Construction Budget per m2: Benchmarks & Buffer to Plan For

The number that most often travels from an early ballpark estimate into an investment case is the contractor cost per square metre. And that is precisely where the error begins. A construction budget that consists only of the contractor’s price describes just part of what it actually costs to get a project off the ground. The soft costs, the unforeseen, and the buffer are rarely minor items — but they are consistently underestimated in the early estimates, where the go/no-go decision is in practice made.

The point is not that you should be able to price everything correctly at phase zero. You cannot, and you should not pretend to. The point is that a construction budget per m2 that has to carry a decision must contain the right categories — including the items that do not yet have a fixed figure. That is the difference between an estimate that holds up and one that falls apart the moment the project becomes concrete.

What actually goes into the square-metre price

When an m2 price is used loosely, it almost always covers only the hard costs: the building itself — structural shell, building envelope, services, interior finishing. That is the price a contractor quotes, and the one that is easiest to obtain. But a complete construction budget per m2 consists of at least three layers, and the other two are usually what determines whether the project carries.

The hard costs are the construction work and materials themselves. The soft costs are everything needed for the building to be legally and professionally sound: design and consultancy from architect and engineer, land surveying, geotechnical investigation, building-permit fees, utility connection charges, insurance, construction-loan interest, and the developer’s own administration costs. The third category is the site and the externals — site servicing, terrain regulation, sewers and roads up to the boundary, and the land purchase itself, which is typically kept separate and handled via the residual method, where you work backwards from the end value to what the site can cost.

Rule of thumb: the soft costs are rarely a negligible residual item. Count them as a category in their own right from the very first estimate — not as an add-on you tack on at the end.

Once site servicing and soft costs are laid on top of the contractor price, the total square-metre price lands markedly above the figure originally quoted. That is not an error in the contractor’s price — it is an error in what people thought the price covered.

New-build benchmarks: use them as a frame, not as an answer

Benchmarks per m2 are useful for setting a frame early on, but they are notoriously sensitive to assumptions. A benchmark for construction costs per square metre only makes sense if you know what it contains and which building type it comes from.

The most significant factors that move the benchmark:

• Building type and complexity. Low-density terraced housing, apartment blocks, and commercial buildings have widely different unit prices. The more complex the geometry and the higher the degree of services, the higher the price.
• Standard level. Material choices, technical services, and finish can move the price substantially between two otherwise identical projects.
• Geography and supply. Contractor prices vary regionally and over time, depending on capacity in the market.
• Scale and repetition. Many identical units give a lower unit price than a one-off house.
• Efficient area. The ratio between gross floor area and the area that can be let or sold determines whether a low m2 price is in reality expensive. Circulation areas, plant rooms, and common areas cost money to build but generate no direct income.

Use benchmarks, therefore, to delimit a likely range — not to lock in a single number. A span where you can see what pulls towards the expensive end and the cheap end is more useful in an early phase than a falsely precise average.

Watch the area concepts

A benchmark is only accurate if the numerator and the denominator are talking about the same area. Construction costs are most often stated per gross floor area, whereas a sales or rental income relates to the actually usable area. Mix the two, and the project looks artificially cheap. It is worth keeping BBR’s — the Buildings & Dwellings Register’s — area concepts in mind here, and the pitfalls they hold we have covered in our review of the typical pitfalls in BBR data.

The buffer is not a safety margin — it is a budget line

The single error that costs the most projects dearly is setting the buffer too low or leaving it out altogether because the numbers “look neat”. A buffer in a construction budget is not an expression of uncertainty about whether you can manage the project. It is a recognition that a project that has not yet been detail-designed has, by definition, items that will change.

The buffer covers two things in particular that should be kept apart:

1. Unforeseen conditions — foundations on poorer ground than expected, contamination in the soil, hidden conditions in an existing building during conversion, or requirements from an authority or utility that were not known at the time of the estimate.
2. Project maturation — a rough m2 price being replaced by concrete figures as the project is detailed. It almost always moves in one direction.

The principle is simple: the earlier in the phase, the larger the buffer. An estimate based on a benchmark and an aerial photo carries a completely different uncertainty than a budget built on finished project material with quotes obtained. The buffer must reflect where you stand — not where you would like to be. And it must stand as a visible line in the budget, not be tucked into an optimistic unit price. A hidden buffer is no buffer.

The buffer is also where the sensitivity of the whole case shows itself. Because construction costs are the largest expense item, even small swings in the m2 price hit hard on what is left for the site and the return. That mechanism — how the budget’s uncertainty propagates all the way through to profitability — is the heart of a proper feasibility assessment that ties residual value, construction budget, and return together.

How to build the budget so it can carry a decision

A budget that has to stand behind an investment decision does not need to be detailed — but it must be honest about its own uncertainty. That discipline matters more than the precision.

• Separate the three layers. Hard costs, soft costs, and site/servicing, each on its own. When they are separate, you can see where the sensitivity lies and what really drives the price.
• Work in ranges. A low and a high scenario say more about robustness than a single midpoint. If the case only carries in the optimistic scenario, you know something important.
• Set the buffer by the phase, not by the wish. And keep it visible.
• Keep the area concepts clean. Make sure cost and income are calculated on comparable areas.
• Tie the budget to the return. A construction budget only makes sense once it is held up against what the project has to yield. How you set the required return itself we have covered in our explanation of the required return on a development project.

Where rates, fees, and charges apply varies between municipalities and utility companies and changes over time. The specific figures should always be verified with the relevant authority or utility before they are locked into a budget — benchmarks and general frames can only take you as far as the initial sorting.

From manual estimate to fast screening

In practice, this is where many early projects stall: assembling a construction budget per m2 with the right categories — hard and soft costs, site servicing, a phase-determined buffer level, and a link to the return — is time-consuming to do manually for every parcel you are considering. The result is that the screening either becomes superficial or is skipped entirely.

Arcili’s Projektvurdering (Project valuation) automates precisely that initial exercise. From public registers — matriklen (the cadastre), BBR, planning status via Plandata.dk (the national planning register) — it draws up a complete project-economics estimate with construction costs, soft costs, and a residual view, so you can quickly see whether a site or a conversion is worth pursuing at all. It does not replace the architect’s design or the engineer’s calculations — but it saves you the 80-100 hours it otherwise takes to reach a qualified decision about what is worth spending them on.

Want to see what it looks like on a specific parcel? Try Arcili or book a walkthrough.