How do I improve my home's insulation?

Insulation measures ranked by payback — what to do first, what to do later, and what is rarely worth it.

Difficulty: intermediate
Time: 4 hr
Read: 2 min

Short answer

Do it in order of payback: draught-proofing, then loft insulation to about 270mm, then a hot water tank jacket, then cavity wall insulation if you have unfilled cavities. Glazing and solid wall insulation are effective but have much longer paybacks.

Insulation measures vary enormously in cost and payback, and the cheapest ones are also among the most effective. Doing them in the wrong order means spending thousands before doing the hundred-pound jobs that would have paid back in a year.

What you'll need

Loft insulation
Draught excluder strip
Hot water tank jacket
Reflective radiator foil (optional)
Torch and boards for the loft (optional)

Step by step

Draught-proof first: doors, windows, letterbox, loft hatch, floorboard gaps.Cheapest, fastest, and among the shortest paybacks of anything you can do. Never block air bricks or vents.
Check your loft insulation depth and top it up to around 270mm.Many older lofts have well under half that. Lay the second layer at right angles to the first.
Do not compress loft insulation with boarding laid straight on the joists.Use raised loft legs so boards sit above the full depth. Compressed insulation loses most of its value.
Insulate the hot water tank and any exposed pipework.A tank jacket is inexpensive and pays back very quickly.
Fit reflective foil behind radiators on external walls.Cheap, and measurably effective on solid uninsulated walls. Almost pointless on an internal wall.
Check whether you have unfilled wall cavities.Houses built roughly between the 1930s and 1990s often have cavities. A survey confirms whether they are filled.
Insulate suspended timber floors if you have access from below.A significant heat loss in older houses, and much easier from a cellar or crawl space than by lifting floors.
Consider glazing and solid wall insulation last, with real payback figures.Both are effective and both have long paybacks. Do the cheap measures first.

Tips

Check for available grants or schemes before paying full price for insulation — availability changes, so check current government guidance.
Loft insulation works both ways: it keeps summer heat out of the rooms below as well as winter heat in.
Insulating without ventilating causes condensation. Every insulation measure should be considered alongside how the house breathes.

Common mistakes

Boarding a loft directly onto the joists — It compresses the insulation and destroys most of its value. Raised loft legs are the fix.
Insulating without ventilating — A better-sealed house with the same moisture production gets condensation and mould.
Starting with expensive measures — Draught-proofing and loft insulation pay back in months to a couple of years; glazing takes far longer.

Questions people ask

What insulation gives the fastest payback?

Draught-proofing, then loft insulation, then a hot water tank jacket. All three are inexpensive relative to their effect, and none requires specialist installation.

How thick should loft insulation be?

Current guidance is around 270mm of mineral wool. Many older lofts have 100mm or less, so topping up is often the single biggest easy win in an older house.