Renovation, transformation, innovation

Faced with the housing crisis in France and the environmental challenges facing the construction sector, reversibility is becoming a major asset in the circular economy, from the point of view of eco-responsible construction, land recycling and the fight against urban sprawl.

As office buildings become increasingly obsolete, developers and landlords are increasingly initiating this type of project. The major urban centres represent the most profitable market in both the housing and commercial sectors. In recent years, there has been a marked decline in demand for commercial property, leading to an overproduction of offices, while the need for housing has only increased.

What are the issues involved in converting offices into housing?

As a preamble to research into the reversibility of office space into housing, it is worth looking at projects that have already been carried out in order to understand the issues and points to watch out for.

Based in particular on the French urban planning agency APUR’s analysis of The conversion of office space into residential accommodation in Paris between 2001 and 2012, we can identify three main types of conversion: historic buildings dating from before 1900 (in particular the Haussmannian fabric), buildings from the 1940s to the 1970s, and buildings dating from after the 1980s.

 

HISTORIC BUILDINGS

 

FIG 1 – Historic Buildings

In many cases, these buildings have already been converted from residential to office use before returning to residential use. They therefore have dimensions that lend themselves to this type of programme: 6 to 14m thick with double orientation, ceiling heights of 2.20 to 4.00m, and facade openings already specific to housing plans. On the street side, the stone facades require internal insulation. On the courtyard side, the less rendered facades allow for external insulation. Re-roofing with dormer windows or roof dormers increases the surface area allocated to the dwellings by converting the attic space.

One of the main difficulties lies in the split-wall structure and the small size of the courtyards, which sometimes make it difficult to arrange the layout, and in particular to add wet rooms – in compliance with French PRM standards – that were not originally planned. Similarly, creating openings for new vertical circulation systems to comply with standards is complicated (wooden floors, etc.) and costly.

 

BUILDINGS FROM THE 40S-70S

FIG 2 – Buildings 40s-70s

These buildings, which were designed from the outset for office use, nevertheless have a number of interesting features that make them suitable for conversion into residential accommodation. The plans for these office buildings are based on a post-and-beam structure; their dimensions, both in terms of their thickness (9 to 15m) and their ceiling heights (2.70 to 4.00m), make it easy to design flats that meet today’s requirements.

However, this design flexibility is offset by the relatively high cost of the work, particularly when it comes to removing all the light façades that are too glazed and not insulated, or removing asbestos from the building, etc.

 

BUILDINGS FROM 1980 AND OVER

FIG 3- Buildings 80’s and over

Since the 1980s, the architecture of office buildings has sought to maximise profitability, by opting for a design that includes specific characteristics: a double-facing thickness of up to 18 or even 20m, a ceiling height of 3.5 to 4m with a false ceiling and/or false floor, a highly glazed façade and a concrete floor that is sometimes very thin.

Because of their rational construction, these types of building are less easily converted. Despite the freedom offered by the post-and-beam structure, the excessive thickness of the buildings means that patios or courtyards have to be created to provide the natural lighting required by the dwellings.

 

Reversibility of offices into housing: transformation of the Orion tower in Montreuil, France

 

FIG 4 – Existing building Tour Orion

Generally speaking, office buildings dating from the 40s to the 70s are over-represented in current projects to convert offices into housing. The freedom of layout afforded by the post-and-beam structure, and the fact that its dimensions are similar to those of housing, make it a very interesting case study in our recent practice.

This is the case of the study we carried out in the city of Montreuil for the project to convert the Orion office tower into coliving accommodation. By developing an analysis of the building, we were able to adapt the layout of the flats to the traditional 1.35 m layout of the office plans. The way in which we have divided up the flats fits in with the façade of the existing part, and in addition we have proposed the design of a new façade on the extensions to the building.

 

FIG 5 – Vegetated roofs, Orion Tower
FIG 6 – Greenhouses, Orion Tower

It is still necessary to consider the issues of fluid management, fire regulations, insulation and ventilation when designing a reversible building, even if certain conditions for conversion are met in existing buildings.