Most homes in the UK lose a significant amount of heat through their walls, roof, and floors. The right insulation stops that, but the approach depends entirely on how your home is built, its current condition, and what else you are planning to do.

Why insulation matters

Most homes lose heat through walls, roofs, and floors, often without the homeowner realising. Poorly insulated homes work harder to stay warm, driving up energy bills and leaving cold spots that no amount of extra heating will fix.

The first thing homeowners tend to notice after insulating is not lower bills (Although that's a great bonus). It is comfort. Rooms that were always cold become usable. The house holds heat for longer, and the heating system does not have to work as hard.

Types of insulation

The right type of insulation depends on your home's construction, its current condition, and what you're trying to achieve. Here's how the main options compare.

Type

How it works

Disruption

Best suited for

Cavity wall (CWI)

Fills the gap between inner and outer walls

Low

Homes with unfilled or existing insulation failures

External wall (EWI)

Adds insulation to the outside of the building

Medium

Solid-wall homes where external changes are okay

Internal wall (IWI)

Adds insulation to the inside of external walls

High

Solid walls where EWI is not possible, or during renovation

Loft

Laid between and over joists in the loft space

Low

Any home with accessible loft space

Room-in-roof

Insulates between rafters in a converted loft

High

Top-floor rooms built into the roof, or loft conversions

Flat roof

Insulation added above or below the roof deck

Medium to high

Older flat roofs, especially during replacement/repairs

Suspended floor

Insulates beneath ground-floor timber or solid floors

Medium to high

Draughty timber floors, or solid floors being replaced

What to be aware of

Insulation changes how moisture moves through your home. If there are existing damp or condensation problems, adding insulation without addressing them first can make things worse, not better. Material choice matters too. Older solid-walled homes need breathable materials that allow moisture to pass through the wall rather than trapping it inside.

Sequencing is just as important. Insulating before fixing the roof, resolving damp, or planning your ventilation can create problems that are costly to undo later. The order in which improvements happen is not an afterthought.

“You can’t ignore damp and just install insulation. It won’t solve the issue and it could also make it worse.”

Adam Wilson, Head of Delivery at Furbnow

How Furbnow approaches insulation

Every home is different, so we start with a whole-house survey to understand your home's construction, its current condition, and where the biggest heat losses are. Our PAS2035-certified retrofit coordinators and CIAT-chartered architectural technologists design an insulation strategy built around your specific home, including the right materials, the correct sequencing, and how it fits alongside ventilation and heating.

We do not recommend insulation in isolation. Everything is designed together so that improvements reinforce each other rather than create new problems.

Start with a plan, not a guess

A Furbnow Home Energy Plan maps your home's heat loss, identifies the right insulation measures, and sets out the correct order of improvements, so nothing gets installed at the wrong time.