Insulating Walls Externally with Naturheld or 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
External Wall Insulation

Installation
Wood Fibre External Insulation on Walls
Finished
Wood Fibre External 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
Naturheld 140/180 or 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 Naturheld 140/180 or Pavatex 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
- 2 coat Baumit render system with mesh
- NATURHELD 140/180 or PAVATEX ISOLAIR MULTI (40 – 220mm)
- Masonry wall (cavity or single-leaf)
- Internal lime plaster finish and water-based paint
- 2 coat Baumit render system with mesh
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. NATURHELD 140/180 or ISOLAIR MULTI wood fibre T&G boards in landscape formation (40 - 220mm). Use Rawlplug R-TFIX-8M Hammer-in Fixings for solid masonry or Rawlplug R-TFIX-8S Screw-in 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 Premium 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.
- REVEAL BOARD – Continuation of insulation into the window & door reveals (fixed with Rawlplug T-FIX-8M Hammer-in Fixing)
- VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
- AMPACOLL PRIMAX – To prime wood fibre before applying VARA SEAL SL TAPE
- CONPRESEAL BG1 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
Downloads
Option 2: External Wall Insulation (EWI) with Ventilated Cladding Finish on Masonry Wall
Naturheld 140/180/220 or 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 Naturheld 140/180/220 or Pavatex 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. The complete Pavatex cladded system has a BBA (British Board of Agrément) certificate.

Masonry Wall
- Cladding system (timber, brick, screen)
- Battens to create a 40mm min. ventilated cavity
- NATURHELD 140/180/220 or PAVATEX ISOLAIR MULTI (22 – 220mm) optionally protected with Ampack Ampatop Protecta Plus Breather Membrane
- Masonry wall (cavity or single leaf)
- Internal lime plaster finish and water-based paint
- 2 coat Baumit render system with mesh
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.
- NATURHELD 140/180/220 or ISOLAIR MULTI wood fibre T&G boards in landscape formation (22 - 220mm). Use Rawlplug R-TFIX-8M Hammer-in Fixings (2 per board) to initially pin into solid masonry. Naturheld 140/180/220 can be left exposed for up to 4 weeks 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 Ampack Ampatop Protecta Plus Breather Membrane.
- 40mm min. vertical batten to create service void fixed with Rawlplug R-FF1-N Frame Fixings for solid or rubble / crumbly masonry 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.
- REVEAL BOARD – Continuation of insulation into the window & door reveals (fixed with Rawlplug R-TFIX-8M Hammer-in Fixing)
- VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
- AMPACOLL PRIMAX – To prime wood fibre before applying VARA SEAL SL TAPE & AMPACOLL XT TAPE
- AMPACOLL XT TAPE – To seal any non-T&G joints at penetrations, perimeters etc to prevent rain ingress (if not using a breather membrane)
- CONPRESEAL BG1 Expanding Foam Tape – To seal junction between wood fibre and XPS and any perimeter gaps between wood fibre and structure
- AMPACOLL BK 530 – 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
Naturheld 140/180 or 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 Naturheld Flex or Pavaflex wood fibre 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
- 2 coat Baumit render system with mesh
- NATURHELD 140/180 or PAVATEX ISOLAIR MULTI (80 – 220mm)
- Stud wall fully filled with NATURHELD FLEX or PAVAFLEX
- Racking board taped for airtightness e.g. 12/15mm OSB or Ampack Ampatex Eco 5 Airtightness Membrane
- Optional: 25mm services void
- Plasterboard
- Plaster skim finish & water-based paint
- 2 coat Baumit render system with mesh
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.
- NATURHELD 140/180 or ISOLAIR MULTI wood fibre T&G boards in landscape formation (80 - 220mm). Use 80mm min on timber frame. Use Rawlplug R-PTX 6 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 Premium 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.
- NATURHELD FLEX or PAVAFLEX flexible insulation fully filled 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: NATURHELD 140/180 or 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 Ampack Ampatex Eco 5 airtightness membrane on inside of studs. Battens to make Services Void, if required, and Plasterboard or Fermacell finishing board
- VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
- AMPACOLL PRIMAX – To prime wood fibre before applying VARA SEAL SL TAPE
- CONPRESEAL BG1 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
- Pavatex Isolair Multi and Render on Timber Frame Walls – System Sheet
- Pavatex Isolair Multi and Render on Timber Frame Walls – Technical Manual
- Pavatex Isolair Multi and Render on Metal Frame Walls – Technical Manual
- Pavatex Isolair Multi Data Sheet
- Naturheld 140, 180, 220 Information Sheet
- Naturheld Flex Information Sheet
- Ampatex Eco 5 Extra Airtightness Membrane Data Sheet
Option 2: External Wall Insulation (EWI) with Ventilated Cladding Finish on Timber Frame Wall
Naturheld 140/180/220 or 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 Naturheld Flex or Pavaflex wood fibre 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. The complete Pavatex cladded system has a BBA (British Board of Agrément) certificate.
U-value examples are shown below.

Timber Frame Wall
- Cladding system (timber, brick, screen)
- Battens to create a 40mm min ventilated cavity
- NATURHELD 140/180/220 or PAVATEX ISOLAIR MULTI (22-220mm) optionally protected with Ampack Ampatop Protecta Plus Breather Membrane
- Stud wall fully filled with NATURHELD FLEX or PAVAFLEX
- Racking board, taped for airtightness e.g. 12/15mm OSB3 or Ampack Ampatex Eco 5 Airtightness Membrane
- Optional: 25mm services void
- Internal plasterboard
- Skim finish
- 2 coat Baumit render system with mesh
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 Rawlplug R-PTX 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.
- NATURHELD 140/180/220 or ISOLAIR MULTI wood fibre T&G boards in landscape formation (22 - 220mm). Use Rawlplug R-PTX 6 Fixings (2 per board) to initially fix to timber frame. Naturheld 140/180/220 can be left exposed for up to 4 weeks 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 Ampack Ampatop Protecta Plus Breather Membrane.
- NATURHELD FLEX or PAVAFLEX flexible insulation fully-filled 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 Ampack Ampatex Eco 5 Airtightness Membrane on inside of studs. Battens to make Services Void, if required, and Plasterboard or Fermacell finishing board
- Optional Plaster Finish: NATURHELD 140/180 or 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.
- VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
- AMPACOLL XT TAPE – To seal any non-T&G joints at external penetrations, perimeters etc to prevent rain ingress (if not using a breather membrane)
- AMPACOLL PRIMAX – To prime wood fibre before applying VARA SEAL SL TAPE & AMPACOLL XT TAPE
- AMPACOLL BK 530 – Double-sided tape for bonding membranes to all substrates including masonry and for bonding membrane ends to each other
- CONPRESEAL BG1 Expanding Foam Tape – To seal junction between wood fibre and XPS and any perimeter gaps between wood fibre and structure
- AMPACOLL INT TAPE – To seal joints in Ampatex Eco 5 airtightness membrane (if using)
Downloads
- Pavatex Isolair Multi and Cladding on Timber Frame Walls – System Sheet
- Pavatex Isolair Multi and Cladding on Timber Frame Walls – Technical Manual
- Pavatex Isolair Multi and Cladding on Metal Frame Walls – Technical Manual
- Naturheld 140, 180, 220 Information Sheet
- Naturheld Flex Information Sheet
- Pavatex Isolair Multi Data Sheet
- Pavaflex Data Sheet
- Ampatex Eco 5 Extra Airtightness Membrane Data Sheet
- Ampatop Protecta (plus) Breather Membrane Data Sheet
- BBA – Isolair Multi and Ventilated Cladding on Walls
CLT (Cross Laminated Timber) Wall
Option 1: External Wall Insulation (EWI) with Render Finish on CLT Wall
Naturheld 140 and Naturheld 100/110 or 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 Naturheld 140 or 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
- 2 coat Baumit render system with mesh
- NATURHELD 140 or PAVATEX ISOLAIR MULTI (60mm)
- NATURHELD 100/110 or PAVATHERM (40 – 200mm)
- DSB2 Airtightness Membrane (if CLT is to be left exposed on the inside) over Cross Laminated Timber Structure
- 2 coat Baumit render system with mesh
Option 2: External Wall Insulation (EWI) with Ventilated Cladding Finish on CLT Wall
Naturheld 140 and Naturheld 100/110 or 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.
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)
- NATURHELD 100/110 or PAVATHERM wood fibre square edged boards in landscape formation (40 - 200mm). Fix with Rawlplug R-PTX 6 Fixings (1 fixing per board to pin in place).
- NATURHELD 140 or ISOLAIR MULTI wood fibre T&G boards in landscape formation (use 60mm). Use Rawlplug R-PTX 6 fixings through the wood fibre layers (9 fixings per m2).
- Baumit MC55 W base coat render at 6-9mm thickness with Reinforcing Mesh inserted into this.
- Baumit Premium 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.
- VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
- AMPACOLL PRIMAX – To prime wood fibre before applying VARA SEAL SL TAPE
- AMPACOLL BK 530 TAPE to seal membrane short ends together
- CONPRESEAL BG1 Expanding Foam Tape – To seal junction between wood fibre and XPS
- RAILS & BEADS - Usually supplied by plasterer

Cross Laminated Timber (CLT) Wall
- Cladding system (timber, brick, zinc etc)
- Battens to create a 50mm ventilated cavity
- Ampatop Protecta Plus Breather Membrane
- NATURHELD 100/110 or PAVATHERM (40 – 200mm). Optionally, this can be combined with 60mm NATURHELD 140 or PAVATEX ISOLAIR MULTI
- Pavatex DSB2 Airtightness Membrane (if CLT is to be left exposed internally) on outside of Cross Laminated Timber Structure
- 2 coat Baumit render system with mesh
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.
- Pavatex DSB 2 Airtightness Membrane taped to structure (if CLT is to be left exposed internally).
- NATURHELD 100/110 or PAVATEX PAVATHERM wood fibre square edged boards in landscape formation (40 - 200mm). Fix with Rawlplug R-PTX 6 Fixings and KC Washers (1 fixing per board to pin in place).
- Naturheld 100/110 and Pavatherm are not water-resistant so the Ampatop Protecta Plus Breather Membrane must be used directly over these boards, if not also using Naturheld 140 or Isolair Multi.
- OPTIONAL: 60mm NATURHELD 140 or PAVATEX ISOLAIR MULTI water resistant wood fibre T&G boards in landscape formation directly over Naturheld 100/110 or Pavatherm. Fix with Rawlplug R-PTX 6 Fixings and KC Washers (1 fixing per board to pin in place). Naturheld 140 can be left exposed for up to 4 weeks 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 Ampatop Protecta Plus Breather Membrane.
- 50mm deep Vertical Battens to support cladding fixed back to CLT structure with Rawlplug R-PTX 6 Fixings (6 min. per m2) or use brick ties if installing a brick wall
- Ventilated Cladding or Brick Wall Cladding
- VARA SEAL SL TAPE – Self-adhesive airtight & windtight tape for windowsill sealing
- AMPACOLL XT TAPE – To seal any non-T&G joints at external penetrations, perimeters etc to prevent rain ingress (if not using a breather membrane)
- AMPACOLL PRIMAX– To prime wood fibre before applying VARA SEAL SL TAPE & AMPACOLL XT TAPE
- AMPACOLL BK 530 TAPE– Double-sided tape for bonding membranes to all substrates and for bonding membrane ends to each other
- CONPRESEAL BG1 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
- Naturheld 180/140 Wood Fibre on outside of stud frame
- Naturheld Flex between the studs
- OSB on inside
- 25mm Services Void
- 12.5mm Plasterboard & Skim

Naturheld 180/140 - 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 Isolair Multi | 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
- Naturheld 180/140 Wood Fibre on outside of solid wall
- 215mm Brick Wall / 450mm Stone Wall / 600mm Stone Wall
- 20mm Baumit Lime Plaster Levelling Coat Internally

Naturheld 180/140 - 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 |
40mm | 0.72 | 0.68 | 0.63 |
60mm | 0.54 | 0.52 | 0.49 |
80mm | 0.43 | 0.42 | 0.40 |
100mm | 0.34 (6 times warmer) | 0.34 (5 times warmer) | 0.32 (4.5 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 |
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 Naturheld 180/140 natural and breathable wood fibre boards can be finished with a rendered finish or a ventilated cladded finish. Naturheld 180/140 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 Naturheld 180/140 with the vapour-open Baumit silicone-based renders and this complete system has a European Technical Approval. The Pavatex 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 also be 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, the wood fibre insulation, and then evaporate to the outside. Moisture won’t become trapped, so the building fabric is much drier, 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 four weeks while construction is taking place. So, as well as improving the energy efficiency of the building, the Naturheld wood fibre external wall insulation system can also enhance the building’s appearance, if required.

The Ideal Solution for our Built Environment and Nature




