Several convenient methods for estimating construction costs and quantities

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Several convenient methods for estimating construction quantities. Utilizing various techniques to calculate quantities quickly and accurately is an important challenge for those working in project budgeting. Next, I will discuss some experiences and tips for manual quantity calculation for reference. Using various bases to calculate quantities: There are some bases that are used repeatedly in quantity calculation. For these bases, we should determine their values before calculating the quantities for each individual item, so that they can be used directly in subsequent calculations, eliminating the need to compute them again each time. This helps save time and improves the speed and accuracy of the calculations. These bases are mainly the \"three lines and one area\", namely the \"outer edge line of the exterior wall\", the \"center line of the exterior wall\", the \"net length line of the interior wall\", and the \"building area\". Regarding the length of the \"third line,\" when the wall thicknesses vary or the floor plans differ from one level to another, the measurements should be taken separately for each wall thickness and each level. In addition, \"net indoor area,\" \"floor area on the ground floor,\" and \"net length of interior walls\" are also commonly used as bases. 1. The building area (S_building_area) and the area of the first floor (S_first_floor_area) are themselves also calculation indicators for various components, such as scaffolding and vertical transportation elements; under normal circumstances, the quantity associated with these elements is equal to S_building_area. The floor area of the first floor of type S can serve as a basis for calculating the quantities required for tasks such as site leveling, ground bedding, leveling layers, surface finishes, and waterproofing layers. For example, in the budgeting standards for construction projects in Beijing, the quantity associated with site leveling was calculated using the formula S = 1.4 × the floor area of the first floor of type S. 2. Net indoor area (S_net indoor area): The net indoor area can serve as a basis for calculating the volume of soil to be used for filling inside the space, as well as for determining the amounts needed for floor leveling, underlayment, surface finishing, and ceiling plastering. There are two points to note when using this base value: First, if the floor is covered with slab flooring, the quantity S for the floor covering should be calculated based on the net indoor area S, plus the area of the slabs at the doorways ； Second, if the ceiling is sloped, the slope coefficient should be multiplied by the net indoor area. 3. Length of the outer edge line of the exterior wall (L_outer_edge_line). The outer edge line of the exterior wall serves as the basis for calculating costs related to the apron, the decoration of the exterior wall surface, and the external scaffolding. (1) Calculation of scuppering. According to the calculation rules specified in the budget quota, the area of the apron is calculated based on its actual surface area. If the shape of the building is a polygon that is not rectangular, it becomes difficult to carry out the calculation using the method of adding up individual areas. In practical engineering, we can calculate it in this way: if the width of the apron is B, then the area of the apron, denoted as S, is given by S = perimeter of the outer wall × B + 4B². This formula applies not only to buildings with a rectangular shape but also to those with non-rectangular shapes. (2) Calculation of the decorative area for the exterior wall (base). If the height of the building’s exterior wall (base) is H, then the decorative area S of the exterior wall (base) is equal to L × H, where L is the outer perimeter of the wall. (3) Calculation of the workload for external scaffolding. The volume of work for the external scaffolding is S = L × H, where L is the outer perimeter of the exterior wall and H is the eave height. 4. Exterior wall center line (L_exterior wall center line): The exterior wall center line serves as the basis for calculating the quantities associated with tasks such as the earthwork for the exterior wall foundation trench, the volume of the exterior wall foundation, and the moisture-proof layer of the exterior wall foundation. (1) Earthwork for the exterior wall foundation trench: V = L (centerline of the exterior wall) × S (cross-sectional area of the trench). (2) The volume of the exterior wall foundation is V = L (centerline of the exterior wall) × S (cross-sectional area of the trench). (3) The volume of the exterior wall is V = L × center line of the wall × H × δ, where H is the wall height and δ is the wall thickness. (4) The area of the moisture barrier for the exterior wall foundation is S = L × center line of the exterior wall × δ, where δ is the thickness of the exterior wall foundation. 5. The net length of the inner wall (L_net_inner_wall). The function of the net length of the inner wall is primarily to be used in calculating the volume of the inner wall; the volume V of the inner wall is equal to L_center_outer_wall × H × δ, where H is the height of the wall and δ is the thickness of the wall. It is worth noting that we cannot use the net length of the inner wall in calculating the volume of soil in the grooves of the inner wall and the volume of its foundation, just as we do with the center line of the exterior wall; this is because the net length of the inner wall is not equal to that of its foundation, with the former being larger in value than the latter. http://img.civilcn.com/d/file/zhishi/gczj/2020-04-29/d5479d375d49154e617758f5a60b8d1a.jpg6. The net length of the inner wall surface (L_net length of inner wall surface). The net length of the inner wall surface is different from the total length of the inner wall; the inner side of an exterior wall is also referred to as the inner wall surface. It is convenient to calculate the quantities for skirting boards and interior wall plastering using the net length of the inner wall surface. (1) The calculation of the length L of the baseboard is based on the regulatory specifications: the quantity required for the baseboard corresponds to the perimeter of the interior space, that is, the length of the inner walls of the room; hence, L equals the total length of the inner wall surfaces. However, the baseboards in the corrosion and acid resistance sections cannot be calculated using this method. (2) The plastering area S of the interior walls is as described earlier. Interior walls are different from regular wall surfaces; if only the net length of the interior walls is used for calculation, it will lead to underestimation of the work volume. To calculate the plastering volume for an interior wall, use the net length of the interior wall; thus, S = L (net length of the interior wall) × H, where H is the net height of the interior wall. Of course, when calculating, we can also use several bases in combination. If we determine the net length of the inner wall surfaces, we can use the formula for calculating the area of a rectangle to find the net indoor area S. The floor area of the first floor can be calculated by using the outer dimensions of the exterior walls. Arrange the calculation order properly. Properly organizing the sequence of calculations for the quantities involved is one of the key factors for calculating those quantities quickly and accurately. For general projects, the sequence for calculating the quantities of various sub-projects should be: first the underground parts and then the above-ground parts; first the main structure and then the decorations; first the interior areas and then the exterior areas. When calculating the architectural and decorative components, it is also necessary to arrange the calculation order properly. 1. When calculating the construction costs, it is necessary to follow the sequence of foundation work, earthwork, concrete work, wooden doors and windows work, and masonry work; it is not appropriate to use the order outlined in the standard specifications. Otherwise, certain items will be calculated repeatedly, resulting in a significant loss of time. For example, once we have calculated the volumes of beams and columns as well as the areas of doors and windows in concrete works, we can use those previously calculated values to determine the volume of concrete components within the walls and the space occupied by doors and windows within those walls when calculating masonry work. When using these figures, two issues need to be taken into account: first, it is necessary to check whether concrete elements such as beams and columns are within the wall being calculated; if they are within the wall, they should be deducted, otherwise not ； Secondly, when the width of beams and columns differs from the thickness of the walls, that is, when beams and columns are not entirely within the wall structure, only a partial deduction is possible; the entire volume of the concrete component cannot be deducted. Similarly, when calculating the backfill volume and soil transportation, the volume of the brick foundation can also be utilized in subsequent calculations. Rules for calculating leveled site area 1. Listing rule: Calculate based on the area of the first floor of the building, according to the dimensions shown in the design drawings. 2. Quota rule: Calculated based on the area of the first floor of the building, according to the dimensions shown in the design drawings. Calculation method 1: Area of the leveled site according to the bill of quantities rules = Floor area of the ground floor.
Calculation method 2: Area of the leveled site according to the quota rules = Floor area of the ground floor.
Notes: 1. In some areas, the area of the leveled site according to the quota rules is calculated by extending 2 meters beyond the outer edge of the exterior walls. During calculation, the area is divided into sections based on a shape that extends 2 meters beyond the outer edge of the exterior wall, and then the results are combined with the floor area of the ground floor ； Or, calculate it by using \"center line of 2m outward distance × 2 = area of 2m outward distance\" and combine it with the floor area. In this case, the following difficulties arise during calculation: ① Dividing into blocks is complicated, and the curved sections are difficult to handle, leading to errors easily ； ②Calculating the center line of 2m is rather complicated and difficult ； ③After extending it 2m, overlapping areas may appear, and it’s difficult to determine exactly how much should be deducted. 2. In an inventory-based environment, bidders may need to calculate the volume of work required for leveling the site based on the actual conditions on site, with different amounts added to each side. Rules for calculating earthwork excavation 1. Listing rule: The earthwork for excavating foundations is calculated by multiplying the area of the foundation cushion base by the excavation depth, based on the dimensions shown in the design drawings. 2. Quota rules: The volume of earthwork excavated by manual or mechanical means should be calculated by multiplying the area of the bottom of the trench by the excavation depth. The bottom area of the trench should be calculated by multiplying the length of the trench bottom by its width; the length and width referred to here are the outer edges of the concrete pad, with the working surface taken into account as well. If there are drainage ditches, their outer edges should also be included in the calculation. The volume of the drainage ditches should be included in the total earthwork volume. When grading is required, the volume of soil for grading should be included in the total soil volume. Calculation Method 1: Checklist Rules ① Method 1 for calculating the base area of earthwork: Use the building area of the bottom layer plus the area from the outer surface of the exterior walls to the outer surface of the cushion layer. The area is calculated as the area between the outer edge line of the exterior wall and the outer edge line of the cushion layer; this can be done by dividing the area into sections based on the shape formed by extending the outer edge line of the exterior wall, or by using the formula \"center line of the extended shape × length of extension\". Method 2: Calculate the area of the outer boundary line of the cushion layer in segments (similar to calculating the building area in segments). ②Calculate the volume of earthwork: Volume of earthwork = Base area of the excavation × Depth of excavation. 2. The fixed-ratio rule uses the volume formula for frustums to calculate the upper and lower base areas of the excavated soil. V = 1/6 × H × (S_upper + 4 × S_middle + S_lower) is used to calculate the volume of earthwork (where S_upper is the area of the upper base, S_middle is the area of the middle cross-section, and S_lower is the area of the lower base). S_lower = the building area of the bottom layer + the area from the exterior wall surface to the edge line of the excavation bottom (including the working surface, drainage ditches, slopes, etc.). Calculate S under and S below using the same method. http://img.civilcn.com/d/file/zhishi/gczj/2020-04-29/43f55a16a2e4ebf488db4d384e69cfaa.jpg Calculation methods for strip foundations: 1. Volume of plain soil cushion: For exterior wall strip foundations, the volume of plain soil = length of the center line of the plain soil layer on the exterior wall × cross-sectional area of the plain soil. For interior wall strip foundations, the volume of plain soil = length of the net length of the plain soil layer on the interior wall × cross-sectional area of the plain soil. 2. Volume of lime-soil cushion: For exterior wall strip foundations, the volume of lime-soil = length of the center line of the lime-soil layer on the exterior wall × cross-sectional area of the lime-soil. For interior wall strip foundations, the volume of lime-soil = length of the net length of the lime-soil layer on the interior wall × cross-sectional area of the lime-soil. 3. Volume of concrete cushion: For exterior wall strip foundations, the volume of the concrete cushion = length of the center line of the concrete cushion layer of the exterior wall strip foundation × cross-sectional area of the concrete cushion. For interior wall strip foundations, the volume of the concrete cushion = length of the net length of the concrete cushion layer of the interior wall strip foundation × cross-sectional area of the concrete cushion