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As an in-depth Inside Housing investigation reveals a wide usage of unsafe panels, former architect Ian Abley explains how legislative changes have played a role
Fire experience during wartime informed guidance for reconstruction, published in 1946 as Post-War Building Studies No.20 Fire Grading of Buildings – Part 1, General Principles and Structural Precautions.
The report was produced for the Ministry of Works by the joint committee of the Building Research Board of the Department of Scientific and Industrial Research and the Fire Offices’ Committee. To prevent fire spreading from window to window Clause 212 suggested:
“A reasonable degree of protection could be obtained by providing at least 3ft of construction (of which at least 2ft should be above floor level) of the same grade of fire resistance as the walls, between the lintel of the lower window and sill of the one above.”
This 3ft or 900mm of “reasonable” separation between windows, with a 2ft or 600mm upstand, had, by 1952, been turned from the Ministry’s ‘could’ into a requirement by the London County Council (LCC).
“Architects embraced their freedom in planning applications to do away with separation between windows and doors.”
In their bylaws for fire safe construction the LCC required non-combustible and fire resistant wall construction between windows.
Any balcony doors had to have the threshold at floor level for obvious reasons, but the LCC expected the non-combustible and fire-resistant balcony to provide a minimum 2ft or 600mm projection instead of the 3ft or 900mm separation between windows.
The non-combustible and fire-resistant projection was assumed to push any flame that had broken out of a room away from the building to give some separation to the door at floor level, being necessarily lower than the window sill.
The architectural consequence can be seen on LCC houses and blocks of flats, including early high rises, from the 1950s. Architects within the LCC, or under contract to it, accepted the separation.
Click below to read Inside Housing’s in-depth investigation into flammable window panels:
But by the 1960s the LCC bylaw based in the fire grading report was architecturally limiting.
After much debate the first National Building Regulations in 1965 set architects free to design out upstands or projections.
Their windows could extend from floor to ceiling, or pass the compartment slab edge. Architects embraced their freedom in planning applications to do away with separation between windows and doors.
The only requirement was for separation between buildings based on compartment size, that allowed up to 100% of the wall to have as little fire resistance as the window or door.
In London the LCC’s replacement , the Greater London Council (GLC), could still try to insist on upstands and projections for high-rise buildings.
However the GLC was abolished in 1986, so in London the freedom allowed in the ‘Approved Documents’ guidance to the National Building Regulations was imposed on London, too.
By the 2012 Building (Repeal of Provisions of Local Acts) Regulations, even the City of London’s District Surveyors Office could not insist on special provisions for high rises.
The Grenfell Tower fire has shown us there has also been increasing permissiveness in the combustibility of the wall, written incrementally into the revisions of the Ministry’s Approved Document B guidance that explains how the latest building regulations have to be complied with.
The law is written in Schedule 1 of the Building Regulations 2010. It is Regulation B4-(1) that is concerned with fire spreading externally from windows and doors, or from one building to another by radiation. The law is simply stated here.
The Approved Document B Volume 2, up to the 2013 amendment, considered residential flats with commercial buildings.
This is the guidance published by the Ministry to tell clients, consultants and contractors how to comply with Regulation B4-(1). As many people now know, ADBv2 (2013) does not guarantee the intention of Regulation B4-(1) will be achieved in reality.
This is a problem for the construction industry and the government setting compliance requirements for building control.
ADBv2 (2013) talks about “walls”, but allows them to be combustible and “unprotected area” without fire resistance.
It has a definition of the ‘wall’ that includes the glass in a window, but not a door, excludes the window and door frame, and is silent about insulated infill panels within windows and doors. Insulated infill panels purchased as part of a window or door might be combustible in high-rise buildings if no-one among the client, consultants, contractors, or anyone in authority during building control processes, think they are part of the wall.
Specialist manufacturing companies make combustible insulated infill panels for windows, doors and curtain walls and sell them widely.
“Today there are buildings with combustible insulated infill panels in window frames, that might also pass the compartment slab edge while being non-fire resisting, allowing rapid fire spread externally.”
That is because they are believed to comply with the Approved Document B guidance, even for high-rise buildings, defined as those with a storey over 18m in height. By their own terminology, there should be no doubt for curtain walls.
But another part of the Approved Document series, Part L for the conservation of fuel and power, contradicts Part B for fire safety.
To add to the confusion, when calculating thermal insulation performance to the Standard Assessment Procedure (SAP) in Part L the insulated infill panel is part of the window.
If the insulated infill Panel were thermally equivalent to a wall it would have to be far thicker, and have a thermal performance far better than that allowed for the window.
Something like a factor of 10 better as thermal insulation.
Most thermal insulations would be too thick to fit in window frame. Particularly if for fire safety the insulated infill Panel also had to be non-combustible, and perhaps have a fire resistance too. SAP allows a lower thermal performance in the window’s integrated insulated infill panel. When ADBv2 is silent on the insulated infill panel, it might not be thought of as part of the wall.
Today there are buildings with combustible insulated infill panels in window frames, that might also pass the compartment slab edge while being non-fire resisting, allowing rapid fire spread externally. As the Grenfell Tower Inquiry resumes after the summer break in proceedings, the significance of the failure to require insulated infill panels to be fire safe will become very apparent. Some new building science is going to be needed to satisfy Regulation B4-(1).
Ian Abley, former architect and window salesman
In the days following the Grenfell Tower fire on 14 June 2017, Inside Housing launched the Never Again campaign to call for immediate action to implement the learning from the Lakanal House fire, and a commitment to act – without delay – on learning from the Grenfell Tower tragedy as it becomes available.
One year on, we have extended the campaign asks in the light of information that has emerged since.
Here are our updated asks:
GOVERNMENT
LOCAL GOVERNMENT
LANDLORDS