ICF and Rebar Requirement

[Midona]

Hi,

 

We've just had the drawings back from the Structural Engineer and he seems to have specified a ridiculous amount of rebar!  Part of our build is a sub-structure/part basement, so I can kind of understand the need for rebar there, but there is also a huge amount in the rest of the building.  We've recently been to a site to help with the building of an ICF house, and there was very little rebar in that build (just the corners and above the windows and doors).  I suspect that my Structural Engineer has little experience of building ICF houses and instead thinks he is building a bridge or a carpark or something.  We have approximately 4km of rebar for a 200m^2 house...and that even includes a garage with nothing on top of it!  Horizontal rebar is ever 25cm, and vertical every 20/25cm as well.

 

Does anyone have any experience of Structural Engineers over-specifying?  What options do we have?  The Building Warrant was just approved today based on his specifications.

 

Thanks,

Alan.

 

 

[Vijay]

would it be an idea to run it past the ICF supplier?

[Conor]

In our basement we had two rows of rebar every 200mm. Once above ground this was reduced to a single row, same 200mm spacing. You have to remember that a concrete building acts as a homogeneous structure, so one part of the building influences another. I.e. even if you think extra loadings apply to just one part, the actual loads and stresses are spread further away and need to be accounted for.

[Happy Valley]

Our ICF is built into a slope and the engineer has specified vertical rebar both sides at 150mm spacing and horizontal every 200mm. The walls not backing onto a slope have vertical rebar at 600mm spacings both sides and again horizontal rebar at 300mm. We also have starter bars and corner bars to put it. 

 

Seems excessive but would rather it be over engineered than not!

 

I have just ordered £1000 of rebar and there will be more!!

[Adam2]

Our ICF build also has what seems a lot of rebar in the lower floor levels where we have semi-basements. Also the floor slabs have loads - not just my view but all steel fixers as well. 150mm spacing for verticals and I think 200 for horizontals -lower levels mainly 16mm bar. I think we're up to about 45T total for the house (4 floors ~360m). 

 

Issues with rebar and ICF also include labour to fit and time this adds. We also needed a crane/hiab to move ours around to save time after each delivery. 

 

Re the engineer - I did discuss this and was told this was all to meet eurocode spec. At the end of the day we have had to rely on our engineer for plenty of questions and that may not have gone so well if we had questioned (too much!) what he was specifying.

 

good luck 

[markc]

You have to remember that a building built with bricks or blocks has thousands of joints and therefore movement and settlement paths. A concrete wall or structure is basically one big very thin block that will endure tension, compression and bending moments, the rebar is there to stop it cracking and falling apart. 

Yes the SE will err on the side of caution but they would be your first call if a crack appeared.

[saveasteading]

If it makes you happier, it is very unlikely that it is costing you too much.

 

Your Engineer has studied for at least 3 years at Uni then in real life.  He has done the complex maths and is insured if it goes wrong.

Any so-called overdesign is usually very slight, and cheaper than the Engineer spending many more hours on reducing the steel a little.

 

Concrete without reinforcement is weak in bending. The steel is strong in tension, and it all acts compositely. Then more steel is added the other way to hold it together ad to control cracking. I'm sure it is all needed.

 

The polystyrene is just holding the concrete in place and you still need steel.

 

and re Eurocode: this is generally more economical than the previous UK design codes were.