Insulation: Attic, Cavity Wall, External Wall & Grants

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Insulation adds layer to your home to protect you from the cold and the heat! With insulation you could make some significant savings on your heating bills, and your carbon footprint! In our insulation guide, we walk you through all the different types of insulations you can install in your home and how you can even install it yourself!


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What Is Insulation?

A small house energy efficiency rating

Insulation is any material that protects you from both the cold and the heat. There are also insulation materials that specialise in noise reduction, fire protection, and impact resistance.

In this guide, we will strictly refer to the properties regarding thermal insulation for residential homes.

Typically insulation is the material located in between your interior and exterior walls. Here are some common insulation materials found in Ireland which we also cover in further detail below:

Why Is Insulation Important?

With the long, harsh winters we have in Ireland, a properly insulated home can save you a lot of money on your energy bills, avoid uncomfortable drafts, and help with the value of your home.

A poorly insulated house is the equivalent of pitching a tent outside. You can turn the heater on as much as you want, but that heat will just dissipate and your heater will have to be continually running to keep you warm.

The hot summer months will be just the opposite where you will be overheating in your home. You can always turn on the air conditioner, but that cool air will just quickly dissipate outside and have to be running all day to keep you cool.

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What Are the Three Types of Insulation?

The bubble that is your home has many sections that require insulation. Some have a larger impact than others depending on your home, whether it is a flat, semi-detached, or detached home.

Below we look in further detail at the three main types of insulation which are:

  1. Attic insulation
  2. Wall insulation
  3. Floor insulation

What is electrical insulation? As mentioned earlier, there are other types of insulation apart from thermal. Electrical insulation is a material that holds the wires in position and separates them from any nearby structure. Reducing the risk of a fire starting in your home at the same time.


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What is Attic Insulation?

Attic insulation is properly one of the more important places one can invest in home renovations to improve efficiency. As heat naturally rises, good roof insulation will help trap the heat a little longer in your living space. The SEAI calculates a home can lose 20-30% of its heat through its roof if not properly insulated.

Not only is it an area of the home that can dramatically improve your home's energy efficiency, but it is also relatively cheap and easy to install attic insulation.

How Much Does Attic Insulation Cost?

Insulating the attic of a 540 sq ft house would cost around €400-€600 depending on the material used (unless your house has a flat roof, in which case it would cost approximately €1000). Flat roofs are the most expensive to insulate, but also need to be insulated the most as they lose more heat than vaulted roofs and are prone to leaking.

How Much Insulation Do I Need for the Attic?

It’s recommended to install roof insulation with a minimum R-value of 38. An R-value is a measure of an insulation material’s ability to resist conducting heat. The higher the R-value, the better the insulation. The recommended R-38 value typically means that insulation with this value will be approximately 10-14 inches deep.

Did you know? You do not necessarily want to go too high in R-value either. A perfectly sealed home might very well keep all the heat inside your home but, it also means it does not let any air out. A certain amount of natural air circulation is still desired to avoid suffocating or having to open the windows to get sufficient oxygen inside the home.

How Can I Tell If I Need To Improve the Attic Insulation?

A small house with attic rafters

If your home already has some insulation installed but if it’s not getting the job done, you can layer more insulating material over it to bring it up to R-38.

Here are a few simple ways to gauge whether you have the appropriate amount of attic insulation:

  • Is the insulation below the floor joists?
  • Is the insulation unevenly distributed?

If you answered yes to either of these questions, you can quickly and easily improve your attic insulation by adding more over the existing insulation layers. You will want to ensure that the bottom layer hasn’t been compromised from moisture or has completely lost its efficiency.

Other processes, such as installing loose-fill, are doable yourself but are a little more complicated. You can consult a professional for further information or look at available SEAI grants for attic insulation. Homes built before 2006 are eligible and can receive up to €1,500 for an attic insulation project.

Helpful Hint!If your insulation in your attic is between the joists, try to either minimise using the attic for storage or place items to be stored over rooms that have less heating requirements, such as the bathroom. This is because anything placed on the insulating material will compress it and decrease its effectiveness.

Can I Insulate the Attic Myself?

handywoman tape measure left

Since attic insulation is relatively easy to access, it also makes it an area where it is relatively painless to install by yourself. Many stores offer rolls of insulation that are the correct width for standard construction, typically the distance is either 400 or 600mm between joists. Here are the basic steps to follow should you choose to opt to insulate the attic yourself:

  1. Replacing or Adding Attic Insulation
    Determine if you are replacing the existing roof insulation or just adding some on top of the existing one. Remove all old insulation material and let the area properly dry before laying down new material. To know which type of insulation is best for the attic, have a look at our in-depth analysis of the different types of insulation in Ireland.
  2. Determine Desired R-Value
    Select the appropriate thickness of insulation according to the job. Loft insulation rolls typically come in thicknesses of 100mm, 170mm, or 200mm. The thicker the roll, the higher the insulation value will be. Keep in mind that the more R-value you want for your attic, the more rolls you will need. That is because each roll is thicker and is, therefore, shorter in length than thinner insulation rolls. You should also know that the Government has a minimum depth for this type of insulation at 270mm.
  3. Alternatives to Insulation Rolls
    If you have a flat roof, you may opt for insulation boards rather than rolls.
  4. Measure Twice
    You will need to do a little bit of measuring and maths to calculate how many rolls are needed. Measure the length and width of the space which will give you the attic area in square metres. You can then deduct 10% of the amount for the space the joists occupy, you won't be filling 100% of the space with insulating material. Repeat these steps for each roof slant as well, which will give you the total amount required.
  5. Safety First!
    Before handling any insulation material, you will want to wear protective glasses, gloves, and a facemask. A long sleeve shirt, pants, and protective boots are ideal as well. Despite certain materials, like sheep's wool, being 100% natural, you still want to protect yourself from other hazards like rusty nails, splinters, screws, etc.
  6. Lay Material
    Start laying the rolls of insulation or boards in the furthest corner from the access hatch or entry point. Laying a large board across the joists to sit on when installing the material makes it much easier and more comfortable.

Should you come across any pipes, tanks or water heaters in your attic, then you will need to take those into consideration as well. A sensible precaution might be to insulate these items with lagging materials, in order to avoid issues such as a pipe bursting in winter.

How do you use your attic space? It is also important to consider what use you put your attic to: Do you use it as an additional room or just for storage? If you’d like to use it as an extra room then you will also want to insulate the rafters, in order to take advantage of the warmer air rising from below.

How Do I Choose a Contractor To Install Attic Insulation?

If you have any doubts about doing the job yourself, it is best to hire a professional. With so many contractors to choose from, it can make this decision a daunting one. To find a high-quality insulation installer, we suggest you ask potential prospects some key questions before signing any agreements. Here are some questions you should ask prior:

  1. What type of material would you recommend for our attic insulation? Why do you recommend this product over others?
  2. Will the insulation be installed as per the manufacturer's guidelines?
  3. How will the risk of dampness and condensation be avoided?
  4. What will be my home's Building Energy Rating (BER) after the attic insulation is installed?
  5. Does the work come with any warranty?
  6. Does the contractor have any accreditations to show such as being on the SEAI's list of Registered Contractors?

Feel free to add as many questions as required until you feel satisfied with the installer's expertise and accreditations. Remember, if you are planning to use some of the attic insulation grants available, you must choose one from the list of SEAI registered contractors.

What Is Wall Insulation?

question mark

As the name suggests, wall insulation is the material in between the walls which separate the inside from the exterior. The ‘exterior’ can be anything from the outside air, a garage, or your neighbours’ wall.

There are three different types of wall insulation in Ireland:

  • Cavity wall insulation
  • External wall insulation
  • Internal wall insulation

We look in-depth at each type of wall insulation below.

What Is Cavity Wall Insulation?

Cavity wall insulation is by far one of the most cost-effective ways to insulate your house. The majority of Irish houses have cavity walls, which consist of two layers of blocks or bricks with a space in between them.

Insulating them is simple and consists of injecting insulation material directly into the cavity. The injected material usually consists of a combination of polystyrene balls and adhesive. Nowadays, using spray foam to insulate a cavity wall is also becoming common. Materials like Icynene foam insulation are great, but they do tend to be more expensive materials.

How Does Cavity Wall Insulation Work?

A hole is drilled into the walls to be filled and the insulation material is injected. Afterwards, the drill holes are filled in and matched as closely to the surrounding wall as possible, although you may still need to touch up the walls at the injection site.

How Much Does Cavity Wall Insulation Cost?

chubby man piggy bank left

Cavity wall insulation typically costs around €7-€10 per metre, so for a typical semi-detached house costs would run between €550-€950.

As a comparison, should you opt for spray foam insulation, the cost can go up between €20 - €28 per m2. About two to three times the price of other insulation materials available.

If your house doesn’t have cavity walls, fear not as you still have the options of internal wall insulation and external wall insulation.

What Is External Wall Insulation?

After Attic insulation, external wall insulation may be some of the most expensive renovations to do but they also result in some of the biggest gains.

How Does External Wall Insulation Work?

An insulating material is fixed to the outside of your home and used to be quite an ugly addition.

Fortunately, nowadays, there are many colours and finishes to choose from. This means you will add value to your house not just through the insulation, but with the outer appearance improvements as well.

Warning!One drawback of external wall insulation is that you will need to check with the relevant local council authority whether any planning permission will be needed for adding the external insulation.

How Much Does External Wall Insulation Cost?

It can cost up to €14,000 for a standard house and you will have to finance the work upfront before being able to apply for any relevant grant. Once again, there are great grants to be had from the SEAI with values up to €8,000 for a detached house. If you will be looking at renovating the exterior wall insulation, you may also want to look at windows and doors grants as well.

What Is Internal Wall Insulation?

house saving money blue

Internal wall insulation (also known as insulation with plasterboard) is a less expensive way to insulate external walls and consists of fixing insulation material to the inside of the house’s exterior walls, and then finishing it off with plasterboard.

As such it doesn’t affect the external appearance of the house which can be important if you have a brick or stone finish you’d rather not cover, and it also doesn’t require any planning permission (unless you live in a listed property).

It can be done room by room to minimise interruption to your schedule.

It will, however, result in an inevitable loss of space, decreasing the useful square footage, and could therefore possibly detract from your house value instead of adding to it if you decide to sell.

How much does internal wall insulation cost?

With all of these advantages (apart from the loss of living space), internal wall insulation can cost around €80-€130 per square metre. This brings the total renovation cost between €6,300 and €12,000 for a typical semi-detached house.


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What Is Floor Insulation?

As mentioned in the attic insulation portion, heat naturally rises. This means that warm air from the earth's crust is continually and gradually rising to the surface. Unfortunately, by the time it reaches your home, this air isn’t quite as warm as we would like it to be and often can be quite moist. This is where floor insulation can be handy, to protect you against this heat loss.

Improperly insulated floors can add an additional 10% heat loss to your energy woes.

How Does Floor Insulation Work?

Floor insulation is there to protect the cool ground air from entering the home.

Most modern homes have spray foam insulation below the concrete base to reduce heat loss, usually Polystyrene.

If you have an older home, the simplest way to overcome heat loss through the ground floor is to lay carpet with foam backing or a foam underlay. However, this is not always viable for high humid areas, such as bathrooms and kitchens.

Otherwise, insulation can be inserted underneath your floorboards between the joists, but this will require pulling up your floors. Rigid insulation, such as rigid foam insulation, can also be laid on top of the under-floor concrete slab.

Important floor insulation tip Similarly, if you live in an apartment and there is another occupied apartment below you, it’s not necessary to insulate your floors. If neither placing carpet nor pulling up your floorboards sound like viable options to you, you can still reduce heat loss by caulking and sealing any gaps.

How Much Does Floor Insulation Cost?

This will depend on the option you choose. If you opt for an old-fashioned carpet, prices can range anywhere from €7-€32 per square metre.

Polystyrene foam insulation can range from €24-€50 per square metre depending on the thickness chosen.

Which Insulation Material Should I Use?

For just about each of these main renovation projects, you will have to choose between similar materials, each with its pros and cons. We examine in detail the different materials available whether you are looking at the attic, wall, or floor insulation.


Fibreglass is formed from spun glass fibres and is the cheapest insulating material option. It is sold in blankets called batts, or as loose-fill. Here are some of the advantages and disadvantages of fibreglass insulation:

Pros and cons of Fibreglass Insulation
It doesn’t shrinkIs fire and pest resistant.
Doesn’t give the tightest seal.There are some health concerns over inhaled fibreglass particles.

If you decide to install fibreglass insulation yourself, and it isn’t in sealed batts, make sure to wear protective gloves, goggles, and a dust mask.

Fibreglass insulation tip Blown fibreglass also has the additional advantage of being better at filling in any gaps, although it is a little more expensive than fibreglass batts.


There are two types of foam insulation, rigid polystyrene foam boards and spray foam insulation. Here are some of the advantages and disadvantages of foam boards:

Pros and cons of Foam Boards Insulation
Reasonably quick to installOffers high R-ratings per inch
Boards need to be cut very accuratelyR-ratings decrease over time, up to R-1 less per year

Here are some of the advantages and disadvantages of spray foam:

Pros and cons of Spray Foam Insulation
Is better at filling in any gapsAlso serves as an effective vapour and air barrier
Is expensiveHas been linked to health concerns like asthma and lung disease

Sheep’s wool

Sheep’s wool insulation is a trending material as it is considered an environmentally friendly solution. Here are some of the advantages and disadvantages of sheep’s wool as insulation:

Pros and cons of Sheep Wool Insulation
Is natural, non-flammable, and sustainableCapable of absorbing and releasing moisture without losing performance
Surprisingly expensive even without the installation costsLower R-rating than other materials


It may seem like a misnomer, but this insulation material does look like wool - except, of course, it’s made from rock, in a complicated heating and spinning process (think candy floss). Here are some of the pros and cons of Rockwool insulation:

Pros and cons of Fibreglass Insulation
Doesn’t have any associated health risksIt’s highly water repellent and it doesn’t degrade over time.
Costs more than fibreglassNot a biodegradable product


Cellulose is one of the oldest forms of building insulation and over the centuries has consisted of newspaper, cardboard, straw, and hemp, to name a few materials. Cellulose products come as loose-fill or spray products. Here are some of the pros and cons of cellulose insulation:

Pros and cons of Cellulose Insulation
Effective at filling in gapsOne of the more affordable materials
Not as effective as foam insulationNot the highest R-rating performers

Summary of insulation materials

We outline below a summary of the different insulation materials available so you may have a quick and easy comparison.

Summary of insulation materials
Fibreglass Batt3.1 - 3.4Cheapest way to insulate. No issues with inhaling particles.Not as good as loose-fill at filling gaps. Compresses over time.
Fibreglass Loose Fill2.2-4.3Economical. Great as filling in all gaps.Health concerns regarding inhaling particles. Slightly more expensive than batts.
Foam (Polystyrene Board)3.8-5.0Mid-priced (cheapest foam option).Needs to be cut very accurately to be effective.
Foam (Spray, Open Cell)3.5-3.6Effective at filling all gaps. Effective air and vapour barrier.Expensive. R-ratings decrease over time.
Foam (Spray, Closed Cell)6.0-6.5Effective at filling all gaps. Effective air and vapour barrier. Highest R-rating for foam insulation.Expensive. R-ratings decrease over time.
Sheep’s Wool3.6-4.3Natural and biodegradable. Effective acoustic insulation.Very expensive.
Rockwool3.1-4.0Sustainable. Effective acoustic insulation. Doesn't degrade over time.Very expensive.
Cellulose3.2-3.9Economical. Very light. Effective acoustic insulation.Not as effective as foam.


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Are There Any Insulation Grants?

A piggybank with piles of notes and coins beside it

Any of these renovation projects involves a hefty investment. Luckily, during these hard economic times and energy crisis, the Government has stepped up and made available generous attic insulation grants, cavity wall insulation grants, internal insulation grants, and external wall insulation grants.

In an effort to reach the Paris Agreement 2050 carbon emission targets, the Government has made these series of grants available to help lower the financial burden these renovations have.

Anybody who owns a house that was built before 2006 can apply to the SEAI for energy upgrade grants.

For the insulation grants to be issued, all upgrades must be made by an SEAI Registered Contractor who is registered for the specific type of work they’ll be carrying out on your home. They must also agree to a contract with you for the work to be done before starting.

Have a look at your eligibility for these grants prior to starting any work on your insulation as you could very well have the bulk of the cost covered.

If you still have doubts about which home energy savings renovations to do, you can explore some of the following guides which cover other options:

Concerned about all the required paperwork to fill? Don’t fret! You can now contact any of the SEAI’s energy partners who are licensed to both carry out the work and deal with the paperwork on your behalf.

The services and products mentioned on this website may only represent a small selection of the options available to you. Selectra encourages you to carry out your own research and seek advice if necessary before making any decisions. We may receive commission from selected partner providers on sales of some products and/or services mentioned within this website. Our website is free to use, and the commission we receive does not affect our opinion or the information we provide.

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