Passivhaus Wall Details
The following article contains details and information from our book Understanding Passivhaus – The Simple Guide to Passivhaus Detailing and Design.
Building Fabric
The building fabric has a key role to play in achieving many of the requirements of a Passivhaus. The Passivhaus standard adopts a ‘fabric first’ approach. This essentially means that key priority is placed on ensuring the envelope of the building performs well including high performing insulation and airtightness, so that minimum requirements are placed on ‘bolt on’ technologies such as water heating, space heating and so on. The Passivhaus approach provides high levels of thermal performance and exceptional indoor comfort. The success of the Passivhaus relies heavily on the building envelope.
The fabric first approach also ensures durability, with long term building performance from the outset, rather than the requirement to update and improve. By specifying high quality, and prioritising the building fabric, the Passivhaus method ensures that the building will continue to perform well throughout the lifetime of the building.
There are a multitude of different construction types and methods that can be used in a wall assembly to achieve Passivhaus standards. Some examples can include timber frame, masonry cavity wall, concrete with rendered external insulation, SIPS, Insulated Concrete Formwork and more.
This high performance continuous envelope includes insulation to achieve low U-values, a good wind tight layer to the outside of the insulation, an airtight barrier on the inside of the insulation and high performance windows and doors.
Insulation
Key to the fabric first approach of the Passivhaus standard, the design will consist of a high performance continuous thermal envelope.
A Passivhaus will require high levels of insulation, sometimes referred to as super insulation, in order to achieve a U-value between 0.08 W/m2K to 0.15 W/m2K. These U-values can be reached with many different methods of construction including masonry, timber, prefabricated components, steel construction and more. The thickness of the walls will vary according to the method chosen.
The exact required U-value will be calculated in the PHPP and will take into consideration other design elements such as location, form factor, solar radiation, fenestration, local climate and other variables.
This increased level of insulation will significantly reduce the space heating demands (or heat load) on the building. The Passivhaus technical requirement of 15kWh/m2.a annual space heating demand, this is around 90% less than a typical UK building. This is in part due to the high levels of insulation, low thermal bridges, along with airtightness and associated reduction in air leakage.
With an airtightness barrier on the inside of the insulation the building can keep heat inside, or unwanted heat outside. Essentially, high levels of insulation with good airtightness will reduce the heat flow through the building fabric. As well as insulation to the general building fabric, any penetrations such as pipework and ducting must be well insulated to minimise cold bridging.
Passivhaus Wall Detail Examples
The following details are from Understanding Passivhaus.
Solid concrete with rendered external insulation Passivhaus wall detail
U-value: 0.115 W/m2K
Solid concrete with rendered external insulation Passivhaus wall detail 3D
Insulated Concrete Formwork (ICF) Passivhaus wall detail
Insulated Concrete Formwork (ICF) Passivhaus wall detail 3d
Masonry Cavity wall Passivhaus detail
Masonry Cavity wall Passivhaus detail 3d
Timber I joist frame Passivhaus wall detail
Timber I joist frame Passivhaus wall detail 3d
Timber I joist frame Passivhaus wall corner detail
Timber I joist frame Passivhaus wall corner detail
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