Fire barrier tape for timber cladding cavity

[markharro]

Having just realised that the architect has drawn in about 125 linear metres of this stuff I have fallen off my seat computing the cost! Its £1000s just for this tiny element. Can anyone point me to a source to obtain this product at a more modest price? thanks

[Kelvin]

It’s dear stuff. We need about 70m so about £1700 ex VAT using the stuff the timber cladding supplier recommended or £752 using an intumescent strip. 

Edited March 16, 2023 by Kelvin

[markharro]

So I can see @Kelvin- can you link to the product you are using if possible?

[Bramco]

11 minutes ago, markharro said:

I have fallen off my seat computing the cost! Its £1000s just for this tiny element.

Welcome to the club!!!

 

It's worth asking the architect if all of it is really necessary - can it be pared down to the absolute minimum.  There's  tendency with this stuff as we found out, to massively over-specify it. It's timber frame must go everywhere surely!!!!

 

We got ours down to a reasonably sensible minimum - but the first ideas were crazy.

 

Simon

[Kelvin]

https://securonorway.com/advantages-of-the-firebreather-cavity-barrier/

 

I’ve not decided if I am definitely using this product or not but it’s what’s been recommended 

Edited March 16, 2023 by Kelvin

[Mr Punter]

I suspect if it is clad in non-fire treated timber, a cavity barrier won't do a great deal.

[jamieled]

Yep, it's expensive. We used stuff from envirograf.

 

You probably only need the expensive stuff where you need the cavity ventilated. Use solid timber elsewhere (like corners).

[markharro]

1 hour ago, Kelvin said:

https://securonorway.com/advantages-of-the-firebreather-cavity-barrier/

 

I’ve not decided if I am definitely using this product or not but it’s what’s been recommended 

That the stuff I saw first - its about £30 a metre!!

[saveasteading]

I have seen it overspecified. If there is no need for through ventilation, then a solid barrier is OK. That can even be wood, as it is to stop spread of flame. 

Likewise any vertical closures don't have to be fancy.

 

The cost can also be reduced by partial filling of a cavity with something else, then a thinner cheaper intumescent product.

 

You might have to convince your architect and the bco.

Go back to the basic rule in the building regs. 

Indoors, roll up rockwool for vertical closures.

[ETC]

@markharro

Where are the cavity barriers specified to be located on your build?

[markharro]

Hi @ETC generally just below roof lines and top and bottom of window openings; top of GF door; and midline between GF and FF

[ETC]

Granny and sucking eggs.

 

Speak to your BCO about the extent of cavity barriers required. Normally in a masonry built house they are required to the perimeter of all openings and at the top of all cavity walls

 

In a timber framed house they are required in similar locations although your timber frame supplier may also ask you to install them horizontally at an intermediate floor level.

 

Where an external wall is timber cladding fixed to a structural insulated timber frame the requirement for cavity barriers should be similar as well as the requirement for FR of the wall depending on the distance of the wall from a boundary or a notional boundary.

 

Check out ADB and speak to your BCO. There are specific locations that the BCO will require cavity barriers.

[saveasteading]

As etc shows, there is no intumescent material stated in this indicative list. It is only required in circumstances where a gap is required (round a door or to close  a gap, usually ventilation) or for paint.

It is easy to spec intumescent, and there is a bit more certainty that the cavity will be closed.

But the priority in fire protection is stopping spread, and a fully closed cavity is better at that, when appropriate.

[ETC]

Generally a cavity barrier can be calcium silicate board, timber, steel or sleeved mineral wool or mineral wool slab. The easiest to install around windows and doors and at the eaves and verge is calcium silicate board. In a timber frame building the easiest is timber around windows and doors and sleeved mineral wool at the top of all cavity walls.

 

However, where there is a called external wall the difficulty will be maintaining a ventilated and drained cavity and installing a cavity barrier. The only way I can see this being done is to vent and drain above and below all horizontal cavity barriers. I have seen intumescent barriers specified for cladded walls but they technically are not listed as a cavity barrier in ADB and you will be relying on the intumescent properties of the product to activate once a fire starts.

[saveasteading]

51 minutes ago, ETC said:

you will be relying on the intumescent properties of the product to activate once a fire starts.

Ie only when fire is close and hot enough to start the expansion. If the gap is already closed, the fire is less likely to go that route.

[ETC]

In a situation where the gap cavity cannot be closed - when timber cladding needs a ventilated and drained cavity an intumescent strip may be acceptable - ie at the bottom of a rain screen timber clad wall. Again depends on how the construction is detailed.