One Steel or two?

Minatoar · 18 Jan 2017

My builder is nearly ready for knock through from my house to my single storey extension.

Structural engineer specified a steel RHS 2550 x 150x100x5 with a 250x8 flange to support the outer leaf. I am waiting for a quote for this and expect it to be expensive and more importantly very heavy.

I have asked the SE as an alternative, if 2 x 150x100x5 steels for both inner and outer, bolted together with M 12 bolts and spacers every 500mm will suffice and await his reply?

Assuming he sanctions this, are there likely to be any pitfalls using two steels?

John D v2.0 · 18 Jan 2017

2 steels would usually be easier and safer to install, so having a single one would be harder to justify under cdm regulations. Our SE even specced flitch beams instead of steel on the roof on that justification.

noseall · 19 Jan 2017

Are regular U beams out of fashion now?

garyo · 19 Jan 2017

noseall said:
Are regular U beams out of fashion now?

It's probably the brexit effect. I'm going to use Whitworth bolts on my next fitch beam, and use a layer of dung and horse hair instead of steel.

tony1851 · 19 Jan 2017

What's wrong with two standard UBs? - certainly a lot cheaper; and why a plate to support the outer skin, if it is now an internal wall?

Your SE clearly hasn't done many of these jobs.

^woody^ · 19 Jan 2017

At 2.5m, I'd just put a steel lintel in

John D v2.0 · 19 Jan 2017

Oh sorry I forgot to mention ours weren't RHS they were PFC, bolted together with spacers where necessary. I'm not sure how much more expensive and how much lighter each one was, but that's what they fitted!

Minatoar · 19 Jan 2017

SE has now replied to my email: "Using two steels is fine, although they do not necessarily need to be bolted together."
"Please note that we specified the shelf plate solution because this is usually preferred by the builders"

My builder said, "Where's he get that from? He's not the b*gger who has to lift the one with plate welded on"!

John D v2.0 · 20 Jan 2017

To be fair for our rear opening 4.8m it was specced as a single uc 152, but the builder added a plate to the bottom because he thought it'd be better, but it caused no end of issues with thermal bridging etc. By all accounts from next door it was a challenge to get it in place! So maybe it just depends on the builder.

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One Steel or two?

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