Insulating Walls Externally with Pavatex

External Wall Insulation (EWI)

  • Breathable, hygroscopic and capillary-active insulation so water vapour and water droplets can pass through the insulation and evaporate away
  • Reduces thermal bridging through the junctions
  • Keeps the walls drier and warmer all year round
  • Can be finished with breathable render or ventilated cladding
  • Suitable for masonry, timber-frame or CLT buildings
  • Suitable for traditional single-leaf buildings constructed from stone, brick or cob
  • Carbon-negative and natural, sustainable insulation – safe to handle
  • Adds thermal mass and acoustic insulation to lightweight structures

Isolair Multi External Wall Insulation

Installation

Isolair Multi Wood Fibre Insulation on Walls

Finished

Isolair Multi Wood Fibre Insulation with Baumit Render on Walls

Jump to your preferred option by choosing one of the below:

Masonry Wall

Option 1: External Wall Insulation (EWI) with Render Finish on Masonry Wall

Pavatex Isolair Multi wood fibre thermal insulation is ideal to use as External Wall Insulation (EWI) over any masonry substrate – brick, stone or concrete block and it can be finished with vapour-open render. We recommend that any existing sand and cement render is removed first because this may trap water vapour or liquid within the structure of the building.

The Isolair Multi insulation can then go straight to the substrate – it doesn’t need to be lime rendered first unless the substrate is very uneven. The plinth area of the building must be insulated with waterproof XPS insulation. We recommend rendering the wood fibre insulation with Baumit MC55 base coat including a reinforcing mesh, and Baumit SilikonTop top-coat render. SilikonTop is self-coloured so does not require painting. This complete rendered system is CE marked.

U-value examples are shown below.

Masonry Wall

  1. 2 coat Baumit render system with mesh
  2. ISOLAIR MULTI 40 / 52 / 60 / 80 / 100 / 120 / 140 / 160 / 180 / 200mm
  3. Masonry wall (cavity or single-leaf)
  4. Internal lime plaster finish and water-based paint
  1. 2 coat Baumit render system with mesh

Downloads

Option 2: External Wall Insulation (EWI) with Ventilated Cladding Finish on Masonry Wall

Pavatex Isolair Multi wood fibre thermal insulation is ideally suited as External Wall Insulation (EWI) over any masonry substrate – stone, brick or concrete block and it can be completed with a ventilated facade. We recommend that any existing sand and cement render is removed first because this may trap water vapour or liquid within the wall.

The Isolair Multi insulation can then go straight to the substrate – it doesn’t need to be lime rendered first unless the substrate is very uneven. The plinth area of the building must be insulated with waterproof XPS insulation. The chosen cladding is installed on to vertical timber battens to ensure adequate ventilation. This complete cladded system has a BBA (British Board of Agrément) certificate.  

Installation Method

Baumit renders have been approved for use with our systems. We can supply all the products below.

  • Plinth area (bottom 30cm approx. of the wall and any wall below the finished ground level) must be insulated with waterproof XPS insulation. Bond this to wall with Baumit MC55 W render at 5mm thickness.
  • ISOLAIR MULTI wood fibre T&G boards in landscape formation (40 - 200mm). Use H1 Eco Hammer Fixings for solid masonry or STR-U Fixings for rubble / crumbly masonry (9 per board approx).
  • Baumit MC55 W base coat render at 6-9mm thickness and insert the Baumit Reinforcing Mesh into this. 
  • Baumit DG27 Primer applied over the dry base coat to accept self-coloured renders.
  • Baumit SilikonTop self-coloured topcoat render is applied. Highly water repellent but vapour-open and so suits our rainy climate. 1.5mm, 2mm or 3mm grain in white or a large variety of colours.
  • Seal any area of the rendered XPS Plinth Board that will be below finished ground level with Baumit DS26 Flex Sealing Layer. This is mixed with water to a paintable consistency and applied in 2 coats over the topcoat at 5mm max thickness. Usage:1.2kg/m2/mm approx.
Ancillary Products
  • REVEAL BOARD – Continuation of insulation into the window & door reveals (fixed with H1 Eco Hammer Fixing) 
  • VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
  • PAVAPRIM – To prime wood fibre before applying VARA SEAL SL TAPE
  • ISO-BLOCO Expanding Foam Tape – To seal junction between wood fibre and XPS and any perimeter gaps between wood fibre and structure
  • RAILS & BEADS – As required by plasterer

Masonry Wall

  1. Cladding system (timber, brick, screen)
  2. Battens to create a 40mm min. ventilated cavity
  3. ISOLAIR MULTI 40 / 52 / 60 / 80 /100 / 120 / 140 / 160 / 180 / 200mm optionally protected with ADB Breather Membrane
  4. Masonry wall (cavity or single leaf)
  5. Internal lime plaster finish and water-based paint
  1. 2 coat Baumit render system with mesh
Installation Method

We can supply all the products below.

  • Plinth area (bottom 30cm approx. of the wall and any wall below the finished ground level) must be insulated with waterproof XPS insulation. Bond this to wall with Baumit MC55 W render at 5mm thickness.
  • Seal any front area of the XPS Plinth Board that will be below finished ground level with Baumit DS26 Flex Sealing Layer. This is mixed with water to a paintable consistency and applied in 2 coats over the topcoat at 5mm max thickness. Usage:1.2kg/m2/mm approx.
  • ISOLAIR MULTI wood fibre T&G boards in landscape formation (40 - 200mm). Use H1 Eco Hammer Fixings (2 per board) to initially pin into solid masonry. Isolair Multi can be left exposed for up to 3 months so long as any non-T&G joints / junctions are primed and taped to prevent water ingress or, if preferred, it can be covered with the Pavatex ADB Breather Membrane.
  • 40mm vertical batten to create service void fixed with Mungo MRS-U fixings for solid masonry walls or Mungo MQL-ST fixings for rubble / crumbly walls (9 per m2 approx). A 50mm cavity is required if the cladding has open joints. 
  • Secure cladding to battens only in accordance with manufacturer’s instructions. Use brick ties if installing a brick wall.
Ancillary Products
  • REVEAL BOARD – Continuation of insulation into the window & door reveals (fixed with H1 Eco Hammer Fixing) 
  • VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
  • PAVAPRIM – To prime wood fibre before applying VARA SEAL SL TAPE & PAVATAPE
  • PAVATAPE 75 or 150 – To seal any non-T&G joints at penetrations, perimeters etc to prevent rain ingress (if not using a breather membrane)
  • ISO-BLOCO Expanding Foam Tape – To seal junction between wood fibre and XPS and any perimeter gaps between wood fibre and structure
  • PAVATAPE 12– Double-sided tape for bonding membranes to all substrates including masonry and for bonding membrane ends to each other

Downloads

Timber Frame Wall

Option 1: External Wall Insulation (EWI) with Render Finish on Timber Frame Wall

Pavatex Isolair Multi wood fibre thermal insulation is ideal to use as External Wall Insulation (EWI) over a timber or metal frame wall and it can be finished with vapour-open render. The studs are filled with flexible Pavaflex wood fibre or Pavatextil P recycled cotton insulation. Wood fibre adds considerable thermal mass to timber frame buildings.

The plinth area of the building must be insulated with waterproof XPS insulation. We recommend rendering the wood fibre insulation with Baumit MC55 base coat including a reinforcing mesh, and Baumit SilikonTop top-coat render. SilikonTop is self-coloured so does not require painting. This complete rendered system is CE marked.

U-value examples are shown below.

Timber Frame Wall

  1. 2 coat Baumit render system with mesh
  2. ISOLAIR MULTI 60 / 80 / 100 / 120 / 140 / 160 / 180 / 200mm
  3. Stud wall fully filled with PAVAFLEX / PAVATEXTIL P
  4. Racking board taped for airtightness e.g. 12/15mm OSB or Pavatex DB3.5 Airtightness Membrane
  5. Optional: 25mm services void
  6. Plasterboard
  7. Plaster skim finish & water-based paint
  1. 2 coat Baumit render system with mesh
Installation Method

Baumit renders have been approved to use with our systems.  We can supply all the products below.

  • Plinth area (bottom 30cm approx. of the wall and any wall below the finished ground level) must be insulated with waterproof XPS insulation. Bond to masonry wall plinth with Baumit MC55 W render at 5mm thickness.
  • ISOLAIR MULTI wood fibre T&G boards in landscape formation (60 - 200mm). Use 60mm min on timber frame. Use Ejot STR-H Fixings - approx 14 fixings per board when studs are at 400mm centres. Use 3 fixings per board per stud.
  • Baumit MC55 W base coat render at 6-9mm thickness with Reinforcing Mesh inserted into this. 
  • Baumit DG27 Primer applied over the dry base coat to accept self-coloured renders.
  • Baumit SilikonTop self-coloured topcoat render is applied. Highly water repellent but vapour-open and so suits our rainy climate. 1.5mm, 2mm or 3mm grain in white or a large variety of colours.
  • Seal any area of the rendered XPS Plinth Board that will be below finished ground level with Baumit DS26 Flex Sealing Layer. This is mixed with water to a paintable consistency and applied in 2 coats over the topcoat at 5mm max thickness. Usage:1.2kg/m2/mm approx.
  • PAVAFLEX or PAVATEXTIL P flexible insulation fully filled in between studs. It is strongly recommended to place the taped OSB3 racking board on the inside of the structure because this will also provide airtightness. In addition, it optimally controls the passage of moisture when on the warm side (inside) of the insulation. However, it can also be placed on the outside of the frame.
  • Optional Plaster Finish: Isolair Multi T&G Boards screwed to inside of timber studs for more insulation, if required, and this can be plastered directly with Baumit lime plaster.
  • Optional Plasterboard Finish: OSB with taped joints for airtightness and racking strength OR Pavatex DB 3.5 airtightness membrane on inside of studs. Battens to make Services Void, if required, and Plasterboard or Fermacell finishing board
Ancillary Products
  • VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
  • PAVAPRIM – To prime wood fibre before applying VARA SEAL SL TAPE
  • ISO-BLOCO Expanding Foam Tape – To seal junction between wood fibre and XPS and any perimeter gaps between wood fibre and structure
  • RAILS & BEADS - Usually supplied by plasterer

Downloads

Option 2: External Wall Insulation (EWI) with Ventilated Cladding Finish on Timber Frame Wall

Pavatex Isolair Multi wood fibre thermal insulation is perfect to use as External Wall Insulation (EWI) over timber or metal frame walls when a ventilated façade finish is desired. The studs are filled with flexible Pavaflex wood fibre or Pavatextil P recycled cotton insulation. Wood fibre adds considerable thermal mass to timber frame buildings.

The plinth area of the building must be insulated with waterproof XPS insulation. The chosen cladding is installed on to vertical timber battens to ensure adequate ventilation. This complete cladded system has a BBA (British Board of Agrément) certificate.  

U-value examples are shown below.

Timber Frame Wall

  1. Cladding system (timber, brick, screen)
  2. Battens to create a 40mm min ventilated cavity
  3. ISOLAIR MULTI 40 / 52 / 60 / 80 / 100 / 120 / 140 / 160 / 180 / 200mm optionally protected with Pavatex ADB Breather Membrane
  4. Stud wall fully filled with PAVAFLEX / PAVATEXTIL P
  5. Racking board, taped for airtightness e.g. 12/15mm OSB3 or Pavatex DB3.5 Airtightness Membrane
  6. Optional: 25mm services void
  7. Internal plasterboard & skim finish
  1. 2 coat Baumit render system with mesh

Downloads

Installation Method

Baumit products have been approved to use with our systems.  We can supply all the products below.

  • Ventilated Cladding or Brick Wall Cladding
  • 40mm deep Vertical Battens to support cladding fixed back to frame with Heco Topix 6 Fixings – (approx 10 per m2) or brick ties if installing a brick wall. A 50mm cavity is required if the cladding has open joints.  
  • Plinth area (bottom 30cm approx. of the wall and any wall below the finished ground level) must be insulated with waterproof XPS insulation. Bond to masonry wall plinth with Baumit MC55 W render at 5mm thickness.
  • Isolair Multi wood fibre T&G boards in landscape formation (40 - 200mm). Use Heco Topix 6 Fixings (2 per board) to initially fix to timber frame. Isolair Multi can be left exposed for up to 3 months so long as any non-T&G joints / junctions are primed and taped to prevent water ingress or, if preferred, it can be covered with the Pavatex ADB Breather Membrane.
  • PAVAFLEX or PAVATEXTIL P flexible insulation fully filled in between studs. It is strongly recommended to place the taped OSB racking board on the inside of the structure because this will also provide airtightness. In addition, it optimally controls the passage of moisture when on the warm side (inside) of the insulation. However, it can also be placed on the outside of the frame.
  • Optional Plasterboard Finish: OSB3 with taped joints for airtightness and racking strength OR Pavatex DB 3.5 airtightness membrane on inside of studs. Battens to make Services Void, if required, and Plasterboard or Fermacell finishing board
  • Optional Plaster Finish: Isolair Multi T&G Boards screwed to inside of timber studs for more insulation, if required, and this can be plastered directly with Baumit lime plaster.
Ancillary Products
  • VARA SEAL SL TAPE –Self-adhesive airtight & windtight tape for windowsill sealing
  • PAVATAPE 75 or 150 – To seal any non-T&G joints at external penetrations, perimeters etc to prevent rain ingress (if not using a breather membrane)
  • PAVAPRIM – To prime wood fibre before applying VARA SEAL SL TAPE & PAVATAPE
  • PAVATAPE 12– Double-sided tape for bonding membranes to all substrates including masonry and for bonding membrane ends to each other
  • ISO-BLOCO 600 Expanding Foam Tape – To seal junction between wood fibre and XPS and any perimeter gaps between wood fibre and structure
  • PAVAFIX 60 BLACK TAPE – To seal joints in DB3.5 airtightness membrane (if using)

CLT (Cross Laminated Timber) Wall

Option 1: External Wall Insulation (EWI) with Render Finish on CLT Wall

Pavatex Isolair Multi and Pavatherm wood fibre thermal insulation boards are ideal to use as External Wall Insulation (EWI) over a CLT wall and they can be rendered with vapour-open render.

The plinth area of the building must be insulated with waterproof XPS insulation. We recommend rendering the Isolair Multi wood fibre insulation with Baumit MC55 base coat including a reinforcing mesh, and Baumit SilikonTop top-coat render. SilikonTop is self-coloured so does not require painting. This complete rendered system is CE marked.

Cross Laminated Timber (CLT) Wall

  1. 2 coat Baumit render system with mesh
  2. ISOLAIR MULTI 60mm
  3. PAVATHERM 80 / 100 / 120 / 140 / 160 / 180 / 200mm
  4. DSB2 Airtightness Membrane (if CLT is to be left exposed on the inside) over Cross Laminated Timber Structure
  1. 2 coat Baumit render system with mesh
Installation Method

Baumit renders have been approved to use with our systems.  We can supply all the products below.

  • Plinth area (bottom 30cm approx. of the wall and any wall below the finished ground level) must be insulated with waterproof XPS insulation. Bond to wall plinth with Baumit MC55 W render at 5mm thickness.
  • DSB 2 Airtightness Membrane outside structure (if CLT is to be left exposed on the inside)
  • PAVATHERM wood fibre square edged boards in landscape formation (80 - 200mm). Fix with Ejot STR-H Fixings (1 fixing per board to pin in place).
  • ISOLAIR MULTI wood fibre T&G boards in landscape formation (60mm). Use Ejot STR-H Fixings through Isolair Multi and Pavatherm (9 fixings per m2).
  • Baumit MC55 W base coat render at 6-9mm thickness with Reinforcing Mesh inserted into this. 
  • Baumit DG27 Primer applied over the dry base coat to accept self-coloured renders.
  • Baumit SilikonTop self-coloured topcoat render is applied. Highly water repellent but vapour-open and so suits our rainy climate. 1.5mm, 2mm or 3mm grain in white or a large variety of colours.
  • Seal any area of the rendered XPS Plinth Board that will be below finished ground level with Baumit DS26 Flex Sealing Layer. This is mixed with water to a paintable consistency and applied in 2 coats over the topcoat at 5mm max thickness. Usage:1.2kg/m2/mm approx.
Ancillary Products
  • VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
  • PAVAPRIM – To prime wood fibre before applying VARA SEAL SL TAPE
  • PAVAFIX 60 TAPE to seal membrane short ends together
  • ISO-BLOCO Expanding Foam Tape – To seal junction between wood fibre and XPS
  • RAILS & BEADS - Usually supplied by plasterer

Downloads

Option 2: External Wall Insulation (EWI) with Ventilated Cladding Finish on CLT Wall

Pavatex Isolair Multi and Pavatherm wood fibre thermal insulation boards are perfect to use as External Wall Insulation (EWI) over CLT walls when a ventilated façade finish is desired.

The plinth area of the building must be insulated with waterproof XPS insulation. The chosen cladding is installed on to vertical timber battens to ensure adequate ventilation.

Cross Laminated Timber (CLT) Wall

  1. Cladding system (timber, brick, zinc etc)
  2. Battens to create a 50mm ventilated cavity
  3. Pavatex ADB Breather Membrane
  4. PAVATHERM 40 / 60 / 80 / 100 / 120 / 140 / 160 / 180 / 200mm. Optionally, this can be combined with 60mm Isolair Multi.
  5. DSB2 Airtightness Membrane (if CLT is to be left exposed on the inside) on outside of Cross Laminated Timber Structure
  1. 2 coat Baumit render system with mesh
Installation Method

We can supply all the products below.

  • Plinth area (bottom 30cm approx. of the wall and any wall below the finished ground level) must be insulated with waterproof XPS insulation. Bond to wall plinth with Baumit MC55 W render at 5mm thickness.
  • Seal any area of the rendered or bare XPS Plinth Board that will be below finished ground level with Baumit DS26 Flex Sealing Layer. This is mixed with water to a paintable consistency and applied in 2 coats over the topcoat at 5mm max thickness. Usage:1.2kg/m2/mm approx.
  • DSB 2 Airtightness Membrane taped to structure (if CLT is to be left exposed on the inside)
  • PAVATHERM wood fibre square edged boards in landscape formation (40 - 200mm). Fix with Ejot STR-H Fixings (1 fixing per board to pin in place). Pavatherm is not water-resistant so the Pavatex ADB Breather Membrane must be used directly over the Pavatherm, if not also using Isolair Multi.
  • OPTIONAL: 60mm ISOLAIR MULTI water resistant wood fibre T&G boards in landscape formation directly over Pavatherm. Fix with Ejot STR-H Fixings (1 fixing per board to pin in place). Isolair Multi can be left exposed for up to 3 months so long as any non-T&G joints / junctions are primed and taped to prevent water ingress or, if preferred, it can be covered with the Pavatex ADB Breather Membrane.
  • 50mm deep Vertical Battens to support cladding fixed back to CLT structure with Heco Topix-Therm Fixings (6 min. per m2) or use brick ties if installing a brick wall
  • Ventilated Cladding or Brick Wall Cladding
Ancillary Products
  • VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
  • PAVATAPE 75 or 150 – To seal any non-T&G joints at external penetrations, perimeters etc to prevent rain ingress (if not using a breather membrane)
  • PAVAPRIM – To prime wood fibre before applying VARA SEAL SL TAPE & PAVATAPE
  • PAVATAPE 12– Double-sided tape for bonding membranes to all substrates and for bonding membrane ends to each other
  • ISO-BLOCO 600 Expanding Foam Tape – To seal junction between wood fibre and XPS and any perimeter gaps between wood fibre and structure

Downloads

U-Value Results

Timber Frame Wall Results

140mm and 219mm Timber Frame Walls

  • Baumit Render System or Ventilated Cladding
  • Isolair Multi Wood Fibre on outside of stud frame
  • Pavaflex or Pavatextil P between the studs
  • OSB on inside
  • 25mm Services Void
  • 12.5mm Plasterboard & Skim
Isolair Multi Thickness (mm) U-Value for 140mm Studs with Ventilated Cladding Finish (W/m²K) U-Value for 140mm Studs with Baumit Render Finish (W/m²K) U-Value for 219mm Studs with Ventilated Cladding Finish (W/m²K) U-Value for 219mm Studs with Baumit Render Finish (W/m²K)
No Insulation 0.28 0.28 0.19 0.19
60mm 0.20 0.20 0.15 0.15
80mm 0.18 0.19 0.14 0.14
100mm 0.17 0.17 0.13 0.13
120mm 0.15 0.15 0.12 0.12
140mm 0.14 0.14 0.11 0.12
160mm 0.13 0.13 0.11 0.11
180mm 0.12 0.13 0.10 0.10
200mm 0.12 0.12 0.10 0.10

Masonry Wall Results

215mm Brick, 450mm Stone and 600mm Stone Single Leaf Walls

  • Baumit Render System or Ventilated Cladding
  • Isolair Multi Wood Fibre on outside of solid wall
  • 215mm Brick Wall / 450mm Stone Wall / 600mm Stone Wall
  • 20mm Baumit Lime Plaster Levelling Coat Internally

Please contact us if you require other U-values calculated.

The Benefits of External Wall Insulation

External Wall Insulation (EWI) is an excellent way of insulating the external walls of a new or existing property because the complete building envelope is wrapped in insulation, and so cold bridges through junctions are avoided e.g. where internal walls meet the external wall. The Pavatex Isolair Multi natural and breathable wood fibre boards can be finished with a rendered finish or a ventilated cladded finish. Isolair Multi boards are installed directly onto the outside of external walls, irrespective of whether the walls are constructed from solid or cavity masonry, timber frame or CLT. The walls must be relatively level before insulating so that the tongue and groove joints of the boards engage fully. If not level, masonry walls may need to be first rendered with a breathable lime levelling coat, or you can use some site mix to seal the boards to the walls around all openings. The importance of correctly insulating solid masonry walls without a cavity is outlined in Insulating Old or Historic Buildings.  We recommend rendering Isolair Multi with the vapour-open Baumit silicone-based renders and this complete system has a European Technical Approval. The ventilated cladding system is BBA certified.

A major benefit of externally insulating a building is that the thermal bridging areas will be insulated so this significantly improves the Psi value.  As a result, the wall U-value figure can now be relaxed as there will be less overall heat loss through the complete building structure. The fabric of the building will be also much warmer and this helps to regulate indoor temperatures all year round due to wood fibre’s unique thermal mass properties which is particularly critical on timber framed and metal framed buildings.  Wood fibre is unique because it is vapour-open, hygroscopic and capillary active, meaning that condensation and vapour within the property can pass through the walls and the wood fibre insulation and then evaporate to the outside. Moisture won’t become trapped so this keeps the building fabric much drier, and therefore, healthier and warmer. This greatly reduces the chances of mould, wet rot or dry rot occurring.

Other advantages of external wall insulation are that the internal decor will not be affected. The sound insulation of the entire building structure will also be enhanced due to the high density of the wood fibre, and the building will be windtight.  Because the EWI wood fibre boards are water resistant, they can be left exposed on the building for up to three months while construction is taking place. So, as well as improving the energy efficiency of the building, the Pavatex by Soprema wood fibre external wall insulation system can also enhance the building’s appearance, if required.

Isolair Multi Thickness (mm) U-Value for 215mm Brick Wall with Baumit Render Finish (W/m²K) U-Value for 450mm Limestone Wall with Baumit Render Finish (W/m²K) U-Value for 600mm Limestone Wall with Baumit Render Finish (W/m²K)
No Insulation 2.11 1.80 1.48
60mm 0.72 0.68 0.63
80mm 0.43 0.42 0.40
100mm 0.34 (6 times warmer) 0.34 (6 times warmer) 0.32 (6 times warmer)
120mm 0.29 0.29 0.28
140mm 0.26 0.25 0.25
160mm 0.23 0.23 0.22
180mm 0.21 0.20 0.20
200mm 0.19 0.18 0.18

Quality Assured Products from Pavatex by Soprema