Building regs - loft conversion problem with the purlin

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Hi I'm after some advice please. We are having a loft conversion with full length dormer. due to the pitch of the roof the entire right hand side will be a flat rubber roof. The builder has constructed the roof in accordance with the plans. The plans showed a wood purlin however this was not stated in the write up. The council passed the plans and on 2nd inspection have now not told us the purlin needs to be steel. My question is how can the council be pass the plans and now say the purlin is to be steel - if the plans didn't state this in writing then shouldn't they have stipulated the fact when approving the plans, they have been paid enough!??? Secondly the builder has ordered the steel in three pieces - is this safe what if they buckle and collapse over time - should it not be in one piece???
 
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Oh and does anyone know why wood isn't adequate enough to hold a rubber roof 6m x 4m??? Is the inspector right to make us remove the wood purlin and replace with steel??? Thanks x
 
When you say purlin are sure of your terminology (no offence)? Do you actually mean the purlin or the beam at floor level beneath the purlin? Or do you mean the beam at the ridge?

Its normal to do the steels in more than one piece its called splicing and will be every bit as strong as one continuous length provided the connections are designed and fixed together properly. //www.diynot.com/forums/viewtopic.php?t=137740&start=15

Did you get a 'full plans approval' on this? Did the conditions ask for calculations or anything else regarding the structure for eg?
 
Thanks for your reply. Yes on the plans showing the flat roof coming off the ridge of the roof, just a metre or so from the ridge there is a square with purlin pointing to it. The write up for the roof says: 10mm stone chippings on 3 layers of built up felt to BS 747 utilising 3G felt base layer partially bonded on kingspan therma roof tr26lpc/fm on 19mm plywood on firings to falls on 47mm x 170mm c16 joists @ 400mm c/c's with plasterboard ceiling plaster skimmed finish blah blah. 100x75mm wallplates strapped @ 2000mm c/c's with 30x6x1450mm long galvanised metal steel straps PVC-u facia and soffits and lead flashing.

No mention of the purlin which is maybe where things have gone wrong but surely when passing the plans the council should have stipulated.

Now we've asked for rubber not felt roof but I can't see that being the reason the roof needs steel to hold it up as opposed to the huge beam of wood up there now, it just seems crazy!!! The inspector is new apparently but the builder has gone away and ordered the steel without us having the chance to challenge it and the thought of 3 pieces of steel being stuck back together along the length of the roof without and support underneath is a bit worrying but if like you say it is common practice well I guess the builder and yourself know what your talking about!!
 
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The steel beam needs to be designed by an engineer our other competent person .... not just collected from the yard by the builder.

Your plan drawer should have put all this on the plans

The inspector is entitled to alter any approved plan following site checks. If you feel that the approved design is adequate, then it is up to you to prove it, else go along with any recommendations from the inspector
 
The builder has liaised with the engineer, he was suppose to come here today and I was hoping to fire lots of questions at him. The builder thinks what he has done is adequate as does the engineer but they both say if that's what BC want then it has to be done.I wouldn't know where to start trying to prove what's done already is fine so guess we'll just have to fork out the extra, just so annoying, it's holding a few rafters and some rubber up not a 2 storey building and it's far stronger than the previous purlin that was holding the previously heavier roof in place!!
 
Whoever drew up the plans should have known what would be required to support his design

Now, he either should have designed the supporting beam himself or got someone (more experienced) to design it.

In any case, you should have been made aware of the costs including the structural design, or at least been told that there may be extra costs if the plan drawer needs to get some structural design work done

This is completely different to the council inspector requiring extra work not evident on the plans and picked up on site, at extra cost to you, as I would expect the plan drawer to either argue his case that a beam was not required or have told you that one would or may be required
 
Thanks for your replies. The purlin is shown on the plans and I assume it's wood it just doesn't have any sizes. It's certainly not suppose to be steel as you can see the steel on the floor /-/ kind of like that but straight and horizontal lol the purlin is shown as a square with a squiggle in it!!! Grrr so annoyed as it's taken a good chunk of our decor money but without knowing what I'm talking about I doubt I'll get anywhere trying to argue it!!
 

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