Rainscreen Facade Systems - Technical Detail

Rainscreen Insulation Installation
Rainscreen Facade Systems

Rainscreen cladding and curtain wall systems

Rainscreen cladding systems

There are a wide variety of proprietary rainscreen cladding systems available most of which have the insulation installed on the external face of a masonry wall, this helps to keep internal temperatures stable by storing heat in the winter and reducing solar gains in the summer. Rainscreen cladding systems are also lightweight when compared to brick and masonry solutions and they can provide the designer with a wide range of aesthetic options.

Our Technical Support Team can supply numerically modelled U-value calculations for rainscreen systems installed on existing walls, new build walls or walls incorporating light steel frame systems, providing all relevant construction information is made available to us.

Contact our Technical Team  View RainScreen Products

Curtain wall systems

Curtain walls usually consist of a proprietary non structural lightweight frame which in some cases is designed to incorporate glass panels which act as the weatherproof facade and also allow daylight to penetrate into the building.

There are several other types of curtain walling including factory built unitized systems which are typically comprised of insulation behind a glass, natural stone or metal facing.

Whenever a proprietary rainscreen cladding or curtain wall system is used, the system manufacturer’s recommendation should be followed.

Weather protection

Rainscreen cladding systems are designed to keep both the structural frame and the thermal insulation dry, due to the rainscreen cladding itself but also due to the airspace between the cladding and the insulation.

Drained and ventilated rainscreen systems work by allowing air to enter at the base of the system and escape at the top of the system, the ventilated cavity allows water penetrating the panel joints to be partly removed by the ‘stack effect’ and partly removed by running down the rear face of the panels and out of the base of the system.

Curtain walls usually consist of a glass facade which is both waterproof and thus weather


For external wall constructions that include cavities (such as rainscreen cladding), cavity fire barriers are recommended at the junctions between the wall and every compartment floor or wall or other wall or door assembly that forms a fire-resisting barrier as detailed in Approved Document B - further guidance is given in BR135, published by the Building Research Establishment.

Fire barriers

Should be made from non-combustible material, and be installed in accordance with current building regulations. Please check this with your barrier supplier.

Solution Optimiser and Pathfinder

Solution Knauf Insulation Product Construction Code U-value Range (High) U-value Range (Low)
Behind rainscreen cladding system Rocksilk® RainScreen Slab Er01 0.34 0.23
Within curtain walling system Rocksilk® RainScreen RS45 / RS60 Building Slab Er02 Contact system manufacturer Contact system manufacturer

Cladded Walls Behind Rainscreen Cladding Systems



  • Friction fitting behind and between cladding rails prevents air movement and infiltration through or around the insulation
  • Lightweight, flexible slab is quick to install and also accommodates imperfections in substrate
  • Knauf Insulation 3D modelling calculation service provides optimised thermal performance


  • Non-combustible with a Euroclass A1 reaction to fire rating
  • A+ Generic BRE Green Guide rating
  • Zero Ozone Depletion Potential (ODP)
  • Zero Global Warming Potential (GWP)

Typical construction

Rainscreen cladding systems comprise outer cladding panels that are bolted to a supporting framework of rails, which are supported by brackets fixed through a thermal break pad back to the building frame. A layer of insulation is fixed independently against the building substructure using proprietary insulation fasteners.

Rocksilk® RainScreen Slab is recommended for this application, as it is lightweight but rigid enough to resist the compression forces generated when installing the insulation slabs on the masonry substrate.


Rocksilk® RainScreen Slab is positioned between the support brackets for the rainscreen cladding system and across the whole area to be insulated. Cut the slabs with a sharp knife to fit around the brackets so there are no gaps in the insulation. To minimise thermal bridging, the brackets should be of sufficient depth to allow the panel support rails to be located clear of the face of the insulation.

The insulation should be close butted and fixed independently against the building superstructure using proprietary insulation fasteners in accordance with the design specification.

Once the insulation is firmly in place, the application of the cladding can proceed. Ensure that a ventilated cavity remains between the insulation and the external cladding. The dimensions of the ventilated cavity should not exceed the limits in the Building Regulations.


Thermal performance

Rocksilk® RainScreen Slab has a thermal conductivity of 0.034 W/mK.

The U-value of a proprietary rainscreen cladding system is dependent on the degree of thermal bridging in the system. Typically 120mm of Rocksilk® RainScreen Slab will achieve a U-value of 0.35 W/m2K or better, but Knauf Insulation advise consulting proprietary rainscreen cladding manufacturers for U-values appropriate for their system.

Fire performance

Rocksilk® RainScreen Slab is classified as Euroclass A1 to BS EN 13501-1.

Typical Junction detail with exposed floor

U-values (W/m2K) for 215mm solid masonry wall of:

Insulation Thickness (mm) Dense Block (λ=1.13) Medium Block (λ=0.51) Cast Concrete Aggregate (λ=1.13)
200 0.24 0.23 0.24
190 0.25 0.24 0.25
180 0.26 0.25 0.26
170 0.27 0.26 0.27
160 0.28 0.27 0.28
150 0.29 0.28 0.29
140 0.31 0.29 0.31
130 0.32 0.32 0.32
120 0.34 0.33 0.34

Note: Fixings assumed to be plastic insulation holders with 5mm dia. steel expansion pin. The U-values have been calculated to
BS EN ISO 10211 and BR 443. For project specific calculations contact our Technical Support Team on 01744 766666.

Cladded Walls Within Curtain Walling System



  • Friction fits in panels for maximum thermal and acoustic performance
  • Suitable for unitised and traditional build curtain walling systems


  • Non-combustible with a Euroclass A1 reaction to fire rating
  • A+ Generic BRE Green Guide rating
  • Zero Ozone Depletion Potential (ODP)
  • Zero Global Warming Potential (GWP)


Thermal performance

Rocksilk® Building Slab RS45 has a thermal conductivity of 0.035W/mK and RS60 has a thermal conductivity of 0.034 W/mK.

The U-values for proprietary curtain walling systems are dependent on the degree of thermal bridging in  the system, Knauf Insulation advise consulting individual curtain walling manufacturers for U-values appropriate for their system..

Fire performance

Rocksilk® Building Slab RS45 and RS60 are classified as Euroclass A1 to BS EN 13501-1.

Typical construction

Curtain walling systems come in several forms. The illustration above shows a unitised curtain wall system.

Unitised curtain wall facades are suitable for various facing materials such as aluminium, steel, natural stone or glass. They are assembled in a factory as large integral units, and taken to site for fast track fixing.

Rocksilk® Building Slab RS45 and RS60 are recommended for insulating curtain walling systems.


Rocksilk® Building Slab RS45 and RS60 are cut to size and installed in the factory as the middle layer of a pre-assembled curtain wall unit.

The panels are typically hung onto and/or mechanically fixed to the building's superstructure.

Contact our Technical Support Team