25 May 2017
The design and construction of a building often require a fine balancing act between aesthetics, function, performance and cost, explains Mark Harris.
WHEN IT COMES to new buildings, issues such as fire safety, accessibility, energy efficiency, speed of construction and quality of build are all essential parts of the equation. We are also seeing more and more mixed-use developments, where residential needs must be addressed alongside commercial ones. Modern methods of construction can help meet these potentially conflicting demands and simplify the creation of complex buildings.
According to the “Faster, Smarter, More Efficient” report recently published by the Construction Industry Training Board (CITB), offsite construction currently accounts for less than 10 per cent of the industry’s output. Yet offsite methods could hold the key to many of the issues the industry currently faces, such as the skills shortage and the need to increase output. There are already signs that offsite will grow rapidly, as the benefits and opportunities it presents are realised.
Using factory-engineered, pre-cut, or assembled elements allows fast-track construction, reduces onsite waste, and facilitates quality control. Building systems with components that are designed and specifically manufactured to work together make life easier for the architect, contractor and, ultimately, the building owner. Performance can be more readily quantified, as can maintenance requirements.
Systems also make it easier to take a more holistic approach to the building design. After all, it is not necessarily the separate elements of a building that determine how it will perform in any given situation but the interaction between those different elements.
Take fire, for example. It could be argued that, for buildings to be completely safe, they should be constructed entirely from non-combustible materials, but this is clearly neither feasible nor desirable. Imagine a world where no buildings used timber! Furthermore, non-combustible materials may not burn in the event of a fire but neither do they provide any real structural strength, so building elements may collapse at an earlier stage.
The non-combustible route also only addresses a single aspect of fire risk in buildings, when probably the most significant factors to consider are the scale and fire load of the building contents. From soft furnishings to electronic devices, plastic furniture to waste paper, we fill our buildings with highly combustible goods, many of which are easily ignited and can produce hazardous smoke and fumes when they burn. We cannot legislate for them all, so how crucial is the building envelope in this respect?
A recent study from PU Europe explored this question, comparing the contribution to toxicity of different construction products in a furnished-room fire. The investigation found that the greatest risk of harm to occupants of the building arose from the smoke, heat and toxic fumes created by the contents of the room burning, long before the building fabric itself became involved in the fire, and regardless of whether the insulation used in the building itself was combustible or not. This supports the view that a fire-safety engineering approach to building design is the most effective way to safeguard life and property, by providing early warning and easy escape routes, as well as potential fire-protection measures, such as sprinklers that help facilitate safe evacuation of people before they are exposed to smoke inhalation.
Clearly, there will always be high-risk applications that require such elements as a 60-minute fire wall, but for the majority of constructions this is not the case, and it is important to strike the right balance between designing out risk and over-specifying the building envelope at the possible expense of other safety measures.
Insulated panel systems can provide all the benefits of offsite construction, together with very high levels of both fire and thermal performance. However, it is vital to make sure that the systems specified will indeed meet the requirements, and one of the best ways to do that is to look at which tests and standards they have achieved.
Tests and standards
The existing Building Regulations tests and the Euroclass Reaction-to-Fire tests do not fully assess insulated panel performance and should not be taken in isolation. This is because the key objective of UK Building Regulation guidance is to ensure that personnel can leave the building safely in the event of a fire, rather than the longer-term objective of preserving the building itself.
Because insurers take a different approach, having an interest in property conservation as well as life safety, they recognise the limitations of the small-scale reaction-to-fire tests used to demonstrate simple Building Regulations life-safety compliance, and have developed their own large-scale tests. Of these, the two most well-known and widely recognised are Loss Prevention Certification Board (LPCB) and Factory Mutual – now known as FM Global (FM).
LPCB’s LPS1181 test, sometimes referred to as the ‘garage test’, comprises a 10m-long, 4.5m-wide, 3m-high enclosure clad in the materials under test. The enclosure is open at the front, with a smoke skirt at the ceiling to prevent the hot smoke layer from escaping and adding to the severity of the fire development, as in a real-life situation. The enclosure has a ventilation window at the side. A wooden crib, which generates a 1-megawatt fire load, is ignited in the corner and the fire development is monitored. Although there are many pass/fail criteria the key parameter is that there should be no fire propagation beyond a 1.5m zone around the crib.
FM has a quite different, but complementary, test standard for assessing reaction to fire performance. The key fire-test standard is FM 4880 Approval requirements for Class 1 fire-rating of building panels. There are various levels of performance, the key one being with no height restriction. Achievement of Class 1 to FM 4880 with no height restriction is dependent on performance in a number of tests, which can include:
- ISO 12136 fire-propagation apparatus;
- ASTM D482 ignition-residue tests;
- ASTM E711 oxygen-bomb tests;
- UBC 26-3 room test;
- FMRC room-corner test (25/50ft test); and
- FM 16ft parallel-panel test.
The 50ft wall test is very stringent, involving two walls 15.24m high with a small ceiling, all lined with panels, and a large fire source (345kg dry timber) positioned in the corner. To achieve approval without any height restriction, there must be no flame spread or fire propagation to the extremities of the panel construction.
Making the grade
Kingspan PIR insulated panels have performed well in all these tests, with characteristic performance being formation of stable protective char, no flashover, no flame spread – particularly in the core of the panel – no fire propagation, no panel collapse, relatively small and acceptable smoke levels and high levels of fire resistance – up to one hour insulation and integrity is achievable with specific systems.
The validity and relevance of the LPCB and FM test regimes are backed by a number of live fire scenarios involving certified insulated panels. For example, a fire occurred in the external compound of a large Audi dealership due to a deliberate act of arson. The insulated panel cladding was subjected to a predicted peak-incident radiative heat flux of 31.8kW/m2 for at least 10 minutes. The panels exposed to these conditions sustained damage in terms of delamination of the exposed steel skin of the panels away from the PIR core, removal of the paint coating and pyrolysis of the PIR core material to a depth of approximately 40mm. There was no evidence of fire propagation within the panels, and the inside of the workshop in an area adjacent to the external fire attack showed no evidence of fire penetration. Numerous other case studies have proved a strong correlation between the large-scale insurer tests, such as LPS1181, and the actual performance of panels in fire.
Research into rigid thermoset insulation technology has led to the development of even higher-performing products in the market. The advanced insulation core forms an exceptionally stable char on exposure to fire, resulting in lower smoke emissions and better performance in fire-resistance tests.
The panel systems use the first closed-cell insulation material certified to FM 4882 for use in smoke-sensitive occupancies, achieving a reaction to fire of B-s1 d0 according to EN 13501-1, the lowest smoke emissions possible. This makes them ideal for use in pharmaceutical manufacturing and storage areas, food preparation and storage areas, with no height restriction. The products achieve fire resistance of up to one hour insulation and three hours’ integrity according to EN 13501-2, outperforming all previous fire tests achieved by PIR core panels.
This improved performance also means that the products can be offered in a wider range of panel widths, and can span up to 7m in some LPS 1208 specifications and up to 12m in certain specifications according to EN 13501-2, further enhancing the fast-track capabilities of offsite construction.
With the different pressures of modern life, we are demanding more of our buildings, and they are becoming more complex in both design and function. Using modern methods of construction, such as high-performance insulated panel systems, we can create spaces that are cost-effective, quick and efficient to construct. Most importantly, the system elements are designed to work together seamlessly to provide safe, high-quality, low-energy buildings.
Mark Harris is Divisional Building Technology Director at Kingspan Insulated Panels.
- Weghorst, R et al (2017): An Investigation into the Relevance of the Contribution to Toxicity of Different Construction products in a Furnished Room Fire