21st Nov 2022 -

Loft insulation is designed to snugly fit within the joists of your loft, limiting the heat escaping through your roof. Whether you are using insulation rolls or batts, they will have to be cut to size, accurately measuring and neatly cutting each piece to ensure a thorough covering of insulation. The best way to cut your loft insulation rolls or batts will vary depending on what material you are using, with options that are best suited for mineral wool, fibreglass (sometimes called glass mineral wool), and sheep’s wool. All methods will involve using a saw or knife to cut your insulation into accurate pieces.

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Preparing Your Loft Insulation for Cutting

Whatever method you use to cut loft insulation rolls or batts, you’ll need to ensure that you have accurately measured both the area where you are installing the insulation and the insulation itself. Insulation needs to snugly fit whenever installed, whilst avoiding compression. When insulation that doesn’t fully cover an area is installed, those gaps will allow heat to escape. Using a tape measure to precisely measure the distance between joists in your loft, and the length of insulation needed will allow you to thoroughly insulate your house. You should always double-check each measurement before drawing a cut line on your insulation.

Cutting Fibreglass Loft Insulation With a Utility Knife

What You’ll Need

  • Solid Board For Cutting
  • Wooden 2x4
  • Tape Measure
  • Permanent Marker
  • Safety equipment
  • Dust Mask and Goggles
  • Utility Knife (preferably disposable)

How to Cut Fibreglass Insulation With a Utility Knife

Before cutting a fibreglass loft roll or batt, you should mark all lines to be cut using a permanent marker, again double-checking with a tape measure to ensure accuracy. You will also need to take safety precautions before touching or cutting insulation rolls and batts. Wear gloves and protective clothing, covering all skin that could come into contact with insulation. This is because fibreglass insulation can cause skin irritation. You should also wear a protective dust mask and safety glasses, to avoid inhaling any fibres or getting them in your eyes.

You can cut fibreglass loft insulation rolls and batts using a sharp utility knife. As fibreglass can dull blades quickly, using a disposable knife with snappable pieces may be a better choice. You’ll need to lay the insulation over a solid board, to ensure that it can be firmly cut to size. If you are using a solid board within your loft to fit insulation you can use this. If your insulation has kraft paper on one side you should place that side on the bottom.

To cut your insulation, you’ll need to place the wooden 2x4 across the marked line, kneeling on it to compress it in place. Using your hand press down on the other side of the 2x4, trying to compress the insulation as much as possible. You can then cut along the insulation, starting on the opposite side to you, making sure that you are firmly pressing down throughout, trying to keep the knife at a 45° angle. Cut the insulation in one movement, before going back to cover any areas that weren’t fully cut. With this done, you should have an accurate piece of insulation, perfectly cut to size for your loft.

insulation roll

Cutting Mineral Wool Loft Insulation Rolls With a Bread Knife

What You’ll Need

  • Solid Board for Cutting
  • Tape Measure
  • Permanent Marker
  • Safety Equipment
  • N95 Respirator and Goggles
  • Bread Knife

How to Cut Mineral Wool Loft Insulation With a Bread Knife

You should start by double-checking that you have marked all lines on your mineral wool loft insulation correctly. You should also be wearing full upper body coverings on your hands and arms, along with an N95 respirator mask and safety goggles, as fibres from mineral wool can cause irritation.

You should roll out the insulation (if using a loft roll) and place it over a solid board to cut, helping to avoid any damage to your floor or surfaces. The best way to cut mineral wool insulation is using a serrated knife, such as a bread knife or a drywall knife. You should press the insulation against the board, cutting along the lines you have drawn using the knife. This should leave you with an accurate piece of mineral wool insulation.

Cutting Wool Insulation With An Insulation Saw

What You Need

  • Solid Board For Cutting
  • Tape Measure
  • Permanent Marker
  • Insulation Saw

How to Cut Wool Insulation With an Insulation Saw

You should ensure that the lines you have marked on your insulation are accurate before starting, to avoid making a mistake. With sheep’s wool insulation, you won’t need to wear any safety equipment, as it is safe to handle and cut.

You can easily cut sheep’s wool insulation rolls using an insulation saw over a wooden board. A method to ensure accuracy is to roll your insulation tightly along its width, place that rolled insulation over the board, and precisely saw it. This can help to ensure that your pieces of sheep’s wool insulation are cut to size, and snugly fitting within the joists of your loft.

insulation roll

What Other Methods Are There to Cut Loft Insulation?

There are electric knives available that can be used to carve loft insulation rolls to size. This can be particularly handy with batts, as they can be stood upright and cut into size, rather than being carved whilst lying flat on a board. Sharp scissors or shears can also be used to cut through thinner insulation rolls. Scissors will also come in handy for difficult or specific cuts, such as those around pipes, water tanks, or light fittings.

Our Range of Quality Loft Insulation

Building Materials Nationwide stocks a comprehensive range of insulation, including mineral wool, fibreglass, and plant fibre options perfectly suited for your loft.

For contractors and trade professionals, Building Materials Nationwide offers special trade accounts to support your loft insulation jobs. Sign up for an account to get personalised assistance from your dedicated account manager who can help you source and order exactly what you need, even hard-to-find insulation boards.

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