Feasibility of Commercial-to-Residential Conversion

An empty office building or a disused warehouse looks like an obvious project. The shell is standing, there are plenty of square metres, and the price per m² looks like a bargain measured against new-build on a bare site. But a feasibility study on a commercial conversion does not follow the same logic as a new-build case. The existing structure is at once the project’s biggest asset and its biggest uncertainty — and it is the deviations from the new-build calculation that decide whether the case holds up.

The crucial shift is that you are not calculating on a blank site. You are calculating on a building that already exists, with a geometry, a structure and a planning starting point you did not choose yourself. That removes some line items and adds others — and several of the added ones are hard to spot during a site visit. A serious feasibility study on a commercial conversion is therefore less about the price per square metre and more about finding the line items that do not show up on the façade.

The planning status decides whether there is a case at all

The first question is not technical but a matter of planning: may the building be used for residential purposes? A commercial property typically sits in an area designated for commercial use, and a change of use to residential generally requires a planning basis. If a local plan exists, it sets the permitted use, and a conversion may require either a dispensation or a new local plan. This is rarely a formality — it is often the longest item on the timeline.

Check the use provisions in Plandata.dk (the national planning data portal) before you calculate any further. If the property is covered by a local plan that designates it for office, warehouse or industrial use, you need to clarify the municipality’s position on residential use early. The Planning Act allows the municipality to grant a dispensation from a local plan’s provisions within the plan’s principles, but a change of use often hits precisely those principles — and then a new local plan is the way forward. The municipality can also impose a prohibition against a project while it prepares a new planning basis.

Rule of thumb: if the change of use requires a new local plan, build 12-18 months and a real risk of changed requirements into the case before the first sod is turned.

The planning status is the classic show-stopper, and the principled method for screening it out early is the same as for new-build — see the walkthrough in the go/no-go screening of a construction project before you spend consultant money. For the deeper reading of the plan itself, we refer to our guide to reading a local plan.

The existing structure: asset and brake at the same time

If you carry an existing shell forward, you save the foundation, the structural frame and part of the building envelope. That is the real upside of conversion. But you also inherit the structure’s limitations, and they are rarely free to work around:

• Storey heights and floor structure. Office and warehouse buildings are often designed with large spans and heights that do not suit a residential layout. Dividing into flats can require new partition walls, additional floor slabs or interventions in load-bearing elements.
• Façade and windows. Dwellings have daylight requirements that differ from commercial use. A deep office building can have a central area that effectively cannot be let as living space — that is lost floor area, but not lost construction cost.
• Services from scratch. The commercial property’s service routes, ventilation, water and drainage are dimensioned for a different use. Often most of it is torn out and laid anew.
• Sound and fire. Separation between dwellings triggers sound and fire requirements that an open office floor is not built to meet.

The Building Regulations set requirements for, among other things, daylight, sound insulation, fire safety, accessibility and energy, and a change of use to residential typically triggers the obligation to meet the residential requirements. The specific requirements and transitional rules should be verified against the current edition of the Regulations and with the municipality’s building-permit department — this is where many conversion cases are actually decided.

Daylight and layout set the ceiling for the saleable area

The most important figure in a conversion is not the gross floor area, but the area you can sell or let as residential. A deep building footprint, an awkward column rhythm or a façade with too little glazing can mean that a considerable share of the square metres ends up as secondary rooms, common areas or outright dead space. That efficiency factor — saleable area relative to gross floor area — is the single line item that most often separates a good conversion from a bad one.

The construction budget: a different curve than new-build

On new-build you can rely on relatively stable benchmarks per m², because you are building a known structure in a known way. Conversion behaves differently. Part of the budget is predictable — the new interior dwelling — but a larger part depends on conditions you only discover once you open up the structure.

So build the budget in two layers. The first layer is the ordinary benchmark budget for the new dwellings, which you can estimate on the same basis as for new-build; the method and buffer rates in construction budget per m² — benchmarks and the buffer you can count on apply here too. The second layer is the conversion’s own line items: demolition and disposal, environmental remediation, structural strengthening, new service routes and the rebuilding required before the existing shell can carry dwellings.

It is the second layer that topples cases. Older commercial buildings can contain environmentally hazardous substances in roofing felt, sealants, floor coverings and insulation, and disposing of these is mandatory and often expensive. A preliminary survey with material samples, before you lock down the budget, is not a cost — it is insurance against the line item that would otherwise appear in the middle of the construction phase.

Rule of thumb: the older the building, and the more you have to touch the load-bearing structure, the wider your buffer needs to be. A new-build level of contingency is rarely enough on a thorough conversion.

The residual value of the existing: gain or goodwill

One of the most misunderstood figures in a conversion case is what the existing building is worth as a starting point. The seller often prices the shell as an asset — “it would cost such and such to build today”. But in a conversion feasibility, the existing structure is worth exactly as much as it saves you on the way to the finished project. Everything you tear out or rebuild anyway is not a residual value — it is a cost in disguise.

The right way to price the acquisition is residual: what could the property be worth as a finished residential project, minus everything it costs to get there (including the conversion’s special line items), minus the profit the project has to carry. What is left is what you can pay for the property in its current state. The residual method is the same as for new-build — it is covered in detail in feasibility of a construction project: residual land value, construction budget and profitability — but on a conversion it is decisive to deduct the demolition and rebuilding items before you believe in a “cheap” shell.

At the same time, check title and easements in tingbogen (the Land Registry) before you calculate further. Commercial properties often carry easements on access, utility lines, parking or neighbour relations that can limit what you are allowed to do — and these count towards what the property is really worth converting.

The exit value: residential on the existing market

The case closes at the other end: what are the finished dwellings worth? Here the same discipline applies as for any development project — assess exit on the existing market, not on a hope of where prices will be in two years. The method is covered in exit value: what is the project worth if it stood finished today?.

Conversion does, however, have a couple of exit-specific nuances. The location is given by the existing building — a former commercial district is not necessarily an attractive residential area, and that must be priced into the exit. On the other hand, a converted building can have characterful features — ceiling height, an industrial aesthetic, a history — that in the right segments can support a premium. That is a real parameter, but it must be substantiated by what comparable dwellings actually trade for in the immediate area, not by the project narrative.

How to calculate the conversion through faster

The manual exercise here is real work: the planning status in Plandata.dk, title and easements in tingbogen, building data in BBR (the Buildings and Dwellings Register), a two-layer budget with the conversion’s special line items, a residual acquisition price and an exit assessment on the existing market. That exercise replaces neither architect nor engineer — it decides whether it is even worth spending their hours on the case.

That initial run-through is exactly what Projektvurdering (Project valuation) automates. You point at the property, and the module pulls together the planning status, building data and the basis of comparable sales and calculates the case through — including for commercial conversion — and assesses it “as if it stood finished today” on the existing market. It does not take the decision out of your hands, but it removes the 80-100 hours of initial work that otherwise sit between an idea and a qualified go/no-go.

Want to see what a conversion case looks like when the special line items are counted in from the start? Read more about Arcili or book a walkthrough.