Structural Insulated panels-structural performance in fires

[Pip]

Anybody have experience in actual fires with this building system?Whilst having to believe that these boards will stand up to fire (when appropriately protected by plasterboard etc) long enough to allow people to escape, I feel a little uneasy about how much 'property' protection is afforded.A client is about to build nearly 50 premises of up to 2 storeys using this system(which I know has been about for a while now) and I have a concern over internal fire spread when using polystyrene insulation material in a board that provides the structural integrity of the building.As I mention, M.O.E. is not the issue, but credibility, if the building will likely to require complete rebuild after a serious fire.

[Ashley Wood]

Pip, can you give more detail on the type of panel you refer to?

Ashley

[John Webb]

There is a brief article in the latest 'Fire Prevention and FE Journal' about the use of these panels. Apparently there is a 'Engineered Panels in Construction' website www.epic.uk.com from which a publication "Insulated Panels and the RR(FS)O" can be down-loaded. I have not looked at this myself.

BRE's 'Fire and Risk Sciences' division has done quite a bit of work in recent years for HO, Building Regs and ODPM etc. including both visiting fires and carrying out fire tests. Their website www.bre.co.uk may be worth a look also.

A number of articles on the problems and use of these panels has appeared in the FP & FE Journal in recent years as well and if you have access to these it would be worth having a look through them

[ian gough]

Pip: you are joking - aren't you? Be very careful!

[Gary Howe]

It would be worth contacting the Insurer of these buildings, as they will be very interested in providing input/advice into the nature and type of combustible materials that are going to be present in the construction of these buildings.

If you were to get internal fire spread within a building of this type of construction, you might as well assume a total loss.

[Peter R]

The first thing to know is what type of structural insulated panels  [SIPS] is proposed. The most common core materials used [polystyrene, polyurethane] behave differently particularity when it comes to fire and structural strength.

The Engineered Panels in Construction site focuses on non-structural steel faced panels used for cladding and roofing and the data is not directly relevant to SIPS.

There is over 50 years experience of SIPS construction in Europe and longer in North America. Fire has not been highlighted as a particular risk with this form of construction. In fact many so called conventional houses are safely built using large amounts combustible materials such as wood, plastic foam insulation, upvc etc.

The normal SIPS internal wall has plasterboard over the SIPS inner face which is generally 15mm OSB/3 board a very high quality material. This delivers class O surface spread of flame plus 30 minutes fire resistance as required by AD B of the Building Regulations. There are also constructions that deliver 60 minutes plus for separating and compartmentation walls. Reputable SIPS manufacturers will have tested these constructions to BS476 Part 22 with realistic axial loading.

Comparing this to a conventional internal  timberframe construction, the plasterboard would be the same, there is likely to be a plastic vapour barrier under the plasterboard and there is no OSB protecting possibly combustible plastic foam insulation between the timber studs.

With regard to fire I would suggest the SIPS construction is likely to be safer.

I would suggest you ensure the SIPS come from a manufacturer with BBA approval and the recommended construction details are followed. You could also look for the LPS 2020 standard developed by BRE Certification - at the request of insurers, mortgage lenders, regulators and manufacturers.

If you use an independently certified product there is no problem getting a warranty from NHBC, Zurich etc which I suggest means they do not see extra risk.

In the event of a fire there could be advantages in a SIPS house. High level of airtighness would delay spread of smoke and high structural strenth would limit danger of progressive colapse.

[ian gough]

Peter,

1) He said it was to be polystyrene - the worst of the lot! There are, of course, other insulation materials that would perhaps be more suitable: PIR or Mineral Fibre for example.

2) Cladding and roofing has been much less of a problem than internal panels in real fire experiences.

3) How could you fire risk assess a building where the structure is highly combustible and then say: "it is 'normal' risk"? Therefore Pip, means of escape may well be a problem for you.

4) How can you fight a fire in such a panel? And how can B5 of the Building Regs be satisfied if firefighters refuse to enter such a building (which is a likely scenario)?

I could go on....

[Peter R]

Ian,

In most fire the problem is knowing the construction of a dwelling. From the outside or inside a SIPS house looks just like, timberframe, brick and block, steelframe  etc.

I cannot see firefighters refusing to enter a dwelling just in case it might be SIPS construction.

In the event of a fire that penetrates 15mm of plasterboard, 15mm of OSB and is then sufficient to sustain burning of the polyurethane SIPS insulation, I would say it is more an issue of containment and not firefighting.  If a fire in any type of house construction involves its combustible cavity or roof insulation the intensity is most likely to involve total write off.

When it comes to choice of building materials my philosophy is:

Most materials and components are in themselves satisfactory and most faults are due to them not being used correctly.
Similarly, most materials are fit for a purpose - but they are not always fit for the purpose for which they are used.
No product is "best" for every application. Simply that some products are superior to others in specific applications.

[ian gough]

Peter,

The original post does not make it clear that we are only talking about single private dwellings - but maybe we are? I have to say, my experience and knowledge comes more from the industrial/commercial use of panels although I've expected problems to arise in the domestic/residential sector with increasing use.  

That being said, my experience of fires in some of the more modern timber frame dwellings gives me even more concern when someone is considering cladding those with polystyrene panels. And I certainly, therefore, would not make any assumptions as to what the fire service will or not do in these cases!

Indeed, that's another particular problem for Pip - because he won't know either until he asks (and, of course, asking a question sometimes makes people think and then give an answer you really didn't want).

[Ken Taylor]

From my experience of construction sites, someone will need to keep a careful eye on the installation of these. Finished work does not always entirely accord with design plans and ad-hoc variations as unforseen issues are encountered on site can compromise the integrity of fire protection.

[Ashley Wood]

One of the problems I am aware of with all panels of this type, even Rockwool or fire retardent foams, is de-lamination. This is when the adhesive that holds the face board, be it steel or plaster board, fails to adhere correctly. The fire then effects the strength of the panel resulting in collapse. Additionally, with polystyrene type sandwich panels, once the fire has entered the panel it can propagate unseen inside the panel resulting in collapse with little or no warning, hence the reason the fire service is not happy to commit fire fighters into a building using this type of panel i. e supermarkets, cold stores, food production facilities, etc.

[wee brian]

Guys - you keep confusing sandwich panels (steel face) with SIPS - OSB (chipboard to the rest of us) faced.

SIPS are mainly used in building single family dwellinghouses but there is a move to using them in flats.

We dont have much UK data on SIPS in real fires yet. I gues thats where the question came from.

[Pip]

Thank you all for your input, was out of office for a day or so, so have only just read the replies.Basically  wee brian hit the nail on the head-SIPS are not the same as the more familiar 'sandwich' panels that we have grown to love/hate where they have been used as 'cladding' on warehouses etc and resulting major lossess and trajedies.SIPs are basically slabs of Expanded Polystyrene foam sandwiched between two sheets of oriented strand board (OSB) that can be used as elements of structure ie support floors and roofs.There appears to be little published(on the internet anyway) information on these SIPS in regards to how well they will survive in a fire(Structurally).As has been pointed out by other posters, and manufacturers literature (who shout about their ability to withstand surface spread etc but silent on how well they last structuraly),when lined with plasterboard etc they are compliant with our B.Regs.My question was how well do they survive after everybody has got out ie would heat damage weaken their structure (they are able to support walls/roofs up to 2 stories) to an extent that the building would have to be demolished?The expanded polystyrene between the OSB can be treated with a fire retardent and this would be the prefered type.However through out europe both treated and untreated expanded polystyrene SIPs are used.I have read a comment that some Fire services in the US are not keen on them,where they are widely used in domestic house construction but no detail.The particular project that my client will be involved in are not 'domestic premises' but will be relatively small single story structures, and as I said,M.O.E. is not the issue.But as public money is involved, it would not look so good if, after a relatively small fire, the structural integrity may be suspect resulting in a demolish and re build rather than, as in most cases with a traditional masonary build,it probably could be repaired.Of course steel framed structures etc are possibly of a similar ilk,they have a tendency to collapse after a decent fire.I suppose it may be a trade off-a cheap and quick system that will last long enough so that  everybody can get out, but after that it is expendable.

[kurnal]

I wonder how the improved insulation and sealing of a building constructed using these materials would contribute to the risk of more rapid flashover or  possibly backdraft on opening up?

[Ashley Wood]

Pip, try e-mailing the NFPA in the USA. I have had a look in my copy of NFPA 5000 2006 but cannot find anything that may be of help. I would imagine the fire departments concerns in the US are related to toxic smoke once the core is attacked by the fire. I would also have said that once the core is heated to a level where it 'shrinks away' (as it says in NFPA 5000), then it must effect its strength!