Fireproof hidden beam?

[DevilDamo]

No I don’t but was always under the impression the plasterboard ceiling along with a 22mm T&G (or similar) board on top is what provides the 30min fire resistance.

Building Control have provided me with a spec in the past about 2 layers of plasterboard or 1 layer of Fireline board to achieve the 30mins, so will question them on that.

On another job where a new ground floor partition forming a protected stair is required, the BCO has stated this should be constructed with 1 layer 12.5mm SoundBloc each side along with Rockwool between the studs, to comply with both Part B and Part E.

 

[DevilDamo]

I’ve just spoken to one of my BCO’s and my interpretation was correct so will not be changing my spec anytime soon. The fire resistance is calculated on the total build up (floor deck and joists included), similar to a u-value calculation. 12.5mm plasterboard on its own will not achieve 30mins. This is also backed up British Gypsum’s White Book.

@WMP When I did speak to my BCO, he asked why you couldn’t encase the beam itself with FireLine board and leave the rest as single layer plasterboard? So in effect you’d have a protected/encased beam within the floor zone.

 

[WMP]

I'll be using one sheet on fire line board across the whole ceiling to give 30mins. The BCO did give me an option of protecting the beam only but with joists running into both sides of the beam across a 5m span it's too time consuming and it's far easy just to use fire lined board all over.

 

[DevilDamo]

Yes, absolutely and would only be practical if the beam was running parallel with the joists.

 

[^woody^]

along with a 22mm T&G (or similar) board on top is what provides the 30min fire resistance.

You T&G above all the bedrooms. Cool

What does your numpty BCO say to that?

 

[Leofric]

I’ve just spoken to one of my BCO’s and my interpretation was correct so will not be changing my spec anytime soon. The fire resistance is calculated on the total build up (floor deck and joists included), similar to a u-value calculation. 12.5mm plasterboard on its own will not achieve 30mins.

Yes, the whole floor construction is considered ,but saying ' 12.5mm plasterboard on its own will not achieve 30mins.' is misleading.
12.5mm plasterboard and skim ceiling has been a standard specification for years for ceilings above ground floors in a 2 storey house. In more recent years 15mm Soundbloc with mineral wool quilt between joists became more common in my experience. A situation where 2 layers of plasterboard and 5mm skim is required (by NHBC ) is a ceiling over an integrated garage with a room above.
Any builders on here not used 12.5mm plasterboard and skim to ground floor ceilings
ps having said all that the BCO has requested Fireline board in this instance for protection to the steel beam and that is what the OP is going to use.

 

[Leofric]

No I don’t but was always under the impression the plasterboard ceiling along with a 22mm T&G (or similar) board on top is what provides the 30min fire resistance.

18mm t&g flooring grade chipboard on sw joists at 400mm crs is quite acceptable and common as first floor construction. The floor finish doesn't have to be 22mm thick t&g boarding.

 

[DevilDamo]

I never said plasterboard and skim would achieve 30mins. Both you and @^woody^ did...

half hour fire resistance required and would be provided by 12.5mm plasterboard and skim ceiling.

12.5mm plasterboard and skim will be 30 minutes.

I was only stating the ceiling treatment on its own will not achieve 30mins, which is probably what you both also meant but wasn’t stated hence why I referred to the complete build up.

 

[Leofric]

I'll be using one sheet on fire line board across the whole ceiling to give 30mins.

You better confirm the thickness .

 

[^woody^]

I was only stating the ceiling treatment on its own will not achieve 30mins,

But it will.

Again, what about bedroom ceilings?

 

[DevilDamo]

Where is the evidence to confirm 12.5mm plasterboard with a skim finish will achieve 30mins fire resistance?

A Bedroom ceiling with no habitable rooms above wouldn’t need to achieve 30mins fire resistance, so ceiling joists with plasterboard and skim under is fine.

 

[^woody^]

A Bedroom ceiling with no habitable rooms above wouldn’t need to achieve 30mins fire resistance, so ceiling joists with plasterboard and skim under is fine.

I see, let the fire go into the roof void and spread to other rooms below the roof void. Great design.

Its a good job the bedroom plasterboard ceiling is 30 minutes.

 

[DevilDamo]

Where is the evidence?

 

[^woody^]

Where is the evidence?

Millions of homes and buildings across the UK. Have a look when the lockdown is over.

 

[Leofric]

Millions of homes and buildings across the UK. Have a look when the lockdown is over.

Yes, standard specification been used for years.