Top up loft insulation

Add a fresh layer of loft insulation over your existing layer to cut heat loss and lower your heating bills.

LI-01Clear the loft and gear upClear boxes and clutter off the loft floor so you can see the joists properly. Wear an FFP2 (or better) dust mask, gloves and long sleeves — old and new mineral wool fibres irritate skin, eyes and lungs. Work only on the joists themselves or a plank laid across them; the plasterboard ceiling below will not take your weight and you can put a foot straight through it.

1 pack · FFP2 dust masks (pack of 10)

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1 pack · Disposable gloves (pack)

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1 each · Head torch

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LI-02Check existing depth and conditionPush a tape measure down to the ceiling in several spots to check the current insulation depth. Look for damp staining, mould, or droppings — these mean a leak or pest problem that needs sorting first, not covering over. Bag up and remove any wet or contaminated insulation before you top up. UK guidance recommends a total depth of 270mm of mineral wool, so measure the shortfall.

1 each · Tape measure

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LI-03Check the eaves ventilationLook along the eaves where the roof meets the walls for small vents or gaps in the soffit. These let the roof timbers breathe and stop condensation building up, so make sure they're not already blocked with old insulation. Keep a clear gap of at least 50mm above any vent when you add the new layer — never push insulation right into the eaves.

LI-04Check cables and fittings before you cover themLift the edge of the existing insulation and check where cables run across or between the joists — note the routes so you don't later stand on them. Modern cable is rated to be covered by insulation, but old rubber or fabric-covered cable should be checked by an electrician if you're unsure. Never cover a light fitting, junction box or downlighter with insulation — leave it clear all round.

LI-05Work out how much insulation to buyMeasure the loft's length and width, minus the chimney breast and any boarded areas, to get the area in square metres. Match the new insulation to what's already down — top up with the same type, or lay a compatible roll over loose-fill rather than mixing them in the same layer. Buy enough 100mm rolls to make up the difference between your current depth and 270mm total.

6 roll · Mineral wool loft roll, 100mm x 1160mm x 5.5m

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LI-06Lay the first layer between the joistsUnroll the insulation into the gaps between the joists, cutting it to length with a sharp knife. Butt the edges together tightly with no gaps, and fill right up to the eaves but stop short of the ventilation gap you checked earlier. Don't compress the insulation as you push it in — squashing it destroys the trapped air that makes it work.

1 each · Retractable utility knife

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LI-07Lay the second layer across the joistsOnce the existing insulation is level with the top of the joists, roll out a second layer running at right angles, straight across the joists rather than between them. This crossways layer covers the joists themselves, which lose heat on their own, and brings the total depth up to around 270mm. Check the eaves gap again once this layer is down.

LI-08Insulate the hatch, pipes and tankFit a foam or mineral wool insulation kit to the underside of the loft hatch, and stick a foam or brush draught strip round the frame — a bare hatch loses a surprising amount of heat. Wrap any exposed cold water pipes with pipe lagging, and fit an insulation jacket around a cold water tank. Leave the area directly under the tank clear of insulation, insulating underneath can let cold air in and cause the tank to freeze.

1 each · Loft hatch insulation kit

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1 pack · Foam draught strip

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3 length · Pipe lagging, 1m lengths

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1 each · Cold water tank jacket

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LI-09Add raised storage boarding if you need itIf you want to keep storing boxes in the loft, fit a raised loft boarding kit on legs or battens set above the joists, so the boards sit clear of the new insulation. Never rest boxes directly on the insulation itself — standing or resting weight on it compresses it and permanently reduces how well it works.

1 pack · Raised loft board storage kit (pack of 4 boards with legs)

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LI-10Clear up and dispose of wasteBag up old contaminated insulation, offcuts and packaging in rubble sacks. Check your council's rules before you bin it — some councils treat mineral wool as bulky waste rather than general rubbish. Store any leftover new insulation somewhere dry for future use, and give the loft hatch area a quick brush or vacuum before you close up.

3 each · Heavy-duty rubble sacks

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