Clerk of works

Clerk of works

Posted By: Blue Print Blog on 7th of November 2013

The Clerk of Works often abbreviated CoW, is employed by the architect or the client on a construction site with the primary responsibility of representing the interests of the client on the project. In addition to recognizing the quality standards of the work the CoW is also charged with ensuring that the quality of both materials and workmanship are in accordance with the design information such as specifications and engineering drawings. The qualification for clerk of works can be held in three specializations: electrical, mechanical and construction. Historically the clerk of works was employed by the architect on behalf of a client or by local authorities to oversee public works. But in modern era the CoW can also be employed by the client (state body/local authority/private client) to monitor design and build projects where the traditional role of the architect is within the design and build project team.  The role The role of this position is based on the impartiality of the clerk of works in ensuring that value for money for the client - rather than the contractor - is achieved through rigorous and detailed inspection of materials and workmanship throughout the building process. He should be independent in decisions and judgments. He cannot normally, by virtue of the quality role, be employed by the contractor –but only the client or normally by the architect on behalf of the client. His role is not to judge, but simply to report all occurrences that are relevant to the role.  In many cases, the traditional title has been discarded to comply with modern trends, such as site inspector, architectural inspector and quality inspector, but the requirement for the role remains unchanged since the origins of the title. Clerks of works are either on site all the time or make regular visits. They need to be vigilant in their inspections of a large range of technical aspects of the work. The role involves; Making sure that work is carried out to the client's standards, specification, correct materials, workmanship, and schedule. Becoming familiar with all the relevant drawings and written instructions, checking them, and using them as a reference when inspecting work. Making visual inspections. Taking measurements and samples on site to make sure that the work and the materials meet the specifications and quality standards. Being familiar with legal requirements and checking that the work complies with them. Having a working knowledge of health and safety legislation and bringing any shortfalls observed to the attention of the resident engineer. Advising the contractor about certain aspects of the work, particularly when something has gone wrong, but this advice should not be interpreted as an instruction.

Glass Blocks

Glass Blocks

Posted By: Blue Print Blog on 31st of October 2013

Glass block is an architectural element made from glass and they are used in a building to add beauty while at the same time to provide visual obscuration while admitting light. The glass block was originally developed in the early 1900s to provide natural light in manufacturing plants but over the years it has been considered as an element of interior design commonly applied as part making the interior of the house more appealing to the eye.  Glass bricks are produced for both wall and floor applications. Glass blocks for use in floors are normally manufactured as a single solid piece, or as a hollow glass block with thicker side walls than the standard wall blocks. These blocks are normally cast into a reinforced concrete grid-work or set into a metal frame, allowing multiple units to be combined to span over openings in basements and roofs. Glass wall blocks should not be used in flooring applications. Hollow glass wall blocks are manufactured as two separate hemispheres and, whilst the glass is still molten, the two hemispheres are pressed together and annealed. The resulting glass blocks will have a partial vacuum at the hollow centre. Glass wall blocks in a house are erected after the floor and wall finishes are completed can be erected in short walls of three feet high to full height walls. They can be used to divide an entry porch and a sunken lounge or dinning. The blocks can also be used in a niche that provides light into a dark lobby as well as in the bathrooms as cubicles or for beauty since have they have good aesthetics. When installing glass blocks the area to be walled should be clean and free of any debris and dust and the abutting masonry should have the plaster complete as the blocks will be an in fill as they are not load bearing. The wall can be reinforced on the sides with aluminum frames to house doors or openings.  The bonding should be carefully done in accordance to the manufacturer’s instructions.  The most commonly used bonding agent with glass wall blocks is Silicon. Care should be taken to ensure that every part of the joint is filled with the adhesive. When all the courses are complete to the desired height the top of the wall can be finished with timber, aluminum or rubber rails. The top finishing is used as a protection for the glass block and can also be used for holding small flower pots, portraits, paintings or any other interior beauty enhancing objects.

Building a Safe Staircase

Building a Safe Staircase

Posted By: Blue Print Blog on 24th of October 2013

The staircase in a building is one means whereby one may travel from the level of one floor to another. The ease with which a stairway can be traveled depends upon the proper proportioning of the riser and tread of each step and the number of steps in one series or flight. The design of the building and the space allowed for stairs will control the type of staircase which may be built. The staircase, when carefully designed and built, adds dignity and charm to a home. The quality of craftsmanship displayed reflects the character of the entire interior of the building. In general, stair-work is considered a special field of carpentry. Stairways can be the cause of the greatest number of accidents in the home. These accidents can be attributed to various factors; some, of course, are beyond the control of those who design and build the stairways. However, there are far too many accidents due directly to faulty construction. The carpenter can make a worthwhile contribution toward accident prevention if he plans and does his work well. The following standards and suggestions should be observed when building the staircase to help avoid some of the causes responsible for the accidents; Stairways should be free from winder The dimensions of landings should be equal to or greater than the width of stairways between handrails (or handrail and wall) Landings should be level and free from intermediate steps between the main up flight and the main down flight. All treads should be equal and all risers should be equal in any one flight. The sum of one tread and one riser, exclusive of the nosing, should not be more than 18 inches nor less than 17 inches. (Stair ratio). The nosing should not exceed 13/4 inches. All stairways should be equipped with permanent and substantial handrails 36 inches in height from the center of the tread. All handrails should have rounded corners and a surface that is smooth and free from splinters. The angle of the stairways with the horizontal should not be more than fifty degrees nor less than twenty degrees. Stair treads should be slip proof, firmly secured and with no protruding bolts, screws, or nails.

The Collapse of Buildings

The Collapse of Buildings

Posted By: Blue Print Blog on 17th of October 2013

Buildings, like all structures are designed with special attention to allow the support certain loads without deforming. The loads that are taken into account during the design stage of any building include both live loads and dead loads like furniture and equipment. For a building to be declared safe for occupation it must be able to withstand the weight of rain and the pressure of wind as well as bear the load of the building itself. Buildings that comprise fewer floors, strength generally accompanies sufficient rigidity and the design is mainly that of a roof that will keep the weather out while spanning large open spaces. With tall buildings that consists of several floors the roof becomes a minor matter and the support of the weight of the building itself should be the main consideration since just like long bridges, tall buildings are subject to catastrophic collapse if considerable care is not taken during the design stage. The main causes of collapse in buildings can be generally classified under the following; Bad Design Faulty Construction Foundation Failure Extraordinary Loads Bad Design Bad design due to errors of computation and failure to take into account the loads the structure will be called upon to carry, erroneous theories, reliance on inaccurate data, ignorance of the effects of repeated or impulsive stresses, and improper choice of materials or misunderstanding of their properties may easily result into a collapse of the building. The engineer should take a keen interest during the design stage as he is bound to be held responsible in the event of these failures. Faulty construction Faulty construction has been the most often cause in recurrence of structural failure. This may occur due to mistakes arising from lax in inspection which includes the use of salty sand during concrete mixing, the substitution of inferior steel for that specified, bad riveting or even improper tightening of nuts, bad welds, and other practices well known to the construction worker. Foundation Failure Even an excellently designed and constructed structure will not stand on a bad foundation. Although the structure will carry its loads, the earth beneath it may not. The Leaning Tower of Pisa is a famous example of bad foundations but it is not the only one. The old armory in St. Paul, Minnesota, sank 20 feet or more into soft clay, but did not collapse. The displacements due to bad foundations may alter the stress distribution upon the building significantly. Extraordinary Loads Extraordinary loads are often natural, such as repeated heavy snowfalls, or the shaking of an earthquake, or the winds of a hurricane. A building that is intended to stand for some years should be able to meet the challenges of extraordinary load that may arise from frequent earthquakes and strong winds. Even a solid masonry building would be destroyed in an event of earthquakes if the foundation is not designed carefully to withstand external natural strains.

Building Demolitions

Building Demolitions

Posted By: Blue Print Blog on 3rd of October 2013

Demolition projects can range from small, simple jobs to complicated undertakings that require sophisticated and detailed planning. Site conditions can vary significantly, and there is always a degree of imprecision to the wrecking of the building itself. For typical building demolition and site improvements the most common procedure is to use heavy mechanical equipment such as wrecking balls, excavation hoes, grapples, crushers, and hydraulic breakers and shears. Several factors need to be considered prior to and during demolition, including the scheduling of demolition activities, protecting the site (especially important with occupied structures), and dealing with hazardous materials. With the demolition of structures, the owner, architect, engineer and demolition contractor need to be aware of the regulations that govern the demolition of buildings. Prior to allowing the demolition squad to start demolition operations, an engineering survey of the building that is marked up for demolition should be carried out by a competent and qualified person to determine the condition of the framing, floors, and walls, and possibility of unplanned collapse of any portion of the building. The demolition team should have in writing evidence that such a survey has been undertaken and the demolition process has been given a go ahead from the relevant authorities. Building demolition can include items that may not be apparent at first such as any below-grade structures that would include various types of footings and foundations. Also underground utilities that provided services to the building and the adjacent buildings will need to be considered during demolition. In rural areas--where buildings are not densely packed--and the built structures themselves are often smaller with fewer recyclable materials, demolition is usually uncomplicated, in that the structure can be knocked down and the debris can be removed all together but in urban and densely packed areas, demolition projects may require the hiring of an architect or engineer to produce documents, drawings, and specifications for building demolition. Contractors who specialize in demolition need to come up with a demolition schedule to manage the project. If the owner will be occupying a portion of the site or building during demolition, a schedule of demolition activities will be useful to avoid interference with any concurrent operations and to minimize any disruption of utilities and services. The owner may have additional restrictions that the contractor will need to consider when scheduling activities. Some typical owner restrictions include the protection of exterior stairs, loading docks, and entries of adjacent buildings, as well as a limitation on hours during which demolition operations may take place. However, every additional restriction the contractor needs to manage will usually be reflected in higher demolition costs. In areas with greater population density, the demolition of structures is not necessarily more complicated. Some situations are complex and mandate a high level of sensitivity to how demolition is handled, for example, demolition that takes place on a hospital campus. In these instances, a careful, piece-by-piece dismantling of the building is usually necessary, with material sorting often taking place on site. For such projects, an engineer or architect will need to be consulted to produce specifications to which the demolition must conform. The architect or engineer will produce the necessary documents which clearly outline the requirements for protecting individuals, adjacent buildings, and any remaining site improvements and utilities during the demolition operations.

Quality Construction of Suspended Floors

Quality Construction of Suspended Floors

Posted By: Nyumba Imara Blog on 7th of November 2013

Building suspended floors that are acceptably flat and level is one of the many challenges that contractors may have to face in the course of a project construction. Whether supported by steel beams or a cast-in-place concrete frame every elevated floor deflects or sags slightly under its own weight. Structural drawings generally require that individual floor framing members have a slight camber, or hump in their profile prior to construction so as when cambered floor framing members are allowed to deflect they ideally will move to a level position. When everything works right, the floor’s finished surface will then perfectly complement structural deflection. Forms and shoring should be designed to allow safe, easy removal, while protecting the structure from excessive deflections at early stages. However buildings come in many shapes and sizes and as the available materials and floor framing are assembled together unique combinations are created thus the resulting floor systems do not always deflect to the engineer’s expectations. That's why the successful contractor must remain flexible and be ready to respond to jobsite developments. Success depends on two things—an effective preconstruction planning program and the ability to identify and adjust to unexpected conditions. Monitoring the Construction The goal in constructing any project is to meet and if possible exceed the requirements of the specifications. When evaluating construction of floors, the following standards, depending on the structural system should apply; Structural steel must be properly erected Steel connections must conform to the contract document requirements Concrete reinforcement must be placed and maintained in the proper location Concrete mix design, strength, and slump must conform to the specification Finished floor surfaces must meet the specified tolerances for levelness and flatness. The following are essential elements to be put in place so as to achieve a quality suspended floor; Preconstruction planning and meetings to minimize potential problems Gathering information during construction to allow evaluation of the work Responding to unexpected results by adjusting the design or construction Confirming that the adjustments are successful. Controlling quality Controlling the elevation of the supporting platform requires that engineering controls be established. The monitoring program for a structural steel frame provides key information about critical components such as base plate, column splice, and beam-to-column connection elevations, along with deflection of typical framing members. On a cast-in-place concrete frame, the contractor should select forming and shoring systems. Forms and shoring should be designed to allow safe, easy removal, while protecting the structure from excessive deflection at early stages. Evaluating concrete mix designs, delivery systems, and finishing techniques provides an opportunity to achieve the quality standards. Each decision will impact the flatness and levelness of the finished floor. Concrete mixes must develop adequate strength while providing good consolidation, consistent set time, and workability. The workers involved on the project must be capable of producing work that conforms to the quality standards. Concrete finishing techniques must produce the desired results. The pre-construction meeting is a good opportunity to address the team's plan for coping with isolated locations where actual deflection of the floor might be different from what is expected. Discussing job site controls for structural steel, form-work, reinforcing steel, concrete, and finished surface profiles will help ensure that backup systems are ready. Changes and substitutions in materials or admixtures should not be made without notifying and obtaining approval by the rest of the design/construction team.

Common Plaster Problems

Common Plaster Problems

Posted By: Nyumba Imara Blog on 31st of October 2013

When plaster dries, it is a relatively rigid material which should last almost indefinitely. However at times the plaster work may start cracking due to several conditions.  Some of the conditions that may cause the plaster to crack, efflorescence (that is to lose moisture and turn to a fine powder on exposure to air), separate, or become detached from its lath framework include; •    Structural problems •    Poor workmanship •    Improper curing •    Moisture Structural Problems 1. Overloading Stresses within a wall, or acting on the house as a whole may end up creating stress cracks. Appearing as diagonal lines in a wall, stress cracks usually start at a door or window frame, but they can appear anywhere in the wall, with seemingly random starting points. The weight of the roof, the second and third stories, the furniture, and the occupants may impose a heavy burden on beams, joists, and studs. Even when houses are built properly, later remodeling efforts may cut in a doorway or window without adding a structural beam or "header" across the top of the opening. Occasionally, load-bearing members are simply too small to carry the loads above them and may lead to deflection or wood "creep" (deflection that occurs over time) thus creating cracks in plaster. Overloading and structural movement combined with rotting floorboard, rusted nails, or poor quality plaster results in the plaster detaching from the lath (floorboard) therefore losing its key. When the mechanical bond with the lath is broken, plaster becomes loose or bowed and if repairs are not made, especially to ceilings, gravity will simply cause chunks of plaster to fall to the floor. 2. Settlement/Vibration Cracks in walls can also result when there is settlement in a house. Houses built on clay or black cotton soils are especially vulnerable to cracks when settlement occurs as clay soils are highly expansive. In the dry season, water evaporates from the clay particles, causing them to contract. During the rainy season, the clay swells thus causing a building that is not structurally sound to be riding on an unstable footing. Diagonal cracks running in opposite directions suggest that house settling and soil conditions may be at fault. Similar symptoms occur when there is a nearby source of vibration-blasting or busy highway. 3. Lath Movement Horizontal cracks are often caused by lath movement. Because it absorbs moisture from the air, wood lath expands and contracts as humidity rises and falls. This can cause cracks to appear year after year. Cracks can also appear between rock lath panels. A nail holding the edge of a piece of lath may rust or loosen, or structural movement in the wood framing behind the lath may cause a seam to open. Heavy loads in a storage area above a rock-lath ceiling can also cause ceiling cracks. Errors in initial building construction such as improper bracing, poor corner construction, faulty framing of doors and windows, and undersized beams and floor joists eventually manifest through to the plaster surface.