Drilling through the cost barrier of high performance buildings
Excerpts taken from Terrell Wong at Green Building Festival in Toronto, October 2019 https://www.youtube.com/watch?v=VXSpcyUgCKM
What is Passive House design currently, but just high-end custom design? Passive House projects come with bespoke engineers, thermal modeling, architects and contractors. In our traditional model, the architects work alone in their silo and only after the basic design is complete and the clients have some buy-in do they then call in the team to shoehorn in the mechanicals and structural. This is the most expensive way to build.
Passive House design encourages integrated project design, where all the team members including the clients work together from the start. This is the first step toward reducing the cost associated with over design, and unresolved details.
Custom design comes with unique parts, sites, and weather. All of these things drive up the price of construction. Inclement weather causes losses in time and harsh conditions lead to destruction of work, driving up costs. Material storage is another factor we need to consider. Management of supplies on the urban site can be difficult when there is limited space. This is critical to the flow of work. The management of a clean and safe worksite includes the storage of waste and recyclable materials and with workers from different trades this is hard to coordinate.
Factor all this in and then you need to worry about making sure contractors source the correct materials. Passive House calls for specific types of products to ensure air tightness and minimal thermal bridging. We need to avoid situations where the wrong material can be ordered and someone declares it “good nuff”. Architects have to work hard to make material procurement as easy as possible for the contractors.
So how do we coordinate our trades when working on a project, and how do we avoid the problems listed like site conditions and waste management?
One can consider prefabricated building components such as Passive House wall panels. These would still be used for a custom building, with varying sizes, door and window locations and materials used, however it allows the entire wall construction to be made inside in a controlled environment with planned openings and a higher level of quality work. Rather than hiring sub-trades to come onto a site for a short period of time, panels are built in a factory by employees trained for their specific positions allowing for higher consistency for the thermal envelope. Bulk ordering would drive down costs further, however this requires a consistent section or detail for the walls and roof panels, and a smaller selection of materials.
Panelization reduces waste and minimizes material storage, but if each panel is custom, the work flow is disrupted and can not drive costs down extensively. Despite this quality is greatly improved from site built stick framing. The less customization the timelines could potentially be much faster than on site construction. If done right, there could be a consistent savings of 10-15%.
Even in our small community of Passive House designers and builders in Canada there are a number of companies working towards affordable, prefabricated buildings. Aerecura (as seen above with their pre-designed rammed earth home, the Freya Home), Pinwheel Structures, Maison Elements, Simple Life Homes and Tooke Tree are just a few of the innovate companies working to make Passive House affordable for all.