EWI DIY

[Ed Davies]

1 hour ago, MikeGrahamT21 said:

What would you do for fire breaks in larsen truss?

 

The couple of houses I looked at at various times were single storey or 1.5 storey with no windows above ground floor in the end gables so I'm not sure if that would have been an issue. Timber cladding crossing multiple stories is normal, isn't it, so maybe it'd just need a break in the timber studs. Not sure. Maybe a block of PIR between?

[ADLIan]

Sorry but PIR will not create a cavity barrier (look at Grenfell Tower!) - needs to be mineral wool.

[MikeGrahamT21]

On 06/11/2018 at 11:49, Onoff said:

 

Rockwool say here than their slabs specific to EWI have a varying density; a soft inner face to take up irregularities in the wall face and a harder outer to render onto...apparently!

 

https://cdn01.rockwool.co.uk/siteassets/rw-uk/literature-downloads/datasheets/ewi-slab.pdf?f=20180917035840

 

I like the fact they're Euroclass A1 - non combustible.

Yeah thats right, i've had a sample from EWI pro of both the EPS and Rockwool systems, and when complete there is no different to toughness. The slabs are called duo-density. Yes the non-combustability is appealing, though i tried to set fire to EPS system too, and it just melted, PIR on the other hand does set alight and burn, until it carbonises.

[ADLIan]

EPS will initially melt away from a heat source but ultimately it will burn fiercely with plenty of black smoke typical of most petrochemical based products. Try to set fire to a sheet positioned horizontally then do the same with sheet held vertically - the latter will give a very different outcome!

[Jeremy Harris]

1 hour ago, ADLIan said:

EPS will initially melt away from a heat source but ultimately it will burn fiercely with plenty of black smoke typical of most petrochemical based products. Try to set fire to a sheet positioned horizontally then do the same with sheet held vertically - the latter will give a very different outcome!

 

Very true!  Just do a web search on "facade fires" and you'll find a lot of really serious EWI fires, some absolutely terrifying in the way that they drip a curtain of burning droplets of molten polystyrene over openings like windows and fire exit doors.  This is an old one, but there are others much the same:

 

 

[gravelld]

On 06/11/2018 at 11:17, MikeGrahamT21 said:

What would you do for fire breaks in larsen truss? With EPS you have to have a rockwool section between floors

 

I think this is only for buildings over 18m in height... as far as the regs go anyway. I guess you could do it anyway if you wanted to be sure, but the systems manufacturers will, I guess, tell you to sling your hook (which might be no bad thing).

[Jeremy Harris]

With the Larsen Truss EWI option you normally use rockwool, so the fire break issue is reduced in importance, as only the external timber ladder frame supports are flammable, and if well-sealed with render board fitted externally air won't be able to get in easily.  All openings would be surrounded by the render board (MgO₂ or similar) so that should constitute an adequate level of fire resistance and resistance to the spread of fire.

[Onoff]

Has anyone ever deliberately smacked a hole in a pir/eps EWI'd wall and torched it?

[Jeremy Harris]

1 hour ago, Onoff said:

Has anyone ever deliberately smacked a hole in a pir/eps EWI'd wall and torched it?

 

Birds have made holes through the render and nested inside the EPS in some places, and there's been at least one case where a bin was set on fire which then managed to set fire to the EWI - not sure if a hole was made first.

[Onoff]

6 minutes ago, JSHarris said:

 

Birds have made holes through the render and nested inside the EPS in some places, and there's been at least one case where a bin was set on fire which then managed to set fire to the EWI - not sure if a hole was made first.

 

I can imagine a fierce fire cracking any render. 

[Mackers]

You could Larsen Truss and blow in cellulose, its fire rated??

[Jeremy Harris]

8 hours ago, Mackers said:

You could Larsen Truss and blow in cellulose, its fire rated??

 

It's treated with borax to be fire retardant, but some of its resistance to fire comes from it being packed in tightly to a sealed cavity, so air can't get in at a fast enough rate to allow it to sustain combustion.  I tested some with a blow torch and found that when compressed into a tight ball it tended to char and burn whilst the flame was playing on it, but self-extinguished when the flame was removed.  If spread out on a surface it would sometimes try to burn slowly once ignited, but still wasn't easy to ignite. 

 

My concern with using it as EWI would be damp penetration.  Unlike rockwool, blown cellulose will support fungal growth, even when treated with borax, I believe.

[Onoff]

8 minutes ago, JSHarris said:

My concern with using it as EWI would be damp penetration.  Unlike rockwool, blown cellulose will support fungal growth, even when treated with borax, I believe.

 

So can you safely bridge the DPC with Rockwool? As in if taking any retro fit EWI down past it (the DPC) to help with cold bridging at floor level.

 

 

[PeterW]

3 minutes ago, Onoff said:

 

So can you safely bridge the DPC with Rockwool? As in if taking any retro fit EWI down past it (the DPC) to help with cold bridging at floor level.

 

 

 

Plenty on this but it’s pretty much you can bridge it regardless of what you use as none of them will promote damp

[Jeremy Harris]

13 minutes ago, Onoff said:

 

So can you safely bridge the DPC with Rockwool? As in if taking any retro fit EWI down past it (the DPC) to help with cold bridging at floor level.

 

 

 

Yes, but as above I'd have concerns with using blown cellulose, as that can hold moisture well and will probably sustain fungal growth.  Rockwool, EPS, XPS etc are all fine when bridging the DPC, AFAIK.

[Jeremy Harris]

I decided to do a bit of digging around to see if I could find some reasonably well documented evidence to support the view that blown cellulose insulation was reasonably fire resistant when used in a timber frame structure.  This video is old, but seems to show that it is significantly more fire resistant than rockwool/fibreglass, something I found a bit surprising:

 

 

[MarkyP]

20 hours ago, Onoff said:

Has anyone ever deliberately smacked a hole in a pir/eps EWI'd wall and torched it?

I don't think it would result in a fire. The EPS would perhaps burn locally where exposed but would struggle to burn behind the render and form the necessary "chimney" required for a facade fire to really get going. I think most facade fires are where there's exposed flammable material (e.g. timber cladding) or where there is a cladding with ventilated void over flammable material creating a chimney effect which we know from recent history lethal once it gets going.

 

I sleep very well at night with my rendered EPS EWI, I think there's negligible fire risk over the previous rendered blockwork. The most likely scenario (still very remote) is that the fire would be started inside the house, this would have to burn through a window and through the render and form a chimney. I think by that point the fire service might have put it out, or the rest of the house would be so ablaze that the EPS would make no difference.

 

 

 

 

[Jeremy Harris]

4 minutes ago, MarkyP said:

I don't think it would result in a fire. The EPS would perhaps burn locally where exposed but would struggle to burn behind the render and form the necessary "chimney" required for a facade fire to really get going. I think most facade fires are where there's exposed flammable material (e.g. timber cladding) or where there is a cladding with ventilated void over flammable material creating a chimney effect which we know from recent history lethal once it gets going.

 

I sleep very well at night with my rendered EPS EWI, I think there's negligible fire risk over the previous rendered blockwork. The most likely scenario (still very remote) is that the fire would be started inside the house, this would have to burn through a window and through the render and form a chimney. I think by that point the fire service might have put it out, or the rest of the house would be so ablaze that the EPS would make no difference.

 

 

 

A search of Youtube with the term "facade fire" will show a few videos of EPS burning quite happily behind rendered walls.  I posted a video showing this earlier in this thread.  The video of birds nesting in a German building's EPS EWI, having pecked a hole in the render, is interesting, too:

 

 

[MarkyP]

I don't doubt given enough heat and exposure to fire my EWI would eventually burn. But it's a single storey, the EPS is to the side rather than over any windows, the soffits would be more at risk. By the time my EPS was exposed to enough heat and fire the house would have to be well and truly alight internally. But the video does highlight the risk of very large vertical expanses of EWI or cladding as a major risk factor in the spread of fire. Worth noting the video appears to have been edited, it's rather unclear just how quickly the fire spread.

 

I haven't seen any birds pecking my EWI so far ?

 

 

Edited November 8, 2018 by MarkyP

[Jeremy Harris]

FWIW I don't think there is a particular problem with rendered EWI on one or two storey houses, as long as there are fire resistant barriers above every opening, to prevent molten EPS from dripping down over what might be a fire escape route.  I'm not sure I'd rely on the render for that barrier, but it should be easy enough to fix a bit of cement board above every opening as a barrier and render over that.

[Onoff]

Talking ballpark here but my external walls are an odd mixture. There's brick & block with a nom uninsulated 60mm cavity, often a mix of brick and block in the same leaf judging by what I found doing the bathroom. I think then I have a 9" block section and also a 9" brick section too. Whatever the wall construction it's all externally rendered. Not sure what's the worst but imagine one of the 9" solid walls. 

 

What nominal thickness of Rockwool should I aim for on a retro fit and what U value should I aim for?

 

Any tables about with what U values for what wall make up?

 

Monkey see monkey do here!

 

Cheers

 

 

[gravelld]

11 hours ago, Onoff said:

So can you safely bridge the DPC with Rockwool?

 

Personally I'm not so sure on that. You're relying on it not getting wet *at all*. Would use EPS or XPS myself (almost all the systems manufacturers use the latter, although the evidence for that is a little scant).

[Oz07]

Do future buyers look for any kind of warranty with EWI?

[Onoff]

6 minutes ago, Oz07 said:

Do future buyers look for any kind of warranty with EWI?

 

Not if they do it themselves!

 

Now...where's my trowel & hawk...

[Mackers]

Blown cellulose is used widely in America in timber framed buildings. I must do some more research