Why estimate before drawing
Three reasons, all tied to the timing of decisions. The estimate precedes the design, it does not follow it.
The heaviest decisions are taken early. Location and form, which dominate the budget, are decided before any detailed drawing.
A late estimate merely records. It arrives once the structuring choices are made and only finish-level trade-offs remain.
Financing is framed upstream, and an unrealistic envelope wastes months before it is discovered.
An early estimate is not there to give the price. It is there to say whether the project is possible.
| Step | What it establishes | Data required |
|---|---|---|
| Framing the need | Area and brief | Number of rooms, use |
| Pricing the land | Land budget | Target municipality, price per are |
| Pricing the works | Construction budget | Price per m² and stage adopted |
| Ancillary costs | Additional budget | Usual percentages |
| Uncertainty margin | A stated range | How far the design is defined |
The method in five steps
They follow on, and each conditions the next. These steps run from the land to the works budget.
Set the living area targeted, distinguishing the necessary from the desirable.
Apply a price range per square metre matching the finish level envisaged, checking its scope and date, as the article on works cost per m² explains.
Add ancillary costs using the observed order of magnitude, covered in the article on ancillary costs and their weight.
Add the full cost of the land, acquisition, servicing and related costs included.
Set the total against the envelope available, and decide before drawing.
Step four is the one that decides, since it carries the heaviest variable.
The margin of uncertainty to accept
A methodological point distinguishing an honest estimate from a reassuring figure. The uncertainty is stated rather than hidden.
An early estimate gives a range, not an amount. Presenting a single figure at this stage is misleading.
Uncertainty narrows as the project takes shape, until the quotation closes it.
The range must be stated with its assumption. A low figure presupposes a given finish level and form, and changing either invalidates it.
An estimate that does not state its assumptions cannot be checked, and therefore cannot be used.
The errors that make the exercise useless
Four errors, all frequent.
Estimating construction cost alone. The resulting envelope is incomplete by tens of per cent.
Taking the bottom of the range. A low figure presupposes favourable conditions in combination, which is unlikely.
Omitting a contingency, when every project meets one.
Not updating. An estimate made two years before commitment describes a market that has moved, as the article on tracking prices recalls.
What an early estimate cannot do
Two limits to state plainly.
It does not replace a quotation. No general method gives the price of a specific project.
It does not replace measurement. Detailed description of works and comparison of offers belong to the guide on measurement and specification.
Its function is to settle a binary question: does the project envisaged fit within the envelope available.
What this means for a professional
Four rules.
Estimate before the sketch, and not only after.
State a range and its assumptions, never a single amount.
Always include land and ancillary costs, failing which the exercise misleads.
Update at project milestones, rather than keeping the first figure produced.
This article reflects a method of professional orientation. It does not replace a quotation or a detailed estimate based on a defined project.