Loft insulation: All you need to know

Installing loft insulation can improve your home's energy efficiency, heat, and comfort levels. Learn more about loft insulation with our complete loft insulation guide.

Loft insulation reduces heat loss by up to 25%, making it warmer and cheaper to heat.

But there are many more reasons that homeowners choose loft insulation.

Read on for a full loft insulation guide - covering everything from loft insulation types to the dos and don'ts.

What is loft insulation?

Loft insulation is a material installed between a roof and ceiling of the top floor.

Its purpose is to improve energy efficiency and reduce heat loss.

What does loft insulation do?

Loft insulation prevents heat from escaping through your roof by trapping heat in air pockets. This allows your home to retain heat in the winter and keep cool in the summer.

Other benefits of loft insulation include:

• Maintains consistent temperatures to improve comfort levels

• Improves energy efficiency, which in turn reduces energy bills

• Some types of loft insulation, like multi-foil, can reduce draughts and cold spots

• Minimises heat loss by creating a thermal barrier that stops heat from escaping

• Lower energy consumption levels lead to a reduced carbon footprint

• Reduces moisture and condensation levels to stop damp in your loft

• Regulates the air to improve ventilation - which is good for you and your home

• Reduces noise from outside and between rooms to create a quieter living space

Insulating your loft can also improve your houses' resale value due to a higher energy performance certificate. Great to know if you're thinking of selling in the future!

Get more expert advice on insulating your loft here.

What's the best loft insulation?

Loft insulation is available in various materials, each with its own uses and purposes.

Deciding on the best loft insulation for your house depends on:

• Your budget

• Property age

• Structure and type of property

• How you plan to use your loft space

So, choosing the best loft insulation material can be a very personal choice.

Loft insulation types

There are several main types of loft insulation that homeowners can choose from.

1. Blanket insulation

Blanket insulation is made from flexible fibres such as fibreglass, mineral wool, sheep's wool, and foil-backed felt.

It's laid in sheets under and between the floor joists of roof rafters and then secured.

Benefits include:

• Easy to install

• Widely available

• Cost-effective

• Won't stop you using your loft

But be careful when installing blanket insulation, as it can irritate skin and lungs.

2. Sheet or board insulation

These rigid boards are most often made of polystyrene, polyurethane (PIR), polyisocyanurate (polyiso), or phenolic foam.

Made of synthetic or natural materials, they're best for insulating the underside of your roof.

Benefits include:

• Can be decorated

• Used on floors or walls

• Excellent thermal insulation

• Can provide structural support

• Perfect for turning loft conversions into living spaces

Sheet or board insulation can come with a pretty price tag and is best professionally fitted.

3. Loose-fill insulation

Loose-fill insulation is usually made from cork granules, cellulose fibre, mineral wool, or even cellulose (recycled paper).

Benefits include:

• Lightweight

• Easy to install

• Can be used to top existing insulation

• Great for hard-to-reach and irregular spaces

This type of loft insulation is not always easy to install and is not as secure as others. But, it can be a great eco-friendly option.

4. Blown-fibre insulation

This loft insulation is installed by blowing loose materials between joists - usually cellulose or mineral wool.

Benefits include:

• Excellent for nooks and crannies

• Can be used to top up existing installations

• Provides premium thermal insulation

But you might want to consider something else for a draughty loft, as it's only a partial solution.

This type of loft insulation is also best professionally fitted.

5. Spray foam insulation

This loft insulation is made from a Polyurethane foam sprayed directly into loft spaces.

Benefits include:

• Premium insulation

• Airtight sealing

• Easy-to-fill gaps

• Aids structural integrity

• Great for insulating irregularly shaped lofts or lofts used as living spaces

However, it can be expensive and requires professional installation. Improper installation can lead to ventilation and moisture issues.

Loft insulation materials

The most popular loft materials include:

• Fibreglass is easy to get hold of, affordable, and great for thermal insulation

• Mineral wool is easy to install and is suitable for soundproofing

• Sheep's wool is a natural, breathable, and eco-friendly option

• Cellulose is made from recycled paper - great for the eco-conscious

• Polystyrene or PIR rigid foam boards provide some of the best insulation

• Spray foam is excellent at filling awkward spaces and creating an airtight seal

• Multifoil is available in thin reflective layers, making it great for insulating tight spaces

When deciding on the best insulation for your loft, consider its age, material, structure, and size.

How you intend to use the space and your budget are also important.

Discussing your plans with a trusted loft insulation installer can be helpful.

How to insulate a loft

How to insulate a loft depends on the property type, the type of insulation, and how the loft is used.

You might be able to install white blanket insulation as a DIY project. In this instance, you only need to lay rolls of blanket insulation between joists.

Here are the basic steps;

1. Assess the space

2. Choose the correct insulation based on property type, size, and intended use

3. Clear and clean the loft

4. Remove any current insulation that's no longer needed, or keep it if it’s being topped up

5. Depending on the insulation, you can lay, spray, or fit it between the joists

Dive deeper into how to insulate a loft with this guide.

Or, contact a trusted loft insulation installer to arrange a quote.

Tips for insulating lofts

Insulating your loft might seem straightforward, but some aspects need extra attention.

• To prevent condensation buildup, leave a loft insulation ventilation gap of around 50mm between the insulation and roofing felt

• Add insulation boards or a raised platform to avoid compression and improve thermal effectiveness when flooring over insulation

• Installing loft flooring and board over your insulation can reduce heat loss and increase your property value

• Be cautious not to block the eaves gap, or you won't have enough airflow and may have damp issues

It's best to enlist professionals to lay more complex loft insulations, such as spray foam or blown fibre.

Approved loft insulation installers

Where possible, use an approved loft insulation installer.

Find insulation installers registered with recognised organisations, like the National Insulation Association. It's an excellent way to ensure they comply with all standards and safety regulations.

You can also find an approved loft installer with our registry of trusted tradespeople.

What's the recommended loft insulation thickness?

The current UK loft insulation thickness regulations recommend a loft insulation thickness of at least 270 mm.

However, this is only a minimum suggestion; your home may need more.

A loft installer can help you decide on the thickness and type of material.

Learn more about the building regulations of lofts here.

Loft insulation do's and don'ts

When insulating your loft, don't forget these do's and don'ts.

• Do make sure you have enough vents

• Don't block your eaves gaps

• Don’t compress insulation when laying flooring over it

• Do call professional loft insulation installers for complex installation

• Don’t block air circulation, which leads to moisture and mould

Did you know that too much loft insulation can lead to ventilation issues? Which can cause moisture problems and dampness.

Creating this moisture trap can lead to;

• Condensation

• Mould growth

• Wood rot

• Damage to the roof structure if left untreated over time

Adequate ventilation is vital to trap humidity. Before installing loft insulation, ensure enough ventilation in your loft area from roof vents or soffits.

FAQs

Is loft insulation fireproof?

Although not fully waterproof, loft insulation in the UK is generally fire-resistant.

But, the fire safety of your loft insulation can depend on the type of material.

Common fire-resistant or non-combustible loft insulation materials include;

• Mineral wool

• Fibreglass (glass wool)

• Stone wool (rock wool)

• Fire-resistant rigid foam boards

• Fire-retardant treated cellulose (chemically treated recycled paper fibres)

Mineral wool is the most fireproof option because its melting point is over 1000°C, much higher than most other insulation materials.

Make sure you choose non-combustible insulation with an A1 fire rating. Look for insulation that doesn't contribute to fire spread and can withstand temperatures hotter than fire.

Does loft insulation burn?

Because modern loft insulation materials are generally non-flammable and fire-resistant, they are safe to use in your property.

Materials like mineral wool or fibreglass require high melting temperatures and are non-combustible.

However, their fire resistance depends on the material. While treated materials offer more protection, no insulation is entirely fireproof.

Is loft insulation flammable?

As mentioned above, loft insulation is generally non-flammable and safe to install on residential properties.

Commonly used loft insulation materials, like mineral wool, sheep's wool, and fibreglass, are non-flammable and need higher temperatures to melt.

Can you use loft insulation in cavity walls?

No. Do not use loft insulation in cavity walls.

Cavity wall insulation is only for vertical use, and loft insulation is only for horizontal use.

What is loft insulation made of?

Loft insulation is made from various materials, including;

• Mineral wool, otherwise known as rock wool

• Fibreglass, otherwise known as glass wool

• Sheep's wool, which is both natural and sustainable

• Hemp, which is softer and lighter than mineral wool or fibreglass

• Recycled polyester is an eco-friendly insulation

• Multi-foil is made up of multiple layers of radiant foil barriers, which is airtight and moisture resistant

How thick should loft insulation be?

The UK government recommends a loft insulation thickness no less 270 millimetres.

Although this is the minimum loft insulation thickness, your home may benefit from 300 millimetres of insulation.

Does loft insulation make house warmer?

Yes, loft insulation can make your house warmer because it;

• Stops heat escaping through your roof

• Maintains consistent temperatures

Why is loft insulation needed?

You might install loft insulation to;

• Improve your home's comfort levels

• Reduce heat loss

• Lower heating bills

• Improve energy efficiency

• Reduce your home's carbon footprint

• Save money over time

• Reduce with loft moisture levels

• Aid your roof's structural stability

How much loft insulation do I need?

How much insulation you install depends on several factors. The size of your loft, materials, thickness, and if you plan to insulate the underside of your roof can have an impact.

Ready to get planning your loft insulation?

Start budgeting here with our loft insulation cost guide.

Or, chat with a loft insulation contractor for more advice.