No Cavity Walls? No Problem. Consider External Insulation Instead

by Brian Flax | Nov 02, 2022
external wall insulation

Many homes built in Ireland before 2006 lack sufficient insulation. This will make a home colder than it has to be during the winter months as it may will not have the ability to retain sufficient heat. Not only is a cold home uncomfortable, but it could lead to health issues for its occupants, damage to the structure of the home such as mould growth, damp and an increase in the amount of money spent on space heating.

While cavity wall insulation may be an option for some, there are plenty of homes across the country where it is not suitable or practical to install. Homeowners looking to insulate may be left with only a few options to choose from: internal dry lining or external wall insulation.

external wall insulation
Expanded Polystyrene has been used to externally insulate this house

Let’s start with internal dry lining

As you can gather from its name, internal dry lining involves installing insulation from the inside of the home. Unlike bonded bead cavity wall insulation that can be pumped into a cavity wall from the exterior of the building, internal dry lining requires working from the inside of the home, where insulation, along with plasterboard is mechanically fixed to the existing internal surface. This process, while effective, can cause major disruption to the home’s occupants while the works are carried out. While internal dry lining will provide the homeowner with new plaster finish after installation, it can also cause a reduction in room size dependent on the thickness of the insulation used. On average homeowners may lose about 100mm per insulated wall.

Like all insulation works installation should only be carried out by properly trained and certified professionals. Improper installation may result in an increase in damp, mould growth and other problems affecting the structure of the home. Internal dry lining may be a homeowner’s only option if the home wasn’t constructed with a cavity wall or there is stone facing on the exterior walls, making it unsuitable for other alternatives like external wall insulation.

Too much of a hassle? External wall insulation could be the way to go

External wall insulation is perfect for homeowners that don’t feel like going through the headache of construction inside of the home. External insulation keeps the internal walls intact while adding sufficient levels of insulation to the outside of the home instead. While it can’t be installed as quickly as cavity wall insulation, it provides excellent heat retention while giving a refreshed look to the exterior of the home.

There are several types of external wall insulation systems to choose from in Ireland. Materials that are suitable include expanded polystyrene (EPS Silver or White), extruded polystyrene, mineral fibre board or polyisocyanurate. The thickness of the insulation will depend on the type of insulating material, ranging anywhere from 100mm (average) to 120mm or more for a retrofit. If insulating a new build, expect the thickness to range anywhere from 150mm to 200mm. It’s important that whatever material used meets at least the U-values required by Irish Building Regulations, Part L 2021. Insulation professionals should aim for the lowest U-value possible based on the site and budget of the customer.

When installing external wall insulation (EWI) it’s important to fix any problems with the exterior walls beforehand. The insulation contractor will be able to point out any problems that need to be remedied during the initial site survey. Fixing major, or even minor problems, after the insulation has been installed can be extremely difficult. External insulation will add thickness to the walls, so keep in mind that window sills and eaves may need to be extended or replaced, and downpipes may need to be relocated. Once the exterior walls are in good shape the external insulation can be installed. Most external wall insulation systems are adhesively and mechanically fixed to the walls. Satellite dishes, lights and any decorative fixtures attached to the external walls must be removed beforehand.

After the external insulation is fixed in place, a fibre mesh and base coat is applied to increase strength and impact resistance. A primer is generally applied using a roller or brush or sprayed on to help increase water resistance and adhesion of the insulation. A render finish is then applied on top of the insulation, mesh and primer to give the house a new look. In most cases this is an acrylic render available in a variety of colours and textures to suit the requirements of the homeowner. The end result is a fully insulated home with fresh new exterior walls. The fixtures that were mounted to the walls can then be reinstalled or new fixtures can be fitted as required.

New ventilation and window sills fitted

If possible, it’s a good time to replace old windows. Consider triple glazed windows to increase the overall energy efficiency of the home and to minimise heat loss. Attic insulation should be installed or topped up to at least 300mm so the homeowner can realise the full benefit of an insulated home. For maximum benefit, external insulation should be installed around all external surfaces including window sills and doorframes.

What about the ventilation requirements?

Correctly installed external insulation will significantly increase a home’s airtightness. An airtight home makes it harder for fresh air to enter, as most draughts are sealed during installation. When installed without proper ventilation, external insulation may cause damp, mould, an increase in radon levels and even a build-up of carbon monoxide in rooms with fuel burning appliances. Proper wall and roof ventilation is critical and should be discussed with the contractor in depth before any measures are installed.

While it may be tempting to install external insulation as a DIY project, it’s important to understand the implications. KORE recommends that external insulation is only installed by a competent and registered contractor. Any reputable contractor will know the building regulations requirements for proper ventilation. If in doubt, ask for references or speak directly with the insulation manufacturer. A poorly ventilated home could cause major health concerns for its occupants so it’s imperative that it’s installed correctly.


External insulation works cannot be carried out in one day. The average time for installation ranges between 7 and 10 days, with some taking longer depending on the size of the home and the weather conditions on the job site. Some projects may require planning permission from a Local Authority before the works begin – especially on historical or protected structures or if the external appearance chances significantly with the choice of render. External insulation may not be suitable for all building types. This includes timber frame, steel frame and timber clad walls. Don’t assume that a house can be insulated using an external insulation system without first speaking with an approved contractor.

External insulation will make the exterior walls of a home thicker. Although it won’t affect the internal floor space, it could affect the window sills, doorframes and the roofline. All must be taken into consideration during the initial site survey.

External Wall Insulation Systems should only be installed by an NSAI approved contractor. A list can be found directly on the NSAI website.

external wall insulation retrofit
External insulation with render creating a new modern look home

Grant assistance is available to reduce the cost

Externally insulating a home can be a major investment depending on the size of the structure. Luckily, SEAI offer grants to help reduce the out of pocket expense to the homeowner. As of November 2022, detached homes are eligible for a grant of €8,000, semi-detached or end of terrace homes can avail of a €6,000 grant while mid-terrace homes can avail of a €3,500 grant or apartments can avail of a €3,000 grant. This grant is for individual energy upgrade measures, and is available for all homeowners, including landlords, whose homes were built and occupied before 2011.

If you would like to upgrade multiple energy efficiency measures at one time, the one-stop-shop grant scheme is a complete home upgrade solution, and includes wall, floor, attic insulation, heat pump, solar PV, mechanical ventilation and more. You can find out more about the one-stop-shop grant scheme and service over on the KORE Retrofit website. 

Long term benefits include:

· Reduced energy usage and total cost for space heating
· An airtight home with no draughts
· Reduced heat loss
· A refreshed, modern look on the outside of the home
· An improvement in the building energy rating
· An increase in property value of 10% or more

If you would like to install external wall insulation and increase the energy efficiency of your home, the KORE Retrofit website has all the information you need to know.