fire stops in cavities

[elmsoft]

I'm building a single story flat roof extension , timber frame and block with the usual 50mm cavity. The architect has specified horizontal cavicheck fire stops at head and ground level. I'm curious what the fire stops would stop a fire from doing. ie where would the fire be going from and to that they would stop it going?
Just curious.

 

[^woody^]

Not required unless these are flats, or its part of a terrace.

The barriers would be part of the compartmentation to stop fire spread

 

[JohnD]

Remembering the stories we've recently heard about Grenfell, I'm quite interested in taking care to improve fire and smoke safety. Easier done during building/renovation than patching up later.

Voids and cavities, in timber frames, can behave badly in fires.

What are these cavity checks made of?

 

[Nakajo]

Probably a copy-and-paste error.

 

[elmsoft]

Probably a copy-and-paste error.

TBH that did cross my mind.
But fire is nasty stuff and we have had a good lesson on unforeseen consequences.

 

[elmsoft]

Remembering the stories we've recently heard about Grenfell, I'm quite interested in taking care to improve fire and smoke safety. Easier done during building/renovation than patching up later.

Voids and cavities, in timber frames, can behave badly in fires.

What are these cavity checks made of?

Take your point of course. Still it is difficult to see how a fire could spread more easily through the cavity than in the room itself.

Don't know the material but CAVI230 claim of course they resist fire for 230 minutes. Which is longer than the OSB sheathing would last.

 

[wessex101]

I'm struggling to think of any circumstance where a horizontal cavity barrier would be required at ground level? Maybe if you were building on top of a volcano?

 

[Nakajo]

Yes, that would be my principal concern in such a scenario.

 

[elmsoft]

I'm struggling to think of any circumstance where a horizontal cavity barrier would be required at ground level? Maybe if you were building on top of a volcano?

Well there is that! Maybe the architect knows something.

 

[JohnD]

I was thinking a wiring fault in a wall-mounted socket would be a more likely cause of a fire in the framing.

We don't like to think of a slow burn catching hold, unseen behind cladding, especially when some insulation is not as fire resistant as we had thought.

Off topic, I am increasingly attracted to Foamglas, which doesn't burn but is hard to find in the UK.

 

[Nakajo]

Rockwool doesn't burn. It's everywhere.

 

[^woody^]

I was thinking a wiring fault in a wall-mounted socket would be a more likely cause of a fire in the framing

Then the whole frame will do go up and no cavity barrier will stop it.

 

[JohnD]

but won't it delay the roof going up?

 

[chappers]

. Still it is difficult to see how a fire could spread more easily through the cavity than in the room itself.

Chimney effect, probably a contributing factor to Grenfell

Don't know the material but CAVI230 claim of course they resist fire for 230 minutes. Which is longer than the OSB sheathing would last.

I wouldn't be so sure especially with a flames burning along the plane of the surface. again its about the rapid spread of fire in a cavity between floors or adjacent dwellings.

As woody says its about compartmentalisation containing the fire rather than stopping it getting in, and as he also said it isn't a requirement in this scenario

 

[Nakajo]

Grenfell seems like a very slightly different scenario in one or two respects