It's a wrap: External wall insulation for your home

Your project is unique. There’s nothing more important than skilled eyes and a full survey to weigh the merit of big, pricey structural inclusions.

Wall insulation can take three forms — cavity fill, external insulation, and internal insulation (what we know as dry-lining) and one or more of them may be cost-optimal depending on your highly personal situation and the condition and structural type of your home. 

You can grant-aid external wall insulation (EWI) using either SEAI grant aid or the Vacant Property Refurbishment grant scheme, but not double-dip both. SEAI grant aid is worth €3,000 to €8,000 depending on the property type. External insulation is often combined with cavity fill where it’s lacking, which is also grant-aided up to €1,700, and familiar to most homeowners.

'The wrap'

EWI is known as “the wrap”, and it’s the most expensive and therefore the most generously supported individual grant managed by the SEAI. You may see it termed as external-thermal-insulating-composite-systems (ETICS) as it’s applied systematically to a very vigorous standard to the surface of all the outside walls — everything over the DPC at 150mm.

EWI is carried out most usually as part of a whole-house, deep-renovation hand-in-hand with other serious improvements to the fabric of the house like comprehensive insulation, cavity fill, window changes, rigorous air-tightness measures and heat-recovery ventilation. It should result in a building that’s efficient enough to be heat-pump ready, with
suitably, managed air exchanges, no draughts, and superb heat retention stem to stern.

Where EWI outstrips internal insulation is that, despite the walls becoming thicker, it doesn’t impinge on internal space whatsoever.

With EWI, the entire exterior surfacing of the wall of the house, plinth to eaves is wrapped in a seamless “blanket”. Insulation boards in expanded polystyrene or mineral wool slabs are fixed with a specialist adhesive to the existing wall.

A dedicated base coat is applied before a wire or glass-fibre fabric reinforcing mesh is set over it all. The mesh is then covered with a handsome self-coloured render. The finished depth will be anywhere between 150mm and 200mm. All reveals heads around windows and doors, and all windowsills should be insulated by appropriate means too.

The benefits of EWI are highly impactful and varied. It can be installed on all or part of an existing building. It has the most perceptible results in homes with poor energy efficiencies lurking in the E to G levels of the BER range. 

Tailored to the house to the split mm, without any breaks or thermal bridging for cold and damp to reach across, there’s the improvement to what’s termed the U-values of the exterior walls. This measures how much energy is retained by the walls rather than dissipated outdoors. This U-value can tumble to as much as 0.27 or even 0.21 following EWI, what you would expect in a new A-rated home.

Presuming the rest of the outer envelope, through the floors, roof, windows and doors has been brought to near passive standard, EWI has a large positive percentage results in fuel energy savings, potentially as much as 30% in a previously chill home labouring with a non-condensing fossil fuel boiler.

Increasing the air-tightness of the house, ventilation must now be managed, and predictable and will contribute to a completely new sensory comfort throughout the home, with even, dry, warm conditions during the winter, and fresh, healthy air exchanges year-round.

When repackaging those outside walls, EWI provides a visual facelift to old renders and brick equally well. Most providers will have a range of colours and textures in self-coloured finishes to explore. With new windows in place, houses treated to EWI have a true glow-up on completion, and you can spot a house with EWI at ground level by a discreet overhang, and deep window reveals.

EWI is not recommended for timber or steel frame construction or solid, heritage walls which rely on “breathing” out condensation created in the home. These latter construction types are best handled with traditional wicking style, internal insulation solution like hemp, wood-fibre or cork-boards dressed in lime renders working from the inside to out. 

The SEAI has introduced a new pilot programme for deep renovations to help with the cost of insulating these heritage types. An architect and/or engineer with an interest in conservation methods can steer you the right way to improve energy efficiency for these very special buildings.

There are some variations in EWI systems, but every product offered by those on the SEAI register must have NSAI agreement certification. It’s very important that no external or interior insulation method interferes with any ventilation process intended in your wall type. Always take advice, even if you’re not going through the SEAI grant process.

In terms of the hassle quotient, beyond the expense and waiting for the return of some of the capital outlay (unless you’re taking part in the One-Stop-Shop scheme through the SEAI), EWI is actually less of an upheaval than internal insulation. Presuming new windows are already in, there will be a lot of noise, coming and going onsite but you can stay in your home and just comfort your kids and pets through the process. 

A standard three-bed semi-D will take in the area of two weeks for the EWI process and yes, you should always check with the local planning authority as it will alter the exterior of the home by more than 25%, and run into Part L stipulations.

Watch those associated builder’s costs when working up your budget and quotes, and establish the funding and timeline for your renovation. There might be unexpected additions like a small but significant change in a roof line or ventilation for the roof structure as the walls have advanced out. 

The NSAI advises: “When getting quotes from contractors (for EWI), it is important to get confirmation that all works associated with the application of the external insulation are included, including costs such as those associated with the relocation of electricity and gas services, and works to external drainage pipes and outlets.”

It’s vital to have a trusted installer, as your contract is not with the SEAI or the NSAI, it’s with the firm putting it up.

For more information on EWI, see nsai.ie.