Converting empty offices into homes that sell

Empty floor plates on one side, housing demand that shows no sign of slowing on the other. For an investor or developer, converting offices into homes can be an excellent operation. It can also become a money pit if feasibility hasn't been tested before purchase. Here's how we approach these projects at STARC.

A real but very uneven resource

The point was made again in January by Melodie Geurts and Kristiaan Borret, on behalf of the Groupe du Vendredi (Friday Group), in an opinion piece published by Architectura. The phenomenon goes well beyond the capital: Wallonia also has close to a million m² of vacant office space. In Brussels, more than a million square metres of offices stood empty in 2022, at least 20% of which could potentially be converted into housing. Since 1997, 1.7 million m² have already been repurposed, proof that conversion is technically feasible.

Market observers agree. According to the agency Latour & Petit, the gradual conversion of offices into housing or mixed-use schemes will contribute to the evolution of the property supply.

But there's a flipside to that figure. According to an analysis relayed by perspective.brussels, 80% of vacant offices cannot be converted into housing. And the investment is often substantial, for architectural reasons, such as "floor plate" constructions that require major transformation. Everything therefore hinges on selecting the right building. That's where an architect saves you time and money.

Reading an office floor as a future home

An office building was not designed for people to sleep in. Before we even talk about price, we look at five things.

• Floor depth. This is the first criterion. These buildings are often designed as open floor plates of several hundred square metres, and their great depth makes it difficult to create homes that meet minimum requirements for natural light and ventilation. A shallow floor, lit from two sides, allows for dual-aspect flats. A very deep floor forces windowless functions (storage, bathrooms, circulation) into the centre, or requires digging out a patio.
• The facade and structural grid. Offices follow a regular grid of window frames and columns. This determines where partitions between bedrooms and living rooms can be placed. A grid that is too tight or too wide can waste square metres in every home.
• Floor-to-floor height. Raised floors and suspended ceilings in offices often leave a hidden margin of height. This is an opportunity to run new drainage and ventilation without lowering ceilings too much.
• The technical core. An office building is structured around a central core housing lifts, stairwells and, above all, a dense network of service ducts. This network is structurally ill-suited to serving a multitude of individual homes. New, well-positioned vertical ducts therefore need to be planned.
• The envelope. Curtain walls, poorly insulated facades, original flat roofs: the state of the envelope weighs heavily on the budget and on final energy performance.

The rules that shape the plan

In Wallonia, the operation requires a planning permit (permis d'urbanisme). As SPW Territoire points out, the CoDT (Walloon spatial planning code) requires a permit for converting an existing building (except for simple maintenance works), and for creating a new home within an existing building. Changing the designated use of a property is also covered by article D.IV.4 of the CoDT. You then need to check what is allowed under the sector plan (plan de secteur), any municipal guidelines and the municipal development scheme.

Habitability standards then shape each home. The Walloon Government Decree of 30 August 2007 sets the minimum health and safety criteria. As the Walloon Parliament has reiterated, the minimum habitable area of a home is 15 m² for a single person, 28 m² for a two-person household, and 33 m² for a three-person household. For homes created through the restructuring or subdivision of a building, the same decree sets stricter requirements, including a minimum habitable area of 24 m². These minimums are not enough to sell a home. They merely mark the threshold below which you should not go.

On top of this come the EPB requirements (EPC, energy performance of buildings) applicable to major renovations and changes of use, fire safety (compartmentalisation, escape routes), acoustics between homes, accessibility and, often, municipal requirements for parking and bicycle storage. Each of these constraints has a direct translation into the plan. That's why we factor them in from the very first sketch, with support from the engineering firm Optibim for structural stability, building services and EPB compliance.

Costing feasibility before you invest

Our advice is simple: don't sign the preliminary sale agreement before seeing a test plan. Here is the method we follow.

1. Precise survey of the existing building. A 3D scan (carried out by BimBot, Optibim's brand) provides the actual heights, grid and floor levels within a few days. No more relying on approximate archive drawings.
2. Planning analysis. Designated use under the sector plan, municipal constraints, the number of homes that can reasonably be justified.
3. Test plan per floor. We draw up an actual layout of homes, with sellable floor areas, for one or two typical floors.
4. Floor area yield. In a conversion, you should expect to lose square metres. A French specialist in the sector, Novaxia, sums up the order of magnitude: for every 1 m² of office converted into housing, 0.8 m² of living space is created. Each building has its own ratio. That ratio makes or breaks the business case.
5. Budget by item. Internal demolition, possible asbestos removal, envelope, building services, finishes, fees, taxes. We provide a range, with the risky items clearly identified.
6. Comparison with the resale price. The total cost per sellable m² is compared with prices in the local area.

If the figures don't add up, it's better to know at this stage. If the building is promising, the test plan provides a solid basis for the preliminary design and for discussions with the municipality.

What makes these homes sell

A home created from offices sells well when it makes you forget its past, or conversely, when it makes clever use of it.

• Light first and foremost. The large windows typical of offices become a selling point when living rooms face the facade.
• Outdoor space. Recessed roof terraces, loggias carved into the facade, added balconies: a flat without outdoor space is harder to sell nowadays.
• A varied mix of typologies. Studios, two and three-bedroom flats allow you to target different buyers and limit commercial risk.
• Well-finished communal areas. Entrance hall, bicycle storage, cellars: they create the first impression.
• Credible energy performance. Buyers, and their banks, scrutinise the EPB certificate (EPC) closely.

The buyer profile also matters. In 2026, on the federal tax front, the abolition of mortgage interest deductions for second homes and investment properties will affect private investors' calculations. All the more reason to design homes that also appeal to owner-occupiers.

Let's talk about it

Have you spotted an office building in Wallonia or Brussels, or do you own one that can no longer find a tenant? We can carry out a survey and a test plan to check, before any commitment, how many homes it can hold and at what cost. Contact STARC in Gembloux to discuss it.

Frédéric Odent, director of STARC