointless!

[Russell griffiths]

@Andrewb

im afraid your question is Sort of how long is a piece of string.  your re bar quantity will be dependant on your house design. 

I have a fair bit of re bar in mine, but that’s because I have a lot of cantilever beams and 5 m wide openings.

Anybody with a basement will have loads, anybody with a square box with 900mm wide windows will have very little.

Its all Down to the house design and your structural engineers knowledge of the product.  

 

At the end end of the day a thousand pounds worth of steel is small change compared to the cost of the concrete, and blocks themselves. 

[Iceverge]

On 29/03/2023 at 23:04, Jenki said:

My PolySteel is ridiculous, having this reviewed by my certifier of design. My spec is two rows every 300 horizontal, and 2 vertical on 150mm ctrs🙈

 

 

Crikey. That is something else. 

 

I do wonder if ICF is over engineered somewhat for low rise houses. Lots have 200mm 40N concrete cores with a mountain of rebar to boot. 

 

Meanwhile most houses are made from 2*100mm 7N block leafs with no reinforcement at all. 

 

 

 

[Jenki]

59 minutes ago, Russell griffiths said:

 anybody with a square box with 900mm wide windows will have very little.

Its all Down to the house design and your structural engineers knowledge of the product.  

 

sq box. 2 windows 2M wide, 11 windows 850 wide, 2 door, . and the spec is for nearly 3KM of 10 mm rebar.  

[saveasteading]

Thoughts with the benefit of  ignorance.

I've tried to use ICF but couldn't make it work commercially.

 

I suspect ICF is under-researched. The manufacturers could commission load testing and provide accepted detailing. This would probably reduce the amount of reinforcement. But they don't want or can't afford the cost.

But as it is, every SE is taking their own decisions on it.

 

An ICF skin has a small core of reinforced concrete. If hollow concrete bocks are used in this way, the  blocks  contribute significantly where eps cannot.

 

Perhaps Jenki' s design is the right solution and the others underdesigned.

 

Is there also a tendency for ICF buildings to have bigger clear spaces? In traditional houses the rooms are small, providing stiffness to the construction: and hundreds of years of practical experence as compared to ICF.

[Tosh]

7 hours ago, Nickfromwales said:

XR35?

No just the standard blocks. Don't think xr35 was available, or at least we weren't made aware of them, when we purchased which is a few years ago now. Would defintely of considered them.

[Russell griffiths]

6 hours ago, Jenki said:

sq box. 2 windows 2M wide, 11 windows 850 wide, 2 door, . and the spec is for nearly 3KM of 10 mm rebar.  

If all those windows divide a wall up into lots of little pillars then I can see the reasons. 

But 500 lengths of bar seems ott and 10mm is very thin, I’ve never seen anything smaller than 12mm used. 

Edited March 31, 2023 by Russell griffiths

[saveasteading]

6 hours ago, Russell griffiths said:

10mm is very thin,

Have not thought this through for EPS, but on water tanks etc the use of lots of skinny bars is the norm to spread  the effect as much as possible, esp avoiding cracks.

[ChrisJ]

Nudura install manual calls for both horizontal and vertical rebar in all their products. Your engineer can override the manufacturer for project specific engineering - many engineers do not require any rebar in England other than lintels, do I agree? Well that’s another topic but who am I to argue with an engineer 

[Renegade105]

My Engineer only specified Rebar over the openings for our ICF build in England too.

 

 

[Andrewb]

Thanks, it's useful to hear from a variety of different projects.

Engineer and Nudura have spoken to each other and both are happy with the no rebar design.