Lintel above a bifold?

28 Feb 2017
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United Kingdom
I'm putting a 4m bifold into a blockwork constructed single storey extension out of the back. Above it is a pitched roof, with velux and inside the ceiling is vaulted so no horizontal trusses.

I've been advised by the SE to use a RHS with plate, but I was wondering if anyone had used a Catnic or IG lintel in place? Its a Smart Visofold bifold that i'll be installing, and there is a deflection limit for the doors to operate smoothly. A heavy duty or greater one seems like it would be ideal if it will take the load, for cold bridging and weatherproofing. The SE seems reluctant to specify one though.
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RHS might be expensive and not easy to fix curtain rails etc.
Cheaper than Catnic would be a 152 x 152 x 30 (plus 250 x 8 plate tack-welded underneath if carrying any blockwork on the outer skin)
If only supporting a vaulted roof, no need for padstones if with min 200mm bearing each end.
Thanks Tony, I was told that the RHS would be easier to conceal, birdmouthed into the truss. I was just going to paint it with bitumastic paint however there's an option to have it galvanised for a few hundred quid. Are Catnics CX lintels not suitable for this kind of application?
The Catnic CX range would be fine, but probably a little expensive?
I doubt the RHS would be any easier than a 'I' or 'H' section beam - the birdsmouth would be done over a timber wall plate which would need to be fixed to the top of the beam, so i don't see what difference it makes.
If you use a steel beam (rather than a Catnic) no need to galavanise, but you need to protect with a dpc/cavity tray.
Catnic doesn't require a dpc as the integral coating does that.
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