Which insulation method for walls?

[peweuk]

Our house is of block and render construction on the main house and brick on the extension.
The house and extension are at least 30 years old and of cavity construction with no insulation in the cavity.
We are looking at adding insulation and are having conflicting advice as to which way to proceed
- injected cavity beads
- internal insulation board
but which way is best from a) a cost point of view, b) offering the best insulation

Some are suggesting that cavity injection, although offering the least disruption, can lead to damp in the walls over time, and internal insulation board would take a lot more work and reduce room size (the amount being determined by board thickness used), but could be done gradually one room at a time on a DIY basis to keep cost down.

I'd be interested to hear comments/views from those with experience of either of these methods to assist our decision.

 

[jeds]

Cavity injection may cause dampness if the cavity is not wide enough and/or is full of snots and debris. Otherwise, injection is safe and will not cause an issue. A reputable company should survey and advise on suitable materials and should not consider it if the cavity is not suitable. Cavity injection is the cheapest, and most straightforward, way to achieve a decent thermal upgrade.

If cavity injection is not suitable, the next options are either external or internal wall insulation. I would investigate cavity injection first.

 

[cdbe]

Consider doing both, subject to assessment of the cavity. 50mm of fluff in the cavity plus 50mm celotex is still way short of current standards. I have blown insulated cavities and am considering EWI as well. I'm currently doing a large rear extension insulated to pre 2022 standards and am now considering a bit of topping up internally with some celotex before the plasterboard goes on.

The latest government scheme may offer some funding for ordinary people.