Which type of loft insulation is best?

Loft insulation is one of the best ways to keep a home warm and comfortable. It’s also one of the easier types of insulation to install! But with so many types to choose from, how do you know which type of loft insulation’s right for your home?

In this article we’ll look at the types of insulation you might want to consider installing in your loft.

To learn more about loft insulation, read Loft Insulation: The Snugg 2024 Guide

Most efficient loft insulation

If you're looking for loft insulation with the highest thermal efficiency, you may want to consider sheep’s wool.

This natural material has a high R-value (a measure of its thermal resistance) of around 3.5-3.8 per inch of thickness. For comparison, fibreglass insulation has an R-value of 2.2-2.7 per inch.

In the UK, loft insulation is usually recommended to have an R-value of 6.1-7. So, you’d need no more than two inches of sheep’s wool insulation, compared to around three inches of fibreglass insulation.

Sheep’s wool is more expensive than most other types of insulation, but it’s easy to install and is environmentally friendly due to its renewable and biodegradable material.

Most affordable loft insulation  

If you’re on a budget, you might want to consider fibreglass insulation. As well as being the most common type of loft insulation sold in the UK, it’s also one of the cheapest.

Although costs vary depending on the retailer, you can find fibreglass insulation for as little as £10 per square metre.¹

Bear in mind that the price will also depend on the brand, thickness and quantity you buy. You’ll also need to pay for the cost of labour if you’re not installing it yourself.

Most sustainable loft insulation  

Insulation materials are manufactured in different ways, and some are more sustainable than others.

Sheep’s wool is one of the most sustainable options, given that it comes from a renewable source and is biodegradable. Plant-based insulation, including hemp, flax and cotton, is also a sustainable choice which can be shredded and reused at the end of its lifespan.

Although these types of insulation are more sustainable than others, it’s worth noting that exactly how sustainable they are will depend on individual farming practices, manufacturing processes and transport choices. Some retailers provide information about this in their product descriptions.

Best loft insulation for modern houses  

Modern houses tend to be built to higher energy efficiency standards than older homes. But since building regulations only required loft insulation to be at least 270mm thick from 2006, you may find your home (if built before then) has less than the recommended thickness.

To top up your insulation, you’ll need to consider the existing material. Being the most common insulation material, it’s likely you’ll need to use fibreglass insulation. Fortunately, this is one of the cheapest insulation materials and shouldn’t set you back too much.

If you’re replacing your existing insulation or starting from scratch, you may want to consider sheep’s wool - one of the most effective insulators and sustainable options.

Best loft insulation for old houses  

Older houses are typically less well-insulated than modern homes. They may not have fully insulated walls and floors, and they may have little (if any) loft insulation.

Older homes also tend to have more traditional rafter and purlin roof structures, and they have less usable space in the loft to move around, which can make installing insulation more difficult.

For these reasons, you may want to consider fibreglass insulation. This is one of the easiest types of insulation to install, as you simply need to cut the roll to size and fit it between rafters.

However, if you want a more efficient material to help with a less well-insulated home, you could consider rock wool insulation. This material can be bought in rolls, which can be easily cut to size and placed between rafters. It’s more expensive than fibreglass insulation, but it’s more efficient, with an R-value of up to 3.3 per inch (fibreglass has an R-value of up to 2.7 per inch).

Best loft insulation for cold climates  

If you live north of the UK, or your home’s particularly exposed to cold winds, you may want to consider sheep’s wool.

Sheep’s wool has one of the highest R-values of up to 3.8 per inch, making it particularly effective in cold environments.

Colder climates are also often wetter and more humid in the UK, requiring loft insulation that’s particularly effective at absorbing and releasing moisture without losing its insulating ability. Sheep’s wool is one of the best insulators in wet environments due to its natural breathability.

Best loft insulation for warm climates  

Let’s face it, the UK doesn’t enjoy a tropical climate. But average temperatures are getting warmer, and our summers are experiencing record-breaking heatwaves (up to 40C in some areas).

To prevent your home from over-heating on the hottest of days, while also ensuring it stays warm in winter, you’ll want to consider a material that has a good balance of breathability and moisture management.

Sheep’s wool ticks both boxes. It will keep your home warm on the coldest of days due to its high insulation efficiency, and it’ll keep your home cool in summer thanks to its breathability.

If you want to spend less on insulation, you could also consider cellulose insulation. It’s another effective choice for keeping your home warm in winter, and it’s not too far behind sheep’s wool in keeping your home cool in summer due to its average breathability.

Best loft insulation for DIY

If you plan on insulating your loft yourself, you’ll want to use a material that’s effective, cost-efficient and easy to install.

Fibreglass insulation is the most common material for DIYers as it meets all these criteria.  

It’s easy to install as you can buy it in rolls, and you don’t need any specialist equipment. However, be sure to wear protective gear, as the fine fibers can irritate the skin and lungs. Simply cut it to length and place between the beams. You won’t need to replace it anytime soon, either - fibreglass insulation can last up to 100 years.

Most Popular Choice for Loft Insulation  

When choosing loft insulation, you’ll want to consider its thermal efficiency, how environmentally friendly it is, how easy it is to install and how affordable it is to buy.

Based on these criteria, it's hard to argue against fibreglass insulation.

Other types of loft insulation may have higher thermal efficiency, but fibreglass isn’t too far behind. It’s relatively environmentally friendly, being made from recycled glass. It’s also easy enough to install yourself, supplied in rolls that can be easily fitted between joists. And it’s one of the most affordable types of loft insulation available. It's also usually odourless, rot proof, damp proof and fungus proof.

That said, fibreglass insulation isn’t suitable for every situation. It's not dense enough to be particularly effective at soundproofing. And if you live in a particularly cold or windy climate, you may want to consider a material with higher thermal efficiency.

Find out how to make your home more energy efficient with our free energy efficiency plan.