Just a thought

I've always worked in the incredibly regulated environments of military, space hardware, pharmaceuticals and nuclear - so rules is rules!

I have a quandary at the moment - I'm building an extension and I've found a tiny error/conflict on the plan - a window dimension is wrong - it needs to be slightly bigger to meet building regs (they signed the plans off without noticing) but if I make it to the legal requirements, I should inform the planning department - but they could cause me all sorts of grief because their rules are completely arbitrary and vary on the judgement of the person's whims on the day - and they could demand a full planning application that they might refuse.    If I don't make it to the legal requirements, the building inspector will spot it as he has to inspect this detail to sign it off.

A third route is to just build it how it needs to be and hope they don't notice or apply for a certificate of normalisation afterwards - which could end up with me having to re-build it to their demands.

This is really bothering me,  

What would you do?

Try and let them know on the quiet first, that you've found an error; without going into a formal complaint procedure. These guys are definitely fallible, and I reckon if you point out to them carefully that they've made a small mistake, they will probably try to rectify it so that neither you nor they lose face. I was once on a site where the planning inspectors turned up and advised us to stop work immediately, saying that a planning application hadn't been received. I pointed out to them that I personally had delivered the application to the planning office application box in good time. But there was nothing acrimonious about this, from which I conclude they knew that it was probably a miscommunication. They accepted that they might have made some mistake, but still advised immediate stoppage. Before we even got back to base, word came through that the plan had actually already been accepted. So we were back on the same site, the next day.

My original plan on leaving school was to study Town & Country Planning. I got as far as being accepted by a couple of polytechnics. I wish now I had stuck to my original plan.

My cunning plan is to casually mention it to the building regs guy - he'll say that I must be compliant with the regs - so it becomes his decision - so I can throw him under the bus if planning disagree after.  

No

What I'm doing is prettier and more 'in keeping' than any other extensions  (overblown need to do the right thing).

I hope you are not planning any "monstrous carbuncles". It might upset Chas, and he's already teed off with Handy Andy. Definitely make sure you bring it up with building regs before work commences. It gets incredibly expensive when you have to build, tear down and rebuild. On another site, I saw the contractor put in a very expensive slot-in replacement window. At which point the householder turned up and told me that the builder's merchant had delivered the wrong design. The contractor frantically decided to try and lever the window out, and I knew straight away that he would probably only be able to get it out by damaging both  it and his own rep. So I immediately suggested that the householder might want to take a look at the new design and see if he liked it. Luckily he agreed, just in time for me to shin up a ladder and tell the contractor to relax. Stressful places, these construction sites!

I hope you are not planning any "monstrous carbuncles". It might upset Chas, and he's already teed off with Handy Andy. Definitely make sure you bring it up with building regs before work commences. It gets incredibly expensive when you have to build, tear down and rebuild. On another site, I saw the contractor put in a very expensive slot-in replacement window. At which point the householder turned up and told me that the builder's merchant had delivered the wrong design. The contractor frantically decided to try and lever the window out, and I knew straight away that he would probably only be able to get it out by damaging both  it and his own rep. So I immediately suggested that the householder might want to take a look at the new design and see if he liked it. Luckily he agreed, just in time for me to shin up a ladder and tell the contractor to relax. Stressful places, these construction sites!

No

What I'm doing is prettier and more 'in keeping' than any other extensions  (overblown need to do the right thing).