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Construction planning is a fundamental and challenging activity in the management and execution of construction projects. It involves the choice of technology, the definition of work tasks, the estimation of the required resources and time limits for certain tasks and the identification of any interactions among the work tasks. An appropriate construction plan is the starting point for developing the budget and the schedule of work. Developing the construction plan is a vital task in the management of construction. It may also be essential to make organizational decisions about the relationships between project participants and even which organizations to include in a project.
Having bought a piece of land and being satisfied that it is capable of being developed, the owner may want to construct a building on the site (like the one in the scenario provided). The relationships between the different parties in a construction project are complex. In general, five different groups of people are involved, namely, the owner (as employer), building contractor, architect, quantity surveyor, and engineers.
The owner of the site will employ various professionals to design and construct a building on their land. In a traditional building contract, the building contractor is employed by the owner to construct a building according to the plans and specifications prepared by the owner's architect. The contractor has a direct contractual relationship with the owner and will then enter into sub-contracts with other builders who will carry out the work. Under the building contract, the main contractor agrees to complete the work set out in the contract in the form of the architect's plans and specifications. Design and build contracts are modern forms of building contracts that function differently from the traditional building contracts. All the design work is carried out by the main contractor's architect. The owner does not have to engage an architect themselves. In practice this means that after indicating to the main contractor their requirements, then owner has to just wait for the building to be finished.
In a traditional contract, the architect will be engaged by the owner to prepare plans and specifications of the building work. The architect will also supervise the execution of work by the building contractor and sub-contractors. When the architect is satisfied with the work done by the building contract they will issue a certificate of practical completion.
The quantity surveyor is engaged by the owner (or by the architect on behalf of the owner) to estimate the quantities of the materials to be used and to set them into bills of quantities. On the basis of these bills of quantities, the building contractor is able to work out the cost of their tender.
In construction projects, there may be a team of consulting engineers engaged by the owner to give advice on matters relating to structural design, ventilation, heating, etc.
For this project I have outlined nine main stages, to which I will expand on, for the construction process of a dwelling. As there are two hundred homes to be built, the same process will be repeated throughout. The procedures outlined below show the different types of construction required for this project:
Pre-construction - Still in the beginning stages, the designs are finalized and all the materials are ordered. A Construction procedure is set out, so duration is given on the project.
Foundations - The suitable foundations are set for the ground. As there are 200 home to be built, the type of foundation that is used in this project is Shallow Foundations. Once these are set in, there is no going back.
Framing - This is the skeleton of the dwelling. Floors, walls, stairs and the roof are constructed.
Exterior finishes - The exterior of the dwelling is carried out.
Mechanicals and Electricals - At this stage mechanical aspect such as wiring and plumbing are completed. The pipes and wires are still exposed at this stage; there are a few more stages before the interior is complete.
Interior finishes - The walls and ceilings are filled in: interior doors are installed along with cabinets, shelves, and flooring. The plumbers and electricians return to complete their jobs, installing all appliances, connecting showers, baths etc.
Landscaping - This stage marks the beginning of the end. The gardens and any driveways are formed. This includes placing plants, grass and trees etc.
Pre-closing - While the landscaping is being finished, final inspections are being conducted. If any problems are found, they are repaired before entering the next stage. Once any repairs are made all remaining construction materials are removed, and the dwelling is cleaned and ready for the closing.
Closing - Minor repairs are carried out to finalise the closing deal. Once the all ok has been given, it is final for the owners to move in.
As the above stages set out briefly the construction process for a dwelling, it does not show the process for a whole community build for 200homes. This requires a lot of planning and detail. The following procedures will be used for each of the dwellings.
Reinforced Concrete Shallow Foundations:
The foundations of the house is the most important part of the build structure, if this part is not done properly it could cause severe problems in the future with the dwelling.
Shallow foundations are constructed relatively close to the ground level. Shallow foundations can only be used where the soil at that level is capable of adequately supporting the load. They are founded at a minimum depth in the UK to resist damage from frost, and in cohesive soils, the presence of nearby trees can affect the depth of the foundation.
Shallow foundations can be sub-divided into the following main types;
Strip foundations (footings) - a linear foundation which generally supports walls.
Pad foundations - a discrete square or rectangular foundation supporting columns or piers.
Raft foundations - a large single foundation supporting a whole structure.
Shallow foundations are generally constructed using in-situ concrete but some substructure elements can alternatively be constructed in precast concrete in part or whole to improve speed of construction on site. For this project the favoured type of shallow foundation required is strip foundations.
Brick & Block Masonry:
Following excavation and installation of foundations, bricklayers erect cavity walls that consist of an inner and outer skin. The inner skin is the main structural element, which supports internal floors and the roof structure. It is constructed using concrete blocks laid on beds of sand and cement mortar. The outer skin is the first line of safeguard against the elements and provides the aesthetic element to the structure. It is constructed using brick, stone or block work, which can take a number of finishes. The two skins are connected by steel wall ties and separated by a cavity that is (in this case) fully insulated. Plastering is then carried out so the interior is made good to decorate. Plastering is a key factor at is eliminates irregularities such as boards and nails. It does not erode when a leak occurs.
The main advantage is using this process is good thermal performance. Masonry materials have a high thermal mass, which is their ability to absorb and store heat. In the summer this keeps the building cool and in the winter the heat stored during the day is slowly released back into the house at night leading to a more constant, comfortable environment. This effect is improved if plaster is applied directly to block work.
Internal floors can be constructed using timber joists, composite timber I beams, or one of the precast concrete systems available. The roof is usually traditional cut timber or prefabricated truss construction
Timber floors and ceilings:
The traditional timber beams, spanned across the inner walls to form a frame for the floor. Insulation is then placed inside the floor frame and then covered on top by chip board or plywood. This method is favoured by most trades people as it makes it easier for them to cut their pipes and wire's into the timber. Advantages are that they are probably the cheapest method of building the floor and easier to work around. Disadvantages are that after a while they can be noisy due to the movement of the wood in the heat and cold.
Pitched Timber Roof Trusses with Tiles:
Here is an example of the type of roof that will be used for this project.
The Roof trusses will be constructed by joining timber members together with galvanised steel plate connectors at junctions. The plates are inserted in factory conditions under heavy pressure on both sides. The roof will then be delivered to the site as prefabricated components where they will be fixed to the wall plate with suitable metal plates. Wall plates will also be fixed to the supporting walls. The trusses will not require any ridge board or purlin, the will be placed at 600mm centres along the wall plate. To ensure overall stability, the trusses will be fixed together with longitudinal, diagonal and chevron timber braces. These will then be fixed to rafter members, internal members and ceiling chords. The truss design will allow for the load that the water tank will impose on it.
Battens are the support system for the tiles or slates. Each tile has to be nailed to the wood and clipped on to the one next to it. When all of them have been put in place, they need to be checked so that each row is off set to each other and not placed in vertical straight lines as this can cause problems when the wind is strong or in heavy rain. The top of the roof is finished off with ridge tiles. Fascia is the next area of the roof to be completed. The fascia covers the end of the wood at the bottom of the roof and allows the air to flow safely through the membrane for venation.
Internal Timber Partitions:
The walls of the house are based on the cavity wall construction, where there is a gap of at least four inches between the outer and the inner walls. These lightweight stud partitions are used throughout in timber framed builds as well as in traditional builds. For load bearing situations, they can be strengthened with plywood or orientated strand board strips of 50 x 100mm softwood and horizontal lengths of wood that fit between them on which sheets of plasterboard are attached The studs are fixed to the floor at regular intervals on sole or base plates and to the ceiling with head plates. The base plates are set in position first, marking the room layout. This gives a visual idea as to the room sizes.
With timber-framed construction, the standard depth of the studwork is 140mm, to allow for mineral fibre insulation to fill the studs. Using phenolic rigid foam boards instead will increase the 'U' value considerably, but to achieve good air tightness, the frame will need to be lined effectively on the inside once it and the internal walls are up. Polythene sheeting is pinned over the studwork. Aluminium tape is then used to seal the joints before the plaster boarding is commenced.
For the Community Hall, the main design features for this is 1 Assembly Hall, a small office, kitchen and a toilet. The construction procedures that will be discussed in detail are as follows:
Here is a design view of the overall view of the Community Hall:
Reinforced Concrete Foundation and Floor:
The foundation concrete that is reinforced with steel allows buildings to be done more stories upwards. This means the concrete base can take more loads. The trench must be excavated to the required depth. Concrete is obviously never to be put in loose soils. This can cause the dwelling to collapse. The diameter for the reinforcement bars to use is from a quarter inch.
In a reinforced concrete foundation, the work commences by excavating a trench to vital depths. The trench width is about two feet wide. The depth should be on hard ground and varies from site to site. High yield bars are cut and tied together. They are made into three long bars that will run the whole length of the trench. These will be the top bars. Additional bottom bars running the across the width of the trench are tied to the top ones. A spacing of eight inches is done when joining the reinforcement bars.
The foundation trench bottoms are made level to receive the concrete. A blinding layer of two inches thick is then added to the trench and made level. The Thickness of the foundation concrete is marked with steel pegs driven into the blinding. This will mark the height of concrete which is eight inches thick. Reinforcement is then laid into the trench. This should not rest directly on the blinding layer. Spacer blocks are put underneath to allow the concrete to flow below. They provide cover to the steel.
Once the reinforcement is placed in the trench, concreting can proceed. Care is taken to avoid debris entering the trench. This should be cleaned out. In the case of a sloping site, the foundation is stepped a full masonry course. The concrete is mixed in the ratio of one part cement, two parts sand and three parts ballast. The ready mix is then poured into the reinforcements. It is levelled with pegs already placed. It then spread as it is being vibrated. It should be thoroughly cured for minimum seven days to achieve strength.
Laying the concrete floor is major construction. Big areas that need to be cemented are prepared before the pouring of the concrete. For big areas that need to be cemented, ready-mixed concrete from batching plants are preferred because this type of concrete is precise. For the most part, hand mixed concrete would suffice for a floor area that is less than 1 cubic meter. In this case the contractors that will be carrying out the work will be using large concrete mixers that will be used on site.
To prepare for the concrete flooring, a line is drawn around the perimeter (via chalk) with a spirit level to mark the height of the new floor (Section 1). This line marks the top of the screed. Then the contractor will measure down from the first line about 50mm down, and this marks the top of the concrete layer (Section 2). From this another measurement downwards is taken about 100mm, the top of this marks the damp proofing and insulation layer (Section 3). From this point again the contractor will measure 50mm downwards - this line is the top of the sand layer. Again another measurement of 50mm is taken downwards - this marks the top of the hardcore layer (Section 4). Finally from this point another 100mm is measured to the base of the new concrete floor (Section 5). In total the minimum depth for this concrete floor from the original will be 350mm.
Here is a picture, showing the different sections required and lines marked out:
Now that the preparation has been done, the sections will then be in-filled with different materials. The first layer is the hardcore, which is made up of rubble of old bricks and tiles. When Section 5 has been reached, the hardcore is compacted. The hardcore is levelled up to Section 4 with a layer of sand. A sheet of damp proof membrane is placed over the sand, ensuring that it also reaches up to the wall just below the line of Section 1. The insulation boards are laid over. The concrete is then mixed and poured to fill the mould. To allow for the concrete to set, a polythene sheet is placed over it and allowed for three days to dry. To provide a smooth surface the contractor will then placed a screed over the floor
Steel Frame with Metal Cladding roof and walls with insulation:
The ability of a steel framed building to perform adequately depends on good interaction between the secondary steelwork and the cladding. Crucial to this interaction is the correct installation of the purlins and side rails. The purlins and side rails are normally installed by the steelwork contractor at the same time, or immediately after, the erection of the hot-rolled steel frame. The precise erection sequence will need to be determined by the steelwork contractor to suit the specific requirements of the building and fit in with the other construction activities. In determining the erection sequence, a governing factor will be the need to provide restraint to the rafters and columns, since the structure will not be capable of supporting its full design loading until the secondary steelwork has been fully installed. For this reason, it is not uncommon for the secondary steelwork installation to begin before completion of the primary steelwork. The lack of restraint in the temporary condition must be taken into account when assessing the capability of the frame to carry construction loads.
The total cost of this project according to my estimate would be at 17.75 million pounds. This includes all construction work, from employing labourers to paying the plans for the architect to purchasing materials etc. By pricing each house at £85,000, this totals to £17 million (85,000 x 200). This allows for half a million pounds to construct the community hall and the rest of the quarter million for any other financial aspects of the project.
The following pie chart shows the percentage costs from a buyer's point of view for any of the 200 properties, the breakdown cost for a typical 3bedroom property.
Sellers share of closing cost
Materials/labour/contractor costs & profits