Fire regulations and a timber-framed build

[TerryE]

The BRegs, and specifically

• B3 Section 2 Internal Fire Spread (Linings)
• B3 Section 3 Internal Fire Spread (Structure)
• B3 Section 5 Compartmentalisation
• B3 Section 6 Cavities
• B3 Section 7 Protection of openings and fire-stopping

have an impact on the construction detailing within the house.  As a self-builder my aims are twofold: (i) to keep my Building Inspector on my side and happy to sign off our build as complying; (ii) to do the right thing in sensibly protecting the house occupants in the case of a fire and to avoid losing the entire house in the case of a fire.  

 

I mentioned on a previous post that one of the fun things that I did whilst I was an army officer in my 20s, was to run a fire station for a couple of months during the fireman's strike in 1977/78, and so I had first-hand experience a quite a few house fires and their aftermath, and which I can still vividly remember.  Now all of these were in Brick / block fabric houses and a couple of garages, but in general my personal view is that you can broadly divide fires into two categories: localised and non-localised. 

• A localised fire is just that: it has a defined seat such as a piece of electrical equipment or a pan on the cooker. 
• A non-localised fire is one that spreads from the room containing the fire into the fabric of the building.

Whatever the type of the fire, the primary goal is to protect life and to minimise any health impacts on the occupants and neighbours.  This being done, the next goal should be to minimise the consequential damage to the property.  In the case of a localised fire, if this is dealt with quickly and correctly then the fire can be stopped, and the major damage localised to the room containing the fire.  Though of course there are still issues of wider smoke damage, risk to occupants, post-fire assessment and remediation, etc..  In the case of of a non-localised fire in a timber framed house, I would suspect that the consequences would almost certain lead to the destruction or condemning of the structure.  So IMO, it makes a lot of sense to incorporate into your design and build sensible measures to help keep fires localised.

 

In general I take the BRegs to be a sensible codification of a set of measures to achieve these goals.  A lot of this is guidance rather than mandatory requirements  (in this discussion, I am assuming a detached single dwelling, as there are extra mandatory requirements in the case of attached multiple dwellings) and so is really up a negotiation between you and your Inspector, though I could imagine that I might well decided to do in excess of what my inspector wants at a minimum.

 

So what should I do to keep the Inspector "off my back" and to do what is sensible for my own benefit?

 

My first question is what readable guidance is out there?  Can anyone recommend any good references or Internet downloadable materials?   What are the particular risks in a Timber-framed or Passive House?  To be honest, I have for more open questions than answers, one issues such as:

• Flammable gas containment.  Even something like a pan fire can produce a lot of hot gases that are past the ignition temperature for some plastics and exposed wood. In a room with plastered walls you might still have a few minutes to kill the fire whilst the plastered fabric contains the combustible gases.  But not if there are gas conduits above the fire.  MVHR for example.  So in another post there was a discussion about the wisdom of how the MVHR should be programmed to respond to a fire.  My view is that it should be powered down as this has the best chance of keeping the fire local to one room.  We have 3 boxed-in ducting cavities carrying a total of 8 MVHR pipes from the ground floor vents to the manifold on the second floor.  What is the best way to implement containment here?
• Compartment closure.  Thanks to our Gerberit loos and hidden plumbing we have boxing in panels to hide all of this.  This should be closed from a fire perspective and not open to floor voids.
• Ceiling and floor breeches for services such as potable water, waste and MVHR.  How best to seal these and where to we do implement some level of self sealing?
• Drywall spaces.  In general we are using acoustic insulation in ceilings and stud walls, and this has secondary advantages for fire suppression.  But we also have a thin (33mm) service cavity on the external walls which we currently plan to leave hollow.  If this best filled out?

So many Qs and not enough answers.  So I would really value your discussion and input to help inform our decisions and dialogue with our BInsp.  

 

 

Edited August 2, 2016 by TerryE

[RandAbuild]

Terry - I'm no expert on fire regs, but would have thought the simplest way of dealing with boxed-in ducting is 2 layers of plasterboard? If you wanted you could uprate this to the pink fire-rated stuff which is one hour rated for a single layer.

As you say, it's all about detailing and 'thinking fire' - what route could smoke take through a building once it gets hold.

[PeterW]

Catch 22 is the point at which the fire barrier is breached. If you use intumescent foam that expands in a fire, the foam will stop expanding before the plastic melts for stuff such as Hep2O and Speedfit, so will leave gaps. You also have the issue of the fireproof spray foam not being ideal for encasing pipes due to its properties.

 

 

 

 

 

[warby]

Thank you Terry for raising this very serious topic. These are some of the items from my own research to supplement Terry's references to B.Regs: 

This is basic but easy reading; https://sipsecopanels.co.uk/data/uploads/pdfs/tech-bulletins/tb2-fire.pdf .The most frightening comment being IMHO: " failure of the floor structure dictated the overall test duration and failure mode".

 

This is a relevant government website referenced from previous link. https://www.gov.uk/firekills

 

This discusses sealing cavities, no pun intended. This company also mentions many other products...

http://www.sealmaster.co.uk/structural/structural-pages/cavity-fire-seal.php see also; http://envirograf.com/shop/

 

This covers closing window and door cavities; http://www.eurocell.co.uk/specifiers/cavity-closers/flameblok

 

This shows details of using different lining board, rather than gypsum plaster board: http://www.fillcrete.co.uk/Products/Fire-Protection

 

This site explains the use of firestops within cavities: http://mayplas.co.uk/products/cavity-barriers-firestopping-cavity-closers/

 

This site details intumescent strip seals: https://norseal.co.uk/

 

This is a good BLOG in its own rights and with decent pictures: https://logiecoldstonepassivhaus.wordpress.com/. A quote from the site: :"One slightly different feature was the use of knauff dritherm 32 as a firestop at a few strategic locations. This had the added benefit of not only being a firestop but added another 50mm of insulation over some locations in the timber frame where we have solid timber running all the way through. This should help to reduce any thermal bridging. We put in a DPM above this to act as a cavity tray to protect the insulation from moisture and any snots of mortar which might fall down the cavity from above. We also used it at the top and middle of the gable ends"

 

 

[warby]

I think @Nickfromwales mentioned this:  Firecryl FR is a one-component intumescent plastoelastic joint sealant based on acrylic dispersions. I think he said; fireproofing plasterboard joints, e.g. Carport ceiling: the very minimum I'd be fitting is 2 layers of fire rated plasterboard, sealed accordingly with intumescent Firecryl / similar. 

 

Don't forget use of Fire sprinkler systems to cover exit route(s)

 

BS 476 - is the source of British standards on fire rating of materials.

 

Don't forget intumecent hoods or fire covers for downlighters, e.g. use a clay flowerpot!

 

This is about using Fire Resistant, zero halogen, low smoke cables: ; https://www.tlc-direct.co.uk/Main_Index/Cable_Index/NoBurn_Fire_Cable/index.html You may recall the problems in the Falklands war where fire spread very rapidly through the cables and the smoke problems it caused on the warships.

 

Terry has also mentioned in an earlier thread about the need for fire blankets and extinguishers..

[TerryE]

Our service cavities on our gables (the sides perpendicular to the joists) aren't top closed and we divide our house into 3 by two loadbearing internal walls.  I've decide to continue this as a fire barrier in the PosiJoists as well.  @jack, @Calvinmiddle you've got MBC timber frames; are there any specifics that you did here?

 

Off for a site visit to @RandAbuild so might might this up later

Edited August 3, 2016 by TerryE

[ToughButterCup]

Oh Gawd, Terry. As usual, you make me think

Ian

[Pete]

i have read with interest all of the thoughts on fire in buildings, with or without MVHR and how people seem to want to overcome this issue. Basically I can assure you that all you need to worry about is early detection and getting out of the building. People have mentioned using fire blankets and extinguishers as a means to preventing the fire getting worse and giving more time to evacuate. All I can say is that unless you have been trained to use either the blanket or extinguisher you are not only putting yourself at risk but can create a rescue situation when there would not have been one if you had just left the building. I am a retired Firefighter and if I had a penny for the amount of people who assured me they could use a fire blanket and when I asked them to show me they would have ended up in hospital with severe burns to their hands, Same goes for using an extinguisher, even with the best will in the world you can turn a small fire that could be contained by just shutting the door if you can safely and getting out of the building or seriously spreading the fire by mis direction/application of the extinguisher. 

The UK Fire service now use a portable fan to fight fires in buildings but the precautions they have to undertake to ensure that the fire is not spread around the building is quite an an art form. Basically they seal the doorway with a large fan placed externally and wait until a team of firefighters go inside to ascertain the room that contains the fire, close all doorways to other rooms, open the door to the room with the fire and create an opening usually by breaking a window in that room They must ensure they have a jet on the exterior of the building to stop fire spread up the outside of the building and then once all that is done they turn the fan on which dramatically reduces the heat in the building and pushes all the hot gases and smoke out of the window.  The reason they do this is to make their working environment easier and aid any trapped people who might still be inside the building.

As far as I can see what would be beneficial is for some sort of damper/ shutter that closed in the ceiling/wall vents so in the event of fire the MVHR trunking does not allow smoke/fire to travel to other rooms/floors and turn the MVHR off as you would not believe how fast a fire can travel  if the only source of oxygen is coming from the MVHR unit, especially in a Passive house.  I still think early detection is what you need to ensure to enable you to get out and always have a plan as to what you are going to do as a family in case of fire in the house.It is imperative that if you have young children then you understand who is getting the children from their bedroom (fires predominantly at night), who is calling the fire service and if you cannot get out what room you need to go to to enable you to maybe escape out of the window or make it easier for the fire service to rescue you.  . 

[TerryE]

Pete, thanks for your thoughtful and expert response.   I agree with many of your points unreservedly, and I also feel that the remainder apply for most house owners: when in doubt priority is:

1. To clear occupants from the immediate property and notify the fire services;
2. To notify any adjoining property occupants in the case of flats and attached buildings, and ensure that any needed evacuation cascade is initiated;
3. To carry out immediate actions which could mitigate the fire impacts, such as shutting doors to contain fires; shutting down ventilation systems; turning off the power to the property (so long as these actions don't prejudice 1 and 2);
4. To prepare for the arrival of the fire services so that they have clear access and the best information to engage the incident. (E.g. has the building been fully evacuated.)

However, in my case I live in a village and the ETA for the fire-service which is based in the local town is a minimum of 20-25 mins.  I will also be living in a timber frame house with eco-joists.  The dilemma that I personally face is that given this sort of best response time, if no immediate actions are taken then by the time that the fire services put the fire out, it's quite probable that the house will be condemned even if still standing and will need a total rebuild.  In my case I've also fought quite a few house fires and as you are also retired then you are probably of an age where you were one of the guys who would turn up with a fireman's helmet in a carrier bag to make sure that we didn't make a total horlicks of it, when I arrived with my Green Goddess(es).  So I have at least done the 101 stuff on how to put out minor fires, and whilst we might differ on the wisdom of individual home owners attempting to carry out immediate actions to target a local (minor) fire, and this must be a personal choice based on experience and local circumstances and one that I can't promote to others.

 

However,  the wider issue that I would like to discuss in this thread in not such immediate actions, but how by design and construction I can practically minimise the risks of a local fire spreading out a sealed room and into the rest of the fabric of the building.

Edited August 4, 2016 by TerryE

[Mikey_1980]

With regards to the MVHR, shutting it off in the event of a fire could easily be done with an external emergency stop switch, or some sort of relay wired in to the smoke alarms to switch off the MVHR while they are sounding.

 

There are also plenty of intumescent seals available for pipes, which clamp round the outside, and crush the pipe and seal the hole when the temperature raises above 180 degress which would all go towards stopping the spread of fire.

[jack]

One of our smoke/heat alarms (Kidde brand, I believe) is mounted to this optional pattress that contains a relay.  

 

When any of the alarms is triggered - they're all linked to each other, per building regs - the relay is tripped.  We have it wired into our home automation system and I'll eventually use it as a trigger to send us an email and/or text if we're out and the alarm goes off.  It could also be used to close a volt-free contact on an MVHR, or as a control signal to a relay that does the same.

 

Re intumescent seals, I think you need a special type of pipe that can be crushed by the intumescent material, plus it needs to be surrounded by brickwork if I remember correctly.  I've seen MVHR inlets with an internal intumescent closure or collar that operate in a similar way - might be a simpler route to this functionality?  

[PeterW]

When I was researching Smoke Alarms, Aico pointed me to a number of their additional modules that can be used in the event the product is triggered. This is one of them - it's a relay base that activates when the smoke alarm goes off 

http://www.aico.co.uk/images/stories/PDF_Documents/Current_Datasheets/Ei128R_Datasheet.pdf

 

In terms of construction detail, the regs do cover for commercial buildings iirc the construction of safe havens for disabled evacuation. Using this as a baseline would give some ideas however I think it starts with 'non combustible fabric' so by definition the timber frame gives a challenge ..! 

 

[Pete]

Hi Terry

I am not sure what your answer would be concerning protection of the fabric of the building. You mention stopping fire escaping out of a sealed room which really depends which way you look at it. Firstly we would always say close the door to a room on fire to limit smoke travel to aid people trapped in the building to travel to a place of safety in a smoke free atmosphere. When you do this this accelerates the ferocity of the fire as the room heats up very quickly and thus all items inside that room reach their critical temperature to spontaneously ignite.From your point of view it would be better to leave the door open (assuming everybody out of the building) to give more time for the Fire Service to arrive (more smoke damage) and the fire would not be at such a critical stage but this is not an exact science and there are so many different factors that are out of your control. 

Apart from fitting fire resisting plasterboard or even doubling up and being really thorough at fire stopping which would give you well over an hour of protection and then concentrate on early detection with a link to you via a mobile to inform you of a fire. What about installing some sort of cctv that could relay pictures of the rooms in your house if you are away or even temperature sensors in the ceilings to enable as early detection as possible. All of these are relying on home automation of some description and my knowledge of such systems is better left to other people on this forum. 

The other possibility is fitting a misting system which works out at about £2000 for an average 3 bedroom house. The only problem with this is they usually only cover the escape corridor to enable people to get out where as you would probably want whole house protection which could work out quite expensive. This price is for one pump and mister, tank and battery back up in case of mains power failure.

The only other option is to build as fire safety conscious as you seem to be doing and hope you never experience the horrors of a fire in your home. Get as good an insurance policy as you can and let the insurance company re-build your house. 

[curlewhouse]

I've thought a bit about this in our design and since the ground floor is pretty much one large space and is open to the stairs and thus second floor, a lot of sealing seems almost pointless for us beyond giving some extra time in bedrooms and bathroom I guess, and given that I cant see posi joists lasting 5 minutes in a fire, doubling up on detection and getting out seems to be the way to go (obviously in a home split into many sections there would be more delay in spread). But then I've laways had smoke/heat detectors in every single room of my house. They are so cheap why wouldn't you? I learned some firefighting in the military including fires at sea, but given the open plan of many new homes like ours will be, anything more than a minor one like a pan on fire and I'm outski! A misting system sounds attractive for "just" £2000 though, though no doubt it would go off in error as soon as the new floors were laid   

Edited August 4, 2016 by curlewhouse

[Mikey_1980]

No special pipes are required, we have some installed just as a safety precaution becuase I brought a load of intumescent seals for the external cladding I went overboard when ordering fire protection stuff 

http://www.ironmongerydirect.co.uk/products/intumescent_and_fire_control/intumescent_accessories/436/pyroplex_4_hour_pipe_closing_collar_stainless_steel/258507.

 

 

[Nickfromwales]

The ones I fit are identical, mostly required on HMO / student rental refurbishments. They are steel belted and have a robust buckle / hasp arrangement so re the comment about them being surrounded by bricks / similar I'm not entirely sure that's the case. These are capable of expanding during a fire, and provide that force by means of expanding against said collar. 
Expanding entirely to close an opening is only possible when the pipe itself deteriorates ( eg the heated / melting plastic of a soil pipe softens and aids the total closure / compression ) but I'd certainly not use the term 'crushes' tbh as it's possible for someone to wrongly assume that it has the strength to do so to any random pipe. One of metal construction for eg will not crush as it will have immense strength when force is applied equally to it's outer diameter  Only nit-picking that statement as this is a particularly important subject  
I've fitted these collars under the watchful eye of BCO's and I can tell you that they're accepted even when fitted to two layers of fire rated plasterboard, with no other mechanical fixing, and no brick / block work / similar solid construction. These will work in a TF house as well as in any brick built house, AS LONG AS THEY'VE BEEN FITTED CORRECTLY. 

Heres a random internet photo to demonstrate such an instance. 

 

The only requirement that the BCO wanted, on the couple of holes where these were fitted into solid walls, was to insert these into the void and cement them in. Then for the mechanical fixings ( screws / other ) afterwards   

[Nickfromwales]

This shows the buckle / hasp a bit better

[jack]

16 minutes ago, Nickfromwales said:

The ones I fit are identical, mostly required on HMO / student rental refurbishments. They are steel belted and have a robust buckle / hasp arrangement so re the comment about them being surrounded by bricks / similar I'm not entirely sure that's the case.

 

Good to see that confirmed.  I'm sure I saw one that was only for use in brickwork - obviously a different beastie to this.

 

17 minutes ago, Nickfromwales said:

Expanding entirely to close an opening is only possible when the pipe itself deteriorates ( eg the heated / melting plastic of a soil pipe softens and aids the total closure / compression ) but I'd certainly not use the term 'crushes' tbh as it's possible for someone to wrongly assume that it has the strength to do so to any random pipe. One of metal construction for eg will not crush as it will have immense strength when force is applied equally to it's outer diameter  Only nit-picking that statement as this is a particularly important subject  

 

Yes, this was the bit that concerned me.  I suppose that at the sorts of temps required to activate the intumescent material, a semi-rigid MVHR duct should be soft enough to be squashed closed by it.  

[Nickfromwales]

3 minutes ago, jack said:

 

Good to see that confirmed.  I'm sure I saw one that was only for use in brickwork - obviously a different beastie to this.

 

 

Yes, this was the bit that concerned me.  I suppose that at the sorts of temps required to activate the intumescent material, a semi-rigid MVHR duct should be soft enough to be squashed closed by it.  

There are, I'm sure, many different types   

A typical installation for ceiling penetrations ( duct / light ) etc. 

 

[Nickfromwales]

There are some make / manufacturer 'name drops' in those images, but these are all just random 'net grabs FYI. 

[warby]

On 03/08/2016 at 16:54, Pete said:

i have read with interest all of the thoughts on fire in buildings, with or without MVHR and how people seem to want to overcome this issue. Basically I can assure you that all you need to worry about is early detection and getting out of the building. People have mentioned using fire blankets and extinguishers as a means to preventing the fire getting worse and giving more time to evacuate. All I can say is that unless you have been trained to use either the blanket or extinguisher you are not only putting yourself at risk but can create a rescue situation when there would not have been one if you had just left the building. I am a retired Firefighter and if I had a penny for the amount of people who assured me they could use a fire blanket and when I asked them to show me they would have ended up in hospital with severe burns to their hands, Same goes for using an extinguisher, even with the best will in the world you can turn a small fire that could be contained by just shutting the door if you can safely and getting out of the building or seriously spreading the fire by mis direction/application of the extinguisher. 

The UK Fire service now use a portable fan to fight fires in buildings but the precautions they have to undertake to ensure that the fire is not spread around the building is quite an an art form. Basically they seal the doorway with a large fan placed externally and wait until a team of firefighters go inside to ascertain the room that contains the fire, close all doorways to other rooms, open the door to the room with the fire and create an opening usually by breaking a window in that room They must ensure they have a jet on the exterior of the building to stop fire spread up the outside of the building and then once all that is done they turn the fan on which dramatically reduces the heat in the building and pushes all the hot gases and smoke out of the window.  The reason they do this is to make their working environment easier and aid any trapped people who might still be inside the building.

As far as I can see what would be beneficial is for some sort of damper/ shutter that closed in the ceiling/wall vents so in the event of fire the MVHR trunking does not allow smoke/fire to travel to other rooms/floors and turn the MVHR off as you would not believe how fast a fire can travel  if the only source of oxygen is coming from the MVHR unit, especially in a Passive house.  I still think early detection is what you need to ensure to enable you to get out and always have a plan as to what you are going to do as a family in case of fire in the house.It is imperative that if you have young children then you understand who is getting the children from their bedroom (fires predominantly at night), who is calling the fire service and if you cannot get out what room you need to go to to enable you to maybe escape out of the window or make it easier for the fire service to rescue you.  . 

Thank you, at last some support regarding imposing controls on MVHR in a fire. Your last paragraph in particular brings about a voice of sanity.

[TerryE]

AFAIK the BRs only mandate compartmentalisation between dwellings so such collars must be fitted between apartments in flats, but they aren't mandated between floors within a single detached residence.  In our house we have a single open stair well void running top to bottom and we must provide 30 minutes fire protection onto this exit corridor, so we need fire doors; pink plasterboard, etc.

 

 

Our house has pluses and minuses as far fire risks go:

• No fires; no smoking inside the house; solid ground floor (concrete/slate); the house is airtight to 0.6 AC/HR; other than the MVHR and doors, the rooms are properly sealed, so no smoke leakage.  We also have far above average fire detection: we have a 3-floor linked fire detector mandated by BRs and I will also be adding per room sensors.
   
• It's got a timber frame and PosiJoist floors. It's occupants are in their 60s and getting older .

So my top-level view is that localised fires will be better contained than in most conventional houses, fire detection far better, and the escape risks less; however, if a fire does escape an individual room and get into the frame structure or inter-floor spaces, then it will be a flatten and rebuild job (if it doesn't collapse itself as a result of the fire).

 

As to a more quantitative view, the governments own Fire Statistics: Great Britain April 2013 to March 2014 makes good reading.  There were 35,000 accidental dwelling fires and just over 200 fatalities, and of these more than half were smoking related or space heating.  So for non-smokers living in a passive house, you are roughly 20 times more likely to die in a road accident than in a house fire.   With over 17M dwellings in the UK, this equates to one fire per 500 years of occupancy.   Incidentally there are about twice as many accidental dwelling fires per capita in Scotland than in England or Wales.  Kitchen fires account for half of all call-outs but very few fatalities.  And picking up Pete's point above, attempting to fight a fire is as likely to get you killed in a house fire as smoking.  

 

These statistics focus on the human impact and aren't broken down into severity of fire in terms of localised / leading to the destruction / condemning of property.  They are also based on the Fire Service Incident Reporting System (i.e 999 fire service calls).  I believe that most insurers require an IRS reference before paying out on a claim, so these figures will include most material fires, but might exclude a large class of minor fires where the cost of remediation was less than the insurance excess.

 

In thinking about all of this one little concern these stats have flagged for me is the issue of electric supply related fires.  The move to LED-based lighting means that we have started to add far more more 240V to LED drivers in our ceiling voids.  The impact of this trend won't have made its way into the statistics yet, but I need to think a bit more about the precautions that we should take here.

 

Sorry about the stats, but this almost veering into Boffin's Corner territory except for it's potentially wider interest.  I would be very interest in @SteamyTea's and @JSHarris's analysis

 

Edited August 5, 2016 by TerryE

[curlewhouse]

I also have concerns about all the little LED drivers in voids, especially since the vast majority come in from overseas (though I've bought lots of stuff direct from China with no issues to be fair - you just have to be more careful with certain items from there  when mains power is involved ... like this classic and terrifying  "2.5kW baby-cutor"    or the "oriental LED death star ")

 

The Building Services Handbook (I've reviewed it on another thread) p658 says "Fire dampers are required in ventilation and air-conditioning systems...." and show diagrams of various ways this is done, including an intumescent "honeycomb" (which you'd think would play havoc with adding friction and noise) which sits in the duct and swells if it gets hot. The book also shows mechanical dampers, one a very simple with just a fusible link which drops down and blocks the duct. These of course both depend on the heat reaching them so seem less effective (or too late) as they would probably work faster on the outflow rather than incoming air.  I do wonder though that given the low velocity of MHVR if it's really an issue as long as you have detection in place.

Edited December 28, 2017 by curlewhouse