Passivhaus is not a new concept. There’s already over 50,000 buildings designed and constructed to Passivhaus standards in Europe according to the Passivhaus Trust. It is gaining increased traction in the Scottish Market, and the industry is keen to further understand what design considerations need to be factored in when delivering to Passivhaus standards.
Faithful+Gould are currently engaged in several projects across Scotland which aim to become accredited by the Passive House Institute. We also have a number of projects which are taking a ‘fabric first’ approach and exploring some of the principles which could be incorporated into the design to make lower energy, more efficient buildings, without becoming fully accredited. These are cross-sector projects, including primary and secondary education, health care, culture and residential, for both new build and retro fit works (using the EnerPHit standard).
Passivhaus is primarily concerned with the fabric and operational energy (particularly heating and cooling) of a building i.e. the building in use following construction. It does not account for the embodied energy that is used in construction, during maintenance, and demolition. Below summarises a high-level overview of some of the key principles that need to be considered when designing to Passivhaus standards:
- Building Form / Shape – simplified building form and shapes, with details which consider buildability during construction and help to minimise detailing which could give rise to thermal bridging.
- Insulation & Thermal Performance – any element of the building which is exposed to the external environment needs to be highly insulated. This includes increased build up to external building fabric, high performance glazing, and ensuring any potential for thermal bridging is designed out.
- Orientation / Sunlight – positioning the building on your site to minimise solar gain in summer and maximise gain in winter, whilst also allowing natural light into the building. This means site selection and positioning on site must be carefully considered.
- Air Tightness & Ventilation – ensuring the building is airtight to the external environment to avoid heat loss / unwanted heat gain, whilst also using Mechanical Ventilation and Heat Recovery systems (MVHR) to ensure any excess heat generated in the building is extracted / put to use elsewhere. Ventilation also ensures consistent air flow and high-quality indoor air standards.
- Rigorous Modelling and Testing – The design for the building needs to be modelled and then extensively tested during construction and at completion to ensure it meets the required standards and forecast modelling.
Moving from Passivhaus to zero carbon in use
By incorporating these ‘fabric first’ principles into building design, energy demand should greatly reduce. This is a huge step in the right direction, yet to get to net zero carbon in use, the remaining energy requirement needs to be offset. This offset could be achieved with the use of local renewables such as solar, geo-thermal, biomass etc. If this is unaffordable for a project, then management strategies can be put in place to ensure the building owner uses energy from a green supplier with fully renewable means to generate the power they supply (hydro, wind, tidal etc.).
Key Benefits, Opportunities and Challenges
Our teams have witnessed huge benefits and opportunities on our Passivhaus projects. The most significant being:
- Reduced energy consumption that Passivhaus brings.
- The associated reduction in life cycle costs – something every building owner should aim for and a key driver for many of our clients, particularly in the public sector.
- The level of comfort that occupants and end users of these buildings find, particularly the consistent temperatures and regular fresh air flow. This can lead to increased wellbeing outcomes for occupants.
- Quality - Due to the rigorous standards required for construction, quality has moved up the agenda. Quality in construction is an inherent part of Passivhaus principles, with projects regularly inspected during the construction process, giving clients confidence in their new asset.
In terms of some of the challenges of implementing Passivhaus, the first is the cost uplift (capital cost), and the associated impact on budget. It is currently unknown as to the exact quantum of uplift of a Passivhaus building versus a like for like comparator, however our projects are forecasting an average of between 7 to 12% uplift. We will explore this further in our upcoming Cost Management article.
Additionally, there is still a gap between the current market demand for Passivhaus certified Trades Persons and those available in the Scottish Market. However, Consultants and Contractors are in the process of upskilling their teams to meet this demand, so this is a reducing risk.
Despite some challenges to overcome, the market is moving in the right direction to embrace Passivhaus, which will allow the benefits and added value it can bring to be realised, particularly for clients managing large estates.
Whilst Passivhaus alone will not achieve net zero carbon, it goes a long way to reducing carbon demands of both new and existing buildings. When combined with careful consideration of material selection, logistics and construction methodology to reduce embodied carbon, it is a highly effective model to help move towards meeting the current 2030 /2050 carbon reduction targets.
Our following articles will discuss considerations from a Project Management and Cost Management perspective when implementing Passivhaus.