Miroirette By Tim Kouthoofd & Piotr Szczesniak


​By Tim Kouthoofd & Piotr Szczesniak (Bygg Architecture V.O.F.​)​​

Canal Saint-Martin, Paris​

The neighborhood around Canal Saint-Martin in the 10th Arondissement is characterized by a variety of building styles and building heights. The typical mansard roof buildings contain up to 7 floors, but during the second half of the Twentieth Century many have been replaced by taller concrete buildings. The location at the banks of Canal Saint-Martin, offers the opportunity to build taller than in most of Paris’ center, due to the wide public space from façade to façade. The challenge is to extend the older buildings upward, with respect to the mansard roof.


Miroirette is a contraction of the words “miroir” and “maisonnette”. It is the name we give to a new apartment typology, specifically developed to provide roof top extensions in the context of the Parisian mansard roof buildings. By extending the mansard roof buildings alongside the canal, we find potential to add 140 extra dwellings in the neighborhood.  

Miroirette enables extending above the mansard roofs of the existing building, without having to demolish the mansard roof. How do we do that? We execute the first level of the roof extension with an upside-down mansard façade, which aligns (in mirror) with the existing mansard roof. The reflection in the canal reveals the respectfulness of the intervention to the architecture.

That way, we keep the elegance of the mansard roof. Every next floor of the extension will have the maximum floor surface available, despite of the existing building ending with a mansard roof. That way we make maximum use of the perimeter of the plot. 

Kerto Structure 

Miroirette makes maximum use of the properties of Kerto LVL for the roof top extensions. The load bearing walls of the existing Parisian blocks can support the new Kerto walls, since the load is spread from front to back. In between the new Kerto Walls, we use Kerto Ripa floors to span from load bearing wall to load bearing wall. We apply an intermediate frame with Finnjoist studs to compensate for the existing slope of the walls. 

The façade of the first floor of the extension resembles the upside-down mansard roof. This type of façade structure would be a big challenge with any other type of material, but with prefabricated Kerto façades with prefabricated bay windows, we are able to install the façade in one go directly from the truck. The façade also spans from load bearing wall to wall and stands in an angle. 

With Kerto, Kerto Ripa and Finnjoist we create a structure that can be supported structurally by the existing building. By prefabricating the elements offsite we minimize the construction time and hassle for the neighborhood, as well as reduce carbon-emissions. With Kerto we are able to provide a flexible system, which can be adjusted to each span and each mansard roof type alongside the banks of Canal Saint-Martin. It enables us to add 140 comfortable and sustainable roof top apartments to the lively neighborhood.​

City Above the City architecture competition

Plan B : City Above the City architecture competition 

Metsä Wood challenged architects and students around the world to push the boundaries of modern wood building design in the urban environment. Entrants from 40 countries created their Plan B to urbanisation using wood (Kerto® LVL – laminated veneer lumber) as the main material. The task was to design a wooden extension to an existing urban building. The entries were designed to 69 cities worldwide.

Explore the designs