Table of Contents for Residential Building Preliminary Estimate Excel–
- Introduction to Preliminary Estimates
- Residential Building Preliminary Estimate
- Components of Preliminary Estimate
- Excavation & Backfilling
- Concrete
- Reinforcement & Shuttering
- Brickwork, Plaster & Painting
- Doors & Windows
- Plumbing, Sanitary Fittings, and Electrical Fittings
- Contingency
- Contractor Profits & Overheads
- Download the Residential Building Preliminary Estimate Excel file
- Conclusion
Introduction to Building Preliminary Estimates
Preliminary estimates give a first-hand idea about the work quantity to be executed for a project. The preliminary cost estimate is related to the cost of the project. Such estimates are prepared at the conceptual phase of the project.
The preliminary estimate forecasts the budget required to complete the project. It is often prepared based on historical data of similar projects and thumb rules. These estimates are easy to prepare, take lesser time and involve no or nominal cost.
Such estimates can even be prepared if no design, drawing and specification have been prepared yet.
Another type of estimate prepared is a detailed cost estimate. Such estimates are prepared after finalising the design, drawings and specifications for the project. The taken to prepare a detailed estimate is higher than a preliminary estimate. The detailed estimate is more accurate and has greater precision.
This article deals with the introduction to a preliminary estimate, methods of preliminary estimate for residential building and different components to consider in the estimate. A free, downloadable, and print-friendly excel file to ease your preliminary estimation for a multistorey residential building.
Residential Building Preliminary Estimate
It is a regular practice to work out the preliminary estimate of the project to develop a business case or to pitch to potential investors. The preliminary estimate for a residential building can be prepared by any of the following methods-
- Plinth Area Method
- Cubic Content Method
- Approximate Quantity Method
Plinth Area Method
The plinth area method is relatively the easiest way to prepare a preliminary estimate. All you need to do is sum up the plinth area of each floor of the building and multiply it with the construction cost per unit plinth area.
The construction cost per unit plinth area is a generalised cost for the residential buildings for a locality. It changes from place to place depending on material availability, local taxation, availability of labour etc.
The plinth area method is the least accurate method as it doesn’t take project site considerations, project exclusive specifications etc. It can be prepared without the design and drawing of the project.
Cubic Content Method
The cubic content method takes the 3-dimensions into account as opposed to the 2-dimensions in the plinth area method. The plinth area is multiplied by the height of a storey to get the cubic content for a storey of a building.
The cost estimate is determined by the product of cubic content and the cost of each storey.
Approximate Quantity Method
The approximate quantities are worked out from the conceptual drawings. The quantities of excavation, backfilling, concrete, brickwork, plaster and paint etc. are calculated and multiplied by their respective rates. The amount of each item is summed up to get the construction cost.
The approximate quantity method is more reliable out of the above three methods as it is based on drawings. However, these three methods are only good for a preliminary estimate.
Components of Building Preliminary Estimate
Excavation & Backfilling
The excavation is done for constructing the foundations of the building. The excavation can be either done manually or by mechanical equipment like a backhoe, excavator. The method of excavation is decided as per the quantity of excavation, soil strata, time availability, availability of equipment and labour etc.
As a thumb rule, 10% area is excavated in the plinth area. For excavation volume, take 3.5 times the quantity of substructure concrete.
Backfilling is the process of soil filling in space left after casting of the substructure of the building. The backfilled soil may be the same as the excavated soil or another soil transported from elsewhere.
The volume of backfilled soil is observed to be 100-110% of excavated soil considering the additional 0.3m high filling above the natural ground.
Concrete
The concrete is used as PCC and RCC. The PCC is used below foundations to provide firm & levelled support for foundation reinforcement. Another use of PCC is screed concrete placed over the floor for levelling and finishing.
The RCC forms the framed structure. It is the main element of building foundations, columns, beams, lintels, slabs etc.
For PCC below foundations, consider 35% of the substructure RCC. For screed concrete, take 1% of the built-up area.
The RCC is estimated as 0.038 times the built-up area in square-foot. The bifurcation ratio of the RCC into substructure and superstructure depends upon the number of storeys and range from 0.25-0.4.
Reinforcement & Shuttering
The reinforcement is the backbone of the RCC structure. The shuttering is the temporary mould for concrete to take up the shape before setting.
The reinforcement percentage for footing, beam, column and slab is taken as 0.8%, 2%, 2.5% and 1% of RCC volume respectively. The reinforcement can be taken as 4.5-4.75 kg per square foot of the built-up area for residential buildings.
The shuttering quantity in square meters is generally considered as 6 times of RCC quantity. Another method to estimate shuttering is to multiply 2.4 by the built-up area.
Brickwork, Plaster & Painting
The brickwork is done to cover the building and also to make internal partitions in the structure. The plaster is the layer of cement mortar applied over brickwork to provide a smooth & uniform finish.
The brickwork is done in two thicknesses. The 230 mm thick brickwork is generally done for the outer walls. The internal partitions are made with a 115 mm thick brickwork wall.
The 230 mm thick brickwork is generally 0.8-1% of built-up area and measured in cubic meters. For 115 mm thick brickwork, consider 6-9% of the built-up area and measure in a square meter.
The plaster is made for various thicknesses ranging from 8mm to 20 mm depending upon the unevenness of the brickwork. The measurement for plasterwork is done in square meters and quantity is considered as 35-50% of the built-up area.
Doors & Windows
The doors & windows can either be measured in number or square meter. The doors and windows should be manually calculated taking standard sizes.
The door height can be taken as 2m while the width varies from 0.9-1.5m depending upon the use.
Plumbing, Sanitary Fittings, and Electrical Fittings
The water supply system and the tank shall be considered as 4-5% of the building cost. This includes the cost of the storage tank, pipe fittings, washbasins, showers, tap connections. For borewell, the actual cost shall be added as extra to the above estimate.
If the sewer line is available in the vicinity of the building, the cost of sanitation works shall be 4-5% including pipe connections, inspection pit, traps, water closets, cisterns etc. For soak-pit formation additional 3-4% of the building cost should be provided, making the total cost of sanitation 8%.
The electrical fittings including fans and lights should be considered as 12% of the building cost.
Contingency
The contingency covers all such expenses that are not covered in the above heads. These expenses often arise due to change in requirement, rework, unexpected site condition, quality up-gradation etc.
The ideal value of contingency should be 3-5% of the construction cost.
Contractor Profits & Overheads
The contractor profit is generally 10% of the construction cost. The overheads that a contractor incurs include work permits, office & stationery, supervision charges, worker’s accommodation, statutory charges, insurance, safety, IT, power and water for construction and workers etc.
The overheads may change from contractor to contractor and vary between 10-25% of the construction cost.
Download the Residential Building Preliminary Estimate Excel file
The residential building preliminary estimate excel file produces fair results for buildings up to G+5 storeys. The user has to input the plinth area and the excel sheet calculates the item-wise quantity break up as per the above-mentioned thumb rules.
On entering the unit rates for each item, the item-wise cost and total cost can be calculated along with the cost per square feet of built-up area.
The pie chart represents the % of each head against the total cost.
Another worksheet is also available for printing. The worksheet presents the data in a more print-friendly manner to save you any manual formatting.
Conclusion
The thumb rules used in the excel workbook are derived from various sources and historical data of many multi-storey residential buildings. Although, the results are fairly good for preliminary estimates. However, the detailed estimate should be prepared as soon as the details as available to minimise the room for error in budgeting.
I hope the article has helped you understand the preliminary estimate for the residential buildings. The various thumb rules mentioned above will definitely level up your estimation skills and help in advancing your career in planning, billing and quantity surveying domains. Also, check out these 5 skills that will help you quickly learn quantity surveying.
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