THE BUILDING FABRIC · VIDEO GUIDE
Internal or external wall insulation?
Two ways to improve a wall. Different compromises. The right choice starts with the building, not a preference for one system.
Illustrative footage. Captions are included in the video; the key points are also written below.
What is the difference?
Internal wall insulation is fitted to the room facing side of an external wall, then finished internally. External wall insulation is fixed to the outside and covered with a suitable weatherproof finish. Both can improve thermal performance when the system is properly designed and installed. Neither is automatically the better answer for every house.
These choices are particularly relevant to solid wall homes. Before choosing either, establish how the existing wall is built, whether it is dry and sound, and how moisture and ventilation will be managed.
Insulating from inside
Where it can work well
It keeps the external appearance, which can matter on a character property or where altering the facade is not appropriate. Work may be planned room by room and can sometimes be coordinated with a wider internal renovation.
What to allow for
It takes up some internal space and can involve moving sockets, radiators, skirtings and finishes. Junctions at floors, partitions and windows need careful detailing to reduce cold bridges. The original wall becomes colder, so moisture risks and the condition of embedded timbers need proper assessment.
Insulating from outside
It leaves the room dimensions and most internal finishes alone. A continuous external layer can make it easier to address some thermal bridges, while renewing a tired exterior at the same time.
It changes the look and depth of the facade. Access and scaffolding may be needed, with details to resolve at roofs, eaves, sills, doors and boundaries. Permissions depend on the property and location, especially for listed buildings or conservation areas. It is not suitable to simply cover unresolved damp or defective masonry.
Compare the whole project, not just the insulation
Neither column is a promise about price or performance. The wall type, condition, thickness, access, detailing and scope of other work all affect the final specification and quote.
The first step is a proper assessment
Find and resolve existing damp and water ingress before covering a wall. Ask how the proposed system deals with moisture movement, ventilation and thermal bridges, including around windows and at joist ends. Check building regulations and any permissions or listed building consent that may apply. Traditional buildings can need a particularly careful, compatible approach.
Get a property specific design and an itemised scope for either option. That is more useful than choosing on a headline cost or a one size fits all claim.
Further reading
- Energy Saving Trust: solid wall insulation
- UK government: internal wall insulation guidance
Considering insulation as part of a renovation?
Start with the building and a clear scope of work.
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