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Attaching to externally insulated walls without compromising performance

by Jennie Ward

The experts at EJOT outline best practice guidance for attaching to externally insulated walls whilst ensuring you don’t compromise on the intended performance level.

Meeting the goal of achieving ‘net zero’ greenhouse gases by 2050 will require significant upgrading to the external envelope of many of the UK’s existing buildings. One of the most effective ways to do this is by using external wall insulation (EWI) systems – also known as external thermally insulating composite systems (ETICS) – which have become a popular refurbishment solution over the past two decades.

While the Decent Homes Standard, published in 2000, was the catalyst for greater use of EWI, modern methods of construction (MMC) have additionally opened up new possibilities for these systems in the delivery of new build projects too where a client is seeking to optimise sustainability, speed and convenience in combination with high thermal standards.

Retrofit presents the major opportunity for EWI, however, with the UK’s existing housing stock regarded as being amongst the oldest in the world. That is why PAS 2035: 2019 is so important, providing a specification for the energy retrofit of domestic buildings and detailing best practice, which TrustMark holders will be required to comply with.

PAS 2035 supports the drive to improve energy efficiency and the Near Zero Energy Buildings (NZEBs) target in-line with EU objectives by championing technically sound and responsible domestic retrofit work. Key to this is the improved functionality and durability of buildings, as well as improved energy efficiency, reduced environmental impacts of buildings, and minimising the performance gap that often occurs with regard to a shortfall of perceived improvements.

But in order to ensure that an EWI or ETICS system delivers on its intended performance level and that it maintains its long-term integrity, it is important that careful consideration is given to the way external elements are attached. If not, something as simple as attaching a downpipe bracket has the potential to lead to much more significant and costly problems with the EWI installation.

Consider the make-up of an EWI system. In simple terms, the insulation is typically attached securely to the wall structure, treated with coatings and mesh, and finished in the chosen render, brick-slips or other external treatment. The main depth of the EWI system is the insulation board, and whilst this should generally be very securely fixed to the building substrate, it will not have the necessary structural strength to allow for load bearing attachments, such as Juliet balconies, canopies or railings.

Also remember that any attempt to achieve a secure fix by driving through to the original building substrate could compromise the thermal insulation level. Unless a fixing is used that incorporates insulating materials as part of its design, the thermal barrier will be broken, and cold bridging will result. This is one of the criteria of PAS 2035, where it needs to be demonstrated that any cold bridging effects have been designed out of the chosen energy efficiency measure, in particular EWI.

As the number of UK homes and buildings treated with EWI or ETICS increases – retrofit or new build – it is inevitable that more incidences will be faced where a load-bearing element will need to be attached in what will still be, for many – for now at least, a non-standard wall construction. That’s why it is important to understand the different types of anchors that must be used.

Iso-Dart anchors securely into substrates and accepts screws upto 9.0 mm diameter.

Plan ahead where possible
Where a medium to heavy element will feature as part of the newly insulated façade, it is important to plan for the location of the attachment as the EWI is constructed so a secure fix can be achieved. For example, when planning for a window which has a Juliet balcony, an installation angle or corner bracket, such as EJOT’S ETA-approved Iso-Corner, can be used to allow for a secure attachment back to the original building substrate.

Made from polyurethane hard foam, the installation angle provides a clear and dependable location for a load-bearing attachment to be made, whilst at the same time preventing thermal bridging. In the case of the EJOT product, a cantilever arm with a length of between 80mm and 300mm ensures any EWI system depth can be accommodated. A similar principle can be used where a sub-assembly, compression backing or pressure pad is required, by ensuring that an insulating material such as EJOT’s Iso-Bloc is attached to the building substrate as part of the EWI make-up.

…and choose the right approach for fitting unplanned lighter elements
Whilst planning for heavier elements is not only good practice but crucial, it is simply not possible to predict the fixing locations of every external element. That is why there are other very effective approaches which are equally uncompromising and secure for lighter weight elements, such as downpipe brackets, house numbers, letterboxes and exterior lights.
For fixing points up to a 5kg load in walls insulated with foam-type insulation such as polystyrene or polyurethane, one way to provide a secure fixing location is to use a spiral-shaped plastic assembly anchor, complete with sealing washer and integrated threaded sleeve (finished with silicone sealant). The design of this, as with EJOT’s Iso-Spiral anchor, is such that it embeds very securely because of its design into the insulation without creating a cold bridge.

Light-to-medium weight mounted elements – up to 15kg per fixing point – will, however, still need securing to the building substrate. This can be achieved with a longer fixing comprising a plastic bush, EPDM washer and a façade anchor. Within the EJOT range this is known as the Iso-Dart (see opposite page), and it is a type of fixing that can be used in EWI applications with an insulation thickness of up to 320mm.

Installation is straightforward, with the concrete, brick or block substrate drilled firstly to allow for the anchor to be inserted, after which the plastic bush and seal are attached, silicone sealant is applied, and then external elements can be attached. The length of the fixing and the fact that its design incorporates plastic and EPDM components not only delivers a secure fix into the original substrate, but it also minimises thermal transmission as a result of thermal decoupling.

Don’t take a risk – seek specialist advice
The potential that EWI and ETICS offer for enhancing the energy performance of UK properties is huge, but it is vital that we don’t allow compromising factors like the attachment of external elements to undermine the goals of clients, architects and system providers. That’s why innovative fixing solutions like those in the EJOT ETICS range are so important, meaning that installers can achieve the right result every time, whether it is a medium-heavy or lightweight element to be mounted onto the façade. Accessing the right support in this area is easy, with plenty of help available online in the form of technical brochures, datasheets, video installation clips and more, as well as directly from EJOT.

ETICS Consultant, Mark Newell. Contact Mark: m.newell@ejot.co.uk.

View a video of the EJOT Iso-Corner installation angle here.

www.ejot.co.uk

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