Technical Data | EWI – Cavity Barriers and Fire Stops for External Masonry Walls | Construction | Products | Siderise

Siderise EWI – Cavity Barriers and Fire Stops for External Masonry Walls – Technical Data

Version: 1.03 - Release Date: March 2022


Siderise EWI Systems have been specially developed via the incorporation of an integral intumescent, which in the event of a fire, provides a reactive method of sealing masonry wall cavities that have an irregular inner face to the outer masonry leaf such as decorative features.

Siderise EWI systems are currently available for horizontal applications with the product codes as below:

  • EW25-CB30 is for use as a Cavity Barrier in accordance with building regulations.
  • EW25-FS120 is for use as a Fire Stop in accordance with building regulations.

These products represent an ideal combination of fully qualified performance and practical installation.

Siderise EWI (open state) for horizontal applications should be installed in conjunction with Siderise EW (full fill) for vertical applications.

Product Description

Siderise EWI Systems comprise of a low resin content stone wool insulation core which is pre-compressed internally to form a resilient strip. The material is faced on two sides with a reinforced Class 0 aluminium foil which is an effective smoke barrier. Siderise EWI incorporates an integral reactive intumescent. The leading edge is encapsulated in a white weather-resistant polymer film.

Siderise EWI is only supplied in pre-cut strips:

  • Pre-cut products are available in 1mm increments of width to suit the cavity size. Please see Table 1.
  • Supplied with appropriate brackets as part of a system (see Table 1).
Siderise EWI should be installed in accordance with PD6697:2019 - 'Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2'.

If Siderise EWI is in contact with the outer masonry (thereby bridging the cavity), it must be installed with a Cavity Tray directly above. Where there is no contact with the outer masonry leaf (i.e. a continuous uninterrupted air gap) a cavity tray is no longer required, except where otherwise called for such as above openings. Please refer to 3rd party warranty providers, such as NHBC, LABC and Premier Guarantee for further guidance.

Fire Performance

Siderise EWI systems have been tested in accordance with TGD 019 Fire resistance test for 'open-state' cavity barriers used in the external envelope or fabric of buildings.

  • Resistance to Fire - is expressed as Integrity (E) and Insulation (I) performance in minutes, please see Table 1.
  • Reaction to Fire - Classification to EN 13501-1 : 'A1' (core), 'E' (intumescent) as permitted by Regulation 7(3).

Table 1 : Fire Resistance to ‘General Principles of ASFP - TGD 19’

Orientation EWI System Thickness
Air Gaps Brackets
Horizontal EW25-CB30 75 76-150 25mm RS 350 90 30 
     151-250 25mm RS 350 90 30 
     251-350 25mm RS 450 90 30 
Horizontal EW25-FS120 120 76-150 25mm B65/110 120 120 
     151-250 25mm B195 120 120 
     251-350 25mm B355 120 120 

Please note:

  • Brackets are available in two forms: (G) denotes galvanised steel brackets and (S) denotes stainless steel brackets.
  • RS Brackets must be installed at 400mm centres based on a 1200mm strip. 
  • B Brackets must be installed at 600mm centres based on a 1200mm strip.
  • For lengths ≤800mm 2no brackets must be used, with spacing reduced pro-rata.
  • All brackets to be suitably fixed to substrate with non-combustible fixings.
  • All brackets to penetrate product at mid-thickness.
  • Please refer to separate installation instructions.

Siderise EWI has been tested in accordance with the stated test standard for masonry assemblies. The stated classifications (EI) have in some instances been stated lower than achieved in test, this is to keep simplicity in the range as either a 30 minute or 120 minute product. When considering Steel Frame Systems (SFS) it is imperative that the supporting structure to be of at least an equal fire performance rating to that of the Cavity Barrier or Fire Stop.

For other void sizes or additional advice, please contact Technical Support.

Thermal Performance

Thermal conductivity : λ10 = 0.038 W/m.K (tested foil to foil)

Damp Proofing

Siderise EWI must be damp-proofed in accordance with PD6697:2019 - 'Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2'.

Technical Specification

Siderise EWI - Cavity Barrier and Firestops

Table 2 : Product Properties

Property Value 
Reaction to Fire Classification to EN 13501-1 : 'A1' (core), 'E' (intumescent) as permitted by ADB. 
Resistance to Fire Please see Table 1 
Thermal Conductivity λ10 = 0.038 W/m.K (tested foil to foil) 
Chemical The base stone wool is chemically inert. An aqueous extract of the rock wool is neutral (pH7) or slightly alkaline. Resistant to most acids and weak alkaline solutions. 
Biological Vermin and rot proof and does not encourage the growth of fungi, moulds or bacteria. 
Effect of water Non-hygroscopic. Unaffected by humid atmosphere. Must be suitably damp proofed in accordance with codes of practice for masonry constructions. 
Compatibility Compatible with all normal building materials. 
Maintenance No maintenance required unless disturbed. 
Handling Easy to handle but should be treated with due care to ensure material integrity and shape are maintained. 
Storage Store in dry conditions. 

Siderise offers a range of ancillary products to complement the EWI range these include:

Fixing Brackets must be used in the installation of the product. Brackets come in two types:‘RS’ – split end brackets and ‘B’ – standard brackets, both available in forms:'G' - Galvanised Steel Brackets and 'S' - Stainless Steel Brackets.

Aluminium Jointing Tape must be used at all joints and intersections:

  • RFT120/45 (120mm wide x 45m rolls)
  • Adhesive backed
  • Supplied in boxes of 8

Fire & Acoustic Sealant may be used for small gaps and undulations:

  • FS120/310ML/WH (310ml cartridge)
  • Supplied in boxes of 25


Siderise EWI systems are environmentally friendly:

  • They contain no Volatile Organic Compounds (VOCs) and no very Volatile Organic Compounds (vVOCs)
  • Zero Ozone Depleting Potential
  • Zero Global Warming Potential
  • Recyclable

Additional Information

The following information is available for download via the website:

  • Standard Details
  • NBS Specification Clauses
  • Installation Instructions
  • Safety Data Sheet

Technical Support

For technical advice or support please contact the technical team:

For Installation Training or Site Inspections please contact:


The information in this datasheet is believed to be accurate at the date of publication. Siderise has a policy of continuous product improvement and reserves the right to alter or amend the specifications of products without prior notice. Siderise does not accept responsibility for the consequences of using the products described outside of the recommendations within this datasheet. Expert advice should be sought where there is any doubt about the correct specification or installation of Siderise products.

Published Version: EWI_v1_03_2022038_179