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How to insulate your loft

Posted on 23 March 2016

If you own your own home, ensuring it’s properly insulated is a worthy investment. In an uninsulated home, a quarter of the heat generated is lost through the roof, which can lead to unnecessarily high energy bills.

But, we hear you ask, is it really worth the initial outlay? Well, the cost of getting someone in to insulate the roof of a detached house is approximately £395, and the price should be less if you live in a semi-detached or mid-terraced building. However, the fuel bill savings per year could reach up to £240, meaning it would take just a year and half to get a return on your investment. In fact, loft insulation continues to be effective for at least 42 years, meaning big savings down the line.

One way to make the initial cost even less is to insulate your loft yourself. Luckily, if your loft is easy to access, you don’t have to be a professional builder to implement this energy saving upgrade to your home. Here’s our step by step guide on how to insulate your loft.

Looking for a few other ways to reduce your energy bill? Check out our infographic on how to make your home more energy efficient.

Step 1: Assess your loft

assess your loft 


Before you get insulating, you need to check your loft for any damp. Since insulation prevents heat from escaping, your loft space will become cooler after you insulate it, which could exacerbate any existing damp problems. Hence, if you do find any damp areas, you’ll need to tackle the problem before you start. In the case of damp, it’s a good idea to seek professional advice before attempting to make any alterations.

Loft use

Secondly, the type of insulation you need will vary depending on how you use your loft space. If you use your loft space for storage, you’ll be looking to insulate between the joists in the floor. On the other hand, if your loft is used as a living space, you can insulate between the roof rafters but you’ll need Building Control Approval.

Flat roofs

Finally, if you have a flat roof, it is advisable to get the roof insulated professionally. Flat roofs often need to be insulated from above, which goes beyond most of our DIY skill sets!

Step 2: Tools and materials

 tools and materials

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‘R’ value

You ideally want to fit your loft with a minimum of 270mm insulation. A material’s insulating properties are measured by an ‘R’ value, which is a measure of thermal resistance. When you’re choosing an insulation material, you’ll need to check its ‘R’ value to ensure it’s thick enough for your needs. The higher the ‘R’ value, the better the material’s insulation properties. The minimum recommended ‘R’ value for a loft insulation material is 6.1, but ideally you should be looking for a material with an ‘R’ value of 7.

Blanket loft insulation material

If you don’t need to use your attic for storage, it’s best to opt for blanket loft insulation. As it comes in rolls, it’s the easiest to work with. To calculate how many rolls you require, measure the length and width of your loft, then multiply the two measurements to find the area. Then, divide that number by the coverage per pack of insulation to work out how many packs you need.

Board loft insulation material

If you want to use your loft for storage, you’ll need to lay board loft insulation along with a layer of blanket loft insulation. This is because if you lay heavy boards and boxes on top of blanket insulation, it reduces your insulation’s ‘R’ value making it less effective. You will therefore require rigid polystyrene board insulation and 100mm loft roll or blanket insulation to fit between the joists beneath. You’ll also need a layer of chipboard to lay on top of the board loft insulation to protect it when using it for storage.

Extra equipment

Before you get started, you’ll need a couple of walk boards to help you move around your loft safely. You should only need about two or three depending on the size of your loft. A strong piece of timber is ideal for this, such as 18mm plywood or chipboard.

If you’re using mineral wool insulation, you’ll need to wear protective gloves and clothing as the fibres can cause temporary skin itching. Even if you’re not, it is still advised you wear a dust mask and protective gloves.

To cut large rolls of blanket loft insulation so the rolls fit between the joists, you can use a handsaw. You can either cut them still in the packaging and follow the pre-marked lines, or take them out of the packaging and measure them yourself. For smaller cuts, or for areas where you need to be more precise, use a sharp pair of scissors.

To cut board loft insulation, you’ll need a handsaw to cut the boards to size and a marker pen to show where the joists are under the boards. You’ll also require a power drill and 150mm screws to fasten the chipboard and board insulation to the joists below. You’ll need six screws per sheet of chipboard.

Step 3: Laying blanket loft insulation

Once you’ve equipped yourself with all the necessary tools and safety gear, you can begin to insulate your loft. Depending on the size of your loft, you may want to pre-cut the rolls before you bring them up.

blanket loft insulation 

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  1. Clear your loft and remove any old storage boards. Use planks to create a place to keep your rolls of blanket insulation. Set up your walk boards along the joists next to the area you want to work on, ensuring they are wide enough to kneel on.
  2. Start at the far end of your loft and work back towards the loft hatch. Put the first roll along the edge of the loft, where the flat ceiling meets the sloping roof. Leave a 25mm gap from the edge for ventilation.
  3. Unroll the insulation back towards the centre of the loft. If it doesn’t reach the other side of your loft, lay a new roll, making sure there aren’t any gaps between the two layers. Once you’ve laid the roll, gently push the insulation down to ensure there aren’t any gaps.
  4. Repeat this process until the whole loft is covered. Be careful not to compress the insulation too much or it will reduce its effectiveness.
  5. Be very careful if you come across any cables or light fittings. If your cables aren’t fastened to the joists, carefully lift them up and lay the insulation underneath. If not, don’t cover cables with insulation as it could overheat. Similarly, if you have a downlight in your loft, don’t cover it with insulation. Ensure you leave a sufficient gap either side of the light, otherwise it could be a fire risk. You may need to fit a heat diffuser around the light fitting.
  6. Once you’ve laid one layer between the joists, you can lay a second layer over the top. This layer is laid at a 90-degree angle to the other layer, but still be mindful of any cables or light fittings. You can lay this layer in larger rolls to save time as it goes on top of the joists.

Step 4: Laying board insulation

If you want to use your loft for storage, you’ll need a layer of board insulation. First, you’ll need to complete the first layer of blanket insulation between the joists. Then, instead of a second layer of blanket insulation, you’ll need to lay board insulation.

board insulation 

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  1. After you’ve fitted the blanket insulation, lay the board insulation across the top of the joists. Each 1200mm board will usually cover three joists. If you have downlights, cut a hole in the relevant section of the board and fit a heat diffuser around the light following the manufacturer’s guidelines.
  2. Cut the boards to size using a handsaw. Draw a straight line on top of the board using a marker pen to show where the joists are beneath the boards – this needs to accurate!
  3. Lay a second layer of board insulation in the same way, copying the centre lines from the board below onto the second layer.
  4. Once you have the second layer of board insulation in place, place a layer of chipboard over the top. Use the screws and the power drill to fasten the chipboard and two layers of board insulation to the joists below. You only need to drill holes in the four corners and the two centre points of the long edges of the chipboard.
  5. Repeat this process until the desired area is covered. You can then use your loft for storage.

Remember, if you come across anything that you’re unsure whether you should insulate over, it’s always best to seek a professional opinion before continuing.

Finally, if you’re not exactly a DIY guru, there’s no shame in putting your feet up and getting a professional to do the work for you!

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