Improving the airtightness of the building envelope can improve overall energy performance in modelling tools and potentially reduce reliance on higher-spec (and higher-cost) insulation by enabling the insulation to perform to its true R-value.

The removal of the Schedule Method from Clause H1 of the NZBC in November 2025 changed how residential buildings under 300m² are designed. From November 2026, specifiers will no longer be able to rely on a simple "R-value checklist". Instead, compliance must now be demonstrated using either the Calculation or Modelling Method, where the performance of the thermal envelope is assessed more holistically.

That thick woolly jumper you wear in the winter doesn't keep you very warm if it's too short or full of holes. Likewise, even 'well-insulated' assemblies will underperform if air is able to freely move through the insulation material itself, or through gaps in the assembly that the fluffy stuff forms part of.

When air within the insulation is allowed to move rather than remain still, thermal performance is compromised. The result is higher heating demand in winter, increased cooling demand in summer, and an elevated risk of condensation within wall and roof assemblies.

Airtightness membranes such as INTELLO PLUS address this directly by forming a continuous internal air barrier, helping designers achieve more predictable thermal performance in H1 calculations, as well as reducing the risk of interstitial condensation.

When working with either of the H1 compliance methods, designers now face the challenge of balancing competing elements such as windows, walls, roofs, and insulated floors to reach the sweet spot of cost, buildability, and performance demands.

Improving the airtightness of the building envelope with products such as INTELLO PLUS provides a valuable lever in this equation. By reducing uncontrolled air infiltration, designers can:

✅ Improve overall energy performance in modelling tools such as PHPP & ECCHO.

✅ Potentially reduce reliance on higher-spec (and higher-cost) insulation by enabling the insulation to perform to its true R-value.

✅ Deliver more consistent and comfortable indoor temperatures for clients.

We put on a woolly jumper to stop our bodies from getting cold; likewise, when we insulate our buildings, we are deliberately slowing the rate at which heat is lost through the envelope. And as moisture goes where heat flows, moisture management becomes increasingly important the more we insulate.

INTELLO PLUS is not just an air barrier — it is an intelligent vapour control membrane. Its humidity-variable diffusion resistance allows it to respond to seasonal conditions accordingly:

• Winter: High vapour resistance reduces moisture entering the structure from the warmer interior side

• Summer: Increased permeability enables the wall cavity to dry back into the interior from the warmer exterior side

So airtightness not only helps us comply with Clause H1, but also supports compliance with Clause E3 (Internal Moisture) and Clause B2 (Durability), by better managing internal moisture loads within the building envelope over the life of the building.

H1 is ultimately about ensuring the best occupant outcomes, not just compliance metrics.

Airtightness contributes to:

✅ More stable indoor temperatures.

✅ Reduced draughts and cold spots.

✅ Lower heating and cooling energy demand.

When paired with mechanical ventilation systems, airtight construction enables designers to adopt a "build tight, ventilate right" approach. This delivers consistent fresh air without relying on uncontrollable air leakage or windows that might not always be open.

This also opens the door to:

✅ Reduced overheating risk through controlled and reliable ventilation.

✅ Better indoor air quality.

✅ Lower dependence on active heating and cooling systems.

As the industry moves away from the Schedule Method, complexity is a major pain point. Designers now work with calculation tools and energy models that require new inputs and assumptions, including airtightness.

Pro Clima supports this change by:

✅ Providing clear airtightness strategies that can be confidently incorporated into H1 calculations.

✅ Supplying detailing guidance for a continuous air barrier across walls, roofs, floors, and junctions.

✅ Assisting with product selection and system design to align with modelling assumptions.

✅ Offering on-site support and training so buildings perform in practice as designed.

Rather than treating airtightness as an abstract concept, INTELLO PLUS provides a practical, measurable solution that helps designers meet the new H1 requirements with confidence. It turns complexity into clarity, and compliance into high-performance designs that deliver what clients expect.