External insulation – Checklist and sample finishes

Plinth detail is very important in any external wall insulation system.
Our short video provides an overview of the important aspects that need to be considered.

The L Detail is a very important part of the external insulation process. For an overview, check out this short video:

With rising energy costs, the recent extreme winter weather and the SEAI Home Energy Saving grants many homeowners are deciding to upgrade the insulation in their homes.

When considering improving wall insulation, the homeowner can potentially choose between a wide variety of material types that are available in the marketplace.

Certain factors such as the wall construction, location of property and cost, will have an influence on the upgrade strategy and whether the homeowner ultimately chooses internal, external or cavity fill insulation.

For refurbishment, external insulation is an ideal option, as it ensures a more effective way to eliminate cold bridges and reduces heat loss. However, it is very important that correct materials are used and that workmanship is of the highest quality.

So what choices of materials are available for external insulation and what are the typical issues to avoid?

Cosihomes showroom

On our recent visit to Cosihomes in Ashbourne, we were shown their extensive display of external insulation in the showrooms. An enlightening presentation provided an overview of the materials that can be used, key things to consider and examples of problems that can occur.

Before you start:

It is good practice for the contractor to effectively prepare the site before installing the external insulation system – this is a key component to the success of the overall project.

  • Access the existing wall build-up using a borescope
  • Repair any structural defects that may be found
  • Ensure that Satellites, communication antennas, alarm boxes and downpipes are made safe and/or removed as necessary
  • Consider special details such as balconies, bay windows etc.

For the homeowner they can use the following key checklist items as a useful aid towards a successful installation:

  • Use Certified Installers
  • Check previous installations and ask homeowners opinion
  • Ask for installation time line and price structure
  • Price can reflect in Quality
  • Check that the contractor has carried out an inspection of the existing wall build-up
  • Check insulation is certified and correct for site specific use
  • Ensure that there are no issues with planning
  • Ask about finish choices

A significant problem that can arise is Thermal Looping in relation to existing partial fill cavity walls. This occurs when air circulates around the (usually inadequately insulated cavity) as a result of poorly installed insulation and cavities which themselves were not completely sealed.

If this type of wall design is not identified at the initial stages and sealed, this can allow heat loss through openings in the cavity


Insulation Materials:

The following provides some brief points of note to consider when you are choosing which insulation to use:

EPS High Density Aged Expanded Polystyrene

This is the most commonly used insulation, and is white in colour. It is a well tried and trusted solution as it has been used in Europe for over 50 years. Although it may require slightly thicker installation than some of the other insulation types, its performance is still the same. It offers the most cost effective solution on the market. It is worth checking the density/weight of the board, to make sure it is as required, all boards look the same but have vastly differing thermal performance.

Rockfiber Mineral Insulation

Like the High Density EPS above this insulation has been used in conjunction with external wall insulation for a long time. It is required in all systems as a firebreak. It has the same thermal performance as the 100 HD EPS and the same depths are required to achieve the desired U Value. It is however slightly more expensive than the EPS and as such is mainly used where extra impact resistance or sound proofing is required

Phenolic K5 Insulation

This is the board that we associate with internal insulated plasterboard. It has higher thermal performance and so requires less depth to achieve required thermal performance. It is very important however that you check that the installer is registered to use this insulation as very few systems are currently certified to use it, and this could affect their ability to offer you a guarantee. In addition extra care is required when installing on site to ensure that boards are not damaged during installation.


What problems can occur with External Insulation Materials?

The following are just a few of the issues that can arise, due to incorrect materials or poor workmanship:

Damaged boards can cause debonding

Boards exposed to the elements for long periods would need to be replaced

Hairline cracks occur when topcoats are not flexible as insulation will expand/contract

Visible joinings/fixings caused by open joints on boards, moisture or a system that is too thin


Acrylic on damp surface

Acrylic on damp substrate


The type of finish that is chosen for the External Wall Insulation system can depend on many factors. A few of the common finishes that Cosihomes provide are:

Parex Lanko EHI Mineral

ParexLanko EHI Mineral Finish:

This has high breathability, is waterproof and is resistant to algae growth
It has a 10 mm finish

Parex Lanko Dash Finish

ParexLanko offer a Dash Finish:

As a replication of a traditional finish, this is also breathable and waterproof
It has a 7 mm finish

Parex Lanko Acrylic Finish

ParexLanko Acrylic Finish:

This is water resistant but has low breathability. This finish requires special treatment when applying, to protect against moisture/dampness.
Recoating is required to this 1-3 mm finish

Brick Finishes:

The traditional brick slips have height restrictions – to maximum 8 feet high
Facade requirements have to be considered

As with the selection of the insulation materials, there are also potential issues to be aware of when choosing finishes. The following are just a few of these:

Algae growth can occur over the entire wall if overhang is insufficient or product isn’t water resistant
“Spotting” and mould growth internally may be due to poor breathability of the finish coat/system
Debond of brick slips can occur because of excess weight loading from a breach in height restriction
Inconsistent colour in finish coat can be due to temperature/weather or poor workmanship


As can be seen from this overview, external insulation can be a very effective method of reducing the heat loss in the home.

However, it is important that the correct materials are used, that the workmanship is of a very high quality, and that the proposed insulation strategy will not cause condensation issues in the structure.