There are five key Certified Passive House design principles;
1
Air Tightness
Elimination of drafts.
2
Super-insulated & thermal bridge-free envelope
Retain heat energy.
3
Heat recovery ventilation (MVHR) Recycles heat energy & provides fresh air.
4
Water tightness
Essential for building durability.
5
High-performance joinery
Building enclosure
5. Joinery & the building enclosure
In a passive house, the building enclosure refers to the assembly of walls, roofs, floors, and foundations that create the exterior envelope of the building. The design and construction of the building enclosure are critical components of achieving a passive house’s energy efficiency, thermal comfort, and overall performance goals. Fixed and moveable shading is designed to make the most of the sun’s energy in the winter and exclude it from the building during the summer months.
The enclosure is the primary barrier that separates the interior of the building from the outdoor environment. By ensuring a well-insulated and airtight enclosure, the passive house design minimises heat transfer between the interior and exterior, reducing the need for active heating or cooling systems. This is because it helps maintain consistent indoor temperatures, avoiding uncomfortable drafts and temperature variations near windows, walls, and other elements. It is tightly sealed to prevent uncontrolled air infiltration, which can bring in outdoor pollutants and allergens.
Vapour barriers and moisture control strategies are included to prevent condensation within the walls and other elements. Excessive moisture can grow mould and compromise the building’s structural integrity. A carefully constructed building enclosure using high-quality materials and detailing ensures the longevity of the building by protecting it from weather-related damage and degradation.
The windows and doors in a passive house are high-performance components; they play a crucial role in achieving energy efficiency, comfort, and overall building performance.
The orientation and placement of these openings are carefully considered to optimise natural light and solar heat gain.
Depending upon the energy model, we may incorporate triple-glazed windows and doors with three layers of glass with two insulating air gaps (traditional double-glazed windows only have one air gap), commonly filled with Argon gas. This extra layer of glass significantly reduces heat and noise transfer and enhances the overall thermal performance of the building envelope.
Low-E coatings are thin transparent layers of metal applied to the glass surface to reduce heat transfer by reflecting radiant heat. It allows sunlight to enter while minimising the heat that escapes. We can control the amount of solar heat gain and heat loss from the building with different glass types, which gives us the greatest control over the energy balance of all the components in the building envelope.
The frames are commonly made from wood, with an exterior aluminium facing for durability and low maintenance, but we can use uPVC (unplasticised polyvinyl chloride) or thermally broken aluminium windows. These have improved standard aluminium windows’ thermal performance and reduced thermal bridging’s effect. The joinery is a part of the insulation, air-tight and weather-tight layers, so high specification is necessary.
uPVC windows are known for their durability and low maintenance as they are resistant to moisture, rot, and insects, making them a practical, low-cost choice for the future. It is a non-conductive material which contributes to reducing energy loss.
Typically, we use European style turn and tilt windows (opens inwards), and where we can, we use smaller glass areas in a passive house to reduce solar gain. It’s a balance to make it cheap to run in the winter but not overheat in the summer.
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