Architects' guide

Residential houses are designed and built according to the needs of occupants. The significance of individuality has increased in this process in the recent years. However, a house must respond to the needs of very different occupants during its life. The ease of placing furniture and a good and healthy microclimate are important factors of habitability. The energy efficiency of a passive house is so good that traditional heat distribution systems are not needed. This releases the full floor area to other uses, also in front of the windows.

Figure: No heat sources are required in front of windows that insulate heat well. However, the height of the windows may cause the feeling of draught and, as a result, windows of more that 1.8 m in height are not recommended.

Passive House doesn´t encumber the architecture

A passive house is suitable for different user groups. Central factors include design and its objectives for the needs of the users. Systems in a passive house are simple; because of which, special competence is not required to use them. However, occupants must be able to maintain their house according to different situations.

A passive house is based on technology that does not depend on the utilisation of solar energy. Good heat insulation, air tightness in the outer shell, low-energy windows and doors and heat intake from exhaust air constitute the bases of a passive house. Even though the orientation of buildings towards south produces energy benefits, experiences in passive houses in central Europe prove that the concept is functional in building sites facing north. The principle makes it possible to utilise the landscape well in design.

Figure: Senior houses based on the passive house concept in Hannover (Architects Art-Plan).

The construction of a passive house is not tied to any certain material or material group. The building frame may be wood, concrete, block or steel, provided that structural heat insulation is at a sufficient level. However, the moisture-technical requirements for structures must be kept in mind when considering thick heat insulation.

The building’s tight shape reduces heat losses and energy need. Energy-saving construction provides design with freedom and the requirements of the owner and architecture are easy to include in passive houses. In principle, the main face should face south in order to utilise daylight efficiently.

Placement of the Passive House

Reduced energy needs require that the building site is inspected and optimised considering the utilisation of solar energy and sun protection. Energy efficiency of a passive house in the Nordic climate does not depend much on solar energy, making it the perfect solution for shadowed sites.

Observation of the cooling need in architectural design

The reduction of the heating need using passive solar heating depends on the direction of the house and windows. Cooling need early in the spring may constitute a problem. Large windows directed to the south may be part of habitability but they require sufficient solutions for controlling the indoor temperature and preventing overheating. Balconies, wide cornices, canopies and shades outside the house are efficient means of fighting against solar heat in summer.

Windows

Shading windows reduces the sun’s thermal load by up to 60 %. Moreover, shading reduces condensed moisture on the outer surface of windows during cloudless nights. Condensation is cause  by the window surface cooling down because of thermal radiation; thus it is also a sign of good thermal qualities of windows.

The area of windows is typically 15-20 % of the floor area. Even if the windows have a good low-energy level (U-value < 0,8 W/m2K), they must not be too high. Even a good window cannot prevent the feeling of draught caused by high windows. For thermal habitability, 1.8 metres can be regarded as the limit for the height of windows. In a cold climate windows should not be at floor level in order to ensure habitability and air-tight structural details.

Routing of technical facilities

Ventilation heating is a cost-efficient heating solution for a passive house. Short routing of ventilation ducts is part of the system’s energy efficiency, and their placement is part of area design. The architect, HVAC designer and structural designer must ensure that the required routing that is as short as possible can be implemented.

Figure: Centralisation of building systems makes routing design easier. Wet areas on the upper and lower floors are on top of each other and the kitchen’s water points are in the same zone. In this case all water pipes are in water-insulated areas. Ventilation ducts can be routed to the intermediate floor and the suspended ceilings in the lobby and hall areas. Terminals can be placed in partitions.

Suspended ceilings in lobby and hall areas, wardrobes, bathrooms, utility rooms and technical facilities are suitable for routing. There may be suitable spaces for ducts in intermediate floors and above cupboards. Terminals in room areas may be installed onto walls, in which case there will be no ducts in the ceiling. The ventilation system ducts must also be located on the warm side of the air seal and vapour barrier so that fresh air and extract air ducts can only penetrate the seal layers. Ducts should not be placed in attic areas, even if they are heat insulated.

Figure: Technical facilities connected to the utility room and routing ventilation ducts to the intermediate floor.

Placement of facilities

Some of the heat need of a passive house is covered using internal heat loads. As a result, the location of the sauna, kitchen appliances or other heat sources in the central sections of the house is beneficial for heating.

The outer shell of a passive house is heat-insulated well and airtight. The air leakage figure of the outer shell referred to in the definition, i.e. the n50 figure, can be a maximum of 0.6 1/h. The air leakage figure represents the building’s heating quality. Air tightness is important for the energy need, thermal habitability and moisture-technical functionality of structures. Well-insulated structures can be more sensitive to moisture than normal structures; therefore, high-quality design and implementation are important.

The air tightness requirement has also an influence on architectural design. A difficult shape, the number of different structural details, inlets, missing space reservations for HVAC systems and difficult connections of building parts increase the possibility of air leaks. Repeatable solutions and ease of sealing are also design objectives.

Structural thickness of the Passive House

Energy savings refer to thick thermal insulation layers. The wall’s structural thickness can be 400-600 mm depending on the structural principle and materials. In ceilings, where insulation is relatively easier, insulation thickness can be up to 700 mm. Insulation thickness in vented floors can be 500 mm but in ground-supported structures, frost protection determines the safe thermal insulation of floors. Finland has experiences in 250-300 mm thermal insulations of ground-supported floors. The current frost protection instructions cover insulation thicknesses up to 200 mm. The risk of the foundations becoming frozen depends on the building site and soil conditions. The heat loss of a well-insulated floor is so small that it cannot prevent the ground below the foundations from freezing without a measured frost protection in shallow foundation structures.