Steels required for extension

[drpepe]

We are having a rear ground-floor extension designed. Below is a cutting from the proposed design, which features french doors with windows above them.

View media item 96110 Our architect has got quotes from a structural engineer for the following:
B1 - knockthrough existing kitchen-diner
B2+B4 - knockthrough existing rear wall
B3 - ridge beam
B5 - cranked beam over apex windows to carry point load of ridge beam

I can understand B, B2 & B4, but are B3 and B5 overkill?

i.e. Every house i've lived in has a timber ridge beam - is it necessary to have steel? is it more expensive to have steel?

 

[freddiemercurystwin]

Regarding B3 you appear to have glazing beneath the slope in the end elevation so you can either provide a post to support the ridge or a cranked beam as proposed. As you have glazing a post is gonna be somewhat impractical here.

Regarding B5 a steel beam is usually used where a timber one would be impractical eg too large/expensive. If you’re ceiling is vaulted then there will be no ties in the roof so the ridge beam is doing more than in a traditional roof where it just sits there with no load on it.

 

[drpepe]

thanks for the reply.

Yes that all makes sense... we are going for a vaulted ceiling, and seeing those plans has made me realise the choices we made (vaulted, glazing) may cost us a lot more than a standard design!

 

[tony1851]

A cranked beam in the gable would be expensive due to the fabrication costs.

Could you have a short box-section post to support the ridge beam, perhaps running the glazing in front of it?

 

[drpepe]

A cranked beam in the gable would be expensive due to the fabrication costs.

Could you have a short box-section post to support the ridge beam, perhaps running the glazing in front of it?

Thanks Tony - that sounds like a good idea - this was meant to be a very basic extension, but things have got out of hand possibly!

My architect has already today submitted the drawings to council BR office. If we get quotes for the job that are way over the top, what happens if we change our design (e.g. to what you suggest, or drop the gable window entirely) ? do we have to go through BR again (and more fees) ?

 

[tony1851]

do we have to go through BR again (and more fees) ?

No. In practice you can make changes as you go along, as long as what you do still complies with the regs.

Your Building Control people may - or may not - ask for revised drawings to reflect the changes, but that's just for the
sake of completeness and is not a new application.

 

[^woody^]

Whoever is designing it should be able to give an idea of the costs to build the thing he is designing.

If you don't like it, or its too expensive, then get him to change it before submitting the plans. He can submit amened plans and ask the council not to start processing the ones he has submitted.

The whole purpose of plans is not just pass the council's checks, but for you to get accurate quotes and know exactly how much you will need to pay to get the thing built. In particular you should have been told the engineer's fees for all that steel work before you agreed to the design. It's bad if your designer has not kept you informed and got your agreement on the final design, or considered more economical options.