New Zealand Sustainable Home Design

At Nala Studio Architects, when designing a new home or building, it's important to take into account the overall sustainability and impact the building has on it's occupants and surronding environment. Our designs aim to prevent mould and durability issues by managing moisture effectively, use insulation and design strategies to keep homes warm in winter and cool in summer. We also try to reduce the carbon footprint of construction materials through careful selection while implementing shading, glazing, and ventilation solutions to maintain comfortable temperatures. 

As a general guideline, where possible, we follow the New Zealand Homestar Design Guide as it's a practical resource aimed at helping architects, builders, and homeowners in New Zealand create homes that are healthier, more comfortable, and have a lower environmental impact. The guide also aligns with the Homestar rating system, which evaluates homes based on their energy efficiency, carbon footprint, and overall sustainability.

If you are building your first home in New Zealand or have decided to embark on a property development venture, having an overview of the Homestar Design guide will be really helpful. As it's quite a comprehensive document, we have summarised some of the key points below.

Chapter 1: Case Studies

Purpose: Demonstrate how different types of homes can achieve various Homestar ratings.

• • Features four typical New Zealand housing types (e.g., standalone houses, townhouses, apartments).
  • Each case study is modelled using the Energy Carbon Calculator for Homes (ECCHO) across three climate zones.
  • Shows specifications needed to achieve 6 Homestar (good practice) and 8 Homestar (best practice) ratings.
  • Illustrates the balance between performance and budget.

Takeaway: Every project is unique, and thermal modelling is essential to optimise design for specific climates and budgets.

Chapter 2: Moisture Control

Purpose: Addressing high levels of mould in homes due to climate and moisture problems.

Key Concepts

• • Moisture Sources: Activities like cooking, showering, and even breathing contribute to indoor moisture.
  • Problems Caused: Excess moisture can lead to mould growth, affecting health and building durability.

Strategies for Control:

• • Prevent Moisture Entry: Use proper building materials and construction techniques to keep moisture out.
  • Allow Moisture to Escape: Ensure the building can "breathe" so trapped moisture doesn't accumulate.
  • Continuous Insulation: Maintain uninterrupted insulation to prevent cold spots where moisture can condense.

Homestar Credit HC4: Focuses on moisture control measures in building design.

Takeaway: Effective moisture management is crucial for healthy, durable homes.

Chapter 3: Assemblies

Focus: Different ways to construct walls, floors, roofs, and install windows/doors.

• • Presents a range of standard and best-practice construction methods (called "assemblies"). 
  • Discusses properties like thermal performance, cost, and suitability for different climates.

Examples:

• • Walls: Options include timber framing with insulation, structural insulated panels, or insulated concrete forms.
  • Floors: Choices between insulated slabs, raised timber floors, or slab-on-grade with thermal breaks.
  • Roofs: Various insulation strategies, such as warm roofs or vented cold roofs.
  • Joinery Installations: Proper installation techniques to reduce draughts and thermal bridging.

Takeaway: Selecting the right construction methods enhances energy efficiency and comfort.

Chapter 4: Embodied Carbon

Definition: Embodied carbon refers to the total greenhouse gas emissions produced from manufacturing, transporting, and installing building materials.

Requirements:

• • All projects must perform a Life Cycle Assessment (LCA) focusing on stages A1-A5 (from material extraction to construction).
  • No mandatory reduction targets yet, but understanding embodied carbon is the first step.

Strategies to Reduce Embodied Carbon:

• • Material Selection: Choose low-carbon materials like sustainably sourced timber instead of steel or concrete.
  • Efficient Design: Optimise building design to use fewer materials without compromising strength or function.
  • Waste Reduction: Minimise construction waste through careful planning and recycling.

Related Homestar Credits:

• • EN2: Embodied Carbon—assessing and acknowledging efforts to reduce it.
  • EN3: Sustainable Materials—using materials with lower environmental impacts.
  • EN4: Construction Waste—promoting waste reduction practices.

Takeaway: Reducing embodied carbon is essential for lowering the overall environmental impact of a building.

Chapter 5: Overheating

Issue: Homes can become uncomfortably hot (in particular in the upper North Island), affecting occupant comfort and health.

Causes of Overheating:

• • Solar Gain: Heat from sunlight entering through windows and walls.
  • Internal Heat Sources: Heat generated by occupants, appliances, and lighting.

Strategies to Prevent Overheating:

• • Shading Design:
    • Use overhangs, awnings, or pergolas to block direct sunlight.
    • Plant trees or install exterior blinds for additional shade.
  • Glazing Selection:
    • Choose windows with low solar heat gain coefficients.
    • Use double or triple glazing to reduce heat transfer.
  • Ventilation:
    • Design for natural ventilation with windows placed to allow cross-breezes.
    • Consider mechanical ventilation to supplement natural airflow. 
  • Homestar Summer Comfort Credit: Evaluates homes on how often indoor temperatures exceed 25°C. Sets maximum allowable overheating frequencies for different star ratings.

Takeaway: Proper design can keep homes cool and comfortable even during hot periods.

Chapter 6: Indoor Environment Quality

Importance: A healthy indoor environment promotes well-being and comfort for occupants.

Challenges:

• • Pollutants: Moisture, carbon dioxide (CO₂), and volatile organic compounds (VOCs) from building materials and activities.
  • Insufficient Ventilation: Reliance on opening windows isn't always effective.

Solutions:

• • Mechanical Ventilation: Install systems that continuously exchange indoor air with fresh outdoor air. Helps remove excess moisture, CO₂, and VOCs.
  • Material Choices: Use low-VOC paints, adhesives, and finishes. Select furnishings that emit fewer pollutants.

Homestar Requirements:

• • Mandatory Mechanical Ventilation: All Homestar-rated homes must have mechanical ventilation.
  • Enhanced Credits: Additional points for superior indoor air quality measures.

Takeaway: Investing in proper ventilation and material selection leads to healthier living spaces.

Additional Tools and Resources:

There are many additional tools and resources that will be useful for your sustainable home design. The Energy Carbon Calculator for Homes (ECCHO) is a tool for modelling energy use, carbon emissions, and thermal comfort. This helps architects assess different options to meet Homestar and passive criteria.

In general, it is important to consider a holistic design approach, considering all aspects of sustainability throughout the architectural design and build. At Nala Studio Architects, we'll ensure all stakeholders (incl engineers, builders and the client) are engaged throughout the design process so the final documentation is tailored for optimal performance. We will use modelling tools to predict how the home will perform and adjust designs based on modelling results to achieve desired outcomes while still remaining cost effective. 

If you would like a copy of the latest Homestar Design Guide or would like to discuss any of the above, please don't hesitate to reach out to the team at Nala Studio Architects.