Understanding the different types of architectural cost estimation 

Cost estimation is a process that benefits everyone involved in building or extending a property. Yet for something that is supposed to provide transparency and clarity, the world of architectural cost estimation can be confusing. Depending on the scale of the project, there are a myriad different ways to estimate costs, each with varying reliability.

Not all of these methods will apply to every build, and some may be more relevant to different end users, whether that’s builders, self-builders or architects. Here’s a breakdown of the different forms of architectural cost estimation, and which type is the right choice for your project.

Estimation vs quantity surveying

The first decision you have to make in any project is whether you will enlist the services of an estimator or a quantity surveyor. The key difference between the two is that quantity surveyors will stick around for the whole project, managing costs as you go. They may provide estimates of costs prior to the project going ahead, but they will also help to manage ongoing costs, and ensure that the project runs as smoothly and cost-efficiently as possible.

An architectural cost estimator provides an estimate for how much a building will cost to construct. Based on key information such as your drawings and intended materials, they will give you a full breakdown of the anticipated costs for materials, labour and plant, as well as how long the build is likely to take. What they won’t do is monitor your site during the construction phase to ensure that you are maximising your resources, and sticking to those plans.

Quantity surveying is generally a more expensive service, and reserved for only large projects. For your average residential construction project, the best choice is likely to be an online estimating provider. Some experienced builders may also do their own in-house estimates, but this can be risky. By estimating based on previous projects, it’s very easy to perpetuate mistakes in your costing, and to fail to account for changes in material prices and working conditions.

Types of cost estimates

There are eight main types of cost estimate, which arrive at different stages of the planning phase for a building project. Some of these are relevant to all projects, but many are more useful for larger projects, where continued assessment of ongoing costs is more beneficial.

A cost estimate is predicted expenditure of a project, which is generally prepared before the project is taken up. It is prepared in different types based on the requirement of the project.

The construction cost estimates can be prepared either in a detailed manner by taking into consideration item by item or can be calculated approximately without going much into the details. Based on these criterias, there are mainly 8 cost estimates followed in construction:

Preliminary Cost Estimate

A preliminary cost estimate is generally an exploration of the viability of a project. This will outline in very basic terms the expected cost of a project by referring to similar projects in the area. This is useful internally as an early planning tool, as well as for securing planning permission or other early stage administration.

Plinth Area Cost Estimate

A Plinth area cost estimate is a good way to predict the cost of a large, single floor construction. This method estimates the cost of the Plinth area of a building, which is determined by its external dimensions, not including external features such as patios or courtyards. This Plinth area is then multiplied by the cost per sq/ft for similar buildings in the area to reach an approximate cost for each individual floor.

Cube Rate Cost Estimate

A cube rate cost estimator is best suited to multi-floor structures. The estimate is reached by multiplying the Plinth area by the height of the building, then cross-comparing with similar buildings in the area. This gives you an approximate total cost for all of the floors in the structure, without accounting for how those floors might differ from one another.

Approximate Quantity Method Cost Estimate

An approximate quantity method cost estimate adds more detail by assessing the cost of both the foundation and superstructure. First, the cost per linear metre for both aspects is calculated using information on materials and excavation. Once this has been established, it is then multiplied by the total wall length of the structure to give a final value.

Detailed Cost Estimate

Often following on from a preliminary cost estimate, a detailed cost estimate uses your schematics to put a price on each item of work (e.g. earthwork, masonry etc). This is generally achieved by assessing the cost of materials and labour based on current rates in that area, with a small percentage added for contingency. It may contain additional drawings and designs to better highlight individual costs, as well as detailed specifications and a schedule of work.

Revised Cost Estimate

A revised cost estimate is exactly what it sounds like – a revision to an existing cost estimate. This is usually called for when a project exceeds its estimated value by a significant amount, usually around 5%. The revised document will seek to explain this rise in costs, and highlight the changes in material prices, labour etc that explains them.

Supplementary Cost Estimate

Similar to a revised cost estimate, a supplementary cost estimate is required when there are changes to the scope of a project. This will usually include the original estimate for the project alongside the new estimate, so that the business can assess the new costs and make a decision on how to move forwards.

Annual Repair Cost Estimate

An annual repair cost estimate, sometimes known as an annual maintenance cost estimate, details the expected cost of maintaining the safety of the structure over time. This will usually account for work such as repainting and minor repairs – information that is often useful and reassuring to clients.

This article was written by Oliver Wilcox, Estimating Director at Proquant Estimating. Still confused about which type of architectural cost estimation you need? Proquant Estimating cuts through all of the jargon by providing detailed cost assessments that are bespoke to your requirements and location.