In this article we look at the construction of a prefabricated timber Passive House in the region of Maresme. This single-family Passive House is located in the municipality of Sant Andreu de Llavaneres, in Barcelona. We designed the building in an L-shape to wrap around the large oak tree which forms a central feature of the site and project.
Construction techniques for a Passive House
Because the building is a Passive House, we chose timber frame as the preferred construction method because the construction process can be excellently controlled. The building structure is made of wood, with lightweight prefabricated timber and CLT (Cross-Laminated Timber) panels. There are two types of finishes for the facades: External Thermal Insulation Composite Systems (ETICS) and a ventilated facade with a charred wood finish.
Obtaining the Passive House certificate means that the building will have a very low heating and cooling demand. As part of the Passive House design, we installed a heat recovery ventilation system to control the temperature and humidity inside.
Construction began in April 2024. During the first weeks, we built the foundations and basement of the house using traditional construction methods. We constructed retaining walls as well as a reinforced concrete slab that forms the basement ceiling and ground floor slab. Above this, we constructed the ground and first floor volumes in wooden prefabricated panels.
The custom-made timber panels that form the envelope of the Passive House are made off-site in a factory. These panels already include thermal insulation and waterproof sheeting when they arrive to site. The total construction time for this phase was only 4 weeks.
The following video shows the assembly phase of the structure and the wooden envelope.
Blower Door test
To certify the house as Passive House, the house must pass something called a Blower Door test. This test detects air infiltrations and evaluates the permeability of the building envelope. Before embarking on the test, we need to tape and seal all the timber panels that make up the thermal envelope of the building. We also need to tape and seal all installation pipes and outlets that pass through this envelope. We then use a smoke machine and air meter to detect and analyse air leakage points, which we then seal.
Shou Sugi Ban charred wood facade
The next step in the construction of the prefabricated Passive House is to add the façade finishes. For the ETICS façade, the exterior insulation is already included in the panel and so we only need to add the plaster. For the ventilated façade, the waterproof layer is already included but we must add the burnt timber cladding. These timber cladding boards are made of cedar and come from Japan where they are treated with the Shou Sugi Ban technique. This is a traditional Japanese technique where you burn the outer layer of wood which waterproofs it and gives it the distinct charred, black finish. We used the company Nakamoto Forestry Europe. Click here to read about this technique on their website.
Currently, we are working on the interior installations of the house. Apart from the usual installations, the house includes a ventilation system with heat recovery and a grey water recycling system where water from the showers is used to flush the toilets.
The construction of this prefabricated timber Passive House is due to be complete in February 2025.
To read more about this timber-frame Passive House, click here.