Insulation: Attic, Cavity and External Wall

By David Tait

Editorial Manager

Proper use of home insualtion including attic, cavity and external walls can help you save money on your home heating bills while also reducing your carbon footprint. The average cost of insulating your home costs from €2,000 to €4,000 depending on the size of your home, the material you choose and the extent of the project. Homeowners can benefit from SEAI gants to help fund home insulation.

What Are the Three Types of Insulation?

Given Ireland's climate, it's important to properly insulate your home in order to reduce the demands on our home heating systems.

Properly insulating your home is the key to maintaining a comfortable indoor environment while also reducing energy consumption from heating and environmental impact.

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

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

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.

What is the Best Material for Attic Insulation?

The best insulation for attic spaces include:

• Fibreglass insulation - easy to install, as it simply has to be rolled out and laid onto the attic floor.
• Cellulose insulation - this type of insulation is made from recycled paper so it can pose a greater fire risk,
• Spray foam insulation - this form of insulation should be sprayed by a professional onto stiff foam boards.

Can I Insulate the Attic Myself?

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.
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.
3. Alternatives to Insulation Rolls
   If you have a flat roof, you may opt for insulation boards rather than rolls.
4. Safety
   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.
5. 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 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?

What Is Wall Insulation?

Wall insulation is the material in between the walls which separate the inside from the exterior.

There are three different types of wall insulation in Ireland:

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

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.

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?

The exact cost of your cavity wall insulation will depend on various factors including:

1. The size of your home
2. The width of the cavity
3. The type of insulation material
4. Accessibility
5. Labour costs

Simply put, the more space that needs to be filled, the more the insulation will cost, but you can expect to pay between €7.50 - €10.50 per m2.

The table below provides a rough estimate of the cost of cavity wall insulation for different sized properties:

Source: Energyefficiency.ie

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.

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.

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?

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.

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.

How Much Does Floor Insulation Cost?

This will depend on the option you choose. If you opt for a 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.

How Much Does It Cost to Insulate a House?

The average cost of insulating your house costs from €2,000 to €4,000 depending on the size of your home, the material you choose and the extent of the project

Solid wall insulation can be more costly, typically between €6,000 and €10,000 significantly adding to the cost of a home insulation project.

Below you will find a breakdown of the estimated total cost:

Solid wall insulation can be more costly, typically between €6,000 and €10,000 significantly adding to the cost of a home insulation project.

Which Insulation Material Should I Use?

When choosing which insulation material to use, there are various factors to take into consideration including:

• Cost
• R-rating
• Enviromental impact
• Ease of use

We examine in detail the different materials available whether you are looking at the attic, wall, or floor insulation.

Fibreglass

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:

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.

Foam

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:

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

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:

Rockwool

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.

Here are some of the pros and cons of Rockwool insulation:

Cellulose

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:

Summary of Insulation Materials

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

Are There Any Insulation Grants?

There are several SEAI grants available for those looking to improve the insulation of their homes.

All homeowners, including private landlords, whose homes were built and occupied before 2011 can apply for these grants.

Below you will find a breakdown of the grant amounts available:

The table below outlines the entire range of grants on offer:

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.

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.

• ⚡ Benefits of an Insulated Home
• Energy Efficiency - Well-insulated homes reduce the need for heating and cooling, which leads to lower energy consumption.
• Cost Savings - By improving energy efficiency, insulation helps to significantly cut down on heating bills.
• Increased Comfort - Proper insulation makes for a more comfortable living environment, keeping the home warmer in winter and cooler in summer.
• Enhanced Property Value - Well insulated homes help to increase their BER rating and in turn, the value of the property.
• Reduce Carbon Footprint - Lower energy consumption not only saves money but also benefits the environment by reducing greenhouse gas emissions.