Double sheet plasterboard

[Tony.]

Evening all,

Can anyone point be of the reg for ensuring the ceiling meets the required fire rating

Its a ground floor shop and a flat above,

Looikng at the scottish non domestic regs and the plasterboard manufacturer, i cannot see where this is specified, or even hinted at.

Along time a go when i was on the tools it was standard practice to double sheet and tape both levels to achieve the appropriate rating.

Many thanks for thos that can shed some light and point me in thenright direction.

Tony

[kurnal]

The board manufacturers submit composite fabrications for testing and where successful the outcomes of the tests and the specification of the composite are presented in their literature such as the British Gypsum "White Book".

The old Cape Boards book was a goldmine for the use of basc materials.

The good old Building Regulations 1976 were really useful in replicating examples of good practice and the relative performance of various different ceiling designs. Well worth buying a second hand copy.

[kurnal]

Sorry Tony misread your posting last Night,

Its down to the Building Legislation, the Scottish Technical Standards or the Building Regs in England. Take a look at the requirements for compartmentation between different purpose groups.

[Fishy]

Do bear in  mind that if you need 60 mins F/R then you won't get that by using 2 x 12.5mm plasterboard cladding to the ceiling alone.  For 60 mins I would always recommend that someone designs the floor according to either the plasterboard manufacturer's technical recommendations, or use Eurocode 5 (Design of timber structures — Part 1-2: General — Structural fire design). 

You might get 30 mins from the two layers, but the joints would need to be staggered, taped & filled & both layers properly fixed at the recommended centres.

BS 5268: Section 4.2 used to be really useful for this sort of thing, but now that it's been superceded by the Eurocode things aren't quite so straightforward.

[Tadees]

Hi,

Why would you not get 60 minutes with 2 x 12.5mm plasterboard.  All the companies I have spoken to say you get 60 minutes.  Interested to know the basis of the conclusion.

[Fishy]

Hi,

Why would you not get 60 minutes with 2 x 12.5mm plasterboard.  All the companies I have spoken to say you get 60 minutes.  Interested to know the basis of the conclusion.

Because (assuming standard wallboard) the two layers will have fallen off within 30-40 mins. 

The basis of my conclusion is that I used to run a fire testing lab, & have seen 1000+ fire resistance tests.

Anyone who says you'll get 60 mins f/r from 2 layers of 12.5mm wallboard alone is guilty of very wishful thinking... I'd ask to see their evidence of fire resistance performance, if I were you.

[Tadees]

I have been told and it is the opinion of many fire safety officers that 2 layers of correctly installed fire rated plasterboard will give the requisite FR. I have not come across any evidence to suggest that this is not correct.

[Tadees]

In fact I have seen the following para in many risk assessments and FSOs that I have worked with are in agreement that for existing buildings, this would be acceptable:

"...overboard the existing ceiling or apply directly to the joists either one layer of 15mm fire rated plasterboard or two layers of 12.5mm fire rated plasterboard with overlapping edges, jointed and sealed, installed by a competent person."

[wee brian]

maybe you should look for evidence rather than just wait for it to run up and say hello.

fixings are important, 300mm centres as I recall. but check the manufacturers blurb.

[nearlythere]

Just looking at this again is it not the case that despite the sheets holding up to 60 mins exposure to fire the fixing of it may not. Conducted heat through the nail to the ceiling joist is bound to cause charring around the nail weakening its grip. Two sheets of plasterboard would be quite heavy.

[wee brian]

the two layers are (should be) fixed independantly.

Plasterboard, when it gets hot, begins to break down and release the water that was trapped in the gypsum when it crystalised (its very complicated but that's the ghist of it) this cools things down - a little bit.

As this happens the plaster gets crumbly and eventually falls to bits.

With multiple layers, this happens progressively. Assuming they were fixed properly........

[Dinnertime Dave]

Just looking at this again is it not the case that despite the sheets holding up to 60 mins exposure to fire the fixing of it may not. Conducted heat through the nail to the ceiling joist is bound to cause charring around the nail weakening its grip. Two sheets of plasterboard would be quite heavy.

My only real observation/question is doesn't it need to be screwed not nailed.

[Tom Sutton]

I think you fix plaster board with clout nails (Slate nails with large diameter head) screws wouldn't work, unless you are dry walling and you use none.

[nearlythere]

I think you fix plaster board with clout nails (Slate nails with large diameter head) screws wouldn't work, unless you are dry walling and you use none.

Modern way us to screw from a drill and magazine.

[wee brian]

nails were used by Noah to protect the structural elements of his Ark. these days we use purposed designed "drywall screws"

http://www.screwfix.com/p/phosphate-twin-thread-drywall-screws-3-5-x-38mm-pack-of-1000/12984

you can use clout nails but they are not recommended for fire protection because of the damage that hammers do to the board (etc.)