PASSIVHAUS
Passivhaus is a low energy building standard developed in Germany. It uses a scientific approach to building design where all the building data is entered in the Passivhaus software (PHPP) to model how it will perform based on it’s detailed design, climate, and surrounding context. To achieve the Passivhaus standard a building must be designed and built to require a very low level of heating (and cooling in hotter climates), and provide a high level of thermal comfort and internal air quality.
In the UK climate, this requires a highly efficient mechanical ventilation system with heat recovery (MVHR), a very high level of airtightness, high levels of insulation with almost no thermal bridges (interruptions to the insulation), high performance triple glazed windows and doors, and a very high level of quality control during design and construction to ensure the building is built as designed. Passivhaus strongly encourages an efficient building shape and optimised glazing design as these make it much easier to achieve the standard. If the site or brief require a less optimal shape or glazing then the standard can still be achieved, but it will require improvements to be made, such as further increasing the level of insulation.
We can calculate thermal bridges to see how much heat is lost through corners and junctions
ENERPHIT & PASSIVHAUS APPROACH
Although the Passivhaus standard has been achieved on retrofit projects, it is much harder to reach when dealing with an existing building so the Passivhaus Institute has created a lower standard for existing buildings called Enerphit. Enerphit projects require all the same information as Passivhaus, and although not as low energy as Passivhaus, an Enerphit project is still significantly better than a house that only meets the Building Regulations requirements for a new house in the UK.
The approach to building design used in Passivhaus can also be applied to non-Passivhaus projects. At Grain we have an in-house certified Passivhaus Designer, and we can use the PHPP software to model our projects to optimise their design even when we are not trying to achieve certification. Though certification does give the advantage of a highly experienced certifier reviewing all the project information, and guarantees the very low energy requirements for the building.
PASSIVHAUS MYTHS
“You can’t open windows in a Passivhaus”
It’s actually a requirement to have opening windows in a Passivhaus to ensure occupants have control over the ventilation, this is especially important in summer to help keep the building cool. However you will not need to open windows in winter to have guaranteed fresh air and good indoor air quality because of the whole house ventilation system.
“You can’t build a Passivhaus with natural materials”
Passivhaus does not define the materials that a building can be built from. Airtight doesn’t have mean vapour tight, so buildings can be built using vapour open, natural materials. There are even Passivhaus certified construction systems based around straw, timber frame, and woodfibre. At Grain we aim to design highly energy efficient buildings using natural materials wherever possible in order to create healthy buildings that minimise the embodied carbon as well as the in-use carbon from heating, hot water, and appliances.
“Passivhaus buildings overheat”
This can technically be true as the Passivhaus standard allows buildings to be designed to go over 25oC up to 10% of the year. However the latest version of the Passivhaus software has a built-in tool to model the risk of overheating in summer, and certifiers in the UK will generally reject designs that are predicted to overheat more than 2% of the year. At Grain we aim to get this down to 0% of the year by making good use of external shading and cross ventilation from opening windows. It is a requirement of the standard to provide occupants with a guide on how best to keep the building cool in summer.
PASSIVHAUS RESOURCES
Passivhaus Trust
The Passivhaus Trust promoters Passivhaus in the UK they have a database of UK Passivhaus, Enerphit and Low energy projects.
Passive House Institute
Passive House Plus
Passive House Database