This work stems from the customer's intention to build a house on a property of theirs, located in the town of Baños de Río Tobía (La Rioja). It is an ambitious project in terms of the characteristics of the building and the construction system, since right from the start dry prefabricated systems are to be used, and excellent technical performance was required.
The implementation of the project takes place in the first few months of 2016. Construction begins in March with the manufacturing in the workshop. Completion of the work is planned for some time in September 2016, which is a much shorter execution time than normal.
The needs programme established the construction of a single-family dwelling, housing a double bedroom, living area, kitchen and dining room, storage room, bathroom and two toilets. The programme was completed with an outdoor covered porch space and an outdoor garden that includes a space for parking a vehicle in open space.
There is also a requirement to do the work using a building system based on prefabricated wood-based panels, and that it meet the sustainability and energy efficiency criteria necessary for obtaining Passivhaus certificate.
Despite it being a standard case in terms of type, programme and size, the usual clichés have been avoided and instead there is a proposal for a house which is contemporary in every aspect: type, construction, space, rejecting conventional aesthetics and/or construction, with energy efficiency criteria being considered at every stage of the design and execution.
The solution chosen has come out of a strict compliance with the programme required by the conditions in all its aspects, emphasising the quality of the spaces created, of the building work and of the energy-saving performance of the whole programme.
The building consists of a single floor with no changes in level over the whole built area. Its long axis is oriented north-south, and it abuts the western edge of the plot, creating a division from the adjoining property. The southern side giving onto the calle veintinueve de junio also matches the plot alignment. Thus, the eastern side of the plot is entirely clear, and is intended for use as a private garden.
The building is topped with a uniformly sloping roof, which slopes towards the garden. On this side, the straight line of the wall is broken by the living room which extends outwards, and thus enjoys a greater influence of the garden area. This part of the house has a sloping ridged roof, which joins up to main roof mentioned above.
The main dimensions are 22 by 4.15 meters, and the living room measures 4.80 by 3.90 meters. The slopes of the roofs range between 16% and 21%. The cornice height is 2.57 meters, and that of the ridge is 3.55 meters.
The garden, meanwhile, follows the original layout of the land, leaving it slightly lower than the floor level of the house.
A 25cm thick concrete slab was chosen for the foundation, laid on the existing ground and insulated on its lower side. The thickness of the slab is due to the thermal requirements (due to its high mass, the slab acts as a heat sink, smoothing out day and night temperatures), so that in purely mechanical terms it is oversized.
This slab supports the whole structural system.
STRUCTURE AND ENVELOPE
The structure and the walls are made of "Garnica Brick" 12/100/12 self-supporting structural sandwich panel, placed vertically with a module size of 1,200 mm. The joints between the panels are made by wooden battens inserted into the panel cores and then screwed to them.
The panel consists of a 10 cm core of extruded polystyrene (XPS) thermal insulation and two 12 mm thick Duraply plywood sheets. These panels have sufficient compressive strength and resistance to buckling as well as to bending and especially to horizontal forces, since they act as a diaphragm in their own plane. Joining panels at right angles, making up a box structure, results in a lightweight, high rigidity unit, capable of withstanding any stresses that the structure is subjected to.
The roof structure is constructed with the same "Garnica Brick" 12/100/12 sandwich panel, resting on the walls. Panel joints and unions are done with autoclaved pine ancillary elements for protection against mould and moisture. Because the span between supports is relatively high (3.60 meters horizontally), the panels are reinforced on their underside with extra wooden battens of 10 x 6 cm, designed to withstand the bending stresses.
Further, the use of two 15 x 15 cm wooden pillars intended to support the part of the roof over the covered porch is proposed, where the use of panels as supporting elements is not recommended for architectural reasons.
The proposed solution is based on a construction system that is inherently much more environmentally friendly than traditional construction techniques. One only has to consider the weight of the built structure compared to the same building made using traditional masonry. It is obvious that the energy use of the two building systems is resoundingly in favour of the lightweight construction. To this can be added the savings due to the fact that that workers and building materials don’t need to be transported to the work area, since they are completely factory-built. Besides being mainly built of wood, the only fully renewable construction material, and with a product life cycle that is free of waste.
Pitched roof made up of 10 cm exterior XPS insulation resting on the roof support panel. A breathable, waterproof, sheet of Tyvek type, battened, and a pre-painted metal sheet of Arval Chantilly 5.40.900 T type. On that sheet there are galvanised steel omega shaped profiles to which the earth-coloured imitation tile roofing sheets are screwed.
Since all the eaves of the roof give on to the private garden, guttering is not needed, and the rainwater falls directly onto the earth.
The façade is made up of 10 cm exterior XPS insulation panel fixed to the structural façade. Tyvek type breathable, waterproof, sheet. Finished with Euronit type fibre-reinforced cement board on galvanised steel omega shaped metal profiles screwed to the structural panel, providing a ventilated air gap.
The structural walls of insulated wooden panels are faced with a Pladur type 13 mm thick plasterboard on self-supporting galvanised steel profiles with a 50 mm rockwool filled air gap, except in the cloakroom, toilet and pantry spaces, where the same sheet is fixed directly to the wall.
Internal dividing walls for splitting the rooms are freestanding partition walls of Pladur type 13 mm plasterboard on self-supporting galvanised steel profiles. Wet rooms have tiles on top of water-resistant plasterboard.
FLOORS AND ROOFS
Flooring of varnished oak boards, except in wet rooms where off-white floor tiles are used. The outdoor terrace is finished in dark grey stoneware tiles, suitable for outdoor use.
Ceiling is finished with visible 12 mm Garnica plywood cladding. In wet rooms, a suspended false ceiling of Pladur type 13 mm plasterboard, and an accessible modular suspended false ceiling in the pantry. In covered outdoor areas the visible finish is of Arval Chantilly type pre-painted white roofing sheet.
PVC Windows fitted to a wooden edge acting as a pre-frame, sealed with silicone cord and adhesive sealing tape. Hinged and fixed windows. Opaque roller blind in the bedroom. The glass used is of Climalit 3 + 3/12/4/12/4 dual-chamber type. The whole frame-glass combination offers a high degree of thermal insulation. The commissioning work has been designed in order to achieve the maximum air tightness possible.
The interior carpentry consists of hinged wooden doors with a white finish and stainless steel hardware with a matte finish.
The air conditioning system is designed to minimise primary energy use. A single point of entry and exit is used for outside air for the entire house, in which a very high efficiency heat recovery system is used. An extraction mechanism built into the system ensures the necessary air changes. Heating is done by a 2 kW electrical resistor.
PREFABRICATION SYSTEM: GARNICA BRICK PANEL
As a result of an intense search for new applications and developments in plywood panel, Garnica has developed a new product range called G-Brick SIP: panels formed with durable plywood resistant to attack by fungi and insects, a XPS core and high compressive strength, for a final product with a very high mechanical, thermal and constructive performance.
It is an ideal construction system for high energy efficiency projects, with excellent thermal insulation and airtightness, and ideal for passive projects, such as the certified “passivhaus” project for a single-family home in La Rioja.
These structural panels ensure maximum durability for the project because the wooden boards used in them are made with a wood treatment technology developed especially for plywood, certified as Class 3.
Furthermore, the panels incorporate a core of XPS, a very low density product but with useful mechanical and thermal performance, which provides the panel’s lightness, rigidity and ease of machining, with a thermal transmittance through their 124mm thickness of 0.32 W/m2K.
In the development of the construction system, all the details of the construction system have been designed, which allows a solution with tightly controlled thermal bridges, easy on site installation, and avoids the need to use sealing tape for most joints, ensuring maximum airtightness of the joints. This important advantage has been developed through collaboration with several architects and construction companies, and is a very important improvement in the building philosophy of passive projects.
SUSTAINABILITY: PASSIVHAUS CERTIFICATION
As already mentioned, in both the design and implementation phases, special emphasis has been placed on achieving a sustainable building. This involves all aspects of the project from the general positioning and internal layout, to the construction techniques and how the facilities are thought out.
In order to highlight the results, it was decided to follow the certification process of the Passivhaus Institut in Germany, undoubtedly one of the most prestigious and demanding in this area. This independent institute has established a calculation method based on algorithms to very accurately determine the behaviour of a building right from the design phase.
In order to ensure the success of the process, the certifier participates in the project from the beginning of the design phase, and accompanies it until its final completion. In the construction phase, one of the most relevant milestones is the leak test, performed once the envelope is finished. This test was carried out in May 2016, and demonstrated the suitability of the system, with a value of 0.47 l/h being obtaining at a pressure of 50Pa, a value well below the 0.6 l/h required by the Institute, and with no need for off the cuff corrections.
At the end of the work, a second leak test was carried out in order to verify that the modifications made in the final phases of the work did not adversely affect the behaviour of the whole, and Passivhaus certification was successfully obtained.