![]() Wind blowing across, or even worse, into the insulation, can reduced the performance of the insulation by as much as 40%.įor more detailed information on this aspect of the passivhaus thermal envelope, I suggest you start with this article on ‘ Thermal Bypass’ by Mark Siddall. Air movement across the surface, or even into the insulation, reduces the effectiveness of the insulation.Ī windtight barrier on the outside of the insulation is also required to preserve the performance of the insulation. ![]() It preserves the performance of the insulation.Where moisture does condense within the building envelope (‘ Interstitial condensation’) it increases the risk of mould and associated dangers, as well as the risk of damage to the building envelope. It prevents moisture from inside the building getting into the building envelope where it might come into contact with a colder surface and condense.This ensures air only goes in and out of the building where intended to through the designed ventilation. It stops air (and therefore heat energy) that is inside the building from escaping through uncontrolled gaps in the building envelope.Insulation reduces the flow of heat energy in both directions through the building envelope.Īn airtight barrier on the inside of the insulation does several things: And equally important, it keeps unwanted heat out. Insulation keeps the heat inside the building. The less surface area relative to the floor area, the less thick the insulation can be. The greater the amount of external surface area a building has (essentially the ground floor, external walls and the roof) relative to the floor area of the building, the greater the thickness of insulation that will be required. ‘Super-insulation’ is a relative term and does not always mean extremely thick insulation though. High-performance windows and doors are also needed. In basic terms, this means super-insulation, an airtight barrier on the inside of the insulation and a windtight barrier on the outside of the insulation. To do this, a high-performance thermal envelope is required. The Passivhaus Standard delivers exceptional indoor comfort and building energy efficiency. The Passivhaus Building Envelope: A High-Performance Thermal Envelope The passivhaus building envelope requires a high-performance thermal envelope, it must be continuous and it is key to the fabric first approach. The passivhaus building envelope is also made up of these elements, but there are some key aspects that make the passivhaus building envelope distinct. In simple terms, this means that the building envelope is made up of the walls, floors, roofs (or ceilings), windows and doors that separate the inside from the outside. The three basic elements of a building envelope area weather barrier, air barrier, and thermal barrier. In passivhaus design and construction, there are frequent references to the “building envelope” and the “thermal envelope.” Neither are exclusive to the Passivhaus Standard, but both are important aspects of the standard.Ī building envelope is the physical separators between the conditioned and unconditioned environment of a building including the resistance to air, water, heat, light, and noise transfer.
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