Building Passive and Energy Efficient Houses
Passive House Builders offer customers a choice of three building systems, which include Block Build, Timber Frame structure and ICF (Insulated Concrete Form). The required U-value can be achieved with any of these three systems.
1. Timber Frame
The timber frame system is a structurally insulated wall which can be clad with cement board and rendered, a block outer leaf can be incorporated if required by the client. The timber frame structure is engineered off site. Once the timber frame house has arrive on site it can be constructed quickly however it would be important to remember that because the timber frame is made to order there can be no changes made to it once it arrives. The timber frame option is environmentally friendly and energy efficient.
2. Block
Masonry build can be done with aerated block and external insulation applied and rendered in a choice of colours. Aerated blocks are made from light weight aerated concrete and provide excellent thermal performance. They are fire, frost and moisture resistant and have thermal resistance which standard blocks don’t have.
3. Insulated Concrete Form (ICF)
This is interlocking modular forms made of expanded polystyrene. The forms are locked together like lego and the concrete is then poured into the middle of the forms to create the structure. Insulated concrete form benefits are reduced air leaks, energy saving, high sound absorption; this can be an excellent system on sites with limited access or storage/working area.
During the building process there are a number of key components which need to be given careful consideration in order to achieve the correct U-value throughout the house. These key components include:
Insulated Foundations
This involves building the concrete foundations on structural polystyrene (EPS) that is strong enough to support the weight of the house. All our houses are built on insulated foundation systems, utility services are all included in the foundation system and heat lost through the floor is totally eliminated with this system. It is extremely important to build a passive house on an excellent foundation.
Heat Recovery Ventilation
Heat Recovery Ventilation is a must in a Passive house. Heat Recovery can be described as the “lungs” of your home. The reason for this is because Mechanical Heat Recovery Ventilation works by extracting the stale air in the home and then passing this air through a heat exchanger; this heat exchanger then produces fresh, clean, warm air which can be used again within the home. Up to 20% of the building energy can be lost through ventilation but by using heat recovery this can be reduced substantially. The common perception is that if you open a window this will ventilate your house (this is known as “ventilation by chance”), however this method does not work.
Benefits:
• Clean fresh warm filtered air
• Health benefits - no dust mites
• Improved thermal comfort – no draughts
• Condensation control
• Security – closed windows
Windows
High performance windows are essential to ensure that they are completely airtight when closed to reduce the heat escaping from within the house. There is a large variety of window shapes and designs to choose from, however unfortunately no Irish company has manufactured a suitable window to date. Due solely to this reason, windows are the only part of our Passive house that we need to import.
Thermal Bridge Free Construction
This is one of the key areas of a Passive house. To achieve thermal bridge free construction, i.e. breaks in insulation connections between roof and walls, windows and doors, wall and floor connections, one must ensure that a continuous layer of insulation is in place throughout all of these areas.
Standard 2007 building regulations use a default U value of 0.8 W/(mK) however in a Passive house we must have a U value of 0.01 W/(mK) this is considered thermal bridge free.
Air Tightness & Wind Tightness
These are both critical in the construction of the Passive house. The air tightness in a Passive house has to be below 0.6 air changes per hour at 50 Pascal (pa). To achieve this superior workmanship needs to be applied. Air tightness needs to be factored in from any early design stage and is near impossible to achieve if not thought about from day one. A wind tightness layer is applied on the outer of the building over the insulation as wind blowing through the insulation decreases its performance.
Solar and Internal Heat Gains
Correct orientation of the house and positioning of windows will ensure maximum optimisation of solar gains. A Passive house is designed and sized according to the amount of occupants and their activities by doing this internal heat gains from their activities will be utilised. This basally means that a house should be built to house the number of occupants that will actually live in it at the end of the day, by doing this internal heat gains will be recovered from the occupant’s activities such as showering, using appliances and the body heat emitted by the occupants.
