UK RAINSCREEN FACADE INSULATION

Rainscreen facade insulation is a second, inner constituent part used in rain-screen cladding systems or ventilated facades that are usually made of fibre cement boards, aluminium, PVC, zinc cladding, copper cladding, terracotta clay tiles, high-pressure laminates (HPL), ceramic tiles, ACP, granite, wire mesh, trellis for greenery or glass concrete wall. While these materials primarily provide protection against wind, rain and sun, insulation provides protection against cold. In fact, a rainscreen insulation board creates an ‘exterior curtain’ to walls leaving a physical separation gap (air chamber) between the insulation itself and the facade cladding layer. Rainscreen insulation product range comes from well-known brands such as Celotex®, Isover®, Xtratherm®, Knauf®, Ursa®, Rockwool® and Kingspan® so you're free to take your pick between whichever suits you. Typically 120mm of rainscreen slab should achieve a U-value of 0.35 W/m2K or better.
 
As rainscreen insulation and cladding are constructively separated from each other so they can be recycled separately when the facade is subsequently dismantled or renovated. This helps to keep internal temperatures stable by storing heat in the winter and reducing solar gains in the summer. Rainscreen insulation not only improves living comfort by eliminating all the possible noise from outside thanks to its high sound absorption capacity but also it is water‐repellent and prevents the progression of fire with a melting point of approximately 1000°C. Rainscreen insulation is usually independently dry fixed (bolted) to the exterior walls by fire rated mechanical fixings (insulation fasteners).

RAINSCREEN INSULATION HISTORY

Rainscreen cladding systems were first introduced in the 1940s. They were first used in practice in the 1950s and became more popular in the 1960s. In fact, rainscreen cladding was originally developed in Norway in the 1940s and 50s. Whilst rainscreen cladding has been a popular choice for commercial buildings for some time, in recent years more specifiers and designers are choosing to utilise their distinct benefits in the residential sector, particularly for inner-city high-rise developments.

TYPES OF RAINSCREEN FACADE INSULATION

Regarding the insulating materials for rainscreen cladding, there are several options. Rainscreen and masonry façade insulation include rolls, phenolic boards and mineral wool slabs. Rainscreen facade insulation can be manufactured with facings with excellent thermal insulation, with a very low thermal conductivity coefficient and excellent thermal resistance even at high temperatures.
 

RAINSCREEN SLABS

Flexible slab is quick to install and also accommodates imperfections in substrate. Slab is positioned between the support brackets for the rainscreen cladding system and across the whole area to be insulated. Slabs benefit from extremely fast install times compared with other types of insulation, and this is especially useful in busy urban settings. Rainscreen slabs usually come in 1220mm x 610mm or 1200mm x 600mm sizes.
 

RAINSCREEN ROLLS

Rainscreen insulation roll is the cheapest and most favoured option for most common types of cladding jobs and it is easy to fit between joists, which means it’s commonly used. In addition to flexibility, rainscreen facade rolls are also very adaptable to different wall shapes such as curves. Rolls work out cheaper therefore they become the most favoured option from all of available wall insulation types. This is one of the most popular types of insulation, mainly due to the fact it’s been around for so long and is widely available from most building merchants such as Screwfix, B&Q or Wickes.
 

RAINSCREEN BOARDS

Rainscreen insulation boards are the most productive type of rigid phenolic core, foil-composite insulation presently accessible for use in cladding projects. The product has a declared thermal conductivity λ value ranging from 0.018 to 0.021 WmK and is light to handle and can be cut easily. The rigid construction comes from the fact that unlike other forms of insulation, it doesn't come loose and compress after installation. Instead it's a solid, hard foam material. As they are high density boards have a good compressive strength and highest fire rating among many organic insulation materials. It can, in an appropriate form, achieve all the European fire certifications - UK Class O and Dutch NEN 6065/6066 Class 1. Generally speaking, the board is fire-resistant, flame-retardant, non-combustible in case of open flame, smoke-free, non-toxic, and non-dropping.  Panels can achieve up to 2 hours fire resistance rating in the 3m furnace test. They are closed cells, they shouldn’t absorb moisture or water vapour, unlike open cell products. 
 
 

RAINSCREEN FACADE BUILDING REGULATIONS

Rainscreen cladding is the most popular architectural choice for finishing buildings in a modern, stylish and aesthetically pleasing way. When using rainscreen insulation products, you need to satisfy yourself that use of the product meets all relevant national Building Regulations and guidance as well as local, national and other applicable standards relevant for your construction or application, including requirements in relation to fire and applicable height restrictions. Recent Building Regulations state that only non-combustible insulation or insulation of limited combustibility can be used in the external walls of relevant buildings over 18 metres in height (England & Wales) or 11 metres in height (Scotland).

The dimensions of the ventilated cavity should not exceed the limits in the Building Regulations. The U-values for proprietary curtain walling systems are dependent on the degree of thermal bridging in the system. The most important thing is making sure the wall supports the weight of the cladding material and insulation per m2. The cavity behind your rainscreen must have the appropriate width, relative to the building’s height, to allow water to drain as well as evaporate. As a thumb rule, a minimum cavity of 25mm should be maintained to allow sufficient air movement. Walls greater than 25m high should have a cavity depth of 1mm per meter in height. For example, a 50m wall with a continuous cavity should have a minimum depth of 50mm. The cavity may be broken and drained at individual floor levels.

On 1st June 2022 the government published an update to Approved Document B to introduce new rules for external walls and balconies for new blocks of flats between 11 metres and 18 metres in height. This new statutory guidance sets clearer, stronger standards which will set limits on the combustibility of materials used in the external walls of buildings. This will mean that lower risk developments between 11-18 metres meet necessary safety standards, while allowing designers and developers flexibility to use environmentally friendly materials.
 
 

RAINSCREEN INSULATION PRODUCTS/MATERIALS

ISOVER POLTHERM MAX PLUS

Polterm Max Plus is a stone wool slab covered with a black glass veil on one side. Certified by the British Board of Agrément (BBA), it can be considered for thermal and acoustic applications within ventilated rainscreen cladding and overcladding systems. Polterm Max Plus contains a water repellent additive to limit water absorption. The black glass veil can contribute to the aesthetics of the installation, as it prevents any ‘show through’ of the insulation from behind the façade system.

KNAUF ROCKSILK® RAINSCREEN SLAB

Rocksilk® RainScreen Slab is a BBA certified Rock Mineral Wool slab designed for use as sheathing insulation in rainscreen façade systems both below and above 18m in height. It is non-combustible with the best possible Euroclass A1 reaction to fire classification, and is manufactured using Knauf Insulation's unique bio-based binder, ECOSE® Technology.
 

KINGSPAN® KOOLTHERM K15 RAINSCREEN BOARD

Kingspan Kooltherm K15 Rainscreen Cladding Insulation Board is an advanced insulation solution with certified thermal conductivity of 0.021 W/mK used for rainscreen cladding and behind rainscreen façades. Kooltherm K15 is commonly used as insulation for rainscreen cladding systems with non-proprietary external finish, rainscreen cladding systems with terracotta clay tile external finish and rainscreen cladding systems on steel frames. Kingspan Rainscreen Cladding Insulation provides the highest R–value per inch when compared to commonly available equivalent insulation products in the UK, allowing U-values to be met with minimal thickness.
 
 
KINGSPAN K-ROC® RAINSCREEN SLAB 

Kingspan K-Roc® Rainscreen Façade Insulation Slab Class A1 is a rock mineral fibre insulation slab designed for use behind rainscreen façades in all buildings regardless of building type, height, construction and location. Rainscreen Façade Insulation Slab Kingspan K-Roc is a great heat conductor with a certified thermal conductivity (lambda value) of 0.034 W/mK (the lower the thermal conductivity, the better the insulation product). K-Roc Rock Mineral Fibre Rainscreen Slab has a density of 45 kg/m3 and comes in a standard insulation slab size 600mm wide by 1200mm long (4' by 2'). Kingspan Rainscreen Slab K-Roc is manufactured to the highest standards under a management system certified to ISO 9001 and ISO 14001. The use of K-Roc® Rainscreen Façade Insulation Slab is covered by BBA Certificate 20/5845.
 

ROCKWOOL® RAINSCREEN DUO SLAB

RAINSCREEN DUO SLAB® is a stone wool insulation product specifically developed for use within ventilated cladding systems, as well as sealed systems such as curtain walling. Manufactured using Dual Density technology, the outer surface of each slab features a distinctly higher density than the underside. This provides a firm and robust surface for the application of fixings, while the resilient underside can accommodate unevenness in the substrate. Once installed, the higher density outer surface works in combination with a factory-applied water repelling agent to give improved resistance to rain ingress during construction. The product can be easily fitted around brackets and other awkward details, and when tightly butted, adjacent slabs effectively ‘knit’ together to provide a continuous insulating layer, reducing heat losses that would otherwise be caused by gaps.
 

URSA® WALLTEC BLACK

URSA® walltec black slabs are BBA approved for use behind rainscreen cladding systems, both new build and refurbishment. The slabs have a black glass fleece facing so they can be used in open joint cladding systems without being seen. It is non-combustible, Euroclass A1, so do not add any fire load to the building or prejudice the overall fire performance of the wall.

RAINSCREEN INSULATION SIZES/THICKNESSES

Rainscreen insulation is available in a wide range of thicknesses and sizes to suit most requirements.
 

SIZES

2400mm x 1200mm ǀ 1350mm x 600mm ǀ 1220mm x 610mm ǀ 1200mm x 600mm

THICKNESSES

50mm ǀ 60mm ǀ 70mm ǀ 75mm ǀ 80mm ǀ 90mm ǀ 100mm ǀ 110mm ǀ 120mm ǀ 125mm ǀ 130mm ǀ 140mm ǀ 150mm ǀ 155mm ǀ 160mm ǀ 165mm ǀ 170mm ǀ 180mm ǀ 190mm ǀ 200mm ǀ 210mm ǀ 220mm ǀ 230mm ǀ 240mm ǀ 250mm

RAINSCREEN INSULATION FIXINGS

Very important to achieve the success and the best possible performance of rainscreen cladding systems are the fastening components ability to resist loadings and to interconnect the component parts from the external facing materials back through the system to the structural supporting wall or framework. Good practice dictates the use of non-ferrous materials with regard to fasteners used within rainscreen build-ups and systems. These typically include stainless steels, aluminium and plastics.
Nylons and plastics are used within the rainscreen insulation layer. It is generally considered that the fixing of insulation boards is a non-structural application. So whilst a less technical approach may be adopted it is worth noting that the insulation will still be subjected to wind loads during construction and that regulations exist concerning wind loads and fire regulations that must be adhered to.
Whilst plastic fasteners may be used for restraining the boards, at least 1 metal fixing should be used per square metre. Generally speaking, on a 1200 x 2400mm board this equates to 9 fixings (min) per board - 3 plastic fasteners down either side and 3 metal fasteners down the centre line. The fasteners should be no less than 50mm and not more than 150mm from the corners or edges. In addition, where the board may be subjected to external wind pressure, the requirement for additional fasteners should be assessed in accordance with BS EN 1991-1-4:2005 (UK National Annex to Eurocode 1 Actions on structures, general actions, wind actions). Individual insulation manufacturers should always be consulted with regard to fixing patterns.

Picture credit:designingbuildings.co.uk/wiki/Rainscreen

Depending on the type of insulation being fixed (foam type or mineral wool) will determine the minimum size of head that the fastener should have - a smaller head 25-40mm can be used on most rigid boards whilst a 70-90mm head will be required for softer mineral wool insulation boards. 
Insulation to steel, timber and sheathing board - for these substrates, a plastic or stainless steel disc in conjunction with the fastener appropriate to the substrate should be selected. 
It is becoming more common to fix insulation to sheathing boards over steel frames. Best practice recommends fixing through the sheathing board and into the steel/timber structure. Where this is not possible, it is advisable to ascertain the fastener performance in the sheathing board prior to installation as the different boards available will offer quite dramatic differences in performance regarding resistance to fastener ‘pull out’.

Picture credit:

1.mcrma.co.uk/wp-content/uploads/2017/06/GD11-MCRMA-rainscreen-fixings-and-fastenings.pdf
 

BIBLIOGRAPHY:

https://mcrma.co.uk/wp-content/uploads/2017/06/GD11-MCRMA-rainscreen-fixings-and-fastenings.pdf

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