Featherston Passive House

WHAT WAS THE CHALLENGE?

When architect Josefine Watterson and her family decided to leave city life behind for a more relaxed countryside lifestyle in Featherston, New Zealand, the eco-conscious family decided to construct a high-performance ‘passive home’ that would require very little heating during the cold Featherston winters. ‘Passive House’, or Passivhaus™ Standard as it is known in German, is a design standard that delivers healthy, comfortable, and efficient buildings. This design standard helps to achieve thermal comfort with minimal heating and cooling by using insulation, airtightness, appropriate window and door design, ventilation systems with heat recovery, and elimination of thermal bridges.

The 200-square-metre house was featured on Grand Designs New Zealand for its unique architectural layout and considered use of passive house elements that included triple-glazed windows and carbon-positive timber. Superior insulation throughout the walls, roof and floor was also installed to meet strict passive house credentials and ensure comfortable indoor temperatures were able to be maintained throughout the year.

Products used:
- Knauf Insulation Acoustic Wall and Midfloor
- Earthwool glasswool insulation: Wall
- Earthwool glasswool insulation: Ceiling
Client: Josefine and Will Watterson
Installer: Maple Build Ltd
Sub-contractor: Go2 Insulation
Project: The Watterson residence, a Certified Passive House built in Featherston, was featured on Grand Designs in November 2022.

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What was the solution?

To help the family achieve its dream of creating a passive home, the Earthwool® glasswool range of high-performance insulation products was selected. The complexities of building a passive house required a clever mix of different insulation R-values and varying thicknesses, with insulation installed into the walls, midfloor and external wall junction, where rafters ran both perpendicular and parallel to external walls. Following these strict insulation specifications was crucial to ensure the home passed the required heat-loss calculations and protect the home’s overall thermal performance.

By installing Earthwool® glasswool Insulation, the family significantly enhanced energy efficiency of the building. As glasswool insulation prevents heat loss during winter and heat gain during summer, it helps to reduce the home’s reliance on artificial heating and cooling systems which in turn resulted in a reduced carbon footprint and energy savings.

One of the core principles of a Passivhaus™ building is that they are super airtight, which means there are very few natural air changes per hour. This means that any VOCs which are off-gassed from materials used in the home are potentially not exhausted as quickly as in a leaky home. This places greater importance in using low VOC materials and materials without chemicals such as formaldehyde. Earthwool® glasswool insulation ensures comfort while supporting sustainability. It’s certified to the highest Eurofins GOLD standard for indoor air comfort. This demonstrates compliance with all relevant VOC-related requirements. The eco-friendly insulation solution has BRANZ Appraisal certification along with Global GreenTag Level A , which means that the building supports the environment while keeping occupants healthy and safe.

What was the result?

Josefine says that, while the project presented many challenges, she’s learnt a lot about the thermal performance requirements of building a passive house. To her delight, the Featherston home exceeded the stringent passive home testing and certification requirements, which required an overall insulation R-value in excess of R8.0.

""Knauf Insulation represent a safe choice when it comes to quality products and service that deliver guaranteed results" - Josefine Watterson, architect"

The family’s efforts have been well worthwhile, with the layers of insulation contributing to home’s lower need for heating during winter, reducing its energy costs and providing an optimal level of indoor comfort. Additionally, the benefits of Earthwool® Glasswool’s silicone treatment, DriTherm® Technology, with a moisture resistance guarantee helps protect the house from wet conditions throughout the year.

The Knauf Insulation team was on hand to provide guidance and advice at all stages of the project, which included assisting with quality assurance measures and checking the correct thicknesses were achieved to the desired outcome which was critical for meeting the home’s thermal performance requirements.

Josefine refers to her passive home as a “clean, green, living machine”. She is enjoying the warmth after years of freezing and says the home’s heating bill is non-existent; her energy bill has been cut in half.

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