9 Types of Estimation in Architecture and Their Purpose
The most important part of any design project is cost estimation. After all, the scope of the design and what elements we can implement depend entirely on the client’s budget.
There are many ways in which this calculation can be done and the mere scale of it might be a little overwhelming to start with.
There are different types of estimation in architecture:
Preliminary or approximate estimate
Plinth area estimate
Cube rate estimate
Approximate quantity method
Supplementary and revised estimate
Annual repair or maintenance estimate
1. Preliminary or approximate estimate
Preliminary or approximate estimate in architecture is the calculation of the approximate cost of the project done in the starting stages of the design. With this calculation, clients can know the rough budget of the project.
Since this estimate is done before the construction even starts, there is a chance that the cost may vary depending on the changes and variations that happen at any time.
Preliminary estimate depends on:
The type of building- The cost of the project obviously varies depending on the type of building. It might be a residence, a multi-storey building, commercial complex etc. Even for two buildings of the same size, the cost varies if they are of different types.
The total square foot area of the building: The cost also depends on the area. Bigger the scale of the project, the more the cost.
Height of structures: Taller the building, more resources, time and work required to do it.
Area of interior spaces: Spacious interiors required less materials for construction.
Material choice: The choice of materials for construction plays an important role in the estimation. This not only consists of the cost of raw materials, but also labour costs for making it and constructing it.
Type of construction: Using mainstream construction methods cost less. Although it should be kept in mind that in the long run, it might prove costly and less durable than other methods.
The approximate budget required for the project is presented.
The choice of materials and construction techniques are finalised.
Helps all the people involved in the project to stick to the budget.
2. Plinth area estimate
Plinth area is the total area, covered by the external most walls of the project. The cost is simply obtained by multiplying this area with the plinth area rate of the locality. For example, if the area is 50 and the rate is 100, then the plinth area estimate is 500.
Plinth area estimate depends on:
The area of the building: More the area, higher the cost. Keep in mind that only the built up area should be taken into account. The space between the building and the site boundary, consisting of open areas or landscape are not added.
The number of floors: The plinth area estimate is separately for each floor, in case the building is multi-storeyed. Even mezzanine and terrace areas should be estimated.
Abutting structures: Porch and verandah areas are included. However, structures like louvers and sun shades are not counted.
Service spaces: Lifts, stairs and service spaces like air-conditioner rooms are also accounted for.
The cost estimate for the area of the project is determined.
The building’s built up area is calculated and finalised.
3. Cube rate estimate
Cube rate estimate depends on the cubic volume of the building. This can be obtained by multiplying the height of the building with the plinth area. This type is more suited for buildings with multiple floors.
The value is obtained by multiplying the total volume with the cost per cubic metre. For example, if the volume is 50 metres cube and rate is 200 per metre cube, the value will be 10,000.
Cube rate estimate depends on:
Volume of the project: More the volume, higher the cost.
Height of the building: The height of the building depends on the number of floors and therefore, the cube rate estimate depends on it.
4. Approximate quantity method
Approximate quantity method is estimated by calculating the total wall lengths and multiplying it with the rate per wall meter. This calculation should be done separately for the superstructure (the structure above the plinth level) and the foundation.
Approximate quantity method estimate depends on:
Length of the wall: More the length of the wall, more the cost.
Plan: A very open plan with less walls reduced this cost.
5. Detailed estimate
Detailed cost estimate, as the name suggests, involves the calculation of the cost of every single resource used for the construction. This is done once all the preliminary and approximate calculations are approved.
Detailed estimate depends on:
The design details of the project: The estimate depends on the plan, structures and other elements the design has.
The measurements of the building: More than area and the number of floors, higher the cost.
Material choices: The choice and amount of material, along with transportation and contractor charges make up for most of the cost.
Labour charges: Skilled labour costs more than unskilled labour.
The cost of every single resource is estimated in heavy detail.
Almost perfect budget is presented to the clients.
The people involved in the construction can make sure to stick to it.
6. Revised estimate
Revised cost estimate is also a type of detailed estimate which is calculated when the cost comes out to be more than 5% of the original value.
Revised estimate depends on:
Sudden hike in prices: Sudden increase in cost of materials, services, labour etc. can increase total amount.
Major changes done in design: Modifications done in the design by adding new elements or taking down already built ones can add to the estimate.
Revised estimates are calculated and presented.
Reasons for the higher cost is also mentioned at the end of the report.
7. Supplementary estimate
Supplementary cost estimate is the additional charges added to the original estimate when the construction is progressing.
Supplementary cost estimate depends on:
New design: Addition of new elements or structures after the construction starts, are added.
8. Supplementary and revised estimate
This type of estimate has both supplementary and revised estimates together. Both the new additions, as well as changes are accounted for together, after the construction process starts.
9. Annual repair or maintenance estimate
Annual repair estimate gives us the figures for the maintenance cost of the building. Painting, coating, repair works fall under this category.
Annual repair estimate depends on:
Regular maintenance work: The cost of the maintenance work on the building comes under this.
Cost of enhancing the building: Giving the coating and coverings of the walls adds to the cost.
The cost of maintenance and repair is calculated.
LCC can be calculated with this to know when the investment will be returned.
While doing cost estimation, it should be noted that sometimes, the initial cost of certain materials or techniques might be high but over time, the maintenance and repair cost is so less that the overall cost is actually cheaper.