Supporting wall design liability

OK. So I am having issues with a supporting wall I have built as part of my extension. Let me start from the beginning..

I receive plans a year ago and start sourcing suppliers etc. Notice that the main supporting wall is specified as being a 150mm dense concrete block wall. None of the merchants or Google had seen these before so most suggested the much more common 140mm block. I phone the architect to discus the change and he says no problems. I am thinking what a dick... Surely he knows 150mm isn't available.

Anyway, months go by and I build my wall, get the inspector over to check the beams etc. He mentions the thinner wall and wants the calcs done. Fine... I go back to architect who produces calcs and I send to BC. The take almost two months to get back to me and say they want a structural engineer involved. By this time, as I had info back from architect saying all OK, I cracked on and the place is now plastered, painted, tiled and kitchen fitted.

Structural engineers say wall is fine but it needs some lateral support. They want ties on top of wall to rafters or a steel angle iron piece fixed into slab, run up wall and fixed to rafters. This would be fine when it was all open but it's now all covered and gonna cost me in money or time to sort.

My architect is saying it's my fault but I think he is in the wrong for specifying the wrong block size and not adding lateral support to the plans.

Thoughts anyone?

Did the architect actually do the calcs for the 140 block himself?

Many who do calcs put a disclaimer in their small print on the lines that no reliance should be placed on the figures unless and until approved by Building Control, in which case he will throw the problem back to you.

This is because b/c's checking engineer may have different ideas as to whether the design is satisfactory or not.

Is it building control's own SE ir an independent one who wants the angle etc? How do we know this is strictly necessary? - have they produced their own figures to show the wall is unsatisfactory, or is it just something off the top of their heads?

Why didn't you use 150mm thermalite blocks?

tony1851 said:

Did the architect actually do the calcs for the 140 block himself?

Many who do calcs put a disclaimer in their small print on the lines that no reliance should be placed on the figures unless and until approved by Building Control, in which case he will throw the problem back to you.

This is because b/c's checking engineer may have different ideas as to whether the design is satisfactory or not.

Is it building control's own SE ir an independent one who wants the angle etc? How do we know this is strictly necessary? - have they produced their own figures to show the wall is unsatisfactory, or is it just something off the top of their heads?

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Yes he did the calcs himself. The drawings were checked and approved by b/c.

The structural engineer is sourced by me. I personally think its fine. Its tied into the roof by way of wooden batterns, the wall is also tied into the perpendicular wall that runs above it and there is a 100mm block wall that is tied into it at the other end (even if that does have a single doorway in it). I have asked them to go away and do the clcs again with this added info as the first report didn't include this.

^woody^ said:

Why didn't you use 150mm thermalite blocks?

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Because a dense concrete block was specified. I don't consider a thermalite block to be a dense concrete block?

an203888 said:

Because a dense concrete block was specified. I don't consider a thermalite block to be a dense concrete block?

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But 150mm was specified!

So rather than ask if you could use a thinner block, perhaps you should have asked if you could use a different block.

Im not sure why anything greater than 3.6N would be needed internally.

^woody^ said:

But 150mm was specified!

So rather than ask if you could use a thinner block, perhaps you should have asked if you could use a different block.

Im not sure why anything greater than 3.6N would be needed internally.

Click to expand...

I did talk to him and said that I can't find a 150mm dense concrete block. Maybe I should have used a lightweight block? Maybe he should have specified what he fecking wanted in the first place. Even still... If it was a 150mm lightweight or dense block, I imagine that the engineer will still want to see some lateral support.

Is it an external wall? Can't quite understand the arrangement.

It's the architects fault anyway, as the revised information he gave was not correct.

tony1851 said:

Is it an external wall? Can't quite understand the arrangement.

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The image is pale, but it looks like there is a double-skin wall running accross the top (?) which would help stabilize it. Is there a roof or ceiling spanning onto it, or are there any ties between the top of the wall and the structure above?
It seems unsupported at the inner end, though presumably there's a lintel over the door with some blockwork above(?) which would help. Even so, millions of houses have unsupported half-brick walls internally, eg where front room and back room doors are next to each other.
Personally I think the SE is going for overkill, though that's just my humble....

Yep there is a double skin wall at the top which is tied into the internal wall. There is a pitched roof spanning the extension but not really tied into it as such.
The wall goes up into the pitch of the roof and is then tied into the existing wall of the house which I think gives it its main stability. And then as you say there is a blockwork wall where the doorway is. Yes there is a lintel over wall with some blockwork whihh is tied into the wall.
Yes I also think the se is going overkill. He initially did a report just with the wall on its own. I have now asked him to redo the report with all the things that we have just mentioned. I will then aim to get the work checked to see if it really does need extra support.