Cost of 9m goal-post frame...

[EvilDonut]

My architect has produced a nice design for our rear/side extension, however it depends on a 9m steel moment frame to support the existing back wall and new side bit.

Anyone care to guesstimate the cost of this bit of the build?

I suspect the horizontal beam(s?)will be quite large, they're supporting:

• Rear existing house wall (+gable) 6.5m wide
  
• First floor joists (3m long joists)
  
• Point load from adjoining UB taking load from 2m existing side wall
  
• Rear wall of new side extension(2-storey) - 2.3m
  
• Whatever load transferred from roof elements

See plan for more detail:


Later on we'll get an SE to spec it up of course, just want to get an idea of rough cost (both the steel material cost and the 'fully fitted' cost)

Cheers!

 

[^woody^]

How does your Architect know that it needs that type of structural support?

 

[wessex101]

I think you need to speak to a structural engineer sooner. That beam will be a chunky monkey and you might be struggling with headroom under it unless you've already got high ceilings. Cost wise? Are you talking just the steel or installation as well?

Just noticed ceiling height 2.3m......that'll be tricky.

 

[freddiemercurystwin]

It looks like he's given very little regard to structure and this should be one of things at the forefront of an open plan design like this.

 

[wessex101]

It looks like he's given very little regard to structure and this should be one of things at the forefront of an open plan design like this.

Why let a silly thing like the structure get in the way of a nice open plan design....that's the engineer's problem.

 

[EvilDonut]

I found a forum post somewhere that said their SE had specified a couple of 203x203x46 columns and a 203x203x86 horizontal UC for an 8.5m span with similar loadings to my scenario. Not saying mine would be identical, but it's nice to have a rough indication.

That would cost about £1k for all three UCs, excluding any plates/bolts/etc and installation costs. The horizontal UC would weigh a massive 700kg. Would that have to be a crane job, or could it get broken into 2-3 smaller sections bolted/welded?

I believe with some effort it can be recessed into the ceiling (existing joists cut into it somehow), but not sure on the details there.

The architect obviously made an educated guess as to what's required but if the SE specifies some kind of massive beast then we may need to re-think the open plan a bit.

 

[dom_k]

Those sizes sound reasonable. If cavity wall just stick in a 305 97 UC beam to properly support both skins of the wall. He has shown pad footings which need to be factored in too. Splicing will add cost - maybe £100-£150 per splice so I'd try get it in one.

That window right next to bi-folds is awful though. Pier looks weak and will maybe need a steel post in there too.

 

[EvilDonut]

Sounds good, I did wonder about how both skins would supported, that makes sense.

Will proceed with this design and see what the SE specifies

 

[tony1851]

Instead of using a 305 x 305 UC, you can use one of the 203 x 203s with a 4mm x 275mm plate tack-welded on top to pick up the cavity wall.
If using a 203 section on that span, deflection might be an issue, but your SE will check that.

 

[EvilDonut]

Ok great, should be plenty of options for SE to ensure the steelwork remains hidden then.

What's the procedure to install the column in place of the existing corner? Underpin the existing strip with a 1m3 pad, or completely break up existing foundation and start again?

I was hoping the knock-through could wait until the new extension was water tight, but sounds like it may need to be done first as this massive beam won't be able to be fitted at the end

 

[John D v2.0]

With ours they demolished a bit at the corner up to skirting level and dug a 1m deep hole under and filled it with concrete. The actual knock through was a bit later. I'm really struggling to add an image bit I hope you can see it correctly!

 

[EvilDonut]

Those pics are a great help thanks - looks like it may be possible to install the frame without fully knocking out the back wall (which would leave us without a usable kitchen, not a good plan as we'll have a toddler and a newborn!)

 

[Darola]

How did this project go?