Loft Insulation Buyer’s Guide

There’s nothing like the shock of a cold snap (or a three-figure utility bill) to put loft insulation at the forefront of your mind. But why wait until winter? From natural sheep’s wool to affordable fibreglass, insulating your attic has its benefits all year round, keeping your house cool in the summer while keeping it toasty through the brisk winter.

If the expense and hassle of finding a reputable tradesperson to do the job for you is putting you off, here’s some good news. If your loft is easy to access and has no damp or condensation problems, insulating it is something you can do yourself, even if you normally struggle to hang up a picture! We understand you may have some questions like ‘which type of loft insulation is easiest to install?’ and ‘how thick should loft insulation be?’ so our guide to buying loft insulation has the answers. When it comes to installing, use our loft insulation installation guide.

Table of Contents

1. How does loft insulation work?
2. What are the benefits of loft insulation?
3. Insulating joists vs insulating rafters
4. What type of loft insulation do I need?
5. What depth of insulation do I need?
6. What materials should I use for my loft insulation?
7. What else could I use to insulate my loft?

How does loft insulation work?

Understanding how loft insulation works is key to knowing what is best for you. From windows, doors and walls, heat can escape from your home in many different places. But a big chunk of this precious energy (around 25% in an uninsulated home) gently wafts out through the roof.

Loft insulation stops rising heat in its tracks, turning your attic into a shield between your warm home and the cold outside world. From sheep’s wool to glass and even rigid boards, loft insulation comes in a variety of materials, but they all work in much the same way – by trapping heat in air pockets, stopping it from being lost into the atmosphere.

It works all-year-round, too. In summer, insulation stops warm air from coming in, helping to keep your home feeling cool and comfortable.

Laying rolls of insulation doesn’t mean you have to stop using your loft for storage either. As long as you don’t compress the blanket of insulation and remember to leave an air gap so that moisture can escape, you can put down floorboards over the top.

What are the benefits of loft insulation?

Thought your loft was only handy for storing Christmas decorations? Here’s why insulating the attic is a clever trick that’s well worth your time and effort.

  • Your home will feel warmer in the winter and cooler in the summer
  • A well-insulated loft means you won’t have as many problems with condensation
  • With a quarter of your home’s heat being lost from the roof, if your home’s currently uninsulated you’ll notice a huge benefit straight away
  • Done properly, loft insulation can be effective for up to 40 years (and up to 50 years if you use sheep’s wool)
  • It’s so cost effective that it’ll easily pay for itself many times over
  • You could save up to £215 on your energy bills each year, according to the Energy Savings Trust
  • You’ll be doing your bit for the environment. Currently a third of all carbon emissions come from heating draughty homes
  • Outside noise will be greatly reduced – good news if your home is under a flight path or next to a busy road
  • Your home’s Energy Performance Certificate rating will be boosted – a huge plus if you were thinking of selling in the future

Insulating joists vs. insulating rafters

If you have a typical house with a pitched (sloping) roof, you’ll need to decide whether you’ll insulate the joists (the floor of the loft) or the rafters (the walls of the loft). And that depends on whether you want to create a cold or warm loft space.

If you only use your loft for general storage, creating a cold loft is normally your best bet because it’s less expensive, less fiddly and a relatively easy job to do yourself. For a cold loft, you only need to insulate the space directly above the ceiling of the top storey of your home. The easiest way to do this by laying a blanket of insulation (known as loft rolls) between and over the joists of the attic. After that you can decide whether or not to lay floorboards over the top.

If you plan to store some heat-sensitive items or want to use the attic for your hobbies, you’ll need to create a warm loft. Warm lofts retain the heat in the winter and stay cool in the summer, but to achieve this means you’ll need to insulate just under the roof in the rafters. This will require a little more technical know-how, but can be really worthwhile as it’s an effective way of keeping the heat in your home.

What type of loft insulation do I need?

Your options for loft insulation vary, depending on whether you plan to insulate the joists or the rafters.

Insulating the joists


For a cold roof you can take your pick of loft rolls, choosing from mineral wool, sheep’s wool, glass wool or even a specialist acoustic wool that’s great for blocking out outside noise.

You also have the option of using loose fill products to top up any insulation you may already have in place. Rather than laying down a blanket of insulation, loose fill comes in bags which you just open and pour into any space that’s looking a bit sparse. It’s a really easy job that requires no DIY skill whatsoever.

If your loft is damp, slab insulation is a great choice. It’s easy to fit, water-repellent and breathable so you won’t get rot or mould.

Planning to use your loft for storage? Going for rigid insulation boards could save you time and effort, as you get boards and insulation in one. Although more expensive than loft rolls, they offer the same heat-retaining capabilities but are half as thick. For example, insulation board with a thickness of 135mm has the same level of insulation as 270mm of mineral wool.

Whatever kind of joist insulation you go for, just remember that the loft space above will feel very chilly in the winter and hot in the summer – not great if you wanted to store anything precious or valuable. You’ll also need to remember to insulate your pipes and water tank before any cold snaps as they could be liable to freeze.



Insulating the rafters

Your options for insulating the rafters are a little more limited. That’s because the products used to create warm lofts tend to be denser and more rigid than those used for insulating joists. Then there’s the little problem of how to get the insulation to stay put without falling down.

Rather than loft rolls, you can buy mineral or glass wool insulation in batts which are held in place by battens of wood attached to the rafters. Or you can use normal insulation that’s held in place by netting.

Insulation boards are also a great option for warm lofts. They can be cut to the right size to fit snugly in between the rafters, while insulated plasterboard can be put over the rafters themselves to make sure your insulation meets the required depth.


What depth of insulation do I need?

The government recommends a minimum depth of 270mm, but many new properties are exceeding this, going up to a depth of 300mm. If you choose to go for 300mm (or more) you will lose a little space, but if your home feels cold it could be worth it.

Bought a house with the insulation already in place? Unless the property is a new-build, it’s worth checking how deep your insulation is because it may be time for a top-up. The recommended depth was 200mm in 1995 so anything built before then likely won’t meet today’s insulation targets.

What materials should I use for my loft insulation?

Loft rolls come in a range of materials, and the type you go for will depend on how you’ll be using it. Don’t know your sheep’s wool from your mineral? Here’s an explanation of each.


Mineral woolmineral wool insulation

Lightweight and inexpensive, mineral wool is made from volcanic rock which is heated until it melts, spun and bound together with resin and oil. It comes in rolls like a blanket which you just lay down between joists and then place on top to take it up to the recommended depth. You can also use mineral wool to insulate the rafters by cutting and fitting it to size and using insulation fixings to stop it from falling down.

Pros of mineral wool: Has excellent thermal and acoustic insulation, is easy to install and offers great fire resistance.

Cons of mineral wool: Mineral wool will compress if you put weight on it and can irritate bare skin.


sheeps-wool-insulationSheep’s wool

Wrap up your loft with soft, natural sheep’s wool. Sheep’s wool insulation is safe to touch and won’t irritate your skin, so you can handle it without wearing protective clothing. It can be used for insulating joists and rafters, and is great for absorbing moisture, preventing mould and rot.

Pros of sheep’s wool: Safe to touch and easy to install, sheep’s wool is lovely to handle. But its major advantage is that it’s breathable, so it’s great for preventing damp from damaging your wooden timbers.

Cons of sheep’s wool: Generally more expensive than glass or mineral wool, plus you need to install more of it to get the same thermal values as usually it’s not as good an insulator as other wool roll alternatives

glass wool insulation

Glass wool

The most popular type of loft insulation in the UK, glass wool (also called fibreglass) is one of the cheapest. It’s made by melting glass and sand together, before spinning them to form fibres which are bound together with resin. The resulting blanket looks like sheep’s wool and is just as flexible.

Pros of glass wool: Fire resistant, insect repellant and eco-friendly because it’s mainly made from recycled glass.

Cons of glass wool: Most glass wool is irritating to skin so you’ll need to wear protective clothing. Glass wool insulation also becomes less effective when wet so it’s not suited to damp areas.

What else could I use to insulate my loft?

While laying down loft roll is a popular choice, it’s not the only option and some of the alternatives might suit you better.

Insulation boards

Rigid boards can be used to insulate both joists and rafters and are a great choice if your loft is large. Although more expensive than rolls, they offer good thermal values at half the thickness. In addition, you can easily store items directly on top of them. They can be cut to size using a saw so that they fit snugly between joists or rafters while holes can be drilled around light fittings.

Insulation slab

Slab insulation products are becoming increasingly popular thanks to how easy they are to install, with most products friction-fitting between joists or rafters. As well as keeping your home toasty, they’re one of the most fire-resistant choices. Some are made from stone, but they’re still easy to cut and fit to your space.


Foil insulation

Otherwise known as multifoils, foil insulation comes into its own when insulating the rafters. It consists of layers of reflective and insulating materials that allow heat to be reflected back into the room. It’s easy to install as you simply staple the foil to the rafters and tape over any joins.

Acoustic insulation

Whether you want to protect your ears from outside noise or stop the neighbours complaining if you’ve decided to take up the drums, acoustic insulation is a great idea. Some acoustic insulation, as demonstrated in the image below, stops noise transfer from room-to-room too so will stop footsteps in the loft travelling to the room below. From acoustic wool to slabs, sound insulation comes in many forms. Sheep’s wool is a popular choice if noise is an issue, as it offers unparalleled warmth alongside effective sound reduction.



For more information on which insulation to buy for your loft, get in touch with us for unbias recommendations on what would work best for you on 01752 692 206


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