Roof joists

[Jb]

My best mate has been doing his own extention, bricks, drains and roof done by builders, the rest by him, over that last six years. He can't get it signed off by the council because their structual engineer has now decided the joist are under sized by 7mm. When the plans were submitted no objections or comments were made (unfortunatley over the times scale there has been at least four different inspectors and only this last flavour has raised the issue of sizes) so until a month ago he was unaware that anything was untoward and expected signing off to be a mere formality. His roofer has gone bust. The company that did the calculations/supplied the trusses etc has been taken over and the inspector cannot advise him on the way forward. In essence anyone any idea how he can increase the sizes of the timbers or strenght to pass inspection without taking the roof off and starting again.

thanks

Jb

[js.b1]

Get a structural engineer to yea or nea the structure?

- Grade of wood has a bearing, C24 can be thinner than C16 for example so dimensions are only 1 parameter. Same goes for spacing and so on.

Check if BR changed over the period from original application?

- BR at time of original application apply, if that has any bearing (I doubt it, but you never know since they may be based on assuming the worst rather than what a structural engineer says you can actually get away with).

[RubberBiker]

Joist sizing will be calculated from span, weight of roof covering, estimated wind loading etc.

I'm assuming this has been done on a building notice, rather than a full plans submission? If full plans have been passed by building control, and you build to plan, you're home and dry.

First thing is to get somebody to go through the calculations and see if any value can be tweaked to get back within regs (e.g. the roof covering may be lighter than the value specified, plasterboard ceiling changed etc.).

If you have to physically change something, beefing up some joists with side-plates is probably the least hassle solution.

[The Natural Philosopher]

Yes. Building control will go 'by the book' unless someone with more authority says 'OK' In this case its a structural engineer.

An if the timbers are accessible like roof rafters, its very simple to fix. You can double up every third one or something and add purlins.

[dennis]

Bolting metal strips or even plywood to the sides will probably do it easily. However you will need an engineer to produce a design so the building inspector will pass it.

[Jb]

All useful info thanks guys. One suggestion from a 'bar room' expert suggests flat steel fish plates, is this feasable/reasonable?

Thanks

[geraldthehamster]

How ridiculous. 7mm, what's that, 3/16"? They won't sign it off because the joists are undersized by 3/16". I'm off for a lie down.

Good luck Richard

[NT]

surely much cheaper to stick a bit more wood up.

NT