Looking at this house: http://cldb.co.uk/cldb/Croft_House.html

"The interior has a novel finish with OSB walls ceilings and floor..."

I'm more than a little surprised they can use OSB like that. Isn't there normally a requirement for plasterboard or something to stop any fire spreading too quickly? What are BC likely to be happy with or not?

Looks like the inside of a SIPs house before it gets lined.

I'm also surprised they can get away without cladding with plasterboard or some such, as I thought that the fire bit in BRs would have needed more than just unfinished OSB.

Yes, very like a SIPs house: OSB boxes made in a factory then assembled on site. Just that the boxes are full of straw or sheep's wool instead of plackie stuff.

Just spent an exciting hour or so reading the relevant bits of the Scottish Building Standards Technical Handbook Domestic 2010.

First startling bit was in 2.3.1: Elements of Structure

However the following elements of structure need not be provided with any fire resistance for structural protection:
• an element of structure in a single storey building which does not...

The exceptions aren't terribly applicable to a single family house well away from anything else.

Still, this is a two storey house so it should have "short" fire resistance duration.

Annex 2.A.3 note 3 says:

In a timber stud wall or partition the following will also be deemed to have a short fire
resistance duration:...

d. timber at least 38 mm thick.

TImber, is that 25 mm with fire retardant?

I'm not absolutely convinced by the OSB finish but the simplicity of the system is very interesting. Putting on a coat of intumescent paint, perhaps white, seems a lot cheaper and less hassle than plasterboard. For the design I have in mind the service void provided by plasterboard is less important than it might be for others.