The ground floor of a typical house in UK consists of various elements. This is demonstrated in the sketch above. There is the foundation, the footing course, the hard core filing, the sand layer the damp/radon barrier and the concrete slab. The first part is the cavity wall and is made of concrete blocks on top of the foundation and this wall goes up the ground level. It is also important to note that the floor level is made at least 230 mm above the outer ground. If the house design will use bricks for the outer wall, there has to be ample foundation for them and they usually start at lest 15mm below the DPC (damp proof course) level.
When the walls are done, the inner structures are filled with hardcore material like limestone. Good construction practice requires that the inner structure of the foundation walls be filled with hardcore which also needs to be compacted well enough to ensure there is no chance of movement in the future. Proper care must be taken into about the hard core rubble when filling up the floor as it may be contaminated with dry rot: the rubble must be treated with fungicide. In addition, the floor must fulfill a number of factors like uniformity of the surface, strength and stability, thermal insulation and fire resistance.
Next a layer of sand is put above the hardcore layer to the measure of at least 50mm; this is done to eliminate any sharp edges from the fill material which may damage the damp barrier. There are many types of ground floor to choose from, like precast concrete or a beam and block floor or hollow concrete. In most cases, the flooring materials or design is influenced by factors such as endurance, individual taste, moisture conditions, climate or moisture conditions and the services that may be added beneath the flooring.
Normally a block floor or hollow concrete costs more than poured concrete slab. Drains and the heating system are placed at this stage. 3 Fire and Safety Engineering/ Building Regulations First floor In UK, the type of foundation and the structure of the walls largely determine the nature of materials to be used for the first floor. For example, dead or imposed loads should not be so heavy that they affect the stability of the house. Some of the materials commonly used to build the first floor include, wood planks and concrete slabs.
External walls Walls may either made in bricks, concrete slabs, and timber, steel or aluminum sheets. Most houses in UK have cavities between the brick work. Cavities were introduced due to their damp prevention properties. 4 Fire and Safety Engineering/ Building Regulations Brick work or concrete is porous to some extent and sooner or later, especially with poorly constructed joints, it will let in water. Without the cavity, there is some chance that moisture or water will find its way indoors. The diagram above shows its construction in detail.
At the bottom of the cavity is the foundation. Then there are the ties. Their function is to “tie” the two halves of the wall together. The ties are built into the wall, so that it slopes towards the inner skin of the wall, this makes water to run down and soak into the inside wall. The ties are designed with a kink to collect water, which then drips off at the lowest point. Clipped onto the wall tie in the diagram, is an insulation retention clip. Insulation can be installed in cavities in two ways.
Either it can be made to fill the cavity completely, or it can be a partial job, as in the diagram, allowing a free air flow of about 60mm for the remainder of the cavity for the function of moisture penetration. If a complete cavity fill is chosen, the fill ideally should be of a composition which will deny the penetration of water from access to the inner skin. Roofing The covering in the uppermost part of the house is called the roof. The main function of the roof, in most cases, is to protect the inhabitants from the vagaries of weather like rain, heat cold and
5 Fire and Safety Engineering/ Building Regulations wind. In UK, the most common outer roofing materials used are, laminated glass, precast concrete, aluminum, ceramic tiles, and in some cases, wooden or asphalt shingles. One of the most important things that designers consider when building the roof is durability. This is because, depending on the design, it is the least accessible part of the house. A typical roof in UK and in other parts of the world consists of the support structure and its outer covering.
In most roof design, an extra layer of insulation is needed beneath the outer covering; this is placed to insulate the house against excessive heat, cold or noise. Forms of insulation may vary depending on cost or availability of material, but most people use plastic sheeting, synthetic foam and other materials with insulation properties. Given that the primary function of roofs is to facilitate good drainage of water, the water that collects when it is raining should be well taken care of.
A proper drainage system should be installed to prevent damage and inconvenience. Comparison between typical UK forms of construction with Kenyan construction methods. In terms of technological advances, UK is by far a more developed country than Kenya. UK has a well developed construction industry and well defined building system, codes and regulations. Kenya on the other hand is a third world country. In UK all construction and building regulations must be followed to the letter, in Kenya owners at times bribe officials, resulting in substandard habitations.
Most Kenyans use cut stone as the primary material for construction. Wooden planks, mud, corrugated iron sheets, and earthen bricks are also in common use. There are also the famed Maasai manyattas. The flooring is usually made of 6 Fire and Safety Engineering/ Building Regulations plaster, or tiles on concrete slab. The use of cavities is not common in Kenya. Kenyan roofing standards are similar British standards, but many Kenyans use timber for the roofing structure except in big commercial buildings. A typical factory made gang nailed truss.
The diagram above shows a typical gang nailed truss. “About the late 1950’s early 60’s prefabricated roof trusses came onto the scene. There were quite a few methods of joining trusses around at the time, but most of them needed some drilling and bolting. The Gang-Nail plate is just a flat galvanized plate that has stamped in a press to produce dozens of pointed spikes on one of its faces. One is placed on each side of a plain timber butt joint, and then a hydraulic press forces the plates together forming an extremely strong joint.
They are no longer the cutting edge of roof design; rather they are used for the thousands of simple cost effective house designs that are mainstay of the house construction industry. They can not be used for flat pitch roofs. ”(builder bill, 2010) The structural science behind truss is fairly complex; the terms primary, secondary, and tertiary serve as a language used to define the roles that the various elements play within a truss system. Trusses are used because they provide strength against the combined dead, imposed and wind load forces within a structure.
Common forces that structures experience include: tension, torsion, bending, and shear. Primary elements are the elements that bear the greatest load. Webs carry the shear force. In the diagram above, the web elements are the bars that tie the bottom and the top members of the truss system. Secondary elements refer to the elements that carry the second greatest force or load. Tertiary elements carry the least load. The function of the chords is to carry the static force of the load applied to the structure. 7 References: 1. Roof truss, 2010. www. Builderbill-diy-help. com/roof-truss. html
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