I remember the 1970s energy crisis, the spiralling costs, blackouts, and petrol shortages.
Today, a whole new generation is trying to save energy. The challenges are different from those of the 70s, but the goal is the same — reduce our energy costs and carbon footprint.
As the Insulate Britain campaign has made painfully clear, one way to achieve this is by insulating our homes. So, in this guide, I will show you how to insulate your house and save on energy bills.
Note: This is a comprehensive guide to home insulation from the bottom up, so only some parts will apply to your situation.
Cut Energy Bills and Save the Planet
Let’s start by looking at the familiar sources of heat loss.
Where Heat Loss Occurs
The diagram below shows the areas where most heat escapes in a typical uninsulated house.
There is a vast range of insulation materials on the market. Here are the main types:
- Glass fibre
- Mineral wool
- Spray foam
- Rigid foam board
- Polyurethane (PU)
- Polyethylene (PE)
- Polyisocyanurate (PI)
- Expanded polystyrene (EPS)
- Extruded polystyrene (XPS)
- Cellulose Loose fill
- Reflective foil
- “Green” products
- Recycled materials — products with a former life
- Compostable materials — products that will rot down
I’m not going to discuss all of these, you’ll be pleased to know, but it’s essential to understand the different forms of insulation available today. You will find a list of products and their potential uses at the bottom of this guide.
R-values and U-values
The R-value of a material is its thermal resistance, i.e., its resistance to heat passing through it.
You may have heard the term ‘U-value’, which is calculated by adding together the R-value of each component. This formula applies to all elements of a house structure — walls, roofs, floors, windows, etc.
For example, a brick wall made up of two leaves of brick, a plastered inner leaf, and a 50mm cavity has a typical U-value of 1.5 (we won’t bother about the units at this stage, but the smaller the figure, the better). This U-value is calculated from the R-value of the bricks, plaster, and air space (even air has thermal resistance!).
Inserting insulation into the cavity may reduce the U-value to below 0.2 (0.3 is the requirement under Building Regulations). Read my guide to cavity wall insulation costs to learn more about this.
Note: R-values depend on thickness, so as the thickness of the material increases, the U-value reduces.
Living in a Conservation Area
If you have a listed building or live in a conservation area, you’ll be limited by the style of doors and windows you can choose. You’ll also be limited by the materials you can use, but there’s always something you can do to insulate your house and reduce energy costs.
Check out the rules in your local area and speak to the planning authority before starting any work.
Costs and Savings for Typical Insulation Measures
The table below compares the cost of insulating a typical semi-detached house against the annual energy savings. This table gives you some idea of payback periods.
|Material||Cost (£)||Saving/year (£)|
|Loft insulation top-up||250||15|
|Wall insulation — cavity||475||160|
|Wall insulation — outside||5,000 to 18,000||260|
|Wall insulation — inside||3,000 to 14,000||260|
|Solid floor insulation||950 to 2,200||40 to 55|
|Suspended floor insulation||300 to 750||40 to 55|
Tools and Materials
The tools you’ll need depend on what you’re insulating and the materials you’ll be using, but here’s an essential list for most tasks.
- Box knife
- Keyhole saw
- Combi drill
- Masonry and wood nails
- Assorted screws and washers
- Insulation materials (see options above)
- Timber battens
Health and Safety Measures
Many insulation materials irritate the skin and eyes, so always wear gloves and eye protection when handling these materials.
Furthermore, breathing in tiny fibres and fumes harms the lungs, so I recommend wearing a P3R face mask too.
How To Insulate Your House — Step-by-Step Instructions
There are many options for insulating your house, so it’s impossible to include everything in this guide. I’ve provided the most cost-effective methods in the four steps below.
Step 1: Floor
With 15% of the total heat loss from your home passing through the floor, adding insulation in this area offers significant energy savings.
However, most heat loss is around the perimeter if you have a solid concrete ground floor. So for a large floor area, only a tiny amount will transfer heat to the outside. In this case, a thick pile carpet with a good quality underlay is all you need.
If you’re considering installing laminate flooring, choosing suitable underlay is essential. For thermal insulation, we recommend expanded polystyrene (EPS).
For suspended timber floors, add insulation between the joists. A rigid board is best because it can be firmly wedged in and then held in place with timber battens.
Note: As suspended floors need ventilation underneath, sealing around the edges is vital to prevent draughts.
Step 2: Walls
Most heat loss in your home is through the walls (around 35%), so it makes sense to focus on this area when looking at ways to save money.
Often it’s necessary to treat dampness in a wall before doing any insulation work. Adding insulation will reduce the chances of damp reoccurring, but you must remove any existing mould or fungal spores.
There are 3 ways to insulate a wall: externally, internally, and inside the cavity (if there is one).
This method is favoured by housing associations managing old council house stock, as external insulation becomes cost-effective if they can insulate multiple homes at once — usually a complete estate.
External wall insulation involves fixing insulation to the wall and applying a render or cladding system over it. Typically, a 100mm layer of rigid foam or 110mm mineral wool batts will bring the U-value of a solid brick wall down to around 0.3.
This method radically changes the appearance of your home, so you will need to check with your local authority to see if you need planning consent.
Battening a wall and adding insulation before plasterboarding is a good way of reducing the U-value, and it’s a relatively simple project. It will, however, be necessary to call in a professional to move or adjust any electrical fittings.
This option is another one for the pros. Insulation is blown or injected into the wall cavity, and the entry holes are sealed with cement that is coloured to match the brick.
The table below shows the most common materials for cavity wall insulation and their respective R-values. I’ve provided costs for comparison only.
|Insulation||R-value per 25mm||Cost|
|Blown mineral fibre||3.8||£|
You can learn more about these materials in our guide to cavity wall insulation.
Pro Tip: If the cavity is already filled, but the insulation is failing, read our guide to removing cavity wall insulation.
Step 3: Doors and Windows
Energy-efficient glazing and high-performance external doors are crucial in reducing your energy bill. The Centre for Sustainable Energy has produced plenty of information on this topic. Below are a few top tips from their website:
Changing your external doors to something more energy efficient is an excellent way of cutting energy costs. However, in many cases, all that’s needed is proper draught-proofing. Simply filling in gaps can save around £60 per year (if you include windows), according to the Energy Saving Trust.
If you’re considering changing your front door, look for a composite door made from a mix of uPVC, timber, and glass-reinforced plastic. These high-performance doors come complete with the frame, already sealed and weather tight.
There is only so much a DIYer can do to improve the performance of their windows.
There are types of secondary glazing that you can install without significant expense. However, some are much better than others, so it’s worth shopping for a high-quality system that fits your budget.
As with doors, ensure your existing windows are fully draught-proofed before spending a lot of money replacing them.
Sometimes the seal breaks around a double-glazed unit, resulting in a misty look. Not only is this unsightly, but it will also affect the window’s energy rating. You can fix this issue using one of the many specialist companies advertising this service.
Consider changing the glass to a low-emissivity (low-E) type. This glass has a thin metal-oxide coating that reflects heat while allowing light to pass through.
Some double and triple-glazed units have argon gas in the gap between panes, which has a better R-value than air.
If the frames are sound, you can change the glass without too much trouble. If not, consider replacing the lot.
Modern frames are made of thermally efficient materials with integral thermal breaks which prevent heat transfer through the frame itself. Fitting these frames is a job for professionals.
You must also consider condensation. By closing off all pathways for heat to escape, you also prevent air from entering the building. The key is to control the airflow into your house using trickle vents in windows.
Having a conservatory that you’re not heating can be beneficial. I.e. the glass wall enclosure and roof help insulate the connecting wall if you close off the conservatory during cold weather.
For those who like to sit in a conservatory, even on cold days, there are still things you can do to cut down your heating bills.
- Ensure your glass is as efficient as it can be.
- Add secondary glazing, blinds, or thick curtains.
- Change the roof from glass to tiles and introduce a layer of insulation.
Check out our cost guide to insulating a conservatory for more information.
Step 4: Roof
If you have a pitched roof with an accessible void above the ceiling (loft or attic), you have several cost-effective options.
The most common way of insulating your loft space is to lay a glass fibre or mineral wool quilt between the ceiling joists and another layer across the joists.
When adding insulation to the loft space, you must be careful not to create other problems. The tendency is to tuck the insulation into the eaves, which cuts off the airflow pathway. However, if you don’t do that, you could get a cold bridge where the loft insulation stops short of the cavity wall insulation, resulting in staining.
To overcome the problems caused by still, moist air, fit roof vents on the cold side of the insulation and install condensation traps around vent pipes.
In older houses without felt underlay (the layer of material fixed between the rafters and the battens), spray foam insulation is a good option.
Spray foam reduces heat loss through the roof tiles and binds them together, holding them in place. A word of warning, though — don’t rely on this to make your roof watertight. You must first fix/replace any loose/broken tiles.
If you had your loft insulated 20 or 30 years ago, don’t assume it’s still good. Standards were much lower back then, and the 50mm fibreglass is probably powder now. Check out our guide on how long loft insulation lasts to learn more.
If you want to use your loft as a room at some point, you can fit the insulation between the rafters. You may need netting or battens to hold it in place, or you could line it with plasterboard.
For more tips on installing loft insulation, check out the video below from Homebuilding and Renovation:
Flat roofs are more challenging because the choices are limited, and access can be problematic.
The two primary options are to insulate the underside or to add rigid insulation above the roof covering.
Insulate the underside
This method is known as cold roof construction and involves fixing polystyrene tiles or similar lightweight insulation to the ceiling.
This approach was common practice in the 1970s when the first oil crises hit, and energy costs went through the roof (pun intended). However, 20 years later, homeowners removed them because they presented a fire hazard.
To avoid fire safety issues, batten out the ceiling first, and fix the insulation between the battens and plasterboard below. This method is also great for hiding unwanted Artex finishes and damaged ceilings.
Insulate the top
This method is known as warm roof construction, where you lay the insulation on top of the roof covering.
First, remove any stone chippings on top of the roof to expose the roof covering. Inspect the covering and carry out any repairs before laying down the insulation board.
To stop the insulation boards from flying off in high winds, lay 50mm of loose stone over them.
Final Thoughts — How To Insulate Your House
As we’ve seen in this guide, many options are available when insulating your house. Some might not be practicable, but there is always something you can do to improve your home’s energy efficiency.
Some of the work you can do yourself, but you’ll need a specialist for the larger projects. For contractors in your area, check out Rated People.
Pro Tip: Some energy providers offer free insulation or assistance through the government’s Energy Company Obligation (ECO) Scheme. To determine if you qualify, read this handy Which? report.
I’ll finish with one more energy-saving tip that won’t cost you a penny. If you have a condensing boiler, drop the temperature of the water flowing out of the boiler to 60⁰C, the temperature at which the boiler condenses water vapour. This adjustment enables it to recover heat, which would otherwise disappear up the flue. You’re welcome 🙂
Here’s a list of insulating materials with examples of where you’d use them.
|Spray foam||Can||Edges||Draught proofing|
|Expanding foam||Tape||Edges||Draught proofing|
|Polyurethane (PU)||Rigid foam board||Below||Internal||Flat|
|Polyisocyanurate (PI)||Rigid foam board||Below||Internal||Flat|
|Expanded polystyrene (EPS)||Rigid foam board||Above or below||Flat|
|Expanded polystyrene (EPS)||Beads||Cavity||Pitched|
|Reflective foil||Roll||Above||Internal||Pitched or flat|
EPA estimates that homeowners can save an average of 15% on heating and cooling costs (or an average of 11% on total energy costs) by air sealing their homes and adding insulation in attics, floors over crawl spaces and basements.How do you insulate a house for energy efficiency? ›
Insulating finished and unfinished attic spaces, rafters, walls, and ceilings is essential for optimal climate control and energy efficiency. This kind of insulation is often done using fiberglass batts or blankets, loose-fill insulation, or both.What is the best way to insulate your home? ›
Internal wall insulation is done by fitting rigid insulation boards to the wall, or by building a stud wall filled in with insulation material. External wall insulation involves fixing a layer of insulation material to the wall, then covering it with plasterwork or cladding.Is it worth it to insulate your house? ›
Unless your home was specially constructed for energy efficiency, you can probably reduce your energy bills by adding more insulation. Many older homes have less insulation than homes built today, but even adding insulation to a newer home can pay for itself within a few years.Can you have too much insulation in your house? ›
It is possible to over-insulate your house so much that it can't breathe. The whole point of home insulation is to tightly seal your home's interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers. That's when mold starts to grow.How much warmer is a house with insulation? ›
How many degrees of difference insulation makes on its own depends on the type of home you have, what the weather is like and what kind of insulation you have. Depending on what you choose, you could see a five- to 20-degree temperature difference just based on the insulation alone.What is the most energy saving insulation? ›
Spray foam insulation is the most energy-efficient insulation to create an air barrier in the attic. Certain spray foams can expand up to 100 times its original size, so it fills all of the nooks and crannies in the attic.What is the highest efficiency home insulation? ›
- Fibreglass. Fibreglass is the most widely used insulating material these days. ...
- Cellulose. Cellulose is made from recycled paper products and isn't just an efficient insulator, it's very environmentally friendly. ...
- Mineral wool. ...
This type of insulation material is widely available and comes in various shapes and sizes. For cold climates, Loose-fill Fiberglass Insulation is the best as it has an R-Value of 60.
Cracks in Walls, Windows and Doors
Around 38% of heat loss in your home comes from cracks in your walls, windows and doors (often invisible to the naked eye). In fact, a ⅛ inch gap under a 36-inch wide door will let as much cold air into your home as a 2.4 inch hole through your wall.
Interior insulation is cost effective, but can reduce usable space and doesn't protect against water. Exterior insulation is expensive and susceptible to insects. Regardless of the insulation choice, efficiency, toxicity and resiliency must all be taken into account as well.Where is the most cost effective place to insulate? ›
Bottom line, insulating the ceiling and attic areas is by far the number one best way to improve the comfort of your home. The greatest comfort benefits and energy savings will be seen by adding insulation to the ceiling areas.What are the disadvantages of insulation? ›
- Should be installed by professionals.
- More expensive than other types of insulation.
- Must vacate your home for at least 12 hours during installation.
- Poorly mixed chemicals can lead to health risks and ineffective insulation.
If you are deciding between insulating the roof deck or the ceiling, Insulating your ceiling should be the priority. Not only is it easier but ceiling insulation is beneficial in a number of ways: Keeps the temperature in the building regulated. Saves on energy costs.Should you insulate walls in old house? ›
Interior Wall Insulation in an Old House
If a house's attic (or roof) is already fully insulated, adding insulation to the walls may be the single best way to reduce heating and cooling costs.
As for attic vs. wall insulation, always go for the attic. The largest pay back will be seen here. You would stop heat loss from natural convection and block solar gain (an increase in heat) in the attic, which can result in energy savings of 30 to 50 percent.How many years does insulation last in a house? ›
Typical Insulation Lifespan
The International Association of Certified Home Inspectors states that spray foam insulation, wrap tape and housewrap insulation can last for more than 80 years. At the same time, cellulose, loose-fill, foamboard, loose fill and rock wool insulation can last up to 100 years.
Exposure to some insulation products can cause certain health effects if the product is mis- handled, mis-applied, or if the wrong product is used in certain environments. Common symptoms may include irritated, itchy, watery, or burning sensation of the eyes, nose, or throat, or itchy skin or skin rashes.What is the cheapest way to heat your house? ›
Natural gas is likely to prove the cheapest way to heat a home if you have this heating option available to you where you live. Although prices have risen, natural gas is the least costly form of space heating. This is followed by electricity, propane, and heating oil, from the next cheapest to the most expensive.How cold should I let my house get? ›
The World Health Organization (WHO) recommends indoor temperatures of at least 64°F (you can drop that down to 62°F at night if you're really looking to save on your heating bill). But if you have infants, sick or elderly people in your household, then it's recommended that you keep the thermostat set at 70°F.
Blood vessels become constricted, breathing becomes shallow and it puts extra pressure on our cardiovascular system to get our body temperatures regulated again, she adds. If your bedroom temperature is lower than 60° F, it's too cold.What is the cheapest insulation method? ›
The most common form of home insulation is the “batt and roll” or “blanket” type, which is the least expensive to purchase and install.What is the cheapest most efficient insulation? ›
Expanded polystyrene (EPS) is a premier material for protecting homes, foods and sensitive materials because of its cost-effective, efficient insulation qualities. In fact, EPS leads the pack when it comes to R-value per dollar.What is the cheapest and easiest insulation? ›
Batt, or roll, insulation is one of the most inexpensive types of home insulation and one of the easiest to install, especially for DIYers.What is the number one material for insulation? ›
Fiberglass. Fiberglass consists of extremely fine glass fibers and is one of the most ubiquitous insulation materials. It's commonly used in many different forms of insulation: blanket (batts and rolls), loose-fill, and is also available as rigid boards and duct insulation.What makes the best insulation? ›
Polystyrene and plastic foam are both used as insulators as they have small air bubbles trapped inside them. This makes them very good insulators because heat energy can't flow through them.What is the thinnest insulation with the highest R-value? ›
Aerogel insulation offers the highest R-value of any insulating material at less weight and thickness—ideal for construction, refineries, pipelines, and thin-gap thermal barriers.What is the new type of insulation? ›
The new insulation consists of MAI panels completely encased in polyiso. The composite has at least two advantages over the vacuum panels that have been on the market for decades: they're much cheaper to make, and they should last for 25 years without a significant decline in R-value.What do you do before insulation? ›
- Clean Up Your Attic. One of the first things that you will want to do before you get your attic insulated is to clean up the attic. ...
- Check for Water Leaks. ...
- Box Out Your Light Fixtures. ...
- Check That Exhaust Fans a Facing Out. ...
- Call A Professional.
Looking up your type of insulation will allow you to determine if it should be replaced or increased in its R value. A home energy audit may find that the walls are actually the most significant cause of heat loss in your home.
Did you know that most of an average homes heat is lost through your windows and doors? Up to a staggering 40% of your homes energy escapes straight out of the window , that is more than the amount lost through the walls and roof.Where not to insulate? ›
Never place insulation close to water heaters, oil burners or anything hot. The backing is especially flammable and will be a major fire hazard for your home.How to insulate an old house cheaply? ›
- Apply a house wrap/vapor barrier to exterior walls.
- Attach 1-inch foam board insulation.
- Install siding over the insulation.
- Replace old windows with energy-efficient units.
- Caulk window trim and use weatherstripping to reduce air leaks.
Proper insulation will help keep your bathrooms a comfortable temperature year-round. Bathroom projects need special consideration because of the humidity and moisture that bathrooms generate. When moisture becomes trapped in walls, mold and mildew can grow, damaging your home and presenting a potential health danger.Which part of the house needs most insulation? ›
Attic. Arguably the most important space in the home to insulate is the attic. This is primarily because heat naturally rises, which means that the attic will hold a lot of the heat generated in the home. During the winter, having that heat escape through the attic will push up energy bills.Where is insulation needed the most? ›
The key areas of your home that need insulation are the attic, roof and exterior walls. Additionally, up to 10% of heat can be lost through the floor of a home with no underfloor insulation. Attic or roof insulation can save you the most in energy bills and is a key area to insulate.What type of insulation is most expensive? ›
Spray foam insulation is the most expensive insulation, and it is available in open cell and closed cell options.What problems can lack of insulation cause? ›
Heat travels from warm to cool air, so improper insulation can cause your heating bills to skyrocket in the winter. Poor insulation can force you to choose between paying enormous heating bills or walking around your house bundled up all winter long. You may even find yourself avoiding the top floor of your home.What is the downside to foam insulation? ›
Mold and mildew can begin growing behind the insulation which can go unnoticed until it's already become a huge problem. This often happens when the spray foam isn't installed correctly and space is left between the insulation and the wall, which allows moisture in and gives mold the perfect place to grow, unfettered.Does insulation stop electricity? ›
Insulation is a material or substance that prevents the transfer of electricity or heat between two objects.
Insulation stops heat escaping from living spaces, so it will make your loft space cooler, which could introduce or worsen existing damp or condensation problems. If you are installing loft insulation yourself, please keep in mind that you may need to increase ventilation.Why don't you insulate the roof? ›
If you install roof insulation, all the heat energy your HVAC generated will rise and become trapped in the attic. Not only will this cause damage in your attic and to your roof through trapped moisture and heat, but it reduces the efficiency of your HVAC.How do you insulate a room without removing drywall? ›
You may add insulation to your walls without removing it by cutting holes into the siding. You can blow spray foam or cellulose into the walls from outside. Just cut a 1 inch to 2-inch hole between the studs at the top of the wall and then spray the insulation into the hole using a hose.Why don t builders insulate interior walls? ›
In most cases, interior walls are not insulated during construction. Unlike exterior walls, which must meet local and state codes for insulation, interior wall insulation is rarely required. This is because interior insulation has much less impact on your home's energy efficiency – but it can still play a role.Why do older homes not have insulation? ›
Houses built before 1940 were rarely insulated, and if they were the products originally used may have settled or deteriorated over time, allowing heat to escape and the cold air to creep in. Common places where your house may be losing heat—such as the walls, roof, and attic floor—are good targets for insulation.Is it bad to put too much insulation in walls? ›
It is possible to over-insulate your house so much that it can't breathe. The whole point of home insulation is to tightly seal your home's interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers. That's when mold starts to grow.How much electricity can insulation save? ›
On average, you can save up to 20% on your home's heating and cooling costs or up to 10% on its total energy costs by adding insulation to attics, floors, crawl spaces, and accessible basement rim joists, and by reducing unwanted air leaks all around your house.Is it worth insulating an old house? ›
It will improve the energy efficiency of the property. Reduce your heating bills. It will allow your home to hold onto its heat longer. You'll make it more comfortable to live in.What are 2 benefits of insulation in the home? ›
Insulation will help you keep the desired temperature in your house all year round, protecting it against cold in winter and excess heat in summer. Insulation is also useful to reduce noise pollution. A well-insulated house is very energy efficient and will need very little additional heating and cooling.What has the highest insulation value? ›
Vacuum insulated panels have the highest R-value, approximately R-45 (in U.S. units) per inch; aerogel has the next highest R-value (about R-10 to R-30 per inch), followed by polyurethane (PUR) and phenolic foam insulations with R-7 per inch.
Typical Insulation Lifespan
The International Association of Certified Home Inspectors states that spray foam insulation, wrap tape and housewrap insulation can last for more than 80 years. At the same time, cellulose, loose-fill, foamboard, loose fill and rock wool insulation can last up to 100 years.
Asbestos: Asbestos is generally heat resistance, but if heated excessively asbestos loses its hygroscopic moisture and therefore becomes brittle. Asbestos absorbs moisture from the surrounding atmosphere which makes it a less effective insulator.What is the best insulation for older homes? ›
The best insulation for an older home that has a lot of drafts is going to be a material that creates an air seal. Spray foam and injection foam are the best options when it comes to making your home energy efficient and comfortable.Should I remove old insulation or just add more? ›
Expert contractors that specialize in insulation advise that removing old fiberglass insulation is best before installing new cellulose insulation because of possible mildew, mold, or rodent excrement.Which is better blown in insulation or foam? ›
Unlike blown-in insulation that can lower your energy bills by 25%, with spray foam insulation in your building you can profit from a 40% decrease on your monthly energy bills. Spray foam has the ability to expand 30-60 times the volume when installed, therefore it can seal all gaps and cracks on your walls.What part of house is most important to insulate? ›
Arguably the most important space in the home to insulate is the attic. This is primarily because heat naturally rises, which means that the attic will hold a lot of the heat generated in the home. During the winter, having that heat escape through the attic will push up energy bills.What provides better insulation? ›
Foam Board or Rigid Foam
They provide good thermal resistance (up to 2 times greater than most other insulating materials of the same thickness), and reduce heat conduction through structural elements, like wood and steel studs.
An insulating material's resistance to conductive heat flow is measured or rated in terms of its thermal resistance or R-value -- the higher the R-value, the greater the insulating effectiveness. The R-value depends on the type of insulation, its thickness, and its density.