DIY loft Insulation to save £355 per year on energy bills

Insulation: Perrey advises on when to insulate your home

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A staggering one-quarter of the heat in your home can be lost through an uninsulated roof, yet millions of households fail to invest in energy-saving insulation. According to Government data, this is to the sum of around eight million in the UK – meaning almost a third of households could benefit from adding it to their property. With labour charges costing around £250 before adding materials, insulation expert Jo Callow has shared her DIY method with 

According to the Energy Saving Trust, a typical semi-detached house could save £355 per year on energy bills by adding loft insulation. And, with further rises planned in April when the universal price cap ends for some, these savings will be even more significant.

However, with current prices, the average homeowner would have to wait several years for their investment to pay off. The Checkatrade cost guide states that while the exact cost depends on the size of the loft and type of insulation, most tradespeople charge a day rate of around £250 for installation.

Once the added cost of materials, electrical rewiring, and pipe lagging are added on, the total figure can quickly jump beyond hundreds.

Speaking exclusively to, Jo said: “Adding loft insulation is one of the most cost-effective ways to improve your home’s energy efficiency, reduce your energy bills, make your home more comfortable, and do your bit for the planet. In many cases, it’s a job you can do yourself in a day for less than £300 using existing tools and materials from your local DIY store.”

However, you should always make a few simple checks before getting started on your DIY loft insulation. Jo explained that first, you should make sure your loft is “suitable”.

She said that the space should be empty and dry, have a pitched roof, and the joists should be strong enough to take your weight. After this point, you can begin measuring the width and length of the space.

Multiply these figures together to calculate the total area you need to insulate. Jo said: “Decide how thick you want to go. 270mm is the minimum in most of the UK, but generally, the thicker, the better (newbuilds are typically built with 400-500mm).You should calculate how much insulation you’ll need based on your chosen thickness. Your bottom layer must be a 100mm thick loft roll, while your top layer(s) can be 170mm thick.” 

You should always buy enough loft-specific rolls to cover the total area of your loft for each layer. Jo Recommended choosing pre-perforated styles to minimise cutting.

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How to install loft insulation

To install the insulation, you’ll need a tape measure, retractable knife, fine-toothed handsaw, crawl boards, overalls, a dust mask (FFP1 minimum), safety glasses, a bump cap and gloves.

Protect electricals

Jo warned that you might need additional materials if there are any air gaps, electrical cables or a water tank.

Before installing, isolate all heat-producing electrical fixtures such as downlights with protective covers, and rest electrical wires on top of the insulation to prevent fire risks.

Seal gaps

Jo said: “Start by sealing any gaps where air could leak into the loft from the room below, using sealant and tape. With your 100mm insulation still in its packaging, cut the roll so the width fits snugly between the joists.

Lay the base layer

Standing in the central loft space, at the point furthest from your hatch, position the end of your 100mm roll up against the free end of the insulation in your eaves.

Unroll the insulation slowly, ensuring it sits “snugly between the joists”. Where it meets the eaves on the opposite side, cut the roll and butt the two ends firmly together. According to Jo, this step should be repeated until your entire loft has a 100mm base layer.

Add a second layer

Now it’s time to fit the second layer. Jo explained: “You’ll lay this insulation at a 90-degree angle to the first layer, beginning in the eaves (and remember to maintain the 50mm air gap).

“If you’re fitting a third layer, you’ll need to do this at the same time so you don’t squash your new insulation. Cut notches in the insulation to fit around rafters as you go.”

Move from the eaves to the central loft space, until your entire loft is completed. Jo added: “You may need to insulate your loft hatch if it isn’t already done. You can find advice on how to do this on the Knauf Insulation Homeowners Hub.”

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