36 MMA Yearbook 2007 Purpose group Height A (not more than 5m) Height A (not more than 18m) Residential and office blocks 30B 60C Shops, commercial, assembly, recreational and industrial 60D 60 A = Height to top floor above ground; B = Increased to 60 mins for compartment walls; C = Reduced to 30 mins in the case of threestorey dwellings houses, and for a non-supporting floor within a maisonette; D = Reduced to 30 minutes with sprinklers. The fire resistance for buildings not more than 30m is typically +30 minutes, and over 30m + 60 minutes – which is a maximum of 120 minutes. A proper assessment of fire resistance is essential to meet the requirements of the Building Regulations. Fire resistance People pay attention to the fire resistance of masonry walls to commercial, warehouse and storage buildings, as this is rightly an important aspect to be considered in design. Although fire resistance is important in all buildings, few will pay much attention to the masonry walls. The reason is that, almost without exception, masonry is seen as a non-combustible product and one that, in essence, will meet the Building Regulations by the common sizes specified. A proper assessment of fire resistance will enable different structural forms to be fully compared against each other. This is particularly important if a life-time comparison is to be made. The fire resistance requirements under the Building Regulations are quite complex and form a major part of the various statutory requirements. The principle objectives of structural fire precautions of Part E the Building Regulations (Part D Scotland) are that the building should not collapse and that the occupants should be protected from smoke and fire until they can be safely evacuated. These are quite complex but the four basic principles are that the building should be designed: . so that the materials used in construction do not assist in rapid development of the fire; . to contain the fire within confined limits both within the building and between buildings; . to provide structural elements with sufficient fire resistance according to the type and size of the building; and . to provide a means of escape for the occupants. Similar requirements and principles apply in Northern Ireland, and additional rules are often adopted for insurance purposes, and tend to require higher resistance than required for the Building Regulations alone, as they cover content as well as life. Fire resistance requirements The minimum periods of fire resistance for new-build projects vary according to the purpose group and height of the top floor above ground. Table 1 shows the typical requirements in England and Wales for different building types (purpose groups). Fire resistance of structure The British Standard covering tests for fire resistance of materials is BS 476, which has several parts dealing with ignitability, flame spread, etc. As mentioned at the beginning of this article, masonry is essentially a noncombustible material and it is generally only necessary to determine the fire resistance of the wall or element. The notional fire resistance of masonry walls is determined with respect to three criteria: loadbearing capacity, integrity and insulation. In this context, loadbearing capacity means that the wall does not collapse, integrity means that the wall does not develop cracks through which flames can pass, and insulation means that the wall does not transmit sufficient heat to ignite flammable materials in contact with the side remote from the fire, during the notional period. In a non-loadbearing wall, the load-bearing capacity (selfweight only) is taken as the time taken to collapse. Numerous tests carried out in conjunction with national research projects and sponsored work by manufacturers have shown that concrete brick and block walling is capable of notional fire resistance periods of between 30 minutes and 6 hours. The notional fire resistance of a wall is the period during which the wall fulfils all the relevant requirements (structural capacity, integrity, and insulation). The typical grading periods are ½, 1, 1½, 2, 3, 4 and 6 hours. If a load-bearing wall has stability failure of 140 minutes, an integrity failure of 120 minutes and an insulation failure of 140 minutes, the wall would be given a notional fire resistance period of 120 minutes. In cer tain cases where one or more of the three conditions can be relaxed, the fire resistance period of the wall may not necessarily be controlled by the lowest of the test conditions. The Building Regulations limit the requirements for loadbearing walls to loadbearing capacity alone, except where the wall is a compartment wall, is part of a protected shaft, enclosure or firefighting shaft, when loadbearing capacity, integrity and insulation apply. But Construction Performance (minutes) Required thickness (T) - mm Loadbearing Non-loadbearing Single leaf wall or cavity wall of solid concrete bricks or blocks 60 90 50-75* 120 100 63-100 240 100-190* 75-170* *Thickness varies depending on whether single leaf or cavity walls/type of masonry units and surface finish. Table 1 Minimum periods of fire resistance Table 2 Minimum periods of fire

MMA Yearbook 2007 37 it should be noted that the notional fire resistance periods given in BS 5628: Part 3 for loadbearing and non-loadbearing masonry walls, cover all three test conditions. Examples of the performance of both masonry walls are shown in Table 2. This table is useful in that it shows that a 100mm-thick masonry wall of single leaf or of cavity construction made of solid units will provide a notional fire resistance of 120 minutes, which is up to four times longer than typically required for house walls, and sufficient for walls in most structures as covered by the Building Regulations (see Table 1). Walls in lightweight-framed houses are designed typically to resist just the basic requirements (typically 30 minutes). Structural elements This article demonstrates that brick and block walling may be used to provide fire resistant structural elements and also as a means of providing effective and economical and robust compartmentation to both new and existing buildings. Masonry walling being non-combustible does not produce smoke or toxic gases and, therefore, attention has only to be focused towards decorative coverings such as paints, applied to the surface of the wall. Another application is the upgrading or protection of elements such as steel columns. Although these are more commonly provided with fire-protective claddings, it does not offer the same robustness as is provided by masonry, which becomes beneficial when assessing whole-life performance. The details given in Table 1 and Table 2 provide a brief indication of the performance and applicability of walls and constructions using bricks and blocks based on information extracted from the Building Regulations and Design Codes. More extensive information may be found in the Schedules to the Building Regulations and Codes. For example, the fire performance that can be so readily provided by masonry walls is further highlighted by reference to BS 5628: Part3, which includes fire periods of up to 360 minutes and which may be required for insurance purposes for some commercial and particularly storage buildings. Fire performance and fire safety It was shown earlier that masonry has a fire resistance period significantly greater than that required for the walls of houses and flats under the Building Regulations. Masonry is also non-combustible and, as such, does not add to the fire load either within a property during fire, or within a cavity wall. Also, defects in a structure caused by workmanship or subsequent trades will have no appreciable effect on loadbearing masonry walls. However, a report by Prof Schneider of the University of Vienna indicates that defects within wall construction in lighter frame structure can lead to an increased safety risk. This is based on results from Austria and other EU countries and is attributed to combustion of structure, fire transfer within cavities in partitions, or external walls caused by walling defects during or post-construction (post-fitted wiring an plumbing). Also frame structures for residential properties are typically designed just to meet the regulations (30 or 60 minutes at most), whereas masonry walls provide typically 120 minutes, which can be fully utilised when used in conjunction with concrete floors, which will normally be further protected by plastered ceilings and thus provide notably higher fire performance. Prof Schneider argues that there is a possible need to plate lightweight frame residential buildings as fire brigades need to know the type of structure they are dealing with because of the possible defects leading to hidden fires or recombustion, and their lower reserve of strength (period to collapse). There seem to be no statistics to support this view on life safety in the UK, although this was last reviewed back in 1985, when few medium-rise, lightweight framed flats existed. . Reader enquiries to: info@modernmasonry.co.uk