Thermally Broken vs Non-Broken Windows: How H1 Modelling Can Cut Costs Without Compromising Performance

"This is wonderful news. Thank you so much…. The cost is killing the scope – cost per SqM was 5 digits, but you’ve managed to pull 20% or a bit more out of the joinery cost." – Mark

This is a regular comment we get from our H1 Modelling clients.

This is one of the most tangible benefits of accurate H1 VM1 modelling: the ability to make smarter, cost-effective design decisions without compromising compliance or occupant comfort.

Using H1 Modelling to Optimise Glazing

One of the key ways we achieve cost savings is by optimising glazing performance. For the majority of our projects, H1 modelling has allowed us to switch from thermally broken glazing to high-quality non-thermally broken glazing, significantly reducing joinery costs—sometimes by thousands per project.

Accurate modelling ensures that these decisions don’t compromise H1 compliance. By simulating the building’s thermal performance in detail, we can determine exactly how much insulation, wall performance, and shading are needed to compensate for any differences in glazing type. This gives clients the confidence to choose more cost-effective glazing without risking energy efficiency or comfort.

Pros and Cons of Non-Thermally Broken Glazing

Pros:

• Lower cost per square metre compared with thermally broken alternatives.

• Compliance-ready when paired with a well-designed ventilation strategy, performing effectively in most NZ climates.

• Can allow for larger glazing areas without significantly impacting compliance, if walls and shading are optimised.

Cons:

• Non-thermally broken glazing can be more prone to condensation

• Must be paired with adequate ventilation and moisture management strategies to prevent issues.

• While thermally broken windows generally reduce condensation risk, we’ve heard reports of new thermally broken windows still experiencing condensation, particularly if the building’s insulation or ventilation isn’t correctly designed.

By understanding these trade-offs, designers and builders can make informed decisions that balance cost, compliance, and long-term building performance.

Practical Benefits for Our Clients

H1 VM1 modelling allows us to:

• Reduce joinery and glazing costs by a significant percentage, sometimes 20% or more.

• Avoid over-specifying high-cost products, freeing up budget for other aspects of the build.

• Identify potential issues early, reducing the risk of redesigns or RFIs during council consent.

• Deliver buildings that are energy-efficient, comfortable, and cost-effective, meeting compliance without overspending.

Accurate H1 modelling isn’t just about meeting code; it’s a powerful tool for managing budgets, controlling project scope, and ensuring that clients get the best possible value. With careful design, appropriate ventilation, and optimised material choices, we can save our clients thousands of dollars while maintaining comfort and long-term performance.

Final Thought

For any project where glazing represents a significant portion of the cost, leveraging H1 VM1 modelling is an investment that pays for itself.

It allows designers, builders, and clients to make evidence-based decisions that save time, reduce costs, and avoid surprises, while still delivering buildings that are warm, dry, and compliant.

To find out more about getting an H1 Report done, contact us here.