What to Consider Before Installing Internal Wall Insulation (IWI)
Solid walled properties are amongst the least energy efficient and most expensive to heat. This construction method was used for the vast majority of homes built prior to 1919 and was often used on the solid block and concrete properties constructed between 1940 and the late 1960s. Yet, the most recent Housing Condition Survey in Northern Ireland showed that over half of these properties are in fuel poverty
Retrofitting solid wall insulation systems on these properties can be an effective means to improving their energy performance and lower bills. Before carrying out this work, however, it is important to identify the right solution for the property and ensure the building is properly prepared.
Should I fit Internal Wall Insulation (IWI) or External Wall Insulation (EWI)?
When insulating solid walls, you have the option to fit insulation either on the external or internal side of the wall.
In most cases, External Wall Insulation (EWI) solutions, such as Kooltherm K5 External Wall Board, will provide a faster and more straightforward option. As the insulation layer wraps around the envelope, detailing is simpler and the external wall construction is kept warm – reducing potential condensation and damp issues.
However, it may not always be possible to fit EWI. For example, some solid walled properties are subject to additional planning restrictions which can limit external alterations (such as being listed or located in a conservation zone). In this case, the only option is to fit insulation on the internal face of the wall.
IWI offers flexibility and reduces constraints around installation, but it can present technical risks that should be managed. If recommendations are not properly considered, there could be a high risk of interstitial condensation and mould growth.
IWI can be installed on most construction types provided the risks have been well understood and mitigated. This includes carefully considering whether the IWI system is moisture open or moisture closed.
Yes, the Kingspan Retrofit One Stop Shop (OSS) provide access to a range of grants offered by the SEAI (Sustainable Energy Authority of Ireland) to support your home energy upgrades.
In Northern Ireland, grants are available for solid wall insulation through the Affordable Warmth Scheme but you will typically need to have completed all other possible improvement works first.
Who can carry out an IWI installation?
IWI installations are amongst the most technically challenging energy retrofit projects. For this reason, we strongly recommend the property is properly considered and that the work is completed by a suitably qualified individual. This should be carried out following a whole house approach. This requires the property to be thoroughly assessed and a phased improvement plan developed to ensure the measures are appropriate.
In the Republic of Ireland, the SEAI provides funding for a Home Energy Assessment (HEA) to be carried out. The HEA requires a Building Energy Rate Certificate (BER) to be produced, detailing existing performance, the development of clear technical designs and pathway options to enable the property to reach a B2 BER or better and quotes to be obtained for the required work. If a property is being improved via a SEAI grant, it is required that the (optional) HEA and subsequent works should be carried out under relevant SEAI guidelines and the guidance in S.R. 54:2014/A2 2022 (Code of practice for the energy efficient retrofit of dwellings). This standard covers the process of planning a retrofit and developing a whole dwelling energy improvement plan, and specific guidance on best practice for installation.
In Northern Ireland, best practice should be for retrofits to be carried out under the process laid out within PAS 2035: 2023 (Retrofitting dwellings for improved energy efficiency. Specification and guidance). This will require a Retrofit Coordinator to be appointed, the property to be carefully assessed and a medium term improvement plan for the entire property to be drawn up. This thorough approach should help to ensure that the work is appropriate for the property.
Please note that PAS 2035: 2023 supersedes PAS 2035: 2019 + A1: 2022, which remains current and will be withdrawn on 30th March 2025. This means that, whilst PAS 2035: 2019 + A1: 2022 can still be used until 2025, PAS 2035: 2023 can optionally be used now ahead of the withdrawal date.
As part of the PAS 2035: 2023 process, all installations need to be carried out by installers qualified to PAS 2030: 2023 (Installation of energy efficiency measures in existing dwellings. Specification). Consultations are ongoing to confirm if Northern Ireland Sustainable Energy Programme grants will require projects to be completed under PAS 2035:2023 in the future.
What to look for when checking the condition of the property
As part of the dwelling assessment carried out under the whole house approach, a number of aspects should be considered in relation to IWI:
• Local weather conditions – particularly driving rain. A map of exposure zones for driving rain can be viewed in the relevant NHBC guidelines for Northern Ireland and a Driving Rain Index map is provided within Figure D.1 of S.R. 54:2014/A2 2022 in the Republic of Ireland. Building specific factors, such as aspects which are open to prevailing conditions and local sheltering, should also be considered.
• How the work will impact ventilation within the property, as installation of insulation measures can improve airtightness dramatically. Any existing provisions (such as air bricks) will need to be considered and the overall ventilation strategy may need to be improved.
• A survey of the building characteristics (such as whether walls are vapour open or vapour closed) and the materials used in all constructions. For example, fines concrete constructions are not suitable for IWI.
• The condition of external walls, including any cracks in bricks or render, missing pointing and broken guttering or downpipes.
• Suitability of sill overhangs, roof eaves and verge overhangs.
• Planning detailing for penetrations such as pipes, cables or ducts.
• Current insulation levels in neighbouring properties and if other elements (floors, roof or ventilation) could receive upgrades in the future.
• Whether a damp proof course is present and if so, its type, if it is sufficiently raised above paths and that paths run away from the external wall.
• Whether there are any signs of damp (such as mould or peeling paint) or insect attack in any part of the wall, floor or roof construction including the timbers.
• How the thickness of insulation will impact internal spaces. This includes ensuring the width of staircases and corridors are not reduced to less than the minimum requirements.
Any issues that are identified, must be fully dealt with and the walls should be dry and in good condition before any IWI installation begins.
How to prepare a property for IWI
Once any underlying issues are dealt with, the installers will need to carry out some additional preparation work including:
• Removing all external and party wall (if being insulated) fittings, including skirting boards, picture rails, wallpaper, gloss/silk emulsion paint, kitchen cabinets, toilets etc.
• Determining whether sockets, radiators or pipes need to be relocated.
• Confirming if window reveals can be insulated if the existing plaster is removed (it is not recommended to leave any wall areas uninsulated).
• Sealing any gaps including around windows and doors and at the perimeter of the room (including junctions between the wall and floor and ceiling).
• Depending on the approach taken and the condensation risk analysis, system specific issues will need to be addressed e.g. with a moisture closed system, there should be a high level of vapour resistance on the warm side of the construction. Alternatively with a moisture open system, the insulation thickness may need to be restricted to avoid moisture becoming trapped within the construction beyond its buffering capacity.
• Ensuring there is adequate protection against driving rain. This may include applying cladding, render or a barrier cream to the external face of walls. Or it could mean ensuring that render drips and parapets throw rainwater away from walls and making sure that all penetrations are effectively closed.
• Checking walls are dry (a typical masonry wall should have around 6-8% moisture content by volume).
