What Makes a Wall Truly High Performance?
When people talk about high-performance buildings, the conversation often focuses on technologies: thicker insulation, airtight membranes, mechanical systems, or higher R-values. But at StrawSIPS, we believe a truly high-performance wall is not defined by a single metric — it’s defined by how well the whole system works together over time.
A high-performance wall must do four things exceptionally well:
Keep heat where it belongs
Control air movement
Ensure high indoor air quality is maintained
Allow any moisture that does enter the wall to dry out again.
If any one of these is overlooked, long-term performance, durability, and occupant health are compromised.
How well a wall can transfer moisture vapour out of the structure is especially critical. The New Zealand leaky home crisis showed us what happens when walls are wrapped up to protect from external but unable to dry out — moisture becomes trapped, mould develops, and structural damage follows. A truly high-performance wall must therefore be designed not just to resist moisture, but to safely release it over time.
Thermal Performance Is More Than Just R-Value
Insulation matters. A lot. But insulation alone doesn’t guarantee comfort or energy efficiency.
In real buildings, thermal performance is shaped by a combination of factors working together:
Continuous insulation
Airtightness
Minimal thermal bridging
Thermal mass that moderates temperature change
Traditional strawbale buildings demonstrated that thick, continuous insulation creates warm, stable interiors. What is less often discussed is the role of thermal mass within the wall assembly and internal finishes, which helps dampen temperature swings by absorbing and slowly releasing heat.
StrawSIPS panels build on this understanding, combining high levels of insulation with materials that contribute to thermal stability. This results in homes that not only stay warm in winter and cool in summer, but also experience far fewer rapid temperature fluctuations. This improves comfort and reduces reliance on active heating and cooling. The added bonus is that energy bills can be reduced by up to 90% compared to standard homes in New Zealand.
Airtight Construction is Non-Negotiable
Older houses are often full of uncontrolled drafts and air leaks — around skirtings, windows, service penetrations and junctions — which allow warmth to escape and cold, moisture-laden air to enter. This constant, unintended air movement wastes energy, creates uneven temperatures, and increases the risk of condensation within the building fabric. Creating an airtight house does not mean sealing the building shut or giving up fresh air or open windows; it means eliminating the unwanted air gaps that lead to unnecessary heat loss and moisture ingress.
In StrawSIPS buildings, airtightness is achieved using the 40–50 mm internal plaster layer as the primary airtight layer, carefully integrated with airtight tapes and purpose-designed fittings at junctions and penetrations. The result is a warm, efficient building envelope where fresh air is introduced intentionally, comfort is improved, and moisture is kept under control.
Moisture Management: The Key to Long-Term Durability
One of the most misunderstood aspects of building performance is moisture.
Modern buildings often rely on vapour barriers and sealed assemblies that attempt to block moisture movement entirely. When these systems fail moisture can become trapped, leading to rot, mould, and reduced building lifespan. In almost every building it isn’t a matter of if moisture will get in, it’s when it gets in where does it go. We are surrounded by moisture in the air and in our building materials, and just by living in a house we are releasing hundreds or thousands of litres of water vapour into the air every year and our house has to be able to manage and remove it without damage.
The New Zealand building system has placed so much focus on stopping moisture entering the building, and by wrapping it in impermeable plastic we have solved one problem and created a much, much bigger one. It’s like wearing a plastic poncho on a hike. It does a pretty good job of keeping water out, but as soon as you start to sweat it also does a great job of keeping moisture in. In a house this means trapping water in the wall framing and it doesn’t take long before mould is forming and starting to rot the house from the inside to the out. This can continue for years without anyone noticing until the whole has has to be condemned.
Strawbale buildings have long demonstrated another approach: manage moisture rather than trap it.
StrawSIPS panels are designed using established principles of building physics and building biology. The wall system allows moisture vapour to move safely through the structure while remaining protected from bulk water. This creates a robust, forgiving assembly that can dry naturally and recover from minor moisture events. We only use materials that have the required water vapour permeability to ensure that the moisture within the wall structure does not get trapped and does not grow mould.
Breathability is not a compromise — it is a performance strategy that supports durability over decades, not just at completion.
Natural Materials, Clay Plaster, and Indoor Air Quality
A high-performance building is about more than just energy-efficiency. Is it healthy for the people living there? Is is sustainable for the planet? Do we know the long term performance?
StrawSIPS panels are made from natural, low-toxicity materials that avoid many of the synthetic compounds commonly found in conventional wall systems. On the interior, walls are typically finished with clay plaster, a traditional material that works actively to improve the indoor environment rather than simply enclosing it.
Clay plaster naturally regulates indoor humidity by absorbing and releasing moisture vapour, helping to maintain comfortable and stable conditions throughout the year. It also has the ability to absorb odours and certain airborne pollutants, contributing to cleaner, fresher indoor air.
Beyond measurable performance, clay-plastered interiors create a noticeably different atmosphere. The spaces feel calmer, softer, and more grounded — a quality that many people recognise immediately when they step inside, even if they can’t quite explain why.
True high performance isn’t about pushing materials to their limits. It’s about designing systems that work in balance — with climate, materials, and people.
