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Canadian Utility Airtightness and Energy Efficiency Study

Background

This study analyses measured heating-energy impacts from airtightness improvements across a large Canadian utility dataset spanning multiple production builders and housing types. Pre-intervention airtightness commonly ranged from 4 to 8 ACH50 or higher, with significant builder-to-builder variation. Leakage reductions of 40 to 70 percent shifted homes toward 1 to 3 ACH50, delivering consistent heating-energy savings of 15 to 30 percent, or 8 to 25 GJ per home per year. Energy reductions scaled closely with initial leakage levels, with the largest gains in homes starting above 5 ACH50. Results confirm airtightness as a dominant driver of residential heating demand and a repeatable pathway for large-scale load and carbon reduction, even accounting for normal construction-stage rebound effects.

Highlights

Airtightness reductions of 40-70 percent consistently lowered heating demand by 15-30 percent across measured homes.
Energy savings of 8-25 GJ per year were recorded.
Homes starting above 5 ACH50 delivered the largest absolute and percentage savings.
Post-intervention airtightness clustered tightly around 1-3 ACH50, demonstrating predictable, scalable performance gains.

Measuring the Energy Impact of Airtightness

The Canadian utility study evaluated the relationship between airtightness and heating energy use across a large sample of new homes built by multiple production builders. The objective was to quantify how changes in envelope leakage affect operational energy demand, fuel consumption, and to determine whether airtightness improvements represent a reliable pathway for reducing load in residential housing stock.

The dataset includes airtightness measurements at various construction stages, energy-modelling outputs, and recorded heating-energy profiles under both pre- and post-intervention conditions. Taken together, the data provides a detailed view of how infiltration impacts energy performance.

Airtightness Characteristics Across the Sample

The study found that airtightness levels in new residential construction vary widely prior to intervention. Pre-intervention ACH50 values ranged from moderately tight to extremely leaky, with some homes performing significantly above expected code or builder targets.

Despite this variability, the dataset shows:

A broad spread of initial infiltration levels (often 4–8 ACH50 or higher)
Strong builder-to-builder variation, reflecting differences in construction detail, trade quality, and sequencing
Opportunities for improvement across all house types, regardless of design or materials

What is notable is that, even with this diversity, all homes demonstrated potential for meaningful improvement once leakage pathways were addressed.

Measured Airtightness Improvements

A key finding of the study is that airtightness improved consistently and significantly after intervention. Across the participating homes, leakage reductions commonly fell in the range of:

40–70% reduction in ACH50, and
Substantial tightening of the effective leakage area

These improvements were not isolated to any single builder or typology. Rather, they occurred across detached, semi-detached, and townhouse units, indicating that improvements in airtightness are broadly achievable in standard residential construction.

The post-intervention airtightness values were far more tightly clustered than pre-construction measurements. This pattern suggests that while initial construction quality varies considerably, airtightness improvements serve to normalise performance and deliver predictable outcomes across a diverse building fleet.

Relationship Between Airtightness and Heating-Energy Use

The study provides clear evidence that reducing air leakage directly decreases heating-energy demand. This relationship was demonstrated through utility modelling results and verified through changes in fuel consumption.

Key statistical relationships observed:

Homes with the largest reductions in ACH50 also demonstrated the largest decreases in annual heating energy.
Energy savings scaled proportionally with the extent of airtightness improvement.
Even moderate reductions in leakage (e.g., 2–3 ACH50) produced measurable energy savings.

This confirms the fundamental building-science principle that infiltration load contributes significantly to space heating demand.

Energy Savings Results

Relative energy savings:

15–30% reduction in heating demand for most homes
Higher percentages for homes starting with the worst leakage

These results demonstrate that airtightness is a major driver of heating-energy cost and carbon emissions in residential buildings.

Effect of Starting Leakage Levels

One of the most important insights from the study is that starting leakage strongly predicts the magnitude of achievable energy savings.

Homes that began with high infiltration (5–8+ ACH50) realised the greatest benefits. Conversely, homes that started near 3–4 ACH50 saw smaller absolute savings, though still measurable and valuable.

This confirms that airtightness improvements are most impactful in homes with high baseline infiltration, which describes much of the existing NZ and Australian housing stock.

Implications for Utility Programmes and Building Policy

The utility study provides a robust evidence base for the role of airtightness in achieving energy and emissions reduction targets. Its findings imply the following:

Airtightness improvements are scalable and repeatable across builders.
They provide predictable, quantifiable reductions in heating-energy use.
They are applicable to both high-performance and standard production housing.
They offer one of the highest impacts per dollar among envelope interventions.
They support the justification for incentive programmes, code enhancements, and builder education initiatives.

For regions like New Zealand and Australia, where airtightness is currently unregulated or poorly controlled, the findings indicate a substantial opportunity for cost-effective energy and carbon reductions.

Overall Findings

The Canadian utility study demonstrates that:

Airtightness is a dominant factor in residential heating-energy performance.
Improvements lead to significant and consistent reductions in operational energy use.
Airtightness improvements offer a reliable pathway for improving building performance at scale

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