Protecting UB from collapse in fire

[garyo]

The design for my new extension includes a UB that will support the first floor joists for two of the upstairs bedrooms.

The UB will be hidden within the floor/ceiling cavity (i.e. no down-stand) The joists will be supported in the usual way: on hangars that are fixed to two joists that are bolted in to the web of the bean.

To provide 30 minutes resistance I want to specify that it'll be encased in 30 minute fireboard, but how would that work in practice given that there'll be 20 joists fixed in to it. I could protect it from the underneath easily... but am I also expected to run the fireboard up the sides in between every joist entrypoint?

Thanks

 

[wessex101]

If it is above the ceiling which is already 30 min FR then that is fine, you do not need to further encase the beam.

 

[garyo]

If it is above the ceiling which is already 30 min FR then that is fine, you do not need to further encase the beam.

Okay - so double layer the whole ceiling in standard PB rather than worrying about the beams specifically. Makes sense... and probably not much in it time wise.

 

[^woody^]

No, single layer.

The ceiling is the barrier.

 

[garyo]

No, single layer.

The ceiling is the barrier.

Ah great. My misunderstanding. I thought one layer was only 15 mins.

 

[JohnD]

unless somebody cuts holes in it for downlighters.

 

[^woody^]

unless somebody cuts holes in it for downlighters.

Or to pass the wires through for a normal pendant of you want to play it by the book.

 

[Ian H]

If the room was 5mtrs wide would you fire board the whole ceiling or just centre a 1200mm board under the beam?

 

[^woody^]

If the room was 5mtrs wide would you fire board the whole ceiling or just centre a 1200mm board under the beam?

Would the fire just burn away under this 1200mm board?

The floor is just as much a structural component as a beam, so is treated the same - 30 minutes fire resisitance required. If a beam is within a floor then the floor provides the protection.

 

[Ian H]

No, I was just thinking why don't regs say to use fire board on all ceilings rather than just those with steel beams in?

Unless they do, in which case I did my lounge ceiling wrong.

 

[^woody^]

No, I was just thinking why don't regs say to use fire board on all ceilings rather than just those with steel beams in?

Unless they do, in which case I did my lounge ceiling wrong.

Because fire board is not necessary for beams or ceilings to achieve the required fire rating.

 

[Ian H]

What is it then? A single fire board or double normal board?

 

[freddiemercurystwin]

Have a gander at The White Book if you want to get picky, a single layer of 12mm PB + skim will give you 30mins depending on the depth of the joists and the floor finish for example.

 

[Ian H]

Cheers, I'll have a look when I'm on my laptop next.

 

[freddiemercurystwin]

It's an exciting read, with many fascinating diagrams and charts, perfect for insomniac's.