The numbers: cost vs savings

Here's a straightforward comparison for a standard semi-detached home in the UK:

Beyond the numbers — comfort and health

The financial case for insulation is compelling, but the full picture includes comfort and health benefits that don't appear in the savings calculations. A well-insulated home maintains more consistent temperatures, eliminates cold draughts, reduces condensation risk, and — for households with elderly residents or young children — can have real health implications.

Cold homes are linked to respiratory problems, cardiovascular disease, and mental health challenges. The NHS estimates that cold homes cost the health service hundreds of millions of pounds per year in preventable illness. Insulation is a public health intervention as much as an energy efficiency one.

When is insulation NOT worth it?

There are a small number of scenarios where the standard insulation calculus doesn't apply:

If you're selling imminently — the upfront cost may not be recouped before sale, though energy efficiency improvements generally increase property value and EPC ratings.

Spray foam specifically — due to mortgage risks and removal costs, spray foam can actively reduce property value. This is the one case where insulation may not be worth it. See our spray foam risks guide.

If major building works are planned — if you're planning a loft conversion or roof replacement, it may make sense to combine insulation with those works to avoid installing and then disturbing it.

Frequently asked questions