Insulating Walls Internally with Pavatex
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
- Isolair Multi can be finished with breathable lime plaster
- Pavadry 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
Isolair Multi Internal Wall Insulation
Installation
Isolair Multi Wood Fibre Insulation on Brick Walls
Finished
Isolair Multi 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 Plaster Finish on Masonry Wall
Pavatex Isolair Multi breathable wood fibre thermal insulation is ideal to use as Internal Wall Insulation (IWI) over any masonry substrate – brick, stone or concrete block and it 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 increases of water vapour condensing into water liquid. This might lead to 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. Please see Insulating Historic Buildings for more information.
U-value examples are shown below.
- ISOLAIR MULTI 40/60/80/100mm Insulation
- Existing or new lime-based plaster levelling coat and Baumit RK70 bonding coat @ 5mm thickness
- External single leaf or cavity wall (masonry, stone, brick)
- Two coat lime plaster finish with mesh
- 2 coat Baumit render system with mesh
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 (0-8mm). OR: Baumit RK38 Dubbing Out Coat (10-30mm) for more uneven walls.
- Baumit RK70 Bonding Coat (5mm). Apply with 7mm notched trowel to complete back of board surface.
- ISOLAIR MULTI wood fibre T&G boards (40, 60, 80, 100mm). Use Ejot H3 Hammer Fixings for solid masonry and Ejot STR-U Fixings for rubble / crumbly masonry (3 per board).
- Baumit RK70 lime base coat 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 (fixed with H1 Eco Hammer Fixing)
Downloads
Option 2: Internal Wall Insulation (IWI) with Plasterboard Finish on Masonry Wall
Pavadry consists of Pavatherm-Combi breathable wood fibre insulation that is bonded to 11mm OSB3 board (which faces into the room). This OSB surface means that plasterboard can be screwed directly to this, which speeds up installation. It also means that reasonably heavy objects such as radiators or curtain poles can be fixed to the plasterboard and OSB3 board without the need for the fixing to penetrate the original wall, so reduces thermal bridging. A services void can also be incorporated between the Pavadry and the plasterboard with this option. Plasterboard and OSB3 are both vapour-open materials.
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 water liquid, 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. The OSB3 layer and airtightness tape at window junctions will provide airtightness. Please see Insulating Historic Buildings for more information.
U-value examples are shown below.
- PAVADRY 51/71mm Insulation
- Existing or new lime-based plaster levelling coat and Baumit RK70 bonding coat @ 5mm thickness
- External single-leaf or cavity wall (masonry, stone, brick)
- Plasterboard or Fermacell board finish (Optional: Services void between Pavadry 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 (0-8mm). OR: Baumit RK38 Dubbing Out Coat (10-30mm) for more uneven walls.
- Baumit RK70 Bonding Coat (5mm). Apply with 7mm notched trowel to complete back of board surface.
- PAVADRY wood fibre square edge boards (51, 71mm). Use Powerline Fixings for solid masonry and Mungo MQL-ST Fixings for rubble / crumbly masonry (3 per board).
- OPTIONAL: Battens fixed to OSB3 to create services void.
- Plaster carrier board fixed to battens or OSB3 directly (plasterboard, Fermacell, wood wool board etc)
- REVEAL BOARD – Continuation of insulation into the window & door reveals (bonded with RK70 and fixed with H3 Hammer Fixing)
- VARA SEAL SL TAPE – Self-adhesive airtightness tape for windowsill sealing
- PAVAPRIM – To prime porous substrates before applying VARA SEAL SL TAPE
- PAVAFIX 60, 20/40, 150 – To seal the window and door reveal junctions for airtightness
- ISO-BLOCO 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 Isolair Multi
| Isolair Multi Thickness (mm) | U-Value for 215mm Brick 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 | 2.11 | 1.90 | 1.57 |
| 40mm | 0.71 | 0.68 | 0.63 |
| 60mm | 0.53 | 0.52 | 0.49 |
| 80mm | 0.43 | 0.42 | 0.40 |
| 100mm | 0.34 | 0.34 | 0.32 |
Masonry Wall with Pavadry and No Services Void
| Pavadry 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 | 2.11 | 1.90 | 1.57 |
| 51mm | 0.62 | 0.60 | 0.57 |
| 71mm | 0.48 | 0.47 | 0.44 |
| 91mm | 0.39 (5.5 times warmer) | 0.38 (5 times warmer) | 0.36 (4 times warmer) |
Masonry Wall with Pavadry and a Services Void
| Pavadry 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 | 2.11 | 1.90 | 1.57 |
| 51mm | 0.56 | 0.54 | 0.51 |
| 71mm | 0.44 | 0.43 | 0.41 |
| 91mm | 0.36 | 0.36 | 0.34 |
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 Pavatex by Soprema wood fibre insulation boards are generally used in refurbishment projects and are fixed directly to either masonry or timber framed walls. The Isolair Multi board can be plastered directly with Baumit breathable lime plaster or the Pavadry boards 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 avoids 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, providing 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 Pavaflex or Pavatextil P insulation material. For optimum results, the front of the studs internally should also be insulated with Isolair Multi or Pavadry 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.
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