How to safely lay insulation in your loft

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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.

The heat-reflecting metallised polythene film surrounding mineral wool provides added insulation, but don protective gloves and overalls before handling it

The heat-reflecting metallised polythene film surrounding mineral wool provides added insulation, but don protective gloves and overalls before handling it

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.


How to safely lay insulation in your loft

0
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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.

The heat-reflecting metallised polythene film surrounding mineral wool provides added insulation, but don protective gloves and overalls before handling it

The heat-reflecting metallised polythene film surrounding mineral wool provides added insulation, but don protective gloves and overalls before handling it

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.


Step One

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.


Step Two

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.


Step Three

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.


Step Four

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.


Step Five

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.


Step Six

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.


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