Insulating Walls Internally with Naturheld
Internal Wall Insulation
- Breathable, hygroscopic and capillary-active insulation so water vapour and water droplets can pass through the insulation and evaporate away
- Wood fibre buffers moisture so keeps relative humidity at optimum levels
- Naturheld 180/140 can be finished with breathable lime plaster
- Naturheld 180/140 can be finished with a services void, if required, and plasterboard
- Suitable for refurbishment of masonry or timber-frame 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
Internal Wall Insulation
Installation
Naturheld 140 Wood Fibre Insulation on Brick Walls
Finished
Naturheld 140 Wood Fibre Insulation with Lime Plaster and Shutters Replaced
Jump to your preferred option by choosing one of the below:
Masonry Wall
Option 1: Internal Wall Insulation (IWI) with Lime Plaster Finish on Masonry Wall
Naturheld 180/140 breathable wood fibre thermal insulation boards are ideal to use as Internal Wall Insulation (IWI) over any masonry substrate – brick, stone or concrete block, and they can be finished with vapour-open lime plaster. Bare stone or brick walls must be plastered with lime, or other capillary conductive plaster, so that they are reasonably flat. Sand and cement or gypsum plaster should be removed, but leave lime or clay plaster in place, if in good condition. There should not be any air space between the insulation and the wall because this will be a cold space where the risk of water vapour condensing into liquid water increases. This might lead to interstitial condensation or even water dripping down the wall between the insulation and the wall, which will cause damage. Water vapour will pass through the complete wall much easier by capillary action if all materials touch each other. An 8mm minimum lime plaster coat will also provide airtightness. Care must be taken to address all issues of dampness or water ingress into the wall before installing any insulation. Please see Insulating Historic Buildings for more information.
U-value examples are shown below.
- NATURHELD 180/140 Wood Fibre Insulation (40/60/80mm)
- Existing or new lime-based plaster levelling coat and Baumit RK70 bonding coat @ 5mm thickness
- External single leaf or cavity wall (masonry, stone, brick etc)
- Two coat Baumit lime plaster finish with Reinforcing Mesh
- 2 coat Baumit render system with mesh
Downloads
Baumit plasters have been approved to use with our systems. We can supply all the products below.
- Baumit NHL Thermo Insulating Lime Plaster (10-80mm) or Baumit RK38 (10-30mm) Levelling Coat, if wall is bare or uneven.
- Baumit RK70 Bonding Coat (5mm). Apply with 7mm notched trowel to complete back of board surface.
- NATURHELD 180/140 wood fibre T&G boards (40, 60, 80, 100mm). Use Rawlplug R-TFIX-8M Fixings for solid masonry or Rawlplug R-TFIX-8S Fixings for rubble / crumbly masonry (3 per board).
- Baumit RK70 lime base coat over wood fibre board at 6mm thickness with Reinforcing Mesh inserted into this.
- Baumit Klima Glätt W smooth lime topcoat finish at 2-3mm thickness. Alternatively use Baumit RK70 for a more textured finish.
REVEAL BOARD – Continuation of insulation into the window & door reveals (bonded with RK70 and fixed with Rawlplug R-TFIX-8M Fixings)
- System Sheet – Internal Wall Insulation on Solid Wall
- Naturheld INTERNAL WALL Insulation Technical Manual
- Information Sheet – Naturheld 140,180,220
- Data Sheet – NHL Thermo Insulating Plaster
- Data Sheet – RK38 Levelling Coat
- Data Sheet – RK70 Base & Bonding Coat
- Data Sheet – Klima Glätt W Smooth Top Coat
Option 2: Internal Wall Insulation (IWI) with Plasterboard Finish on Masonry Wall
Naturheld 180/140 breathable wood fibre thermal insulation boards can alternatively be finished with plasterboard. This can be very useful if a services void is required.
Naturheld 180/140 wood fibre boards must be installed directly to the wall, as per Option 1. Bare stone or brick walls must be plastered with lime or clay plaster, so that they are reasonably flat. Sand and cement or gypsum plaster should be removed, but leave lime or clay plaster in place, if in good condition. There should not be any air space between the insulation and the wall because this will be a cold space and water vapour may condense into liquid water, creating interstitial condensation, which is undesired. Water vapour will escape through the complete wall much easier by capillary action, if all materials touch each other.
An airtightness membrane must be fitted to the front face of the wood fibre board because plasterboard isn’t airtight. Airtightness Tape is also required at the junction between the window frame and the reveal. Battens are installed to create a services void and this is finished with plasterboard. Care must be taken to address all issues of dampness or water ingress into the wall before installing any insulation. Please see Insulating Historic Buildings for more information.
U-value examples are shown below.
- NATURHELD 180/140 Wood Fibre Insulation (40/60/80mm) with Airtightness Membrane on inner face, well-sealed to perimeter edges
- Existing or new lime-based plaster levelling coat and Baumit RK70 bonding coat @ 5mm thickness
- External single-leaf or cavity wall (masonry, stone, brick etc)
- Plasterboard or Fermacell board finish (Optional: Services void between Naturheld 180/140 boards and plasterboard)
- 2 coat Baumit render system with mesh
Downloads
Baumit plasters have been approved to use with our systems. We can supply all the products below.
- Baumit RK70 plaster for levelling uneven plastered walls (5-8mm) or Baumit NHL Thermo Insulating Lime Plaster (10-80mm) for more uneven walls.
- Baumit RK70 Bonding Coat (5mm). Apply with 7mm notched trowel to complete back of board surface.
- NATURHELD 180/140 wood fibre T&G boards (40-80mm) fixed with Rawlplug R-TFIX-8M Fixings (1 or 2 per board if using battens) to pin into masonry.
- Ampack Ampatex Eco 5 Airtightness Membrane - ensure it is well sealed to the surrounding structures.
- Battens to create a services void fixed with Rawlplug R-FF1-N-10 Fixings for all masonry walls (7.5 per m2).
- Plaster carrier board fixed to battens only (plasterboard, Fermacell, wood wool board etc).
- REVEAL BOARD – Continuation of insulation into the window & door reveals (bonded with RK70 and fixed with Rawlplug R-TFIX-8M Hammer-In Fixings)
- AMPACOLL FENAX AIRTIGHTNESS TAPE – To seal the window and door reveal junctions for airtightness (slit in backing-liner)
- AMPACOLL FLEXX PRO TAPE – To seal the edges of airtightness membrane together
- AMPACOLL RA ADHESIVE – To bond the airtightness membrane to masonry on side walls, floors etc
- BAUMIT JOINT SEALING BAND EXPANDING FOAM TAPE – To seal gaps at wall, floor and ceiling perimeters
U-Value Results
215mm Brick Wall, 450mm Stone Wall and 600mm Stone Wall
Masonry Wall with Naturheld 180/140 and Lime Plaster
| Naturheld 180/140 Thickness (mm) | U-Value for 215mm Brick Wall with No External Render (W/m²K) | U-Value for 450mm Limestone Wall with No External Render (W/m²K) | U-Value for 600mm Limestone Wall with No External Render (W/m²K) |
|---|---|---|---|
| No Insulation | 2.12 | 1.84 | 1.52 |
| 40mm | 0.65 | 0.62 | 0.58 |
| 60mm | 0.48 | 0.47 | 0.44 |
| 80mm | 0.39 | 0.38 | 0.37 |
| 100mm | 0.33 | 0.32 | 0.31 |
Masonry Wall with Naturheld 180/140 and Plasterboard - No Services Void
| Naturheld 180/140 Thickness (mm) | U-Value for 215mm Brick Wall with No External Render - No Services Void (W/m²K) | U-Value for 450mm Limestone Wall with No External Render - No Services Void (W/m²K) | U-Value for 600mm Limestone Wall with No External Render - No Services Void (W/m²K) |
|---|---|---|---|
| No Insulation | 2.12 | 1.84 | 1.52 |
| 40mm | 0.63 | 0.58 | 0.54 |
| 60mm | 0.47 | 0.44 | 0.42 |
Masonry Wall with Naturheld 180/140 and Plasterboard with Services Void
| Naturheld 180/140 Thickness (mm) | U-Value for 215mm Brick Wall with No External Render - With Services Void (W/m²K) | U-Value for 450mm Limestone Wall with No External Render - With Services Void (W/m²K) | U-Value for 600mm Limestone Wall with No External Render - With Services Void (W/m²K) |
|---|---|---|---|
| No Insulation | 2.12 | 1.84 | 1.52 |
| 40mm | 0.57 | 0.53 | 0.49 |
| 60mm | 0.43 | 0.41 | 0.39 |
Please contact us if you require other U-values calculated.
The Benefits of Internal Wall Insulation
Internal Wall Insulation (IWI) is a good option for thermally insulating the inside of external walls, especially on properties with a unique external appearance that cannot be altered – see our page on listed or older buildings.
The Naturheld wood fibre insulation boards are generally used in refurbishment projects and are fixed directly to either masonry or timber-framed walls. The Naturheld 180/140 boards can be plastered directly with Baumit breathable lime plaster or they can be covered with plasterboard or similar. These breathable, hygroscopic and capillary-active insulation boards can absorb water vapour from inside the room and then release it either out through the walls or back into the room as the humidity level lowers, without any detrimental effects to the integrity of the insulation boards. This helps to avoid condensation, mould growth and humidity in buildings and creates a very pleasant, comfortable and healthy interior climate. Interstitial condensation should not get trapped in the structure which can cause untold damage, provided the walls are not over-insulated.
If the external wall is an existing timber frame stud wall, it is generally best to insulate between the studs with the flexible and hygroscopic Naturheld Flex insulation material. For optimum results, the front of the studs internally should also be insulated with Naturheld 180/140 wood fibre boards, if external insulation is not possible. Contact us for specific advice.
The main disadvantage of insulating walls internally, rather than externally, is that the junctions (e.g. where an internal wall intersects with the external wall) will not be insulated and so heat will escape from these un-insulated areas. Also, the internal floor area will be reduced. A lower (better) U-value can be achieved when externally insulating because the walls will be warmer and drier all year round, so no risk of interstitial condensation. However, the unique characteristics of wood fibre thermal insulation will remain the same whether the boards are installed internally or externally.
The Ideal Solution for our Built Environment and Nature
