Antohi House, a passive house project with many challenges solved

Project Antohi House came with a number of challenges for the architect, designer and builder. The owner, Claudiu Antohi, wanted first and foremost a passive house on a wooden structure, set back from the city and with an energy generation system. The architecturally more special house was to have a fireplace, a living room high up to the roof, upstairs rooms with cantilevered floors, a wall without a ceiling, a staircase floating, sliding door to the outside, photovoltaic tiles on the roof. Each one of them equally challenging. The very good and continuous collaboration between all parties involved has ensured that these challenges have been solved so that the site is running smoothly. Now we all agree that the Antohi House is a very successful one.

About the project we talked to Octavian Timu from Creative Engineering and Vlad Liteanu-Voinescu, Litarhthe designer and builder of the house, during the public presentation at the nZEB Week in Cluj. The video is at the end of the article.

Central wall, fireplace and beam from the 19th century

Inside, the challenges were more and more varied. The house is composed of three parts, two side parts on two levels and a central open vertical area. The roof practically connects the ends to the central area. In the central part there is a partition wall separating the living room from the staircase leading to the first floor. As the area is open vertically, the wall does not meet the ceiling but a beam that seems to support it. The beam, salvaged from a disused shed in Brasov that was built in the 19th century, had to be incorporated into the project. The wall also had to be attached to the beam without spoiling its aesthetics. Clever solutions found by the builder and designer solved both situations and thus the owner's wish could be respected.

The main challenge, however, was the fireplace which was positioned on the front wall facing the living room. Its exhaust system could affect the interior ventilation and thus not achieve passive house parameters. That's why a passive house certified fireplace with a special exhaust system was installed. The chimney also required adaptations to the floor-mounted insulation so that its weight would not be affected.

On the other side of the wall will be the staircase to the first floor. It's designed to look like it's floating. Special places have been provided on the wall to hold the stairs on one side, and a wall comes down from upstairs to hold the other side of the stairs. The wall does not reach the floor and so the staircase appears to float.

Upstairs - the bedroom in the console

Upstairs are the bedrooms. The first of these is cantilevered, meaning the floor does not rest against a wall on the side facing the stairs. The forces that should have been discharged on the supporting wall have been transferred to other walls. Octav resolved the situation at the design stage by fitting bracing to the wooden walls of the structure and providing additional bracing on the exterior retaining walls. The ongoing collaboration between the designer and the builder meant that the Litarh team had a good understanding of how to deal with this situation on site and it was resolved.

The challenge of external doors - atypical shapes and sizes for a passive house

Very important in achieving passive house parameters are windows and exterior doors. The big test was a 5m sliding door. Sliding doors are sometimes problematic because the closure fails to seal. The door at the Antohi house was manufactured by Danprod and is Passive House certified. Danprod also made the arched door for which the installation problems were solved by the Litarh team on site.

The vapour barrier was installed on site to ensure continuity and integrity. Latest leak test showed a number of air changes n50=0.578/h (number of air changes/hour, at a pressure of 50 Pascals), below the permissible limit of 0.6.But in the meantime improvements have been made on the site that will further decrease the number of air changes.

Although fewer than on the inside, there were also challenges on the outside

The Antohi house is on wooden structure with prefabricated walls. The walls were made in the factory, inside they are filled with 20 cm basalt wool insulation. The remaining 20 cm, required to achieve the passive house standard, was provided by the exterior wood fibre envelope.

On the outside, the ventilated wooden facade on the first floor had to be connected to the thermosystem on the ground floor. In order for the ventilation to work properly, the design was such that the ventilated facade protruded a few mm outwards. This provided the necessary ventilation and water drainage on the wood without stagnation at the end. It is the way to protect the wood from mould and rot.

So that the sun does not heat up the walls of the house too much on hot summer days, a shade was installed on the most exposed area. The challenge was to trap it so that the vapour barrier was not breached. The choice was made for light wall fixing with very good back insulation to allow no infiltration, coupled with roof anchoring.

The plinth will be finished with stone to imitate old peasant houses. In order to avoid infiltration, the DHF fibreboard cladding for insulation has been abandoned for the plinth part and Aqua Panel, a special material for stone cladding, has been used.

The first house in Romania to be fitted with photovoltaic tiles

The roof of the Antohi house is a gable roof, each with a 38° pitch. The south-facing side has solar shingles Terran GeneronThe rest are ordinary concrete tiles, also from Terran. There are 400 photovoltaic tiles, each with a power of 15 W, resulting in an installed power of 6 kW. These are ordinary concrete tiles over which the photovoltaic cell has been factory-fitted. The conventional tiles are coated with black polyurethane paint that is UV and weather resistant, including hail.

The thermal insulation of the roof was made with 30 cm of basaltic wool mounted between the rafters and another 10 cm mounted on top. Over this was fixed the DVD batten, a special construction MDF. As the house was intended to be covered with photovoltaic tiles, more ventilation space was needed underneath to allow for cooling. The manufacturer recommended a minimum of 75 mm. For safety, the builder made this space a minimum of 80 mm, as the cables connecting the tiles to the storage batteries also run through this space.

Casa Antohi proves that you don't have to give up the dream of having a passive house with special architecture. The key is to find teams ready and willing to solve any challenge. Communication between them is essential.