How to insulate a loft, step by step

The stage-by-stage details you need to know about DIY loft insulation
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  • Insulating your loft is one of the most effective options to help reduce the cost of heating, improve the thermal efficiency of your home, as well as keep your property toasty during the colder months. If your loft is easy to access, doesn’t have damp issues and is not a flat roof, how to insulate a loft is a DIY job worth considering to save on costs.

    However, if any existing insulation is wet, or has shown signs of being wet in the past, it’s likely there is a leak somewhere, or that your home suffers from damp. In this scenario, you’ll need to instruct a professional installer and potentially a roofer, to inspect the loft before work can be carried out. For DIY novices, insulating with blanket rolls is probably the material to work with when it comes to how to keep your house warm.

    How to insulate a loft, step by step

    Follow these guidelines for installing loft insulation…

    1. Work out how much insulation you need

    loft bedroom ith twon beds grey feature wall and mustard rug

    Image credit: Future PLC/ Polly Eltes

    You need to measure the area of your loft space in square metres by multiplying the length by the width of the space. ‘If there are difficult to reach areas, simply measure the rooms beneath the loft space and work it out that way,’ says Jenny Turner, Property Manager at Insulation Express. Rolls of blanket insulation will come in different widths, so you need to measure the width of your joists and purchase a width of insulation similar to this to minimise cutting.

    The blanket insulation should come up to the top of the joists when fitted correctly. Make sure you match the insulation thickness with the joist height. When the surface is even, you’ll lay down more insulation on top. The second layer will need to take you up to the 270mm recommended depth. ‘It’s a good idea to pick up an extra roll or two to be on the safe side,’ says Thomas Goodman, Property and Construction Expert at Once you have done this, you will be able to work out how much loft insulation costs.

    2. Prepare and clear your loft

    Firstly, remove all your belongings from the loft, take up any fitted boards attached to the joists, check for loose nails and screws and give the loft a vacuum to get rid of excess dust. Next, check for signs of damp or leaks, if there is, any old insulation will need to be removed to prevent dampness and mould from spreading and a professional installer and roofer should be employed to evaluate the problem.

    If existing insulation is dry, then you don’t necessarily have to remove it, you can install new insulation over the top. Make sure any wiring is dealt with safely. Wires and electrical cables should be kept above the insulation to avoid fire risk, but not stretched. If you don’t think there will be enough slack in the cables to lift on top of the insulation, contact a qualified electrician for advice.

    3. Make sure you have the right equipment

    Tent-like attic living room with sloped ceilings on both sides

    Image credit: Polly Eltes

    Small particles from blanket insulation can break off when cutting it to size which can irritate the skin (unless using sheep’s wool). Wear long sleeve, full-length clothing, a face mask, goggles, lightweight work gloves and a hat to cover your hair. You’ll also need crawl boards handy and a knee pad so you can move around safely and comfortably. For the installation process, you’ll need a tape measure, a sharp knife and a pair of sturdy scissors.

    4. Lay insulation between the joists

    Measure the distance between the joists and then cut (if you need to) your insulation to the correct width. Gently roll it out between the joists and lightly press it to fit between the joists. ‘You need to be careful not to apply too much pressure to avoid crushing it and reducing its insulation value,’ says Thomas Goodman. Once installed, the insulation should come up to the top of the joists and there shouldn’t be any gaps at the ends.

    5. Lay insulation over the joints

    white bathroom in loft space

    Image credit: Future plc/David Giles

    Lay an additional layer of insulation at a 90 degree angle to the joists. This second layer should have no gaps between the strips that you lay out. If fitted correctly, you shouldn’t be able to see the joists. ‘Don’t overlap the rolls, as this will cause the inefficiency of thermal retention,’ says Jenny.

    6. Insulate pipes and tank

    A layer of insulation material should be placed over the water tank and pipes, but not directly underneath them. ‘If you insulate underneath you’ll prevent warmth from the rooms below the loft reaching them. This can cause the water in the tank to freeze in cold weather,’ says Jenny Turner. For ease, buy insulation jackets for water tanks; for pipes, cylindrical foam insulation that can be cut to size and simply pops onto the pipework.

    7. Insulate loft hatch

    Cut out a layer of your chosen insulation material. Glue or attach it to the back panel of the hatch. Then attach adhesive draught proofing foam strips around the edge of the hatch door. This will stop draughts coming through and heat escaping.

    Remember, that there are loft insulation grants available.

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