We worked on the first system certification for passive houses in a warm climate: we try and explain what it's all about.
A "construction system" includes different assemblies for the thermal envelope of a building, and their junctions. There you have vertical envelope structures (external wall, wall to ground, wall to unheated space and so on); slab on ground, on external air or on unheated space; roof. You also have the installation details for external windows and doors, as well as skylights.
The certification is offered to builders, regardless of the type of construction they use (masonry, concrete, steel frame, wood and so on). A contractor can certify its system, and make it available to designers and clients who intend to build a passive house.
In the certification process, the thermal quality of the assemblies and of the junctions is verified by the Passivhaus Institut, in terms of heat flow (PSI), internal surface temperatures (fRsi), and air tightness.
The goal of this certification is to allow a broader diffusion of the passive house standard, with certified components.
In the "business as usual" design workflow of a passive house, structure assemblies are designed for the one specific project, and dozens of thermal bridges are calculated to be then used only once. It is quite evident that this BAU method becomes quite costly on the design/consulting side, and requires very specific skills from the professionals involved.
In the case of a certified system, instead, it is the contractor to provide the assemblies and their junctions, including the thermal values (transmittance, PSI, fRsi). Furthermore, it is the contractor to provide the specifications for the airtightness of the building envelope.
A house built with a certified system becomes automatically passive?
No, but it's well under way.
With the use of a certified system, architects and designers can focus on the architectural design, taking care of the orientation of the building, the compactness ratio, the type and the distribution of the openings and of the shading devices. This can be easily done by implementing preliminary design tools such as DesignPH.
In the design process of an actual building, the thermal calculation needs to be further developed in PHPP, to optimize the envelope and the services. Anyhow, the data of a certified system (both assemblies and thermal bridges) are included in the components database in both DesignPH and PHPP.
The contractor's job is simplified, because the engineering process of the building and the construction documentation are carried out "in house".
A pre-designed system redistributes work and responsibilities between designers and contractors: the goal is to guarantee a state of the art passive building, according to technical requirements (energy performance, comfort, airtightness), and to project budget.
Several contractors around the world offer their own systems (certified or not), to build passive houses. This is not only the case of prefabricated wood constructions: construction systems for masonry, steel frame, concrete etc. are also available.
We're going to present the first certified construction system for passive houses in a warm climate at the next International Passive House Conference, scheduled for April 2016 in Darmstadt.