Insulation options compared — if you do one thing, what should it be?

Insulation is often described as the most sensible home energy upgrade — but there are several types, and they don’t all make sense for every home.

This page compares loft insulation, cavity wall insulation, and external wall insulation, focusing on costs, disruption, suitability, and common reasons people delay.

No quotes. No signup. Just the trade-offs.

The short answer

Loft insulation is usually the best first step if:

your loft is accessible
insulation is thin or missing
you want low cost and minimal disruption

Cavity wall insulation can make sense if:

your home has suitable cavity walls
installation is straightforward
disruption needs to be low

External wall insulation is usually only worth considering if:

your home has solid walls
major work is already planned
you’re comfortable with high upfront cost

Many homes only suit one or two of these options.

Insulation options — side by side

Category	Loft Insulation	Cavity Wall Insulation	External Wall Insulation
Upfront cost	Low (£300–£800)	Medium (£1,000–£2,500)	High (£8,000–£15,000+)
Installation time	Hours	1 day	Several weeks
Disruption	Very low	Low	High
Typical savings	Moderate	Moderate	High (when suitable)
Works best when	Loft is accessible	Cavities are suitable	Solid walls, major refurb
Visual impact	None	None	Changes exterior
Planning needed	No	No	Often yes
Payback certainty	High	Medium	Low–medium

Costs and savings vary by home and installation quality.

What installation is actually like

Loft insulation

Usually completed in a few hours
Little to no disruption
Often the simplest improvement

Cavity wall insulation

Installed via small drilled holes
Completed in a day
Not suitable for all properties

External wall insulation

Involves scaffolding
Alters the exterior of the home
Often part of wider renovation work

Disruption and suitability matter as much as savings.

Why many households delay insulation upgrades

Common reasons include:

uncertainty about suitability
concern about disruption
cost relative to other priorities
waiting to combine with other work

Delaying is often a practical decision, not a lack of awareness.

So which insulation should you choose?

There isn’t a universal answer.

Loft insulation is often the simplest and cheapest place to start
Cavity wall insulation can be effective when the property suits
External wall insulation is usually a long-term, high-commitment choice