Insulating Walls Externally with Naturheld
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 180/140 wood fibre thermal insulation boards are 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 be removed first, because this may trap water vapour or liquid within the structure of the building.
The Naturheld 180/140 insulation boards are bonded to the substrate using Baumit MC55 W lime render, which should eliminate thermal bypass behind the insulation. The wall doesn’t need to be lime-rendered first unless the substrate is very uneven. The building’s plinth area must be insulated with waterproof XPS insulation. We recommend rendering the wood fibre insulation with Baumit MC55 W base coat, including a reinforcing mesh, and Baumit SilikonTop or StarTop top-coat renders. SilikonTop and StarTop are self-coloured, so do not require painting. This complete rendered system is CE-marked.
U-value examples are shown below.
Masonry Wall
- 2 coat Baumit render system with Reinforcing Mesh
- NATURHELD 180/140 Wood Fibre Insulation (40-220mm) bonded to wall with Baumit MC55 W render @ 5mm thickness
- 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 Naturheld wood fibre insulation 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 180/140 wood fibre T&G boards in landscape formation (40 - 220mm) bonded to the wall with Baumit MC55 W render at 5mm thickness. Mechanically fix with 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 with the Baumit Reinforcing Startex Mesh inserted into this.
- Baumit Premium Primer applied over the dry base coat to improve the adhesion of self-coloured renders.
- Baumit SilikonTop or StarTop self-coloured topcoat render is applied. Highly water-repellent but vapour-open, so these suit 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)
- AMPACOLL FENAX TAPE – Self-adhesive airtight & moisture-variable tape for windowsill protection - can be rendered
- AMPACOLL PRIMAX – To prime wood fibre before applying AMPACOLL FENAX TAPE
- BAUMIT JOINT BAND SEALING EXPANDING FOAM TAPE – To seal junctions 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 220/180/140 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 be removed first because this may trap water vapour or liquid within the wall.
The Naturheld 220/180/140 insulation boards are bonded to the substrate using Baumit MC55 W lime render, which should eliminate thermal bypass behind the insulation. The wall doesn’t need to be lime-rendered first unless the substrate is very uneven. The building’s plinth area must be insulated with waterproof XPS insulation. The chosen cladding is installed onto vertical timber battens to ensure adequate ventilation.
Masonry Wall
- Cladding system (timber, brick, metal etc)
- Vertical battens to create a 40mm min. ventilated cavity
- NATURHELD 220/180/140 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 220/180/140 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 220/180/140 can be left exposed for up to 4 weeks, if all non-T&G joints or 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 a ventilated cavity. Secure 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)
- AMPACOLL FENAX TAPE - To provide an airtight seal on inside of windows. Can also be used externally for windowsill protection if a membrane is not being used
- AMPACOLL PRIMAX – To prime wood fibre before applying AMPACOLL FENAX and XT TAPES
- BAUMIT JOINT BAND SEALING EXPANDING FOAM TAPE – To seal junctions between wood fibre and XPS, and any perimeter gaps between wood fibre and structure
- AMPACOLL XT TAPE – To seal any non-T&G joints at penetrations, perimeters etc to prevent rain ingress (if not using a breather membrane)
- AMPACOLL FLEXX PRO TAPE – For bonding membranes to all substrates, including masonry, and for bonding membrane short ends to each other
- AMPACOLL RA ADHESIVE - For bonding membranes to all substrates, including masonry
Downloads
Timber Frame Wall
Option 1: External Wall Insulation (EWI) with Render Finish on Timber Frame Wall
Naturheld 180/140 wood fibre thermal insulation boards are ideal to use as External Wall Insulation (EWI) over a timber or metal framed wall, and can be finished with vapour-open render. Timber studs are filled with flexible Naturheld Flex wood fibre insulation. Wood fibre adds considerable thermal mass and acoustic insulation to timber frame buildings.
The building’s plinth area must be insulated with waterproof XPS insulation. We recommend rendering the wood fibre insulation with Baumit MC55 W base coat with a reinforcing mesh inserted into this, and Baumit SilikonTop or StarTop top-coat render. SilikonTop and StarTop are self-coloured, so do not require painting. This complete rendered system is CE-marked and has a Kiwa BDA Agrément Certificate.
U-value examples are shown below.
Timber Frame Wall
- 2 coat Baumit render system with Reinforcing Mesh
- NATURHELD 180/140 wood fibre insulation boards preferably fitted to a vapour-open racking board
- Timber stud wall fully filled with NATURHELD FLEX
- Optional: 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 Naturheld wood fibre 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 180/140 wood fibre T&G boards in landscape formation (40 - 220mm). Must use 40/60mm Naturheld 180 or 80mm min Naturheld 140 on timber frame walls. Use Rawlplug R-PTX 6 Fixings - approx 13 fixings per board when studs are at 400mm centres. Use 2-3 fixings per stud, per board.
- Baumit MC55 W base coat render at 6-9mm thickness with Baumit Startex Reinforcing Mesh inserted into this.
- Baumit Premium Primer applied over the dry base coat to improve the adhesion of self-coloured renders.
- Baumit SilikonTop or StarTop self-coloured topcoat render is applied. Highly water-repellent, but vapour-open, 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 flexible insulation fully-filled between timber studs. It is 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 220/180/140 T&G Boards screwed to inside of timber studs for more insulation, if required, which can be plastered directly with Baumit lime plaster.
- 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.
- AMPACOLL FENAX TAPE – Self-adhesive airtight & moisture-variable tape for windowsill protection - can be rendered
- AMPACOLL PRIMAX – To prime wood fibre before applying AMPACOLL FENAX TAPE
- BAUMIT JOINT BAND SEALING EXPANDING FOAM TAPE – To seal junctions between wood fibre and XPS, and any perimeter gaps between wood fibre and structure
- AMPACOLL FENAX TAPE for providing an airtight seal on inside of windows
- RAILS & BEADS - Usually supplied by plasterer
Downloads
- Naturheld External Wall Insulation Technical Manual
- Information Sheet – Naturheld 140,180,220
- Information Sheet – Naturheld FLEX
- Installation Instructions Naturheld FLEX
- Data Sheet MC55 W EWI Base & Bonding Coat
- Data Sheet SilikonTop Render
- Data Sheet StarTop Render
- Data Sheet Ampatex Eco 5 Extra Airtightness Membrane
Option 2: External Wall Insulation (EWI) with Ventilated Cladding Finish on Timber Frame Wall
Naturheld 220/180/140 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. Timber studs are filled with flexible Naturheld Flex wood fibre insulation. Wood fibre adds considerable thermal mass and acoustic insulation 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.
U-value examples are shown below.
Timber Frame Wall
- Cladding system (timber, brick, metal etc)
- Vertical battens to create a 40mm min. ventilated cavity
- NATURHELD 220/180/140 optionally protected with Ampack Ampatop Protecta Plus Breather Membrane. Wood fibre can be fitted to a vapour-open racking board on outside of frame
- Timber stud wall fully-filled with NATURHELD FLEX
- 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, where required, have been approved to use with our Naturheld wood fibre 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 220/180/140 (22 - 220mm) wood fibre T&G boards are fitted in landscape formation directly over the timber frame or over a vapour-open racking board. Use Rawlplug R-PTX 6 Fixings (2 per board) to initially fix to timber frame. Naturheld 220/180/140 can be left exposed for up to 4 weeks if all non-T&G joints and junctions are primed and taped to prevent water ingress or, if preferred, it can be covered with the Ampack Ampatop Protecta Plus Breather Membrane.
- Install 40mm deep Vertical Battens to support cladding, and fix back to frame with Rawlplug R-PTX 6 Fixings (approx 10 per m2) or use brick ties if installing a brick wall. A 50mm cavity is required if the cladding has open joints.
- Install Ventilated Cladding or Brick Wall Cladding as per manufacturers' instructions.
- Internally, fully-fill between the studs with NATURHELD FLEX flexible insulation. 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. Install battens to make Services Void, if required, and Plasterboard or Fermacell finishing board
- Optional Plaster Finish: NATURHELD 220/180/140 T&G Boards screwed to inside of timber studs for more insulation, if required, and this can be plastered directly with Baumit lime plaster. Naturheld 180 must be used if fitting 40 or 60mm insulation directly to the inside of the studs, and finishing with lime plaster
- BAUMIT JOINT BAND SEALING EXPANDING FOAM TAPE – To seal junctions between wood fibre and XPS, and any perimeter gaps between wood fibre and structure
- AMPACOLL FLEXX PRO TAPE – For bonding membranes to all substrates, and for bonding membrane short ends to each other
- AMPACOLL RA ADHESIVE - For bonding membranes to all substrates
- AMPACOLL FENAX TAPE - To provide an airtight seal on inside of windows. Can also be used externally for windowsill protection if a membrane is not being used
- AMPACOLL XT TAPE - To seal any non-T&G joints at external penetrations, perimeters etc to prevent rain ingress (only required if not using a breather membrane)
- AMPACOLL PRIMAX - To prime wood fibre before applying AMPACOLL FENAX and XT TAPES
Downloads
CLT (Cross Laminated Timber) Wall
Option 1: External Wall Insulation (EWI) with Render Finish on CLT Wall
Naturheld 140 and Naturheld 110 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 110/140 wood fibre insulation with Baumit MC55 W base coat to include a reinforcing mesh, and Baumit SilikonTop or StarTop top-coat render. SilikonTop and StarTop are self-coloured renders, so do not require painting. This complete rendered system is CE-marked and has a Kiwa BDA Agrément Certificate.
Cross Laminated Timber (CLT) Wall
- 2 coat Baumit render system with mesh
- NATURHELD 110/140 wood fibre insulation boards
- Optional: NATURHELD 100 wood fibre insulation boards
- Ampatex Solero Plus Airtightness Membrane (if CLT is to be left exposed on the inside) on outside of Cross Laminated Timber Structure
- 2 coat Baumit render system with mesh
Downloads
- Naturheld External Wall Insulation Technical Manual
- Information Sheet – Naturheld 140,180,220
- Information Sheet – Naturheld 100,110
- Data Sheet – Ampatex Solero plus Airtightness Membrane for CLT
- Data Sheet – MC55 W EWI Bonding & Base Coat
- Data Sheet – Premium Primer DG27
- Data Sheet – SilikonTop Top Coat Render
- Data Sheet – StarTop Top Coat Render
Option 2: External Wall Insulation (EWI) with Ventilated Cladding Finish on CLT Wall
Naturheld 100/110 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 building’s plinth area must be insulated with waterproof XPS insulation. The chosen cladding is installed onto vertical timber battens to ensure adequate ventilation.
Baumit renders have been approved to use with our Naturheld wood fibre 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.
- Ampatex Solero Plus Airtightness Membrane on external face of structure (if CLT is to be left exposed on the inside)
- NATURHELD 100 (40/60/80mm) square-edged wood fibre boards can be fitted next to the CLT, if extra insulation is required. This cannot be rendered directly. Fix with Rawlplug R-PTX 6 Fixings with KC Washer (1 or 2 fixings per board to pin in place).
- NATURHELD 110 square-edged (100-200mm) or T&G (60-120mm) wood fibre boards are fitted in landscape formation over Naturheld 100 or CLT. Use Rawlplug R-PTX 6 fixings with KC Washer through the wood fibre layers (10 fixings per m2).
- Baumit MC55 W base coat render at 6-9mm thickness with Baumit Startex Reinforcing Mesh inserted into this.
- Baumit Premium Primer applied over the dry base coat to improve adhesion of self-coloured renders.
- Baumit SilikonTop or StarTop self-coloured topcoat render is applied. Highly water-repellent, but vapour-open, to suit 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.
- AMPACOLL FENAX TAPE – Self-adhesive airtight & moisture-variable tape for windowsill protection - can be rendered. Can also be used to provide an airtight seal on inside of windows
- AMPACOLL PRIMAX – To prime wood fibre before applying AMPACOLL FENAX TAPE
- BAUMIT JOINT BAND SEALING EXPANDING FOAM TAPE – To seal junctions between wood fibre and XPS, and any perimeter gaps between wood fibre and structure
- AMPACOLL FLEXX PRO TAPE – For bonding membrane to CLT, and for bonding membrane short ends to each other
- RAILS & BEADS - Usually supplied by plasterer
Cross Laminated Timber (CLT) Wall
- Cladding system (timber, brick, zinc etc)
- Vertical battens to create a 40mm min. ventilated cavity
- Ampatop Protecta Plus Breather Membrane
- NATURHELD 100/110 wood fibre insulation boards
- Ampatex Solero Plus 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.
- Ampatex Solero Plus Airtightness Membrane taped to outside of structure (if CLT is to be left exposed internally).
- NATURHELD 100 (40/60/80mm) square-edged wood fibre boards can be fitted next to the CLT, if extra insulation is required. Fix with Rawlplug R-PTX 6 Fixings with KC Washer (1 or 2 fixings per board to pin in place).
- NATURHELD 110 square-edged (100-200mm) or T&G (60-120mm) wood fibre boards are fitted in landscape formation over Naturheld 100 or CLT. Use Rawlplug R-PTX 6 fixings through the wood fibre layers (1 or 2 fixings per board to pin in place).
- It is strongly recommended to fit the Ampatop Protecta Plus Breather Membrane over the wood fibre boards asap
- 50mm deep Vertical Battens to support cladding fixed back to CLT structure with Rawlplug R-PTX 6 Fixings (7 approx per m2) or use brick ties if installing a brick wall
- Install Ventilated Cladding or Brick Wall Cladding as per manufacturers' instructions.
- BAUMIT JOINT BAND SEALING EXPANDING FOAM TAPE – To seal junctions between wood fibre and XPS, and any perimeter gaps between wood fibre and structure
- AMPACOLL FLEXX PRO TAPE – For bonding membranes to all substrates, and for bonding membrane short ends to each other
- AMPACOLL RA ADHESIVE - For bonding membranes to all substrates
- AMPACOLL FENAX TAPE - To provide an airtight seal on inside of windows. Can also be used externally for windowsill protection if a membrane is not being used
- AMPACOLL XT TAPE - To seal any non-T&G joints at external penetrations, perimeters etc to prevent rain ingress (only required if not using a breather membrane)
- AMPACOLL PRIMAX - To prime wood fibre before applying AMPACOLL FENAX and XT TAPES
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
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 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 Naturheld 180/140 | 0.28 | 0.28 | 0.19 | 0.19 |
| 40mm | 0.22 | 0.22 | 0.16 | 0.16 |
| 60mm | 0.19 | 0.20 | 0.14 | 0.15 |
| 80mm | 0.18 | 0.18 | 0.13 | 0.14 |
| 100mm | 0.16 | 0.16 | 0.13 | 0.13 |
| 120mm | 0.15 | 0.15 | 0.12 | 0.12 |
| 140mm | 0.14 | 0.14 | 0.11 | 0.11 |
| 160mm | 0.13 | 0.13 | 0.11 | 0.11 |
| 180mm | 0.12 | 0.12 | 0.10 | 0.10 |
| 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 | 2.06 | 1.63 | 1.33 |
| 40mm | 0.70 | 0.64 | 0.59 |
| 60mm | 0.51 | 0.48 | 0.45 |
| 80mm | 0.41 | 0.39 | 0.37 |
| 100mm | 0.34 (6 times warmer) | 0.33 (5 times warmer) | 0.31 (4.3 times warmer) |
| 120mm | 0.29 | 0.28 | 0.27 |
| 140mm | 0.26 | 0.25 | 0.24 |
| 160mm | 0.24 | 0.23 | 0.22 |
| 180mm | 0.21 | 0.21 | 0.20 |
| 200mm | 0.19 | 0.19 | 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 and a Kiwa BDA Agrément Certificate.
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
