While both insulation and airtightness play vital roles in reducing heat loss, understanding their distinct functions and cost implications can guide builders, architects, policymakers, and homeowners towards smarter decisions in constructing greener homes.

Airtightness v insulation

Airtightness minimises uncontrolled airflow—draughts and leaks—through gaps and cracks in the thermal envelope of a building. Insulation, on the other hand, reduces heat conduction. While the two work hand in hand, airtightness controls heat loss due to air movement, which can often account for 20-50% of a home’s total heat loss.

Beyond a certain point and over time, insulation yields diminishing returns and will often need to replace and adding to. Any addition will only reduce heat loss by a small amount and can be costly.

Airtightness that is addressed during construction reducing the need for costly materials. Small, targeted improvements in airtightness combined with controlled mechanical ventilation can deliver significant reductions in heat loss and enhances heating efficiency, often at a lower cost than adding additional layers of insulation.

Our partner, MAST Architects, highlight these dynamics (details below), underscoring the value of airtightness with MVHR (Mechanical Ventilation with Heat Recovery) over additional insulation in reducing heating demands and costs.

Reducing energy waste and improving comfort

Sealing air leaks ensures heating systems work effectively, cutting energy consumption and therefore bills. For the average UK home, this simple measure can translate to substantial savings and lower environmental impact through reduced carbon emissions.

Improved airtightness ensures consistent indoor temperatures, eliminating draughts and cold spots. It also reduces the ingress of outdoor pollutants, dust, and allergens, fostering healthier indoor environments. For tightly sealed homes, Mechanical Ventilation with Heat Recovery (MVHR) systems enhance air quality by circulating filtered air without energy loss.

Practical steps for builders and homeowners

For developers and self-builders alike, airtightness can be improved systematically and cost-effectively by:

Case study: Mast Architects’ insights

In a recent MAST masterclass we saw a comparison between a new built home with standard air leakage vs. a tightly sealed home, showcasing the heating demand and building cost difference:

This data illustrates that improving airtightness alone has a greater impact on heating demand reduction than simply increasing insulation levels. For instance, reducing air permeability from 4.5 to 1 m³/m²/hr delivers significant efficiency gains with a build cost increase of just 2-3%. Conversely, adding insulation alone at higher U-values leads to a 20% cost increase with minimal improvement in heating demand.

Building a greener future

To meet the UK’s energy efficiency and sustainability goals, we must rethink traditional construction priorities. Airtightness, when paired with appropriate ventilation systems like MVHR, can reduce energy waste, lower emissions, and enhance comfort—all at a more affordable price point.

By integrating these principles, architects, builders, and policymakers can make significant strides towards a greener future. With airtightness improvements offering clear environmental and economic advantages, it is time to prioritise this often-overlooked aspect of homebuilding.

According to pbctoday.co.uk