Note
- Accepts the cladding build up used on Grenfell.
- Silent on hazard of polyethylene as a fuel
NHBC Technical Services Building Regulations Technical Guidance Note -
TS-EXTGN-BC-ADB-514v1-July 2016
p.4
Appendix 3 - Aluminium composite panels
Key issues
Similar to cement based panels, mineral cored aluminium composite panels tend to crack and break up under sudden flame impingement. Once burn-through occurs, flames affect both the internal and external faces of the panels, giving the potential for flames to spread via the cavity. For this reason, reliable cavity barriers are necessary around window/door openings (to reduce the likelihood of fire entering the cavities at these points) and at compartment lines to restrict the unseen spread within the wall build-up.
The performance criteria of BR135 - Fire Performance of External Thermal Insulation for Walls of Multistorey Buildings are that fire spread should be restricted within
the first fifteen minutes of breakout via an opening. With the measures below, it is considered that an aluminium composite panel facade finish will meet these criteria.
These appropriate measures include:
- The use of minimum Class B (in accordance with BS EN 13501:1) aluminium composite panels which provide a Class 0 surface spread of flame
- The use of a cement particle board behind the insulation (minimu m Class B) and a thickness no less than 12mm)
- The use of reputable and robust cavity barriers - both mineral wool filled and intumescent products to compartment lines and around all openings.
Restrictions on use
The use of polythene or polythene / mineral cored aluminium composite panels which do not achieve a minimum Class B combustibility classification fall outside of the scope of this guidance note. Such product s are unsuitable for use in high rise situations. It is also imperative that substitution with a less fire resistant product doesn’t take place on site.
Guidance
Where a building has a floor level exceeding 18m from outside ground level, a Class B aluminium composite panel finish is specified and the builder can demonstrate that the following precautions are incorporated into the specification, design and installation of the facade, NHBC will accept the build-up as meeting Requirement B4(1).
From inside to out:
- Double layer of 12.5mm plasterboard
- Minimum 100mm lightweight steel frame internal leaf (which may incorporate combustible or noncombustible insulation)
- No less than 12mm thick cement particle board of minimum combustibility Class B (when assessed to BS EN 13501:1)
- Insulation (maximum 140mm thick) comprising one of:
- Kingspan K15
- Celotex RS5000
- Xtratherm SR/RS
- Drained and vented cavity
- Aluminium support rails
- Minimum Class B (when assessed to BS EN 13501:1) aluminium composite material boards with a Class 0 surface spread of flame classification.
The use of reputable and robust cavity barriers to compartment lines and around all openings is imperative. These should be formed from one of the following materials:
- Steel at least 0.5m m thick
- Timber at least 38mm thick
- Polythene-sleeved mineral wool, or mineral wool slab, under compression
- Calcium silicate, cement-based or gypsum based boards at least 12mm thick
- Proprietary products which have shown to achieve the reguirements for closing cavity without needing to be covered by a plasterboard lining.