Home insulation: where to start (and why it pays)

A draughty, poorly insulated home is like trying to fill a bath with the plug out. You can upgrade your boiler or switch to a heat pump, but if the heat disappears through the roof, walls and gaps around your windows, you're still wasting money. Insulation fixes the root problem.

Where heat escapes from a typical home

Heat moves from warm areas to cold ones through three routes: conduction (through solid materials), convection (air movement carrying warm air out) and radiation (infrared heat through glass and walls). Understanding this helps you prioritise:

• Roof and loft: Heat rises, so the roof is often the biggest single source of heat loss in a poorly insulated home — and usually the easiest and cheapest to fix.
• Walls: Walls make up a large surface area. Cavity walls (two layers of masonry with a gap) can be filled; solid walls (older homes, many pre-1920s properties) are harder and more expensive to treat.
• Floors: Suspended timber floors can let cold air in from below; concrete ground floors lose heat through conduction, though less dramatically than roof and walls.
• Windows and doors: Single-glazed windows lose heat quickly; older double glazing with failed seals is also poor. But windows are a smaller fraction of the total heat loss than many people assume.
• Draughts: Uncontrolled air leakage — gaps around pipes, floorboards, letterboxes, loft hatches, electrical sockets — lets cold air straight in and warm air out. This is distinct from necessary ventilation.

Start with the cheap wins

Before committing to any significant spending, tackle the measures that cost little but deliver real savings.

Draught-proofing

This is the single most cost-effective thing you can do in most homes. Foam or rubber strips around door and window frames, brush strips on letterboxes and the bottom of external doors, chimney draught excluders (if the fireplace isn't in use), and flexible filler around where pipes enter walls all reduce uncontrolled air leakage at minimal cost. A draught-free home feels warmer at the same thermostat setting.

One important distinction: draught-proofing reduces uncontrolled leakage. You still need controlled ventilation — trickle vents in windows, extractor fans in kitchens and bathrooms, and air bricks for underfloor spaces. Do not block these.

Loft and attic insulation

If your loft is accessible and currently uninsulated or under-insulated (less than about 270 mm of mineral wool), topping it up is one of the best-value upgrades available. The material is inexpensive, it's usually a DIY-friendly job on a flat ceiling, and the improvement is immediate. If your loft is used as a living space, you'll need to insulate between and over the rafters instead, which is a bigger job.

Hot water tank jacket

An uninsulated hot water cylinder loses heat constantly, even when no one is using it. A properly fitted insulating jacket is inexpensive and easy to fit yourself. If your tank already has one, check it's at least 80 mm thick and fits snugly.

Pipe lagging

Foam pipe insulation on the first metre or two of hot water pipes leaving your cylinder — and on any exposed pipes in unheated spaces like the loft or garage — reduces standing heat loss and also protects pipes from freezing in winter. The foam tubes slip over pipes and cost very little.

Bigger insulation jobs

Cavity wall insulation

Homes built roughly between the 1920s and 1990s often have cavity walls — two layers of brick or block with a gap between them. Injecting insulation into that cavity (mineral wool, polystyrene beads or foam) is a relatively quick job for a professional and can make a meaningful difference to wall heat loss. It requires a survey first to confirm the cavity is suitable and not already filled. Not all cavities are the same: walls that are exposed to heavy wind-driven rain need careful material choice to avoid damp bridging.

Solid wall insulation

Older homes with solid walls (a single thick layer of brick or stone) are harder to insulate. The two options are internal wall insulation (fixing insulated panels to the inside of exterior walls, which reduces room size slightly and requires moving skirting boards, sockets and radiators) or external wall insulation (cladding the outside of the building, which is more disruptive and expensive but doesn't affect interior dimensions). Both are significantly more costly and complex than cavity wall or loft work, but solid-walled homes often have the most to gain.

Floor insulation

Suspended timber floors can be insulated by fitting mineral wool or rigid insulation between the joists — accessible from below if there's a crawl space, or by lifting floorboards from above. It's worth doing if floors are noticeably cold, but it's typically a smaller saving than loft or wall insulation. Solid concrete floors can have rigid insulation laid on top, but this raises floor levels and requires adjusting doors and skirtings.

Windows and glazing

Replacing single-glazed windows with double (or triple) glazing improves comfort and reduces heat loss through glass. However, windows are a relatively small fraction of overall heat loss in a typical home, and replacement is expensive — so the financial payback period is long. If your current windows are in good structural condition, secondary glazing (an additional pane fitted inside) or good-quality thermal curtains or shutters can improve performance at lower cost. Replace windows when they genuinely need it rather than as a first insulation step.

A sensible order of works

1. Draught-proofing — low cost, DIY-friendly, immediate benefit. Do this first.
2. Loft or attic insulation — usually very cost-effective; top up to current recommended depths.
3. Hot water tank jacket and pipe lagging — inexpensive and quick to install yourself.
4. Cavity wall insulation — if your home has suitable cavities, get a survey and professional quote.
5. Solid wall or floor insulation — larger investment; weigh up cost, disruption and available incentives.
6. Window upgrades — worthwhile when windows need replacement anyway, or as a comfort measure.

DIY vs professional installation

Some insulation work is genuinely DIY-friendly. Laying loft rolls between joists, fitting pipe lagging, applying draught-proofing strips and fitting a tank jacket are all tasks most people can do themselves with basic tools and a free afternoon.

Cavity wall injection, external or internal wall insulation and any work involving structural elements or vapour barriers should be done by a professional. Poor installation — particularly around vapour control and ventilation — can cause damp problems that cost more to fix than the original work. For any professional insulation job, get at least two or three quotes, check that the installer is registered with a relevant trade body or certification scheme in your country, and ask for details of how they handle ventilation and moisture management.

Grants, rebates and incentives

Many governments and utilities offer financial support for home insulation — grants, subsidised or free installation schemes, low-interest loans, or tax credits. These vary enormously by country, region, income level and the type of measure. Before spending, check:

• Your national or local government's energy efficiency schemes (search "[your country] home insulation grant" or "[your country] energy efficiency scheme").
• Whether your energy supplier offers any incentives or obligation programmes.
• Whether your home's current energy rating makes you eligible for priority schemes (lower-rated homes often qualify for more support).

Schemes change frequently, so look for current information rather than relying on older sources.

Common mistakes to avoid

• Blocking ventilation. Sealing a home too tightly without maintaining controlled ventilation leads to condensation, mould and poor air quality. Always keep trickle vents open, leave air bricks unblocked and ensure extractor fans work properly.
• Insulating before fixing damp. If your home has penetrating or rising damp, insulation can trap moisture and make the problem worse. Resolve damp issues first.
• Under-filling the loft. Many older homes have some loft insulation but not enough. Check it's at the currently recommended depth, not just present.
• Ignoring the loft hatch. The loft hatch is an often-overlooked source of heat loss. It should be insulated and draught-proofed like an external door.
• Not getting a survey for cavity walls. Not all cavities are suitable for filling. A survey identifies problem areas (wall ties, partial fills, damp) before work begins.

Insulation checklist

• Draught-proof external doors, letterboxes and obvious gaps around pipes and skirting boards.
• Check loft insulation depth; top up if it's below the recommended level.
• Insulate and draught-proof the loft hatch.
• Fit or check the hot water tank jacket (at least 80 mm thick).
• Lag exposed hot water pipes in unheated spaces.
• Get a cavity wall survey if your home was built between the 1920s and 1990s.
• Check local grants and incentive schemes before spending on bigger jobs.
• Confirm ventilation is maintained — trickle vents open, extractor fans working.