House by the lake - Fitting windows, raising the roof and building the terrace

After the interior and exterior walls, windows were installed at the Lake House, the roof was raised and the terrace was built. The previous stages - the foundation and the assembly of the exterior and interior walls - can be found on drumulsprecasa.ro, where there is also the project presented in detail, including photo and video images taken by the owner. The project is a passive house built by Litarh in Pantelimon, near Bucharest, for the Iosif family. For a passive house - which represents the highest level of energy efficiency - fitting the windows and raising the roof are very important steps. It's not that they aren't important for other types of house, but these areas are very sensitive in terms of thermal bridges and heat loss, and the smallest deviations can cause the house to fall outside the passive house parameters. The video of this step can be found at the end of the article.

Passive house windows must meet certain standards

The parameter used to determine the performance of a window is called heat transfer coefficient which, as with thermal insulation, is measured in W/m²K. The lower the W/m², the better the window performs, providing good insulation from the outside. For passive houses, the heat transfer coefficient must be less than 0.85W/m²K. The window consists of a frame and a glazed part, each made of different materials with different thermal coefficients. For passive houses, each of these materials must have a heat transfer coefficient below 0.85W/m²K.

Windows energy efficient houses have glazing consisting of two or three layers of glass. Between them is dry air or inert gas (argon or krypton) to reduce heat transfer. The glass used is high quality, strong, of uniform thickness and may contain UV absorbers. Strips are placed between the layers of glass to keep the distance constant even with variations in atmospheric pressure. The strips prevent the build-up of moisture or leakage of inert gas from the inside. Passive houses use three-layer glass windows with a total thickness of 40-50 mm, which are very energy efficient. Foils are mounted on the glass to store heat and release it when the temperature inside drops.

Installation is also very important, as the area around windows is the most prone to thermal bridges. In passive houses, windows are fixed with narrow films that are glued both inside and outside. The foils are glued around the window to continue the insulation of the wall, preventing the formation of energy bridges.

Shading elements are also very important and can be fitted with intelligent systems that open and close them according to the amount of light and heat from outside.

Construction of the roof and terrace

Under the supervision of design engineer Constantin Tudosă, the Litarh team built the roof following the same rules imposed by the passive house standard. Studies say that the greatest heat loss occurs through the roof and therefore the insulation layer must be thicker than the one on the walls (in passive houses, min 15-20 cm in the walls and 25-30 cm in the roof). To minimise thermal bridges, the foils were installed continuously, without interruptions or gaps. The DVD sheets ensure that condensation is eliminated, with vapour circulation in one direction only, from inside to outside.

The terrace was also built at this stage. It only took one day to fix the posts, beams and rafters. The posts were fixed with footings so that they would not come into direct contact with the concrete and draw moisture from it. It's not news that wood is water-loving. To avoid absorbing water at risk of rotting, wood is not mounted directly on the ground or concrete. Another important factor is air circulation, which ensures that the wood is kept fresh if it has been soaked by rain. The feet with which the posts are fixed also serve this purpose, to leave a space through which air can circulate.

In the video below you will see the features of passive house windows, their installation and the roof height.