Closing cavities

[Roundtuit]

Hi.  I'm about to start fitting fire-rated cavity closers (Kingspan Thermabate) around window and door openings - 50'ish mm cavity between timber frame and brick outer skin.  They have a flange which will nail to the frame to hold them in place, and I was planning to foam them in with Soudafoam to seal the gaps.  The question is, is a B2 fire rated foam OK for this job, or does it need to be B1?

 

cheers

[Dudda]

Have you bought the Kingspan Thermabate? They're a bit expensive and messy for what they do. Most people just make their own cavity closers from ply and insulation, etc.

[TerryE]

We just used the same sort that MBC used.  We have an 15mm ply (IIRC) liner which acts as a sleeve within the frame window opening to carry the front of the  window to the back of the cavity.  The closer is essentially strips of rock-wool with the reqired depth in a polythene tube which you staple around the window.

[Barney12]

Watching this topic with interest as we have an almost identical detail (Timber frame, 50mm cavity, 100mm Blockwork, Render) I'd looked at the Thermabate and went slightly cold when I realised the cost.

[Roundtuit]

14 minutes ago, Dudda said:

Have you bought the Kingspan Thermabate? They're a bit expensive and messy for what they do. Most people just make their own cavity closers from ply and insulation, etc.

Yes, unfortunately - bullet bitten and thermabate delivered... 

The frame erectors battened around the outside of the windows onto the frame as a closer/fire break, but I took them all off before the brick skin went up, as I want a better solution from a cold-bridge point of view.  I did consider a combination of using the 'fire stop sausage' that Terry describes, combined with PIR insulation or timber or something, but decided that by the time I'd messed about with that and created something which may or may not be compliant, I might as well get the Thermabate (ended up a £3.75/m delivered if anyone wants a benchmark). 

[Barney12]

1 minute ago, TerryE said:

We just used the same sort that MBC used.  We have an 15mm ply (IIRC) liner which acts as a sleeve within the frame window opening to carry the front of the  window to the back of the cavity.  The closer is essentially strips of rock-wool with the reqired depth in a polythene tube which you staple around the window.

 

Our windows are sitting flush with the exterior of the frame. This is due to the weight of some our (large windows).

The Kingspan closers do make for a simple install due to their flanged design but I guess it could still be done with a timber batten (say 50mm x 50mm) screwed to the outside of the frame and then the rockwool in polythene stapled to that. But, that provides no fire resistance?

[MrP]

Any mineral or rock wool, including the sausages wrapped in polythene, under suitable compression (crucial) will provide fire protection and is what is widely used along with a 2x2 solid timber for closing cavity.

Be generally warned of any so called 'fire rated' b1 & b2 type expanding foams - these are not fire rated. I did a bit of research on this stuff for a previous company and they are only tested for surface spread of flame and for use as a gap filler in conjunction with an intumescent mastic. Bit naughty of them really to have fire ratings plastered all over the fron of the cans.