IG Lintel or two RSJs to span 3 metre gap?

[Bodgedbuild]

I'm still picking up the pieces having been deserted by my (close to useless) builder. One of the last major jobs on the build was to knock out the back wall of the kitchen enough to create a 3 metre wide gap for Bi-fold doors. The architects drawings show a heavy duty IG lintel over the span and as part of a package, I paid a structural engineer to provide calculations for this.
My dilemma now is that I'm concerned that retro fitting an IG lintel to a 50mm cavity wall will be problematic and that individual RSJ's might be a better idea. My concern is the height of the IG lintel that has to be pushed up into the cavity, I believe around 290mm in height. If the cavity is not actually 50mm wide because of poor workmanship or motar snots inside I can see a lot a faffing about coming my way.
Would it be worth paying for an engineer to do calculations for a pair of RSJs and do it that way instead? I'm also thinking ahead for what might be best for securing the bifolds to...

 

[tony1851]

On a 3m span with normal domestic loading, consider a 203 x 133 beam, with a steel plate welded below to carry the outer skin.
You would need to include a cavity tray over the beam to direct outwards any water penetrating the outer skin.

 

[^woody^]

Lintel.

 

[tony1851]

Beam.

 

[Bodgedbuild]

Woody, do you think the lintel will go in ok in your experience, mortar snots and cavity width tolerance and all?
Something I didn't mention is that because of delays in building control inspections (as in my other post AEDIS going belly up) I may only remove enough of the wall to get the lintel or beams in and may have to wait for a while before I can get it inspected.

Tony1851, thanks for the beam suggestion to save on two steels

I'm still sitting on the fence at the mo now though, it's purely the least hassle that i'm bothered about and if that means paying for more calcs, a couple of hundred quid won't make much difference. Would it be possible to trouble you guys to elaborate on your advice at all please?

 

[23vc]

Won’t you need to needle/strong boy prop the wall anyway, then take the masonry out where the lintel or beam(s) are going, so I don’t quite get why fitting beams is more hassle, were you banking on the bottom couple of courses staying hanging unsupported while you push the lintel up into it? For that to work you’d also have to have no bearings either end at that point surely?
Basically I don’t quite follow your method for pushing a cavity lintel upwards into the existing wall and how the wall is supported and where the bearings are at that point.

 

[^woody^]

Woody, do you think the lintel will go in ok in your experience, mortar snots and cavity width tolerance and all?
Something I didn't mention is that because of delays in building control inspections (as in my other post AEDIS going belly up) I may only remove enough of the wall to get the lintel or beams in and may have to wait for a while before I can get it inspected.

We used to do loads of these on the mods, back in the day. If the cavity is 50mm, they slot in, and are easy and less disruptive than box lintels or beams. Knock any snots off with piece of timber.

When using standard lintels, you don't need SE calculations. If you were told otherwise, get a refund.

 

[Bodgedbuild]

Thanks for clarifying Woody, I think I'll go with the original plans then and save any extra expense. I didn't pay for calculations for this lintel by itself as I paid for a package for the architect and engineer for the entire build

 

[Bodgedbuild]

23vc, I am on the fence between getting a new builder to do just this part of my build or whether to go it alone, albeit with a couple of friends that are chippies rather than builders per se. I guess expecting much of the brick work to hang below anything supporting it is just expecting a bonus. I'll just get a brickie to re-brick above the lintel and to do the pads