The great timber vs composite fire door debate rages on, still fuelled by the government’s investigation following the Grenfell Tower disaster. There is still frustration at what’s been described as the glacial pace of remediation work eight years on and widespread, ongoing confusion as to how councils, housing associations and other landlords are meant to keep buildings and residents safe. Time for a little clarity…
First, a 60 second recap. Cladding may have dominated the headlines following Grenfell, but fire doors came a close second with the government launching an investigation into fire door performance. The timber fire doors tested passed with flying colours but composites fared less well, leading to a temporary moratorium on the sale of glass reinforced plastic (GRP) composite fire doors and several Advice Notes from the Ministry of Housing, Communities and Local Government (MHCLG) advising, among other things, that replacement flat entrance doors be tested to ensure they can resist fire and smoke adequately from both sides.
What’s the issue with composite fire doors and testing from both sides?
Starting with the basics, a typical composite front door consists of: a composite central panel or core, usually with insulating performance and timber stiles and rails to allow installation of hardware and control the trimming process; a steel, PVC or aluminium frame; PVC-type façade and glazing.
Along with a letterplate, it will have security features, such as a three-point lock and maybe a pre- fitted spyhole. Again, for security, the glazing will typically be safety glass. All perfectly serviceable in a private dwelling where there’s no requirement for fire and smoke resistance.
Now, let’s turn our attention to a multi-occupancy building, where you have a series of flat entrance doors on one or both sides of either an open or closed internal walkway or corridor. The corridor is a means of escape so needs to be protected from risks, which in this case, are the flats leading off it.
This was the situation in Grenfell where the fire started in a kitchen in one of the flats, but the fire requirements are the same whether it’s a multi-occupancy residential building, school, hospital or office block. Whatever the situation, the composite door now needs to fulfil a vitally important additional function – fire and smoke resistance. As such, it will have to satisfy the relevant standards, which in the British market are BS476 Part 22 or EN1634 Part 1 for fire and BS476 Part 31.1 and EN1634 Part 3 for smoke, and offer a minimum of 30 minutes’ protection.
So, composite fire doors need to be tested, just like any fire door. Why the government’s insistence on testing them from both sides?
This is where it gets interesting. To reiterate, in addition to its basic security function, the composite door may now have to provide fire resistance as well. And that’s where a potential conflict creeps in. A single piece of glazing can’t usually fulfil both functions – fire glass can be semi-secure, but security glass isn’t typically fire glass. So, composite fire doors rely on a double-glazed unit instead of a single glass panel, with security glass on the outside to prevent break-in and fire glass on the inside to prevent fire from escaping.
While this might afford a degree of insulation, the fact that you have different types of glass on the inside and outside of the door means that the composite fire door is asymmetrical. As a result, it will respond differently depending on where the fire threat comes from.
Glazing isn’t the only asymmetrical element either. To help protect against weather, composite flat entrance doors tend to have hollow rebated frames with rebated door leaves, which further compromise the symmetry of the doorset.
Then there’s the door frame itself. Most are made from hollow PVC with steel reinforcement, which again makes these doorsets asymmetrical.
So how does an asymmetrical composite fire door perform in the event of a fire?
Considering the glazing first, if the fire comes from inside the flat, on the side with the fire glass, this should offer a degree of fire resistance. But what if the fire is outside, in the corridor? The security glass on the outside of the door isn’t designed for that, so a thermal shock situation can develop. The security glass becomes hotter than the frame surrounding it and the whole thing disintegrates, undermining the integrity of the fire glass on the unexposed side as it does so.
That’s one type of catastrophic failure. The other thing that can happen is that the fixing systems fail due to the high level of heating.
Similarly, the asymmetrical nature of the door frame, with its steel reinforcing and unbalanced frame and leaf interface, makes its fire performance difficult to predict testing only one face.
“The government’s investigation into fire door performance found that three-quarters of the GRP composite fire doors tested failed to meet the 30-minute requirement, with two of them lasting less than 10 minutes.”
It might sound like a minor detail – there’s only one letter difference between asymmetrical and symmetrical fire doorsets after all – but it’s absolutely critical when you consider they are one of the most fundamental elements of building safety. The government’s investigation into fire door performance found that three- quarters of the GRP composite fire doors tested failed to meet the 30-minute requirement, with two of them lasting less than 10 minutes.
That’s why Building Regulations insist on testing asymmetric door constructions from both sides.
Why are timber fire doors different?
It’s simple really – timber fire doors, unlike composite fire doors, typically have a symmetrical construction.
If you’re adding glazing to a timber fire door, for example, you put a single piece of fire glass right in the centre of the thickness of the door. The glass is therefore fire proof from both sides, so it wouldn’t matter whether a fire came from inside a flat or outside, in the corridor.
It’s not rocket science but it does make all the difference, as the results from the government’s investigation show.
How did timber fire doors perform in the government’s tests?
Subjected to the same furnace tests as the composite fire doors, the entire test sample of 25 timber fire doors4 returned passes, exceeding the 30-minute requirement on both sides of the door.
Tellingly, Building Regulations don’t actually specify that timber fire doors must be tested from both sides, as they do for composite fire doors. Recognising the inherent benefits of a symmetrical construction, BS476 Part 22 infers and EN1634 Part 1 states that if a symmetrical inward opening door achieves the required level of performance, then it can be deemed that the outward opening side will do at least the same if not better. The government’s investigation, our own tests and those conducted by members of the Architectural and Specialist Door Manufacturers’ Association (ASDMA), of which Halspan is a member, all concur.
What can councils and others take from this?
The introduction of the Building Safety Act has sharpened the focus on accountability and performance. It is no longer enough for a fire door to meet a standard in a single test. Consistency must be proven, be traceable through the whole supply chain and provide assurance in real life situations. There are many composite fire doors out there that will satisfy the inward and outward testing requirement and be fit for purpose. However, there is a strong surge in composite fire door manufacturers developing and investing in their fire door performance, meeting the demands of the Building Safety Act, head on.
Some will argue that if councils, housing associations and other landlords want a fire door they can rely on to do what it’s meant to, then a properly manufactured, installed and maintained timber fire door is the safe choice.
What’s the verdict?
This debate will remain relevant for some time and inline with any changes to building regulations and fire door testing, but the picture
is more nuanced, and composite doors that comply with the newer, stricter testing (both-sided fire resistance, smoke control, proper certification, correct installation) can and do meet safety standards. The major risks come from non-certified or older doors, or doors that aren’t tested fully, or improperly fitted/maintained.
Timber fire doors (from what the testing has shown) remain more consistent in terms of performance for the basic fire resistance test, especially for flat entrance doors, but composite manufacturers have improved their standards and brought many products up to a reliable benchmark.
If you wish to respond to any of the information in this article please email: christina@firedoor-journal.co.uk.
For more information on Halspan timber fire doors, please visit: www.halspan.com.
Tel: +44 (0)3300 563836 Email: info@halspan.com
This edition of the journal carries articles and product spotlights on both timber and composite fire doors, with views expressed and information provided, from various manufacturers.
