How to Cut Loft Insulation Rolls

Cutting Loft Insulation Rolls

Loft insulation is great for the planet, great for your utility bills, and great for your home. While it can be pricey to install, cutting and installing loft insulation yourself is one way to knock hundreds of pounds off the price you’ll pay. One of the most common types of insulation is blanket insulation, which comes in either rolls or batts. These rolls and batts tend to be made from mineral wool, fibreglass, or sheep’s wool. 

If you’re planning on installing blanket insulation yourself, here’s a handy how-to guide to show you how to do it. 

The Benefits of Using Blanket Insulation

There are plenty of types of insulation on the market, but rolls and batts of blanket insulation are undoubtedly the most common. Here are just some of the reasons rolls and batts are so popular. 

Suitable for DIY insulation

For homeowners looking to save on costs, blanket insulation is the obvious option since you can install it yourself relatively easily. You’ll only need basic equipment, but do bear in mind that some types of blanket insulation irritate eyes and skin so you will need to invest in protective gear. 


The last thing you need when installing insulation is a material that’s highly flammable or prone to mould. Luckily, blanket insulation is resistant to both fire and water, so it gives your house an extra layer of security. 

High energy efficiency

The more energy efficient your home is, the less money you’ll have to spend heating it, and the lower your carbon footprint will be. Luckily, blanket insulation provides a high degree of energy efficiency, keeping your home at a more constant temperature year-round. 


Making your home a more pleasant and thermally efficient space to live in shouldn’t mean breaking the bank. One of the biggest benefits of working with rolls and batts is that they’re one of the most affordable types of insulation on the market. 

Cutting Loft Insulation: A Simple Guide

Loft insulation should fit snugly within your loft’s joists, this will reduce the amount of heat that’s able to either escape through your roof in winter or get in through your roof during the summer months. Be careful not to leave any gaps in your insulation as this can allow heat to move through it, making the insulation less effective. 

Both rolls and batts need to be accurately measured and cut to size so that each piece promises to thoroughly cover the space. The easiest method of cutting your rolls depends in part on which material your blanket insulation comprises – mineral wool, fibreglass, or sheep’s wool

In general, most materials will be able to be sliced neatly with an electric knife, which comes in especially handy with batts. Thin insulation rolls can sometimes be cut with a sharp pair of garden scissors and shears, and you can also use these materials to clip the edges of insulation that cover the side of pipes and water tanks. 

Preparing Your Loft

Naturally, you’ll have to adequately measure your loft space before you start cutting your insulation rolls. The key to getting insulation installation right is to fit it snugly but avoid compression. If there are gaps in your insulation, it won’t prove as effective. 

It’s also worth considering the thickness of insulation you’ll need. According to building regulations, new build properties must have insulation with a thickness of 270mm. While these rules don’t apply to older properties that are having insulation fitted, it’s a good figure to use as a guideline. 

If there’s already insulation installed, assess its condition before deciding whether to remove it and start again or simply add more insulation to improve its effectiveness. 

Cutting Sheep’s Wool

This form of insulation is safe to handle, so you won’t need to wear protective equipment. It is recommended, however, that you invest in an insulation saw to cut this particular material. A very sharp Stanley knife can do the job, but you have a better chance of cutting through wool the first time with an insulation saw. 

You’ll need the following tools:

  • A solid surface for cutting on
  • A permanent marker pen
  • Adequate sheep’s wool insulation
  • A tape measure
  • An insulation saw or Stanley knife.

First, you’ll need to use your tape measure and marker pen to mark precisely which part of the insulation needs cutting. If possible, clamp and compress the material lightly to ensure it doesn’t slip during the cutting process. Alternatively, roll it over a board.  

Once the sheep’s wool roll is in place, use the insulation saw to cut it on the marked spots, going slowly and taking care to be as precise as possible. 

Cutting Fibreglass

Unfortunately, fibreglass is one of the blanket insulation materials that can be irritating if you come into direct contact with it, so you’ll need to wear protective gear over your body, hands, and eyes. 

You’ll need:

  • A solid surface for cutting on
  • Fibreglass insulation
  • A dust mask, goggles, and gloves
  • A utility knife
  • A tape measure
  • Protective clothing
  • A permanent marker
  • A wooden compression tool. 

As with all rolls of insulation, you should measure and mark your fibreglass insulation using a permanent marker to ensure they fit within your loft. Once your insulation is adequately measured, you’ll need to put on protective clothing, gloves, a mask, and glasses. Don’t let any skin come into direct contact with the insulation, and don’t get it in your eyes.

Fibreglass insulation can be cut using a sharp utility knife, but be warned, fibreglass is quite a hard material and is prone to dulling blades. If at all possible, use a disposable knife instead to avoid damaging a knife that you’ll need to use again. 

Before cutting the insulation to size, lay it over a solid board or other surface. Place a compression material such as a wooden 2×4 across the marked line and kneel on it. You’ll need to keep the insulation as tightly pulled as possible for the cut to be precise. 

Cut along the insulation starting on the opposite side to you and keep the knife as close to a 45-degree angle as possible until it’s the size you need.  

Cutting Mineral Wool

Mineral wool is another material that can cause serious irritation and discomfort to your eyes and skin. For that reason, you should wear protective gear and an N95 respiratory mask to avoid breathing in mineral wool fibres. 

You’ll need:

  • A solid surface for cutting the insulation
  • A tape measure
  • A permanent marker pen
  • Protective clothing, gloves, and goggles
  • A serrated bread knife. 

You don’t need any fancy equipment to cut mineral wool – simply use a serrated bread knife. Roll out the insulation and place it over a solid surface to avoid scratching your floor, before cutting the insulation according to the marks you measured. 

Not Interested in a DIY Installation?

Naturally, if you’re new to installing DIY and have limited experience with other DIY projects, you might prefer to call in the pros. 

Using our free contractor quote finder tool, you can easily access a quote from a professional who covers your area and has a reputation for excellent work installing insulation on properties just like yours. 

To find out more about their capabilities, ask for testimonials, reviews, or even a portfolio of work. It’s also worth sourcing quotes from a few companies to compare prices and check the going rate for your area. 

If you choose to opt for a different type of insulation such as loose-fill or blown-fibre, you’ll need to work with a professional for installation. 

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