Can You Partially Insulate a Building? – Can I Just Ask? – Episode 4

Can You Partially Insulate a Building? Risks, Strategies, and Best Practice

It’s a question that comes up regularly: can you insulate a building in stages, rather than all at once?
In short—yes, you can. But the real answer is more nuanced, because while a staged approach can work in certain circumstances, it carries risks that can undermine both performance and durability.

If you’d rather hear Andy and Chris talk through the ideas in this article, you can watch Episode 5 of Can I Just Ask? below. 👇

The Problem with Partial Insulation

When you insulate only part of a building, you inevitably create a mix of warm and cold surfaces. The warmer internal air—now able to hold more moisture—will come into contact with the uninsulated, colder areas. Those cold surfaces then bear a greater moisture burden, increasing the likelihood of condensation and mould growth. This not only damages finishes and fabric but also degrades indoor air quality.

From an energy efficiency perspective, partial insulation is also inherently compromised. Heat will always take the path of least resistance, escaping through the uninsulated sections just as water finds the lowest gap in a dam. While you might improve comfort in one room, the overall building performance remains well below potential.

Moisture Risks at Insulation Junctions

Another key concern is what happens at the edges of insulated sections. Where insulation stops and meets uninsulated fabric, thermal bridging occurs. These junctions are prone to localised heat loss and—more critically—localised condensation. Thermal bridge modelling makes this very clear: the perimeter of an insulated area often shows the highest risk of condensation, even if the rest of the wall is performing well.

Staging Insulation Without Creating Problems

If you must take a phased approach, the time frame matters. Extending the gap between stages to five years or more increases the risk of persistent moisture problems. A shorter window—say, two to three years—reduces that risk, particularly if heating and ventilation are well managed during the interim.

It’s also worth considering coverage strategy. Even a thin, continuous layer of insulation across the whole building is preferable to concentrating a large thickness in only a few locations. For example, 40 mm of well-fitted, continuous insulation across the envelope is often more effective than 100 mm installed haphazardly in patches.

The End Goal

Whatever the route, the aim should always be full, continuous insulation of the building envelope. This ensures a high-performance, low-risk, comfortable home with consistent surface temperatures, reduced thermal bridging, and optimised energy efficiency. Staging can be done, but it should be planned with the long-term performance of the whole building in mind—not just the comfort of one room.