How Much Loft Insulation Is Required?

The amount of Loft insulation Required

If you’re looking for a way to save money on your energy bills, reduce your carbon footprint, and stay warmer in the winter, loft insulation is a natural solution. But if you’re new to insulation and looking to install it yourself, the first hurdle is figuring out exactly what insulation you require and how much insulation you’ll actually need.

Luckily, we’ve put together a guide to how much loft insulation is required, the types of loft insulation to choose from, and how it is installed to be most effective.

Why Install Loft Insulation?

If you’re new to the idea of loft insulation and wondering why it’s worth installing, let’s get into some of the benefits. 

The main advantage of loft insulation is that it makes your home more energy efficient. This means that heating or cooling your property requires less energy. Not only does this allow you to save money on your energy bills, but it also helps you to reduce your carbon footprint. 

Because we tend to heat or cool our homes by burning fossil fuels, the less often you need to put your heating or air conditioning on, the less fossil fuels you’ll need to burn.

Types of Loft Insulation

There are multiple types of loft insulation to choose from, each one with its own advantages and downsides. Here are some of the most common. 

Loose-fill insulation

Loose-fill insulation comprises a compacted or loosely-poured material that’s then blown into spaces using specialist equipment by professional installers. Often, this type of insulation is made from recycled materials, making it the go-to choice for environmentally friendly homeowners. 

Some forms of loose-fill insulation are even pest, mould, and fire-resistant, so it’s a great option if you want to keep your home safe from mould, fires, and unwanted visitors!

If you have a loft that’s small or particularly hard to reach, you’ll benefit from installing loose-fill insulation, as it can be blown into tight spaces. 

Loose-fill works best on a cold roof, not a warm roof. It’s not, however, suitable for DIY installation, so you’ll need to hire a professional installer to work with this material who will be able to provide you with a better idea about how much loft insulation is needed. 

Blanket insulation

Blanket insulation is probably the most popular type of loft insulation and it’s one of the easiest to measure because it comes in rolls and slabs, which you can then cut to size. This type of insulation tends to be made from materials such as rock wool, mineral wool, fibreglass, and even sheep’s wool.

Blanket insulation is suitable for DIY installation, so if you’re looking to measure up and install insulation by yourself, blanket insulation is your best bet. 

Plus, it’s fire and water-resistant, so if you’re looking for a home that’s safer from potential damage, installing blanket insulation is an excellent choice. 

Rigid insulation boards

Rigid insulation boards are one of the best materials for creating a warm roof. They’re versatile, so they can be fitted in various different parts of your loft for whichever type of insulation works best for you. 

Solid insulation boards are water-resistant, relatively cheap, and boast high insulation value (R-values), so they’re a decent option for making your home more thermally efficient. You will need to leave enough space for adequate ventilation to avoid instances of damp and mould and you might want to cover the boards or sheet insulation with plasterboard for an attractive finish that works particularly well in lofts that are used as rooms. 

Blown-fibre insulation

Unfortunately, blown-fibre insulation can’t be installed as a DIY job and requires a professional installation. Similarly, it can be harder to predict how much blown-fibre material is needed vs other materials such as blanket insulation, which is straightforward to measure. 

As the name suggests, blown-fibre is installed by blowing fibres into your roof joists. When these fibres stick together, the effect is foam-like. Like loose-fill, this type of insulation is ideal for hard-to-reach spaces because it can be blown in – you won’t need somebody to enter the space in the same way you would with blanket insulation. 

Blown fibre is often one of the greener insulation options since you can opt for recycled materials, such as paper or wool. 

How Much Loft Insulation Do I Need?

You’ll need to calculate exactly how much loft insulation is required before going ahead with purchase and installation. If you’re doing a DIY installation you’ll need to purchase your own loft insulation, and if you’re hiring a professional, knowing how much you need can help you accurately estimate your costs beforehand. 

Firstly, you’ll need to look up building regulations to find out the minimum insulation thickness your home needs to have. Back when insulation was first around in the 1980s, people would install as little as 25mm of thickness. 

Nowadays, the minimum required thickness of insulation stands at 270mm for new-build properties. While strict building regulations don’t apply to existing properties, it’s a good ballpark figure to consider when installing insulation in your property. 

Increasing Existing Loft and Roof Insulation

If you already have insulation in your property, measure how much before purchasing more. If you already have up to 200mm of existing loft insulation up there, you can work out how much more you’ll need to purchase to get the recommended thickness. 

During this process, don’t forget to check whether the insulation comes above the joist or fills the gaps between joists. You may even find that additional insulation has already been laid on top of the joists. 

Just because there’s already insulation in your property, it doesn’t mean you wouldn’t benefit from increasing its thickness. You’d be surprised at how effective results can be simply from increasing thickness up to the recommended 270mm. 

According to the Energy Saving Trust, for example, increasing your insulation from 120mm to 270mm could cost as little as £420, and provide annual bill savings as high as £55, meaning the insulation increase could be paid for in just a few years. Here’s a more detailed look at their findings when homes in England, Scotland, and Wales increase their loft insulation from 120mm to 270mm: 

 Detached HouseSemi-Detached HouseMid-Terrace HouseDetached Bungalow
Cost of installation£570£440£420£570
Annual energy bill savings£55£35£30£55
Annual energy bill savings from increasing the levels of loft insulation

Adding loft floor boarding

Many people opt to add boarding to their loft floor as they intend to use it for storage space or to carry out a loft conversion so that it can be used as an extra room in the home. The loft floor boarding will effectively add to the existing loft insulation, reducing heat loss and having a positive impact on heating bills.

The addition of loft boarding will often be accompanied with the installation of a loft hatch and this will need insulating too to ensure that it does not become a point of excessive heat loss in the loft area. Improving the thermal insulation of your loft is an additional benefit of boarding out a loft space which will provide more practical use in the home whatever your intended purpose for it.

How Many Rolls Of Insulation Do I Need?

Once you’ve established the desired thickness of your insulation, you’ll need to take some measurements to establish how many rolls of insulation to buy. Don’t forget to factor in the thickness of any existing insulation, too. 

You’ll need to measure the total area of your loft. To do so, measure both the width and length of the space in metres, then multiply the length by the width. This will give you the square metre measurement of your loft. 

Once you have your measurements, you can buy your insulation. If the type of insulation you’re buying isn’t sold in square metres and you’re buying rolls instead, you’ll need around 2 insulation rolls for every square metre. Insulation rolls do vary in length, though, so check the length with the manufacturer before purchasing. 

While the rule seems to be that the more insulation, the more energy efficient your home is, this obviously has its limits. Installing insulation that’s too thick can decrease the amount of ventilation in your loft space, which can cause serious issues such as damp and mould. As a rule of thumb, stick to 270mm of thickness and don’t go too far above it. 

It’s also worth remembering that the insulation in between your joists already counts. So, if you have 100mm of insulation in between your joists which are 100mm high, you’ll need another 170mm to take it to the recommended amount.

Where Is Loft Insulation Installed?

The answer to where to put your loft insulation depends on an important distinction – whether you’re trying to create a cold loft or a warm roof. 

In a cold roof, you insulate the joists, but in a warm roof, you insulate the rafters. The results are quite distinct, so you’ll need to establish which one you need before getting started. 

The cold roof method makes your loft space cold, so it’s only suitable for lofts that either don’t get used or are used for storage. The warm loft insulation method, however, is ideal when you’re trying to create a habitable space in your loft, to use as a bedroom, for example. Typically, warm roof insulation requires more material and costs more as a result, so don’t create a warm roof space unless it’s necessary. 

When using the warm roof method, you’ll need to install insulation in two layers – one of which is between the rafters in a pitched roof to keep the timbers warm. Having inadequate ventilation in your loft is a recipe for disaster (in the form of damp!) so leave at least a 25mm air gap between the insulation and your roof tiles or slates. 

Suitable insulation materials for creating a warm roof include rigid boards, insulation slabs, and in some cases, multi-foil. You can then cover the material with plasterboard for a more finished look. 

A cold roof is insulated at the floor level between the joists. As a result, you have a wider pick of materials, from mineral wool to loose-fill or blanket insulation, all of which have good insulating properties.

Where to Find a Loft Insulation Installer

If you don’t fancy the effort that goes into installing your own insulation or you’re using a material that’s not DIY friendly, you’ll want to find a trustworthy installer in your area that specialises in loft insulation. After all, poorly installed insulation can cause problems for your home down the line.

Luckily, we can put you in touch with installers with a proven track record of installing effective insulation in a range of settings including loft spaces. 

To find a quote from a contractor that installs insulation in your area, use our quote-finding tool completely free of charge. The installer will be in touch to discuss your requirements and advise you on the insulation options best suited for your home so you can soon start enjoying the significant savings that properly insulating your loft space can bring.

On This Page
Get Your Insulation Quote