Planning question

londoner1 · 3 Oct 2015

Hiya,

I'm about to submit plans for a loft conversion in a 1930's terrace in London.

One builder who saw the plans questioned the need for a 254x146x37ub and a 203x133x30 ub beam together with a flitch beam and suggested 152x152x37UB x 2 plus a smaller size beam instead. I don't doubt the builders judgment as he has built a few lofts on my road over the last 10 years plus eleswhere.

The structural engineer says the beams in the plans are more than strong enough and will not deflect at all plus are sized to exceed building regs.

So can the beam sizes change during the course of the build as teh plans would feature different sizes during the initial submisssion?

freddiemercurystwin · 3 Oct 2015

Only if the engineer provides calcs to suit. But is the engineer saying they could be smaller?

londoner1 · 3 Oct 2015

freddymercurystwin said:
Only if the engineer provides calcs to suit. But is the engineer saying they could be smaller?

The engineer is saying they could be smaller and be cheaper but not worth it as in his opinion they could deflect in the future and could cause cracks to appear.

tony1851 · 3 Oct 2015

The 152 UCs will deflect a little more than the taller beams the SE has specified, but not by that much.
Have used them many times in loft conversions.

What does the SE mean by 'sized to exceed building regs'?
You could put in a 914 x 419 x 388 and that will 'exceed building regs'.

Has he done calcs for them, or just picked sizes off the top of his head?

^woody^ · 3 Oct 2015

londoner1 said:
The engineer is saying they could be smaller and be cheaper but not worth it as in his opinion they could deflect in the future

Is he a proper engineer, because he is taking nonsense?

Beams don't deflect "in the future", else they are useless in the present.

His job is to design aa suitable beam of the most economical section size for the situation. Not over specify.

Nakajo · 5 Oct 2015

Beams defelect in the future because in the future you have a dinner party with one too many guests stamping around upstairs.

^woody^ · 5 Oct 2015

Nakajo said:
Beams defelect in the future because in the future you have a dinner party with one too many guests stamping around upstairs.

That is why there is a 1.6 dinner party factor in BS 5950.

Who the hell has dinner parties anyway?

Nakajo · 5 Oct 2015

It's a London thing. You wouldn't understand.

londoner1 · 5 Oct 2015

His response:

'There is no uniform spec for lofts. Beam sizes will vary depending on span length and applied loading. It is not right to assume that a beam size in particular loft will be ok for all lofts.'

The builder i approached has not even come across a flitch beam in a loft (yes i know weird) but he has completed over 4 lofts on my road alone over past 10 years with LABC approval plus other lofts elesewhere.

diynot

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