Did you know the cheapest way to insulate a loft can also be the most effective? Even better, with a 40-year lifetime, loft insulation pays for itself with the money it saves on your energy bill. But it’s important to install it correctly. Whether you’re upgrading existing insulation or starting from scratch, there are a few considerations when choosing the best loft insulation solution for you.
What is loft insulation?
Up to 25% of the heat generated in your home is lost through warm air rising and escaping via the roof. Insulating your roof space is a simple way to stop that happening - and keep your house cooler in summer too.
Loft insulation acts as a barrier layer in your roof to stop the warm air getting out. It’s either fitted between the joists, the horizontal beams along your attic floor, or between the rafters which support the roof.
Without loft insulation, your boiler has to work harder to create more heat to keep your home cosy. That means you're generating more heat than you need, increasing your spend and carbon footprint.
Loft insulation also improves your Energy Performance Certificate (EPC) - and that adds value to your property as well as reducing your gas and electricity bills. According to the Energy Saving Trust, you could save up to £430 a year by adding loft insulation to an uninsulated roof space.
There’s a range of options available for roof insulation, some of which are relatively inexpensive and easy to fit yourself. Other roof insulation options require specialist equipment and you’ll need a professional to do the job.
How is loft insulation installed?
Loft installation comes in various forms. The main ones are:
- Blanket insulation - comes in rolls and is the most common. It’s typically made of rock, glass or mineral fibre
- Loose-fill insulation - good for topping up existing loft insulation. It’s very cheap, especially if you choose recycled options. It’s made of cork granules, cellulose fibre, mineral wool and even shredded newspaper
- Blown-fibre insulation - not intended to insulate a whole loft, this fills hard-to-reach gaps. It’s more expensive as it needs professional loft installation
- Sheet or roll insulation - natural or synthetic, this is used to insulate the underside of the roof where blanket insulation isn’t suitable. It's another expensive option that usually needs professional fitting.
What’s roof insulation made of?
Roof insulation materials include:
- Mineral wool made from glass (melted) wool and sold in rolls. Loose yarn can also be blown into gaps. It’s cheaper than the 100% sheep’s wool alternative, but equally non-flammable, mould resistant, recyclable, and has a low carbon footprint
- Polystyrene slabs, sometimes foil covered and usually cut to size
- EPS (expanded polystyrene) squeeze products which concertina into place
- Spray loft insulation is a foam that is sprayed into place and hardens, filling gaps and creating an airtight seal. It’s quick to install, lasts a long time and is mould-, bacteria- and mildew-resistant. It must be professionally fitted. Avoid makes that include HCFC, CFC, HFA or formaldehyde. Eco-friendly versions of spray loft insulation are available.
Does the type of roof I have affect my options for loft insulation?
The best loft insulation for your home will depend on the type of roof you have.
- Pitched (sloping) roofs are easiest to insulate and there are more options available. The options for insulation are warm or cold loft insulation
- Flat or dormer roofs are more challenging and best dealt with by a professional. The options are warm, cold or inverted loft insulation.
Whichever roof type you have, finding the best loft insulation for your home depends on your space, budget and whether you plan to install it yourself or hire a professional.
What’s the difference between a warm loft and a cold loft?
If you have a typical house with a sloping roof, or have the top flat in a block and are responsible for the loft space and roof above, you can either choose to have a warm loft or a cold loft,. This affects the type of insulation you might have:
- A warm loft is where you insulate immediately under the roof, which means your loft space is warm as well
- A cold loft is where you insulate immediately above the ceiling of the top storey, so no heat from your home gets into your loft.
What’s warm loft insulation?
Warm loft insulation involves adding insulation immediately under the roof, so your loft space stays warm in winter and cool in summer. It’s ideal for storing temperature-sensitive items or creating an extra room which can add value to your property. But don’t confuse this with a full loft conversion. You can put lighter furniture up there, but to use the space as a normal room you need to reinforce the floor.
To install warm loft insulation, you’ll need specialist help and it’s usually more expensive than a cold loft.
If you’re not using your loft space as a room, you’ll need to add cold roof insulation too, with raised boarding as required.
With a warm loft solution, you also need ventilation to prevent a build-up of condensation or water getting in. This means having a space for air to flow parallel to the rafters and immediately under the tiles across the whole roof to reduce the risk of rot.
The only exception to the ventilation rule is if you’re using polyurethane spray foams.
What’s cold loft insulation?
Cold loft insulation is installed above your top-floor ceiling, between and around the joists on the attic floor. It keeps the warmth in your home, but leaves the loft cold - although it can still get very hot in summer and there’s also the risk of condensation.
This option is cheaper and easier to install yourself than warm loft insulation. You may also be able to apply for an energy-efficiency grant to cover all or some of the cost.
Any professional loft insulation services you pay for don’t include loft clearance. If you use your roof space for storage, you’ll have to empty it yourself first.
After fitting cold loft insulation, you may also need to.
- Insulate the pipes to stop them bursting in freezing temperatures
- Insulate the water tank, leaving the underside exposed unless it’s 10cm or more above the top insulation layer
- Leave electric cables exposed to keep them cool, raising them above the insulation if possible
- Protect any recessed halogen lights in the rooms below. They concentrate heat in a small area and pose a serious fire risk if they’re covered by insulation. Invest in some loft caps/loft covers
- Insulate the loft hatch. Use a polystyrene panel and seal gaps with draught-proof strips. As with other draught-proofing tasks, this is an easy job to do yourself.
How thick does loft insulation need to be?
The government recommends that loft insulation should be 270mm deep. Even if you’ve already got insulation installed, it’s worth checking that you’ve got the best loft insulation for maximum money and energy savings.
And remember, even if you have the right loft insulation thickness, if it’s squashed under boxes, it won’t work effectively.
What if there’s already some insulation in my loft?
Check the condition and depth of the existing loft insulation. Properties from the 1970s and earlier tend to have just 25mm of insulating material: the kind of insulation that was subsidised back then.
Any insulation less than 100mm deep is probably worth replacing. It can’t be topped up to the recommended 270mm due to the sizing of modern insulation.
Today’s loft insulation materials come in two depths: 100mm (to go between the joists) and 170mm (laid over and across the joists).
Loft insulation that’s around 100mm deep - typically from the 1980s onwards - can be topped up rather than completely replaced.
How do I know if I already have loft insulation?
If there are boards in your loft, it can be difficult to tell whether you have insulation or not, let alone how thick it is.
You could look under the boards in a corner of your roof to check for loft insulation - but remember there could be pipes and cables there too.
If you don’t know what you’re doing, it’s always better to get professional help - and some companies will offer you a free loft insulation survey.
Can I still use my loft for storage once the roof insulation is in place?
With loft insulation correctly installed, putting items directly on it or fixing boards onto the joists will compress it and make it less effective.
There are some insulation-friendly storage alternatives, but they won’t be covered by grants.
- Add cross-joists so loft boards are high enough to accommodate the loft insulation below. It’s usually a job for a professional joiner.
- Install insulation with a polystyrene or wooden layer on top. If you’ve already got insulation up to 100mm, this is the cheaper and easier option.
How do I fit loft insulation for a flat roof?
Insulation can be installed on top of or below a flat roof It’s a job best done by an expert but there aren't any energy-saving grants to subsidise the cost.
- Warm roof insulation is fitted above the roof deck, the panel below the roofing material. It’s recommended in damp, cold countries like the UK.
- Cold roof insulation goes below the roof deck and joists. You’ll need a gap for ventilation.
For both warm and cold roofs, a weather membrane to protect against rain forms the top layer.
- Inverted roof insulation goes above the weather membrane, protecting it from heat and cold. The top layer is typically gravel.
A good time to insulate a flat roof is when it’s being replaced, although loft insulation can be retro fitted.
How do I find a professional loft insulation fitter?
Visit the National Insulation Association (NIA) website and make sure your chosen roof and loft insulation expert is registered with TrustMark. This is a government-endorsed quality assurance scheme.
Can I get any grants or funding to cover the cost of loft insulation?
ECO (the Energy Company Obligation) says larger energy suppliers must provide funding towards energy efficiency improvements in UK homes. This includes loft insulation and cavity and solid wall insulation. Some of the funding is for people on certain benefits.
Other ways to take control of your energy bills
- Add more insulation! Give your walls and floors the same treatment
- Install draught-proofing around doors, windows and floors
- Read our article with 100+ energy-saving ideas for your home.
- Install a smart meter to keep track of your usage
- Compare energy prices to make sure you’re getting the best deal from your gas and electricity supplier.
