Specifying joists from span tables

[PragmaticWench]

Our architect has vanished (subject of a whole other thread) so I'm looking to see if I must have someone qualified to specify the size of joists on my extension, or if I can do it myself?

Our architect has specified a size of joist for the first floor and now they are in situe, it has become apparent that they are too deep for our ground floor ceilings to be at the same height as the current ceilings. Looking at the published span tables, I believe the architect has mis-specified the joist depth and we could have had them at 170mm deep instead of 220mm.

Obviously building control will have to sign off on the joist size used but I'm wondering if I can specify the size myself, or if I need an architect or structural engineer to put this in writing officially?

I think the structural integrity of your house is more important than a flat ceiling below... you can always pack the ceiling down!
But 10x2 are usually used for spans over 5m

The internal span is 3.7 so I'm seeing on the span tables that we could use 170mm deep joists. We absolutely can't have the lower ceiling, ourcurrent ceilings are very low so 5cm lower would be ridiculous.

There isn't a legal requirement to have particular people put it in writing. Whether it's a good idea or not is a different matter. Bear in mind that building control do not provide any sort of insurance, so you can't rely on them if it's wrong, and I don't know where you would stand in terms of home insurance etc. If it's a simple job then a structural engineer shouldn't charge much. I'd look for a one-man band type who is used to doing this sort of thing.

For the sake of a couple of hundred pounds is get an engineer to size them. There are quite a few factors re load, end fixity etc.

You can specify them from tables but I would definitely get building control to agree them in writing - the size, spacing and type of timber - there are different strength grades.

Thanks for all the advice, I'm genuinely not trying to save money/cut corners, and am happy to pay a structural engineer to specify sizes, more trying to see if we can prevent a delay in the build progress.

Our builder has spoken with the company we have dealing with the building control, so they are visiting site tomorrow to discuss if we need an official specification and also if we can cut down the already-installed C24s or if we need to replace.

I'm happy to pay for calculations and also to replace the installed joists if necessary, just hoping we don't have to! Also trying to juggle all this without involving DH as DFIL is dying so he has enough going on.

Don't need to use the council service if they are being a pain try PWC building control service . they will advises and issue certification without council involvement