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About a quarter of the heat in an uninsulated home escapes through the roof. If your loft insulation is thin, old, or missing altogether, that's a lot of warmth - and money - disappearing above your head every winter.

The good news is that insulating a loft is one of the more DIY-friendly home improvement jobs, and it can pay for itself in a few years through lower energy bills.

This guide walks you through:

• The different types of insulation

• How to lay it safely between your joists and rafters

• How to tell when it's time to bring in a professional instead

Let's get into it.

What types of loft insulation are there?

Before you start, it's worth knowing your options. Loft insulation generally comes in one of four forms:

• Blanket (quilt) insulation - rolls of mineral or glass wool that fit between and across your joists. The cheapest and most common choice, and the easiest for a confident DIYer to fit

• Loose-fill insulation - loose granules, often recycled cellulose or fibreglass, poured or blown into place. Good for topping up existing insulation or filling awkward gaps

• Sheet (rigid board) insulation - rigid PIR boards, typically used when insulating a roof from underneath, such as in a loft conversion

• Blown-fibre insulation - professionally blown into place using specialist equipment. Useful for hard-to-reach areas but not a DIY job

This guide focuses on blanket insulation laid between and over the joists, since it's the most effective option for beginners and doesn't require specialist equipment.

If you'd rather compare all your options and current prices, our loft insulation cost guide breaks down each type in more detail and the current government grant schemes that could reduce what you pay.

Before you start: what to check first

Not every loft is a straightforward job. A few things are worth checking before you lay a single roll of insulation:

• Recessed halogen lights - these can be a fire hazard once covered. Fit insulation guards around them or consider switching to LED downlights first

• Pipes and water tanks - leave a clear path from your loft hatch to any tanks so a tradesperson can reach them in an emergency, and insulate pipework separately to stop it freezing

• Damp or condensation - insulating over a damp problem tends to make it worse, since the loft becomes cooler once heat stops rising into it. Deal with any damp before you insulate - see our damp proofing cost guide for typical prices if you need a professional to sort it first

• Flat roofs - these need a different approach, with insulation fitted either under the roof covering or under the joists rather than the standard "between the joists" method

• Ventilation - your loft still needs to breathe. Avoid blocking eaves vents, grilles or air bricks when you're laying insulation, or you risk trapping moisture instead of keeping it out

Tools and materials you'll need

The success of your DIY loft insulation job lies in the prep. Make sure you have:

• Rolls of loft insulation (blanket/quilt)

• Wooden walk boards, to spread your weight and protect the ceiling below

• Wooden offcuts or battens

• A dust mask, to protect against airborne fibres

• Protective clothing and gloves

• A long knife with a serrated edge

• A panel saw

• Scissors

How much insulation do you need?

Measure the length and width of your loft floor and multiply the two together to get the total area. Because insulation is laid between joists rather than covering the whole floor, take off roughly 10% from that figure to get a more realistic estimate.

If the maths (or the measuring) isn't your strong point, a checked loft insulation installer can measure up and quote accurately in one visit.

Every Checkatrade job is backed by our £1,000 guarantee

Up to £1000. Eligibility criteria and T&C’s apply.

How to insulate a loft between the joists

Once you've prepared the space and gathered your materials, here's how to lay standard blanket insulation between your joists.

Step 1: Prepare the space

Vacuum up dust and debris between the joists, and repair any small cracks or damage as you go. Significant damage or rot to the joists should be dealt with by a professional before you insulate over it.

Make sure you have enough light to work safely, and always start from the corner furthest from your loft hatch.

Step 2: Deal with electric cables

Carefully lift any electrical cables and lay them on top of your first layer of insulation, rather than underneath it, to reduce the risk of overheating.

Step 3: Lay your first layer

Cut insulation to fit snugly between the joists, leaving no gaps at the edges. This base layer should be around 100mm thick.

Step 4: Work around pipes and tanks

Cut your insulation to fit around obstacles such as water tanks, pipes and extractor ducts. You can also use offcuts to lag pipes directly, wrapping them to prevent freezing in cold weather.

Step 5: Add your second layer

Lay a second layer at right angles to the first, this time running across the joists rather than between them. Laying the second layer across the joists also helps reduce heat loss through the timber itself.

This layer should add roughly 170mm, bringing your total insulation depth up to the recommended 270mm.

Step 6: Check for gaps

Go back over the whole area checking for gaps between the insulation and the joists, and make sure everything is lying flat.

How to insulate loft rafters (a "warm roof")

Insulating between the joists (a "cold roof") keeps heat in your living space below, but leaves the loft itself cold.

If you want to use the loft as a warmer, more usable space, you'll need to insulate the rafters instead - known as a "warm roof" approach. This works well for lofts with deep rafters and is typically done using 12.5cm-thick rigid boards, though reflective foil is also an option.

To insulate your rafters:

• Check your rafters for rot, damp or a damaged roofing membrane, and repair these first

• Lay out boards across the joists so you can move around safely

• Wear protective equipment throughout

• Measure the space and the distance between each rafter

• Fix wooden battens to the rafters, leaving a 5cm ventilation gap between the insulation and the roof itself

• Cut your rigid boards to size, then nail them to the rafters - a nail gun makes this quicker if you have access to one

If your loft has particularly complex rafters, or you're converting the space into a room, it's worth reading our guide on insulating roof rafters with Celotex for a closer look at rigid board installation.

Loft insulation cost calculator

Want to know more about what your job might cost before you commit to more materials or start getting quotes?

Checkatrade's AI-assisted pricing tool gives you a quick guide price based on real past jobs, so you know roughly what to expect.

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How to insulate a loft hatch

It's easy to overlook the loft hatch, but an uninsulated one lets warm air escape straight out of the room below. How you insulate it depends on the type of hatch you have:

• Hinged hatches - fit a foam strip or compression seal around the outside edge of the hatch itself, and another around the frame it closes onto.

• Non-hinged hatches - run a foam strip or compression seal around the lower outside edge of the hatch to create a tight seal against draughts.

For extra insulation on either type, tape a plastic bag filled with loft insulation to the inside face of the hatch.

Insulating a loft conversion

If you're converting your loft into a liveable room rather than using it for storage, you'll need to think about insulation across three separate areas: the sloped roof, any residual storage space, and the stud walls.

• Sloped roof - insulation is fitted between the roof and a stud wall, in a similar way to the rafter method above. Measure, cut and install as before

• Residual space - any leftover storage area outside the main living space can simply be insulated between the joists, as with a standard loft

• Stud walls - loft conversions typically use stud walls, which can be insulated between the studs and the attic joists using standard rolls or rigid boards

Loft conversions come with their own building regulations around insulation, fire safety and ventilation, so it's worth checking our guide to building regs for loft insulation before you start.

For the bigger picture on budgeting, check out our loft conversion cost guide.

Loft conversion cost: 2026 UK price guide & breakdown

Find out average loft conversion costs in the UK for all types of loft conversions including a breakdown of material costs and the professional services you'll need.

Learn more

How much does loft insulation cost?

If you'd rather not do the job yourself, hiring a professional installer is usually quick and affordable relative to the energy savings involved.

Here's a quick guide for 270mm quilt insulation installation costs:

• Detached house: £1,206

• Bungalow: £1,206

• Semi-detached: £825

• Terraced house: £654

But for the full breakdown by insulation type, including loose-fill, sheet and spray foam options, see our complete loft insulation cost guide.

Or get quotes from checked loft insulation installers near you.

Can I get help paying for loft insulation?

Depending on your circumstances, you may be able to reduce the cost through a government-backed scheme such as the ECO4 Scheme or the Warm Homes Local Grant, both aimed at eligible lower-income or vulnerable households.

Eligibility varies, so it's worth checking the current criteria before you commit to a full DIY spend.

Green home grants available in 2026

Looking to make your home more eco-friendly and energy-efficient? Discover the latest green home grants that could help you save money while reducing your carbon footprint.

Learn more

DIY or hire a professional?

Blanket insulation between the joists is one of the more manageable DIY jobs in this guide.

That said, some parts of the process are better left to a specialist - particularly:

• Rafter insulation

• Loft conversions

• Anything involving damaged joists, damp or old insulation that may contain asbestos

• Jobs involving moving pipework or wiring

• Working at height in an awkward space

• Or you're simply short on time

It's often worth comparing quotes rather than risking a job that needs redoing or invalidates your home insurance.

Not sure who to call? Whether you need an insulation specialist, a roofer, an electrician, or a damp proofer, you can compare checked and reviewed trades in your area and get the job ticked off with Checkatrade.

On Checkatrade, you'll only find trades who meet our high standards and pass up to 12 checks.

How to find a loft insulation specialist

If you decide to hire a professional, it's worth asking a few questions before you book:

• Are they experienced specifically with loft insulation, not just general building work?

• Can they show evidence of previous jobs or reviews?

• Do they carry public liability insurance?

• What does their guarantee cover, and for how long?

• Is the quote itemised, including disposal of any old insulation?

Compare a shortlist of vetted installers, ask each one the questions above, and get an itemised quote before you agree to any work.

For more detail on what to look for, see our guide to hiring an insulation contractor.

Or get your insulation project underway today by contacting one of the tradespeople below.

Loft insulation checklist

Before you start:

• Check for damp or rot first

• Fit light guards or LED bulbs

• Clear a path to tanks and pipes

• Gather tools and materials

• Measure your loft area

• Wear a mask and gloves

• Leave gaps around vents

FAQs about how to insulate a loft

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