Trouble with council over my structural calcs!

[kcseb]

Hi all

We're coming to the end of a single-storey extension, and I submitted Building Control the structural calcs for making a 2-metre wide opening in the main rear wall - there are two smaller openings already in that wall, see diagram below.

After about three weeks of sitting on the calcs, the Council have now come back with the below query. I'm not sure what to do as the build is almost complete!

Any ideas?

The size of openings in the main rear wall appears to exceed the dimensional criteria given in Diagram 14 of the Building Regulations; Part A. Check its adequacy for lateral restraint to supported flank walls.

Ta!

RSJ

• kcseb
• 29 Apr 2015
• 2

 

[freddiemercurystwin]

They're saying that the openings in that wall exceed what is allowed for in the diagram in the Building Regs Document http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_A_2013.pdf (page 31 of the PDF) and as such in order to meet approval you'll need to get your SE to do some number crunching to prove it works, unless the calcs demonstrate this already which I would expect them to if the SE has half a brain and he has been provided with adequate information. Speak with your SE.

 

[tony1851]

if the SE has half a brain

I shouldn't bank on it; SE should have seen that one coming.

 

[freddiemercurystwin]

One would hope .....

 

[kcseb]

Thanks guys. Yes I've been in touch with him, he offered to design a portal frame but surely if it was unsafe he should have suggested it originally!

The thing is:

1) I can't afford to install a portal frame: we've skimmed and are ready to paint, it will be a horrendous mess to do this now too

2) surely it's not needed? There's a wide pier in place already, to the right of existing lintel (lintel is denoted blue in my pic above). Then we've also put a steel post in, under where the lintel and RSJ "meet"

 

[freddiemercurystwin]

Hmm, it kinda sounds now like you built something that the SE didn't design and provide calcs for?

 

[kcseb]

Nope: he specified the steel post which is why we put it in. Calcs came first. But he never mentioned a portal frame until now!

 

[freddiemercurystwin]

OK so now sounds in a roundabout way, for clarity, that you're saying that he provided a design and calculations that did not comply with Part A?

 

[^woody^]

The wall is not a continuous panel and is buttressed by the wall parallel to the stairs, so diagram 14 should not apply to the wall as a whole.

 

[tony1851]

As Woods, there may well be sufficient lateral stiffness in the house as a whole without resorting to a moment frame.

It is possible in most cases to do calcs to prove that all the existing walls parallel to the rear wall are sufficient. Rather than put in a frame now, speak with your SE.

 

[Nakajo]

This is why your engineer has professional indemnity

 

[kcseb]

Thanks guys. I spoke to my SE. I'm going to send him a few additional measurements tomorrow and he will do calcs to show that there is not an issue with lateral stability - he explained to me that the current regs in effect want your house to be structurally sound even if the next door houses (it's a terrace) weren't there.

As he feels it may have been a slight oversight on his part, he's going to do it for £50! So it's not all bad news!

 

[freddiemercurystwin]

Should be free!

 

[^woody^]

Should be free!

Not at all. I often miss whole floor plans off my designs, and when planning query it, I offer to add then at a reduced price.

Heaven forbid clients realising that it's actually all part of the job they asked me to do.

 

[kcseb]

Dear all

I've done some measuring for my SE, and now I'm surprised that the Council has queried the openings in the first place! We've opened up about 48% of the main rear wall only! And we've put a steel post in (see vertical red bar), which my SE stated is only taking about 15% of its full load capacity!

See below!

Best