Attic Insulation is one of the simplest and most cost-effective ways of improving the energy efficiency of any home. The attic is one of the largest sources of heat escaping from a property, and reducing that should be the first priority for home upgrades

Installing attic insulation has many benefits in the comfort and warmth it brings to a home, and its potential to save money on energy bills.

There is a lot for homeowners to consider, however, on how they want their attic insulated, and the different insulation products which can be used.

Attic Insulation
The key takeaways:
  • Up to 30% of your home’s heat can be lost through the roof
  • Attic insulation can save you 15% of your home energy bills (Average annual gas bill in Ireland is €1,474.27)
  • Types of attic insulation: Rolled Wool Insulation / Cellulose Insulation / Polyurethane Insulation / Polystyrene insulation
  • The cost of attic insulation can range from €600 – €4,000, depending on the size of your attic and the materials used
  • Claim up to €3,000 in grant funding

Table of Content

What is Attic Insulation

Attic Insulation consists of adding layers of insulation to the internal surface of your attic and roof to prevent heat from escaping. 

Up to 30% of your home’s heat can be lost through the roof, so this should be one of the first steps taken for anyone looking to make their home more energy efficient and environmentally friendly.

There are two main areas where you can add insulation to your attic:

  • Between the joists of the ceiling
  • Between the rafters of the pitched roof of the building

The effectiveness of insulation used in your attic is typically measured through either its R-value or its U-value. A higher R-value is good, whereas the lower the U-value the better the result.

An R-value, expressed as Km²/W measures the thermal resistance of an insulation material, how good it is at blocking heat from passing through.

The U-value, expressed as W/m²K, measures how much heat passes through an area. This takes into account more values in the complete project such as the thickness of the insulation layer, and other factors.

Do I Need Attic Insulation

If you have an attic in your home there’s a good chance that there will already be some insulation present. Fiberglass insulation is typically the most common older type of insulation, and can typically be found laid between ceiling joists in the attic.

But even if you already have insulation, that doesn’t mean you should disregard improvements in that area. Having a thicker layer of insulation, or adding more modern insulation can drastically improve how much heat can be kept in your home.

The existing insulation should be inspected to see if it is damaged or degraded. If so, it might need to be removed. If not, fresh insulation can be laid on top of it.

If your home doesn’t have any insulation in the attic, more likely with older buildings, then it’s an even easier choice to make.

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How Much Can You Save With Attic Insulation

Attic Insulation at either the loft or rafter, or both, can deliver massive savings on heating bills by reducing the amount of heat lost through the roof.

As much as 20-30% of a home’s heat is lost through the roof, meaning that a fully insulated attic can cut hundreds of euros from heating bills each year.

The exact amount of those savings will depend on the quality and thickness of the insulation installed, and what a homeowner’s heating bills are.

Property Type Heating Requirements Heating Bill Reduction Annual Savings
Apartment 7,480kWh 20% €167
30% €251
Mid-Terrace 7,699kWh 20% €172
30% €258
End-Terrace 8,635kWh 20% €193
30% €289
Semi-Detached 9,875kWh 20% €221
30% €331
Detached 13,563kWh 20% €303
30% €454

*Heating figures based on household gas consumption in 2020. Source Central Statistics Office
** Energy Bills calculated based on Bord Gais price of 11.17c per kWh with 2% discount

Benefits of Attic Insulation

When considering home insulation, the following factors should be considered.

Having good insulation in your attic will cut down the heat escaping your home, and save money on your heating bills in winter.

Insulation in your attic can help reduce or prevent altogether a lot of problems which come from damp and water vapour. Insulation can act as a barrier against water vapour seeping into your property and damaging the walls and roof, along with preventing mould and rot.

Attic Insulation is probably the simplest type of insulation to have installed on an existing home, as it requires no other material alterations to the existing property.

Where a hot water cylinder is present in the attic, adding insulation to the tank is a common part of any project. This means that your hot water cylinder will lose heat more slowly, reducing hot water costs. This is of particular benefit for homes with fewer occupants, and low hot water needs.

Insulating your attic will help to make your home a more comfortable place by making it easier to keep it warm and cosy.

Anything that cuts down on the amount of heating required in your home, whether through oil, gas, or electricity, will cut emissions from your home and give you a reduced carbon footprint.

Any type of energy efficiency improvements to your home will help increase its BER and raise the value of the property. This helps to make your home into a better long term investment and asset.

Types of Attic Insulation

There are two main ways of installing attic insulation in a pitched roof building. The first of these is loft insulation, laid down between and on top of the joists at the ceiling level. The second is at the rafter level, with insulation placed between the rafter joists.

Loft Roll Insulation

Loft Roll Insulation is the simplest and least expensive way to insulate an attic space. Loft Insulation typically consists of mineral wool insulation or another soft batt type of insulation laid on the floor of the ceiling.

Sheets of loft insulation tend to be more cost-effective than spray foam or rigid board insulation, which are the preferred methods of insulating rafters.

Insulating at the loft level will create a cold attic space by preventing any heat from leaching from below into the attic. This creates a smaller space for your heating system to deal with.

Mineral Wool Insulation rolls can be installed directly on top of existing insulation such as fibreglass, so long as it has not been damaged by dampness or otherwise begun to degrade.

The most common types of loft roll insulation are:

  • Mineral Wool Insulation (Earthwool or Rockwool)
  • Fibreglass Insulation
  • Sheep’s Wool

Volcalis Easy Light Loft Roll Insulation

  • Lightweight, high-performance mineral wool insulation suitable for any loft space.
  • Eco Friendly product made with sustainable processes and 100% recyclable.
  • Strong thermal insulation, acoustic protection, and fire resistance.
  • Variable thickness insulation for any loft type and homeowner needs.
Thickness (mm) 100 150 200
Thermal Resistance (m²/KW) 2.25 3.40 4.50
Thermal Conductivity (W/mK) 0.044 0.044 0.044
Fire Resistance A1 A1 A1

Rafter Level Insulation

Insulation can also be installed between the rafters of a pitched roof. This has the added benefit of creating an airtight barrier between the interior and exterior of the building to prevent heat loss. The insulation can also provide added protection from the elements.

The most common ways of installing insulation at the rafter level is to affix rigid boards of polystyrene insulation, or for Spray Foam insulation to be used.

Spray Foam Insulation is a polyurethane foam which expands greatly as it dries, filling any small spaces and ensuring an airtight seal in the roof.

When using spray foam insulation it is essential to avoid covering up any existing ventilation ducts in the ceiling.

A layer of reflective foil quilt insulation can be used to reflect infra-red radiation, keeping the space cool in summer as well as cold in winter. It can also act as a vapour control membrane.

Blown Cellulose Insulation acts in much the same way as spray foam, but does not perform as well and has become less common.

  • Rigid Board Insulation (Polystyrene)
  • Spray Foam Insulation (Polyurethane)
  • Reflective Foil Insulation

Installing Attic Insulation in Your Home

Installing Attic Insulation is the easiest and least disruptive insulation method which can be done on a home. The installation process can be completed in a single day depending on what works are being done.

The first step which needs to be done ahead of time is to make sure the loft space is cleared so that there are no obstructions.

  • Mineral Wool Insulation or another loft roll insulation can then be laid down on the loft floor in between and on top of the joists.
  • Different layers of insulation should be placed perpendicular to one another to reduce thermal bridging until the required thickness has been achieved.
  • Ensure that a gap is left at the eaves to allow for airflow and ventilation throughout the attic.
  • Any piping, hot water cylinder, or cold water tank which is located in the loft space should also be insulated in order to reduce the risk of freezing.
  • If there is a gap between the attic hatch and the cold water tank, or if it is intended to keep using the attic as a storage space, then insulating walking boards can be installed atop the insulation rolls.

  • Decide whether to use spray foam or rigid insulation boards to fill the space between rafters.
  • When using Spray Foam Insulation, care must be taken not to cover up any existing deliberate ventilation.
  • A vapour control membrane should be installed on the warm side of the insulation layer.

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How Much Does Attic Insulation Cost

The cost of having your attic insulated will depend on numerous factors related to the size of the area and the insulation being used. The final price of the project can be determined by:

  • The size of the attic
  • Is Insulation being placed in the ceiling and/or rafters?
  • If any insulation is already present
  • What type of insulation is being used
  • What thickness of insulation is being installed
How Much Does Attic Insulation Cost

The insulation material you choose will have the most impact on the final price. While selecting a cheaper option might give some savings up front, you must also consider their thermal performance.

Selecting a cheaper insulation option might seem like a good decision up front, but it will reduce the amount you can save on your heating bills. Some materials might also have shorter lifespans than their more expensive counterparts. 

The cost of insulation materials for your attic per m² will fit in the average range of:

  • Sheep’s Wool/Mineral Wool/Fibreglass: €10 – €30
  • Polyurethane Foam: €25 – €60
  • Polystyrene Board: €10 – €20

The exact cost of the materials will depend on the thickness of the layer of insulation being put down. This is only the cost of the materials, the full cost per m² will also include labour, which will add significant expenditure.

The cost of attic insulation can vary anywhere from €600 – €4,000 depending on the size of your attic and the material used.

Rafter insulation for a pitched roof will typically cost more, with a larger surface than the base of the attic, and with more expensive polystyrene and spray foam insulation as more popular materials.

These are only rough estimates and are subject to change based on the cost of materials and each individual property.

Attic Insulation Grants

The SEAI provides grant funding for homeowners to help homeowners with the cost of having insulation installed in their attic and rafters.

These grants are available for all homeowners, including private landlords, so long as the home was built and occupied prior to 2011.

Insulation Type Grant Value
Attic Insulation Apartment (Any) – €800
Mid-Terrace House – €1,200
Semi-Detached/End-Terrace – €1,300
Detached House – €1,500 
Rafter Insulation Apartment (Any) – €1,500
Mid-Terrace House – €2,000
Semi-Detached/End-Terrace – €3,000
Detached House – €3,000

Homeowners who make use of grants for attic or rafter insulation through the Better Energy Homes scheme are required to achieve a final U-value of 0.16 W/m²K for ceiling insulation or 0.20 W/m²K for rafter insulation.

FAQs

The thickness of the attic insulation you have installed should be determined by what kind of performance you are looking for in concert with what your budget for the project is. Thicker layers of insulation will provide a better thermal performance, but will also cost more.

Fibreglass or cellulose insulation should probably be inspected after 15 years or so, at which point it may be replaced. However other materials such as mineral wool, polystyrene boards, or spray foam can be good for up to 100 years if installed correctly.

While it is of course possible to buy all the materials and equipment required for a DIY job, installing insulation yourself can have severe consequences if done incorrectly. Not only may you not get the desired benefits, but you could also end up damaging your home.

The exact thickness of loft insulation will depend on the R-Value of the material being used, and how much insulation is already in place, if any. Ideally you should aim for roughly 300mm thickness of insulation. This can include insulating walking boards.

If it has been well installed attic insulation should not require any maintenance on the part of the property owner for the duration of its lifespan.

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