Home insulation: How to insulate a house

What does insulation do?

Insulating your home is one of the best things you can do to save on your energy bills. Although there is an initial outlay, the long-term benefits can’t be beaten to prevent heat loss. As well as protecting your home against the cold, it’ll help keep it cool in the summer months. When it comes around to reducing heat loss in the winter, you’ll save money on energy bills, reduce your energy consumption and therefore also your CO2 emissions.

How much heat is lost without insulation?

Different places in your home lose different amounts of heat. The following are approximate /average figures.

• Walls – 30-40%
• Roof – around 25%
• Windows and doors – around 20%
• Lowest floor – around 10%.

A sizable loss will occur because of draughts, excess ventilation and lack of airtightness –and draughts can also be attributed to floors, doors and windows, the walls or roof.

Types of home insulation

There are myriad ways to insulate your home, some good, some not so good. All insulators are essentially attempting to mimic the genius of sheep’s wool with its capacity to trap the air within tiny pockets of the material itself. All types of insulation are given an ‘R-value’, which is a measure of how well it resists the conductive flow of heat. R-values can range from 1* (glass wool) to 39* (polystyrene).

However, there are other factors to consider when assessing materials, alongside heat resistance. These include physical strength, fire resistance, mould resistance, and non-toxicity. Cost is also another important consideration, and where or what you’re insulating, so here’s a rundown of some good insulators and their benefits:

• Mineral and glass wools
  This material is the most popular home insulation solution and is sold in rolls like a blanket. Alternatively, you can get what they call ‘batts’, which are thicker slabs that you can slot in between joists. Higher density batts are available for up to 25% better insulation.
• Hemp and cotton
  Just as natural as sheep’s wool and just as effective. Hemp is also a cheap and very sustainable way to do it. Available in roll and slab form.
• Wood and wood-based products
  Wood has always been a great insulator – it’s essentially why doors are made of wood. For loft insulation, MDF, plywood, and hardboard are the better materials to choose from.
• Recycled paper and plant cellulose
  Another wood-based product; recycled paper. Plant cellulose also does a great job at insulating your home, which is equally sustainable, coming from crop waste. Once they’ve been treated to make them fire-resistant, they’re great insulators that are perfect for stuffing in tight spaces.
• Polystyrene
  The kind of polystyrene you’re thinking of (the one that’s used for packaging and cups) wouldn’t be a good insulator, but this denser polystyrene is actually 50% more effective than mineral or glass wool – and it’s also fire-resistant. Polystyrene insulation is sometimes known as EPS (expanded or extruded polystyrene slab) and is often used in floor insulation.
• Spray foam
  Spray foam is great for filling in crevices and gaps when nothing else will do it. It’s usually polyurethane-based and the final foam is made by mixing two chemicals together which starts a hardening process. This traps tiny pockets of air, thus acting like the sheep’s wool or mineral wool. Foam is great for getting rid of draughts around door frames for example, and actually strengthening roof tiles and other structures. Remember, this is not a quick-fix or cover-up solution. We recommend to always use a reputable installer and ensure the roof is dry and in a good condition before insulation is added.
• Papier-mache mastic
  Crazy but true; one of the cheapest types of ‘insulators’ is papier mache and it works by stopping the flow of air (draughts) through cracks and gaps. You can DIY papier-mache with torn-up paper and wallpaper glue.
• Foil
  Heat can be reflected, and so multi-foil products combine metal foils with plastic to reflect heat. These types of products are great for places where there isn’t space for wool, big batts or EPS. Some polystyrene products are also coated with foils.

Ways to insulate your home

We’ve provided a list of different areas within the house you may need to look into insulating. Let’s dive into the different insulation options available to you:

1. Insulate the loft

Loft insulation will last you at least 40 years and it should pay for itself many times over. For example, the Energy Saving Trust says a standard installation for a semi-detached house is around £300 and you’ll save £150 a year. So in 2 years you’ll be making money on it. If your loft is easy to access and has no damp or condensation problems – in most cases – it’s a simple enough job to DIY.

How to insulate your loft: Standard installation

Most new-build homes will be up to standard with loft insulation but if you have an older building it’s worth taking a look at how to improve your energy efficiency with loft insulation. Mineral wool insulation can be used to insulate between regular loft joists like so:

• Lay the first layer between the joists – the horizontal beams that make up the floor of the loft.
• Then lay another layer at right angles to cover the joists and make the insulation up to the required depth – it needs to be 270mm (27cm) deep.

If you want to use the loft for storage, you’ll need to lay boards over that extra layer of insulation. There may need to be some clearance between the insulation and the board to prevent condensation, so additional work to raise the boards will need to be completed.

Warm loft

Another way is to create a ‘warm loft’ by insulating between and over the rafters, i.e. the sloping timbers that make up the pitched roof itself. This will give you maximum warmth and also take the maximum chunk out of your wallet. Your home will be toasty warm as long as you insulate all gable walls, party walls and chimneys – don’t leave a surface uninsulated, otherwise, the heat will find a route to bypass your new insulation, giving you a shoddy return on investment.

Bear in mind that creating a warm loft is a job for the pros, not a DIY pastime, as your installers will need to either spray foam insulation between the rafters or lay rigid insulation board.

Room in the roof

If you want to convert your loft into a room, or it’s already being used as a living space, you need to make sure you insulate all the walls and ceilings between that heated room and any unheated space, plus full insulation around dormer windows or skylights.

Again, this isn’t a DIY job. You’ll need a professional installer to ensure a proper and complete insulation job is carried out, and ventilation is adequate.

Inaccessible loft spaces

If your loft is largely inaccessible, you can have blown insulation installed by a professional. This means they use specialist equipment to blow appropriate insulation material into awkward spaces, using mineral wool fibre, treated cellulose or polyurethane foam.

Flat roofs

If you have a flat roof, a common practice is to actually insulate it from above. The best advice is to do it when it’s time to replace the roof covering – you’ll have to insulate it anyway, to comply with current building regulations.

It’s possible to insulate a flat roof from underneath, but if it’s not done properly you can end up with condensation problems. The good news is that it can save you similar amounts on your heating bills to standard loft insulation.

2. Cavity wall insulation

Installing cavity wall insulation involves injecting insulation material into the void between the inner and outer layer of brickwork to form an effective barrier that guards against heat loss. It works like a flask, creating a layer around your home, and is a great option if your budget is relatively small. Read how to install cavity wall insulation for more information.

3. Floor insulation

An uninsulated concrete subfloor can absorb up to 30% of your home’s heating. Wooden, carpeted and vinyl floors can all be insulated underneath if you are renewing them. If you have a tile floor, consider a rug, as the tiles are laid on top of that super-absorbent concrete. We have a more detailed how-to guide on installing floor insulation if you’re interested in learning more.

4. Windows and doors

A professional installer will draught-proof your home for around £200, but you can draught-proof your windows and doors very cheaply yourself. For windows, pop down to the DIY shop and get yourself some draught-proofing strips. Size up your gaps so you get the correct size of the strip.

For doors, there are a few more options:

• Keyhole – buy a purpose-made cover that drops a metal disc over the keyhole.
• Letterbox – use a letterbox flap or brush. Make sure you measure your letterbox before you buy.
• Gap at the bottom – use a brush or hinged flap draught excluder.
• Gaps around the edges – fit foam, brush or wiper strips like the ones used for windows.

5. Water tanks and cylinders

Did you know you can insulate your water tank and cylinder? It’s so easy and quick to do yourself; you just need to buy a British Standard cylinder jacket, which you can pick up for under £20. Coldwater tank jackets are equally as cheap. Find out all the details in our how to insulate your water tanks and cylinders article.

Do I need planning permission for insulation work?

Planning permission is usually not required for loft, floor and door insulation, however in some areas external cavity wall insulation and double glazing may require planning permission. It’s best to always check with your local authority if building regulations apply.

Home insulation grants

Free home insulation is very nearly a reality in the UK, with a new government grant scheme launching in England at the end of September 2020. If you’re in Scotland, check out the Warmer Homes Scheme, in Wales the Nest scheme and in Northern Ireland, see the Affordable Warmth Scheme.

Green Homes Grant

England’s Green Homes Grant is a government voucher scheme that contributes up to £5,000 or £10,000 to help cover the cost of making energy efficient improvements to your home.

How does it work?

Both homeowners and landlords are eligible to apply, and the scheme stands to help you save up to £600 a year on your energy bills. Unfortunately this scheme has now ended but if you applied before March 31st 2021 your application will still be processed. How this scheme worked:

You may be subject to an assessment, eg. to answer questions such as:

• Where your home is and isn’t properly insulated
• What type of insulation you currently have
• The R-value and the thickness or depth (inches) of the insulation you have

Keep your home cosy

Now you’re armed with the best ways to keep your house cosy and warm through insulation, don’t forget to protect yourself and your family by keeping your boiler in check with our range of gas and boiler cover options.

Outside of home insulation, there are many other ways to save energy. Why not check out HomeServe’s energy saving tips for the home to see how else you can be saving money.