Cladding steels

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Hi. I have steels in my new build, vertical and horizontal, bolted together, and in an external wall. Within the oblong shapes in the steels are large windows.
I want to box in the steels, in timber, to finish with the windows surrounded by a box construction.
I have been told that I need to clad the steels prior to cladding them with timber. I've been told 2 layers of plasterboard, which seems possible, I suppose, but unlikely.
Any advice, please?
 
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Hi. I have steels in my new build, vertical and horizontal, bolted together, and in an external wall. Within the oblong shapes in the steels are large windows.
I want to box in the steels, in timber, to finish with the windows surrounded by a box construction.
I have been told that I need to clad the steels prior to cladding them with timber. I've been told 2 layers of plasterboard, which seems possible, I suppose, but unlikely.
Any advice, please?
Your primary concern, as far as Building Regulations is concerned, is that the steel is adequately protected from fire, for the exposure time period required. Whether this is by two layers of plasterboard or by a clever but expensive intumescent paint, is down to you and your inspector.
 
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Your primary concern, as far as Building Regulations is concerned, is that the steel is adequately protected from fire, for the exposure time period required. Whether this is by two layers of plasterboard or by a clever but expensive intumescent paint, is down to you and your inspector.
Intumescent paint requires about a 50mm air gap clear all around, so an inadequate solution here. Either a layer of 12mm Supalux or Kemwell board will likely do it, beware as to how picky your BCO is, theoretically BC shouldn't be accepting anything that a manufacturer does not have a specific fire test for. Currently there's a massive void in the industry with regards to fire tests relating to specific situations.
 
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As the intumescent paint expands in the heat it expands to about 50mm and it's that thickness of insulation surrounding the steel that insulates it from the heat. If it cannot expand to an adequate thickness it cannot insulate the steel.
 
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I've only explored that route once and the jump-through hoops were just too frequent. Two layers of pink board for this chicken.
1 layer Firecase board will more than likely be adequate, see here: https://www.british-gypsum.com/~/me...e-Book-C03-S02-Steel-Encasements-FireCase.pdf

If it were me I'd be fixing the Firecase boards to say 25x25 steel angles that were fixed to the steel initially, then after the boards have been fixed to the angles fix the timber battens with their fixings into the angles, through the boards. Pack the voids in the steels with mineral wool. You might need to allow for some mineral wool around the outside too to prevent cold bridging etc.

In any case I'd check whatever you propose will be accepted by BC before you do it, they are (rightly so) getting very finickity about this stuff since Grenfell, though much more so in multi storey/commercial.
 
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BC were happy with one layer of fireboard on mine, albeit for regularisation of an existing beam.
Edges and joints were filled with intumescent sealant.
 

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Did you also clad that face that's unclad ATM? As that's a classic example of what's been accepted for years through lack of knowledge, in a fire, the timber will expand and twist and buckle against the steel, as the screws heat up they'll char the timber they're fixed into and can fail too. In reality it'll probably all be OK seeing as it's in a house but really it's not right.
 
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Did you also clad that face that's unclad ATM? As that's a classic example of what's been accepted for years through lack of knowledge, in a fire, the timber will expand and twist and buckle against the steel, as the screws heat up they'll char the timber they're fixed into and can fail too. In reality it'll probably all be OK seeing as it's in a house but really it's not right.
Yup, that was a work in progress shot.
I have a feeling BC wasn't that bothered about anything!
He came around for a roof change and we added on the regularisation, as he was here :)

Steel brackets would be the way to go!
 

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