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How To Install Loft Insulation

Topping up your existing loft insulation to the recommended 270mm can help your home to retain heat during the cold winter months. This step-by-step guide to insulating your loft also offers advice on choosing materials.

Between 15 and 25 percent of the heat lost from our homes is lost through the roof. Loft insulation helps to trap that rising hot air — and, by topping up existing insulation to the recommended 270mm, the average household saving on annual heating bills can be more than £150. You’ll also be helping to save the planet by reducing your home’s carbon footprint to the tune of one tonne of CO2 a year.

If 270mm of insulation sounds like a lot, you’re right — it’s only 27mm less than the length of the page you’re currently reading. By the time you’ve put 100mm of insulation down, it will be level with the top of many ceiling joists. To get the extra depth of insulation you need, employ a cross-laying technique (as explained below).

Thickness is one thing, quality of material is another. Synthetic materials such as glass fibre and mineral wool, and natural sheep’s wool are popular choices for insulating. However, cost and quality can vary — see our guide on materials (below) for further information.


Fitted with the full 270mm of insulation, your loft may be no good for storage. However, you can still improve insulation and create a safe place for storage by using a product like Space Board from Space Insulation (space-insulation.com). This 52.5mm-thick board goes on top of the ceiling joists (that you’ve already filled with 100mm or more of insulation material). Chipboard loft boards go on top and are screwed down through the Space Board to create an insulated storage platform.


  • Tape measure

  • Scissors

  • Overalls

  • Gloves

  • Dust mask

  • Loft insulation material

  • Board to work from

  • Knee pads

  • PVA glue


1. A typical loft needs clearing out first. If the loft has been previously insulated with glass fibre you should get kitted out in hooded overalls, gloves and a dust mask before entering. Perching on ceiling joists is a perilous business, so it’s a good idea to take a long board that you can span across several joists. Find something that’s wide enough to kneel on comfortably and kit yourself out with kneepads — there’s a lot of bending down.

2. Once within the loft, measure the depth of insulation you already have. Calculate how much insulation material you require by measuring the width and the length of the area you want to insulate in metres. Multiply the width by the length to calculate the area in square metres. The area covered is shown on the pack.

3. Take the material into the loft area and unpack it a roll at a time. Slide one end into the eaves. Leave at least a 25mm gap at the eaves end to allow for a free flow of air in the loft space. If you’re using the enclosed, metallised type of mineral wool, don’t forget to lay the silver side upwards.

4. Lightly press the insulation down between the ceiling joists and continue across the loft. When you reach the eaves on the opposite side, cut the insulation 25mm short as before. Carry on fitting the insulation this way across the rest of the loft but avoid insulating under the water tank (if fitted), as warm air will rise from the room below and help to stop the tank freezing in the winter. Electrical wires should be laid on top of the insulation to stop them overheating. Any light fittings that come through the ceiling (recessed spotlights, as shown here) should have the absolute minimum of a 75mm insulation-free zone all around them.

5. If you’ve been using 100mm-thick insulation, it’s likely to be level with the top of the joists after the first pass. If it’s not, you can double the insulation over on itself and do a return trip across the loft. But to build up to the ideal 270mm thickness or beyond, you’ll need to cross-lay the insulation. To do this properly, lay the insulation at right angles to the joists until you’ve achieved the desired depth.

6. Nearly finished, but don’t forget the loft hatch. Cut a section of insulating material and glue it to the hatch. Replace the hatch and get ready for lower energy bills.


Glass fibre wool on the roll is cheap (from £2/m2 for 100mm depth), readily available from DIY stockists and very effective. On the downside, if it comes into contact with your skin you’ll be itching for days afterwards — always wear hooded overalls, a dust mask and gloves.

Mineral wool is slightly more expensive, but far more fire-resistant than glass fibre wool and offers the same insulation benefits. As standard, it has the same unpleasant- to-handle characteristics as glass fibre, but increasingly mineral wool is being sold on the roll, enclosed in a heat-reflecting metallised polythene film. This makes the product far easier to handle. From around £5/m2 for 100mm depth.

Sheep’s wool is a great natural insulator (10% better than man-made material alternatives). Unless you are allergic to wool you can install it wearing regular work clothes. Wool is also easy to tear into shape and, as a result, can be installed quicker than the synthetic varieties that need cutting with scissors or a knife. Sheep’s wool, typically £8.75/m2 for 100mm depth, is, however, a more expensive option.


On September 11th 2008 the Government announced a range of measures to improve energy efficiency in our homes. One of the measures was to offer half-price loft insulation, regardless of income, with those on benefits and/or over 70 entitled to free insulation. The measure, part of the Home Energy Saving Programme, will cost UK energy firms some £910m. So how to take advantage? The Government announced a helpline (0800 512 012) . Despite repeated attempts H&R has managed to get through to nothing but an answer-machine. Best bet is to try est.org.uk or, if you qualify for benefits, warmfront.co.uk. We’re guessing that these measures will not necessarily reduce the retail price of insulation, rather reduce the price charged by approved installers


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