When homeowners think about improving the thermal performance of an older property, insulation is an obvious place to start. Loft insulation, cavity wall insulation and upgraded glazing are all familiar options. Internal wall insulation, however, is a more specialist solution that can be particularly useful in older homes where external insulation isn’t practical.
It can also be one of the more complicated improvements to get right.
Why Insulate Walls From Inside?
Internal wall insulation involves installing an insulating layer to the inside face of an external wall. It can significantly improve the thermal performance of a solid-wall property without altering its exterior appearance.
That makes it particularly attractive for period properties, homes with decorative brickwork and buildings where changing the external façade would be undesirable.
There is, however, a trade-off. The insulation system takes up some internal floor area and can affect skirting boards, sockets, window reveals and other details.
The Moisture Question
One of the biggest considerations with internal wall insulation isn’t actually heat. It is moisture.
Traditional solid-wall buildings were often designed to manage moisture differently from modern cavity-wall construction. Brick, stone, lime mortar and breathable finishes can allow moisture to move through the building fabric.
Adding an insulation system without understanding how the existing wall behaves can therefore create problems.
This is why simply choosing the thickest insulation board available isn’t necessarily the best approach.
Vapour Control and Breathability
Different insulation systems deal with water vapour in different ways. Some rely on vapour control layers, while others are designed to be more vapour-open.
The correct specification depends on the construction of the property, the condition of the wall, exposure to driving rain and the materials already present.
For older buildings, compatibility is particularly important. Replacing breathable lime plaster with inappropriate modern materials at the same time as insulating the wall can alter the way the building manages moisture.
Don’t Forget the Details
The main wall surface is only part of the job.
Window reveals can become cold spots if they are not properly considered. Junctions between insulated and uninsulated walls can also create thermal bridges, while floors and ceilings may require careful detailing where they meet the new insulation layer.
Electrical sockets, radiators and fitted furniture may also need to be repositioned.
These details can have a surprisingly large effect on the final performance of the project. A theoretically excellent insulation system can underperform if the installation is full of gaps and poorly treated junctions.
Is Internal Wall Insulation Worth It?
For the right property, it can be an extremely effective home improvement. But it is not a straightforward cosmetic upgrade.
The best results come from treating the building as a whole rather than simply adding insulation to its walls. Understanding the existing construction, dealing with damp issues first and choosing compatible materials are all important steps.
For homeowners with older solid-wall properties, particularly where external changes aren’t desirable, internal wall insulation can offer a way to make the house warmer and more energy efficient while retaining the character of its exterior.
Featured image credit: AI generated.
