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Polystyrene insulation


MichaelG

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Hi all, I have seen a 1990s narrowboat that I was interested in but it is shown as having polystyrene insulation. From what I have read it is the least desirable type of insulation with sprayfoam, rockwool and slab materials such as kingspan being much better. I understand it can also shrink back over time causing cold spots and degrades electrical wire insulation if the wiring is in contact with it rather than in conduit. I just wondering if polystyrene is such a poor material I should disregard any boats shown as insulated with it. Would be interested to hear from peoples own experiences with it. 

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It was that was available when I built, but I too the precaution of having it fireproofed (I did test some scrap and the proofing was very effective). If you are looking at older boats, then I suspect that was all that was used. The roof and below the gunnels  have 2". The remaining sides. 1" Everything is covered with 1" oak planking, 1" ply and 9mm in the ceiling. The result is very toasty. So IMHO it's a matter of how thick, how well done  and what covers it. I certainly would not reject a boat just on a basis of it having polystyrene in its construction - unless of course you can see that the rest if the fitout is poor quality.

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I should think if a good job has been done, then polysytrene is ok.Trouble is, you won't neccessarily be able to tell. Sprayfoam  will likely avoid this problem to a certain extent.

If a liveaboard,polysytrene would be high up on my things to avoid, but I've only had minimal experience on a small area of our boat that used it.

I guess it depends on budget and intended use.

 

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My boat has expanded polystyrene insulation and its fine if properly fitted and of adequate thickness. In my view as good as spray foam of a similar thickness. Open joints in spray foam, "Kingspan", slab materials, rock wool or polystyrene will all aid condensation on the  inside of the hull under the insulation. In fact rockwool types may well be vapour permeable so would need a vapour barrier.

The down side of Polystyrene is that you have to keep electrical cables away from it but a run of duct tape easily sorts that.

This would not stop me buying a boat I though was ideal.

PS So called self extinguishing Polystyrene has been in use at least since 1991.

Edited by Tony Brooks
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Polystyrene, in my opinion, is not as good as sprayfoam but, so long as it is installed reasonably well its OK. The problems of condensation arise when there are voids, have a look at the lining, any damp bits? signs of water damage? staining? If so then there are cold bits and condensation behind or on top of the lining. It does not get soaked like fibreglass wool but if it burns it is a menace, Personally if the boat was free of condensation damage (And that is quite a tall order for any boat if you look hard enough) I would be happy with it. Others may disagree.

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Our latest boat has polystyrene insulation, probably installed well over 25 years ago.

No attempt had been made to segregate electrical cables from it.

Wherever I have had panels down and exposed the cabling, the cables have embedded themselves into the insulation, by what appears to be a chemical process, but if you pull them out of the grooves so formed, those cables appear in "as new" condition, with no visible damage whatsoever.

So by my own observation, polystyrene insulation doesn't actually damage electrical cables, although the reverse isn't true.  I think this potential problem is, in some cases at least, overstated.

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I have lived on a boat with Polystyrene insulation for almost 10 years. I would have preferred sprayfoam but we really liked this boat and so chose it over other boats that did have sprayfoam. I suspect poly is not as effective as sorayfoam; I note that some boaters walk round in underwear in winter whilst we might even wear a jumper in the evening when its really cold :D. Its 18 degrees in here right now (about right) and -2.6 outside. I do suspect that getting too hot in summer is the bigger issue. Boats have ventilation and windows (or ideally portholes) so loose heat in various ways, so going for ultimate insulation is a bit of diminishing returns.

The things that appear good to me about sprayfoam are that its well stuck on so minimal chance of voids and condensation.

I have spoken to two experienced boat welders who both said they would always prefer to work on a polystyrene lined boat.

............Dave 

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Just now, dmr said:

I have spoken to two experienced boat welders who both said they would always prefer to work on a polystyrene lined boat.

Unfortunately though, if it is the kind of slab polystyrene we have in Flamingo, where welding has been done on the hull, whilst it doesn't catch fire, it melts to a fraction of it's original thickness.

I removed a load from our hull sides just two days ago, and whilst it was 2" thick over most of it, the bottom parts had been reduced to a small fraction of an inch by welding works on the hull.

Clearly those areas were now nor providing the insulation they should have been.  I don't think hull welding is compatible with this type of insulation.

We are slowly working through the boat replacing Polystyrene with Rockwool.  Typically can put in up to twice the thickness in Rockwool than the Polystyrene we are removing.

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26 minutes ago, alan_fincher said:

Unfortunately though, if it is the kind of slab polystyrene we have in Flamingo, where welding has been done on the hull, whilst it doesn't catch fire, it melts to a fraction of it's original thickness.

I removed a load from our hull sides just two days ago, and whilst it was 2" thick over most of it, the bottom parts had been reduced to a small fraction of an inch by welding works on the hull.

Clearly those areas were now nor providing the insulation they should have been.  I don't think hull welding is compatible with this type of insulation.

We are slowly working through the boat replacing Polystyrene with Rockwool.  Typically can put in up to twice the thickness in Rockwool than the Polystyrene we are removing.

I think their idea was that for a local repair (chimney collar, skin fitting etc) you can get your hand in behind the lining and break the poly away, but for sprayfoam would probably need to remove some lining to cut away the foam.

................Dave

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11 hours ago, alan_fincher said:

Our latest boat has polystyrene insulation, probably installed well over 25 years ago.

No attempt had been made to segregate electrical cables from it.

Wherever I have had panels down and exposed the cabling, the cables have embedded themselves into the insulation, by what appears to be a chemical process, but if you pull them out of the grooves so formed, those cables appear in "as new" condition, with no visible damage whatsoever.

So by my own observation, polystyrene insulation doesn't actually damage electrical cables, although the reverse isn't true.  I think this potential problem is, in some cases at least, overstated.

Those are my observations as well but the BSS went on about it at one time. I suspect it depends upon the plasticisers used in the cable. Perhaps Dr B & Duck can comment.

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3 hours ago, Tony Brooks said:

Those are my observations as well but the BSS went on about it at one time. I suspect it depends upon the plasticisers used in the cable. Perhaps Dr B & Duck can comment.

C'mon @Dr Bob 's duck, you' re made of plastic, please comment (and no silly eco-fan jokes please) :)

Edited by rusty69
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3 hours ago, Tony Brooks said:

Those are my observations as well but the BSS went on about it at one time. I suspect it depends upon the plasticisers used in the cable. Perhaps Dr B & Duck can comment.

Spot on Tony. It's all about the Plasticisers.

The duck isn't very good on Plasticisers. He's made of poyethylene.

Most electrical cables in the UK are sheathed with PVC and to make them bendy and supple the PVC contains a far whack of plasticiser....without that it would be brittle and prone to cracking. Typical plasticisers were made from phthalates or other fatty acid type compounds. When these cables are laid in polystyrene foam, a couple of things CAN (but not always) happen. Firstly the plasticiser can migrate out (or leech out) into the polystyrene foam and collapse it. Other than this the plasticiser will not really 'damage' the foam or the plastic. I think this is the effect Alan is seeing on his boat with the wire forcing itself into the foam. The second effect is that if all the plasticiser migrates out, the PVC sheathing is then left in a brittle state and can therefore crack if put under stress. Typically the brittle PVC will still have good insulation properties but cracks could lead to short circuits and potential for fires. You can see this migration as the outside of the wire becomes sticky or the colour of the wire sheathing changes.

How dangerous is this? I can remember in the 80's and 90's incidents of house fires caused by failed PVC cables ie cracking and shorting out,  but these were not common. In the 90's the PVC manufacturers started to switch to plasticisers that did not 'react' with PS foam so by 2000 the problem was much reduced (not convinced it has gone away though). Many polymer experts see PVC as the devil's polymer (incl me). Taking my 'expert' hat off, If I had a narrowboat with PS foam insulation, I would not be worried as long as I had 2 or 3 smoke alarms (that I knew worked....try the bacon test) and a few CO monitors. This migration of plasticiser doesnt always happen and not usually to the extent the cable sheathing is totally brittle........and if it did the wire should still be insulated.

While we are on about insulation foam and at the risk of being verbose (as normal), it might be useful to throw in a few more thoughts.

Polystyrene is a plastic, so melts into a low viscosity liquid (as runny as water) if heated to over 200°C. This explains why Alan saw his foam disappear in areas that had been welded. In a fire, PS foam will collapse and melt and run down to the floor. This to me is a big fire risk and although some PS foam was sold as fire retardant (by adding fire retardant additives), it will still burn and be a source of fuel in a fire (in a similar way to the PE foam in the Grenfil fire disaster). Don't weld if you have PS foam behind it. At best it will melt the foam and at worst could start a fire in itself. On the other hand, polyurethane foam ie the yellow stuff that I think is being described here as 'sprayfoam' is a thermoset and is crosslinked so cannot melt. It will be far better in the event of a fire. Yes it will burn a bit but not as much as PS foam. It should be ok if you weld near it.

Having said all that, by the time the insulation started to burn in a fire in a narrowboat, I would suspect the boat is well alight, has been burning for a while and the occupants have got off (2 or 3 bacon tested smoke alarms). There is usually so much wood on board that the insulation is not going to make that much difference.

If I was re-insulating a boat now, I would look at rockwool or mineral fibres and stuff it into all nooks and crannies. (….thats a non expert view).

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Thanks Dr Bob for detailed thoughts.

I must admit that it crossed my mind that if plasticiser leaches from cable insulation to eat into the polystyrene foam, that has to mean a chemical change in where it has leaked from.

All I can say was that in our case, the presumed reduction of the plasticiser in the cable insulation didn't appear to have caused any degradation of it at all.  You could freely bend it as if it were new, and no brittleness or cracking was present.

What I didn't say is that most of the cabling was in domestic "twin and earth" grey cabling, with solid drawn copper rather than multi-stranded conductors, (not recommended by the BSS, but only actually outlawed in "non private" boats).  I'm not sure, for example, if proper low voltage "twin wall" cabling had been used whether the results would have been the same.

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Expanded polystyrene gives off large quantities of toxic smoke when it burns (and it does burn, even if it eventually 'self-extinguishes').  

Unless I was dead set on a particular boat for lots of other reasons, I'd avoid it if at all possible.

Just my opinion.

(Our boat is insulated with mineral fibre slab/blanket)

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1 hour ago, Machpoint005 said:

Expanded polystyrene gives off large quantities of toxic smoke when it burns (and it does burn, even if it eventually 'self-extinguishes').  

Unless I was dead set on a particular boat for lots of other reasons, I'd avoid it if at all possible.

Just my opinion.

(Our boat is insulated with mineral fibre slab/blanket)

Which I would say the same about your chosen materials as you said about expanded polystyrene.

Just shows there are probably no wrong answers as long as its fitted properly.

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On ‎28‎/‎02‎/‎2018 at 17:35, Tony Brooks said:

My boat has expanded polystyrene insulation and its fine if properly fitted and of adequate thickness. In my view as good as spray foam of a similar thickness.

I'm afraid that just not true at all. Look at any study comparing the R values of expanded polystyrene (EPS) vs expanded polyurethane (EPU) sprayfoam & rigid board insulation of equivalent thicknesses, and you will find that the EPU always comes out on top.

Edited by blackrose
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18 hours ago, Tony Brooks said:

Which I would say the same about your chosen materials as you said about expanded polystyrene.

In point of fact, mineral fibre is incombustible, unlike polystyrene. The binding resin flashes off in a fire and there is very little of it anyway. 

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2 hours ago, Machpoint005 said:

In point of fact, mineral fibre is incombustible, unlike polystyrene. The binding resin flashes off in a fire and there is very little of it anyway. 

I never said it was not combustible but that I am as opposed to any fibre type insulation as you are to expanded polystyrene. Over the lift of a boat I feel condensation is far more of a danger that fire and in any case, as someone else said, by the time the polystyrene caught fire the boat would be very well alight and if you were going to get out you would have done before the polystyrene fumes would become an issue.

I have had welding done after testing my polystyrene and finding it to be "self extinguishing". Unless you apply prolonged heat over a largish area the polystyrene starts to burn, runs away from the flame and then goes out.  All that happened on the welds was it just melted away.

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1 hour ago, Tony Brooks said:

Unless you apply prolonged heat over a largish area

...such as would be the case in an out-of-control fire, but not with a farty little blowlamp or a welding electrode. A high temperature doesn't mean there is lots of heat!

Where's our resident firefighter when we need him?

I don't see condensation as a 'danger' but I admit it could be an inconvenience or cause a need for additional expenditure. Being poisoned in your bed, on the other hand, is a danger.

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On 28/02/2018 at 19:51, alan_fincher said:

Our latest boat has polystyrene insulation, probably installed well over 25 years ago.

No attempt had been made to segregate electrical cables from it.

Wherever I have had panels down and exposed the cabling, the cables have embedded themselves into the insulation, by what appears to be a chemical process, but if you pull them out of the grooves so formed, those cables appear in "as new" condition, with no visible damage whatsoever.

So by my own observation, polystyrene insulation doesn't actually damage electrical cables, although the reverse isn't true.  I think this potential problem is, in some cases at least, overstated.

That is what I have found over the years

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10 hours ago, Tony Brooks said:

Over the lift of a boat I feel condensation is far more of a danger that fire

 

I'm not sure what you mean here Tony. Is there a danger from condensation worse than fire?

Or do you mean condensation is more likely to destroy a steel boat in the long term than a fire?

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The later Mike and help engender more condensation and damp within the living area.

When assessing risk I was taught to consider both the likelihood of an even and the severity of the effects of that event. The two events (burning insulation and the defects from condensation, especially if trapped in fibres next to the steel hull) are at opposite ends of both considerations. Fire - very unlikely, condensation - very likely. Fire - could be lethal, condensation - no short tern danger at all unless you have lung problems.

My conclusion, and others can come to a valid different conclusion, is that the risk associated with "self extinguishing" expanded polysyllable (that I have seen put themselves out) is all but negligible for the majority of boaters so I prefer it to fibre products that I have seen to have adsorbed and held quantities of water and that are not vapour tight.

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A lot of what's been said is true and polystyrene will burn very well in a big fire so be extra vigilant if your boat is so insulated, it also is only a out half as good as celotex ie when insulting houses we would  need almost twice the thickness of polystyrene to reach the same value as celotex.

Neil.

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