VIEWPOINT HELPING YOUR
RAINSCREEN CUSTOMERS Matt Neary, national sales manager at Knauf Insulation.
RAINSCREEN SPECIFIERS AND contractors are facing unprecedented pressure to deliver buildings that are efficient, sustainable, safe and stand up to scrutiny. But these challenges are not insurmountable – merchants and distributors are well-placed to help rainscreen specialists achieve the real-world performance they need with buildable, durable, non-combustible, and lower carbon solutions.
Buildability is key Buildability is the ease with which a product can be installed and should be a chief consideration. The Building Safety Act’s three ‘gateways’ mean that, for a building to be certified and occupied, it needs to pass compliance with Building Regulations at the planning, design and finished construction stages. Choosing materials that are easier to install helps to ensure the finished construction will pass all three ‘gateways’. Rigid board insulation, for example, is challenging to install correctly and won’t sit flush against a cavity unless it is perfectly uniform and flat. Boards also need to be precisely cut and taped, all of which can introduce air gaps that compromise thermal and fire safety performance. By contrast, mineral wool insulation is flexible and maintains close contact with the substrate.
Where slabs meet, the ends also ‘knit’ together, making it easier to install correctly. This minimises air gaps and maximises thermal performance. Choosing buildable insulation at the design stage helps to ensure that it is installed efficiently, correctly, and contributes to the expected thermal, fire and acoustic performance once built.
Mitigate risks
Building a rainscreen façade is never easy, but on-site delays and installation challenges could be costing your customers more than time. For example, best practice for installing insulation in rainscreen façades is to use a ‘rolling front’, but a survey of façade contractors suggests that this is only achieved in approximately 50% of projects. If insulation is left exposed to the elements for too long during construction, it could be damaged, and its performance compromised.
The solution in this case is to use a product that is resistant to prolonged weathering such as Rocksilk RainScreen Slab EE, the UK’s first non-combustible rainscreen sheathing insulation with an enhanced water-repellent facing. This gives you flexibility if things don’t go precisely to plan on site without risking the fire, thermal and acoustic performance of the rainscreen.
While reducing operational carbon is crucial to achieving net
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zero, the construction industry is already turning more attention to embodied carbon – the emissions released in producing a building (from things like raw materials and transportation). These emissions are projected to make up roughly half of all construction emissions over the next 30 years.
Several countries in Europe have already adopted embodied carbon reporting in construction and regulations are likely to follow in the UK, such as the proposed ‘Part Z’ of the Building Regulations. This makes choosing lower carbon alternatives a priority for rainscreen designers and contractors, both to earn credits in schemes such as BREEAM, and to futureproof the construction.
Many rainscreen façades use rock mineral wool slabs for both the sheathing insulation and the second layer that sits between the studs, but an alternative approach is to use a glass mineral wool product, such as OmniFit Slab 32, for this second layer.
Glass mineral wool has many of the same qualities as rock, including non-combustibility, but has the lowest levels of embodied carbon of any mainstream insulation material. By using rock mineral wool for the outer leaf and glass mineral wool for the inner leaf, your customers can reduce the embodied carbon of the whole façade without compromising performance.
Approved Document B now requires non-combustible
materials to be used in certain external wall system build-ups, such as rainscreen façades, on all residential buildings between 11m and 18m. The only exception is if a full-scale fire test to BS 8414 has been conducted. Many third parties have already introduced blanket non-combustible policies. The Greater London Authority’s Homes for Londoners programme states that “no combustible materials may be used in the external walls of all homes and buildings, regardless of height.” We surveyed specifiers working on large-scale rainscreen projects and found that half of respondents said their organisations had adopted a non-combustibility policy that goes above and beyond the regulations. In most cases, this blanket policy applies to walls and roofs in all buildings, regardless of height or use.
Non-combustibility policies reduce risk substantially for all parties involved in the construction process, and the products to deliver them already exist. Customers should always look for the Euroclass reaction to fire classification – any insulation achieving either an A1 or A2-s1,d0 rating is considered non- combustible.
Futureproof façades It is a uniquely challenging time to be designing and building rainscreen façades, and every part of the supply chain needs to offer the right support to ensure these projects go well.
Merchants and distributors can offer expertise to ensure customers prioritise buildability and non-combustibility, are aware of lower carbon alternatives and can futureproof the build-up. With the right knowledge and support, customers can deliver façades that stand the test of time both in terms of functionality and compliance. BMJ
www.buildersmerchantsjournal.net November 2024
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