External Roof Insulation with Pavatex Wood Fibre
External Roof Insulation for Pitched & Flat Roofs
- Breathable, hygroscopic and capillary-active insulation so water vapour can pass through the insulation, preventing mould growth and condensation
- Wood fibre buffers moisture so keeps relative humidity at optimum levels
- Adds thermal mass to lightweight roof structures so greatly reduces summertime overheating
- Excellent acoustic insulation properties due to high density and fibrous structure
- Thermal bridging eliminated due to all rafters being insulated
- Tongue & groove joints reducing risk of rain and thermal leakage
- Carbon-negative and natural, sustainable insulation – safe to handle
- External pitched roof system is BBA Certified
Jump to your preferred option by choosing one of the below:
Pitched Roof
Option 1: New Pitched Roof or Existing Roof with Tiles Removed
Pavatex Isolair Multi wood fibre thermal insulation is ideal to use as External Roof Insulation over the rafters in a new build or retrofit project if the tiles etc are being removed. The roof is insulated at rafter level if the loft area is being used as living space or if the building has a vaulted ceiling. If the attic space is purely for storage, then insulate the attic floor instead. Isolair Multi is water retardant so can be left exposed for up to three months before covering with roof tiles or similar. We strongly recommend that you protect the Isolair Multi with the Pavatex ADB Breather Membrane due to our rainy climate in Ireland and the UK, but it is not strictly necessary on pitched roofs. The tongue and groove joints mean that there will be no thermal bypass through the junctions as often happens with square edged insulation. The rafters can then be fully filled with Pavaflex or Pavatextil P flexible insulation to give an excellent U-value while also ensuring that your roof will be vapour-open to prevent condensation and mould growth.
A huge benefit of using wood fibre insulation on roofs is that it adds considerable thermal mass to the roof so helps with summertime overheating – see Summer Heat Protection. The high density of Isolair Multi also means that it adds excellent acoustic insulation to the roof area so reduces rain, traffic or airplane noise.
U-value examples are shown below.
- Roof Covering on horizontal tile battens
- Vertical counter-battens 38 x 50mm (HxW) to create a ventilated space
- ISOLAIR MULTI 30 / 40 / 52 / 60 / 80 / 100 / 120 / 140 / 160 / 180 / 200mm Protected with PAVATEX ADB Breather Membrane
- Rafters fully filled with PAVAFLEX or PAVATEXTIL P flexible insulation
- OSB (racking support and airtightness) or PAVATEX DB 3.5 Airtightness Membrane
- Optional: 25mm services void (can be insulated for improved performance)
- 12.5mm Plasterboard & skim finish
- 2 coat Baumit render system with mesh
We can supply all the relevant products below.
- Tiles or Slates
- Horizontal tile battens
- Vertical Counter-battens for ventilation: 38mm min x 50mm (HxW). Use HECO TOPIX 6 Fixings (6 - 7/m2, fix through the batten into rafter - 40mm embedment)
- ISOLAIR MULTI wood fibre T&G boards in landscape formation (30 - 200mm). Use HECO TOPIX 6 Fixings (2 per board - 40mm embedment) to initially pin to rafters. 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 (recommended).
- Rafters fully filled with 600mm wide PAVATEXTIL P (45, 80, 100, 145mm) or 375 / 575mm wide PAVAFLEX (50, 80, 100, 140mm) flexible insulation batts
- Optional Plasterboard Finish: OSB with taped joints for airtightness OR PAVATEX DB 3.5 airtightness membrane under rafters. Battens to make Services Void, if required, and Plasterboard or Fermacell finishing board
- Optional Plaster Finish: ISOLAIR MULTI T&G Boards screwed to underside of rafters for more insulation, if required, and this can be plastered directly with Baumit lime plaster.
- 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)
- PAVAPRIM – To prime wood fibre before applying PAVAFIX PAVATAPE
- PAVACOLL – Adhesive for sealing membranes onto Wood Fibre boards
- PAVATAPE 12 – Double-sided tape for bonding membranes to all substrates including masonry and for bonding membrane ends to each other
- PAVAFIX 60 BLACK TAPE – To seal joints in DB3.5 airtightness membrane (if using)
Downloads
- External Pitched Roof Insulation – System Sheet
- External Pitched Roof Insulation – Install Overview
- External Pitched Roof Insulation – Installation Manual
- Isolair Multi Data Sheet
- Pavaflex Data Sheet
- Pavatextil P Data Sheet
- ADB Breather Membrane Data Sheet
- DB 3.5 Airtightness Membrane Data Sheet
- BBA Cert – External Pitched Roof Insulation
Option 2: New Pitched CLT Roof
Pavatex Isolair Multi and Pavatherm wood fibre thermal insulation boards are ideal to use as Roof Insulation externally over a CLT roof. Isolair Multi is water retardant and has tongue and groove junctions, so it is recommended to place a 60mm thick board over the Pavatherm boards for extra protection. Isolair Multi can be left exposed for up to three months before covering with roof tiles or similar. We also recommend that the Isolair Multi is protected with the Pavatex ADB Breather Membrane due to our rainy climate in Ireland and the UK, but it is not strictly necessary on pitched roofs. The vapour-open nature of wood fibre insulation ensures that mass timber roofs will be able to release moisture effectively and not sweat.
U-value examples are shown below.
- Roof Covering on 25mm high horizontal tile battens
- Vertical counter-battens 38 min x 50mm (HxW) to create a ventilated space
- PAVATEX ADB Breather Membrane (pitch 18° +)
- 60mm ISOLAIR MULTI (recommended) over PAVATHERM 80 / 100 / 120 / 140 / 160 / 180 / 200mm
- PAVATEX 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
We can supply all the relevant products below.
- DSB 2 Airtightness Membrane taped to structure (if CLT roof is to be left exposed on the inside). If a plasterboard ceiling covering is to be used internally, the DB 3.5 Airtightness Membrane can be used internally instead.
- PAVATHERM wood fibre boards in landscape formation (80 - 200mm). 80-120mm boards are square edged and 140-200mm are ship lapped. Fix with Ejot STR-H Fixings (1 fixing per board to pin in place – 40mm embedment).
- OPTIONAL BUT RECOMMENDED: 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 – 40mm embedment). 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, the roof insulation can be covered with the PAVATEX ADB Breather Membrane (strongly recommended).
- 38mm min. deep x 50mm wide Vertical Counter-Battens over wood fibre fixed back to CLT structure with Heco Topix-Therm Fixings (6 min. per m2 - 40mm embedment).
- 25mm deep Horizontal tile-battens, if using tiles etc.
- Roof tiles / slates etc.
- PAVATAPE 75 or 150 – To seal any non-T&G joints at external penetrations, perimeters, ridge etc to prevent rain ingress (if not using a breather membrane)
- PAVAPRIM – To prime wood fibre before applying PAVATAPE
- PAVATAPE 12 – Double-sided tape for bonding membranes to all substrates and for bonding membrane ends to each other
- PAVACOLL – Adhesive for sealing membranes to the wood fibre boards
Downloads
Flat Roof
Option 1: New Ventilated Flat Roof (3° Min Pitch)
When insulating a flat roof with wood fibre, Soprema only recommends that a very well-ventilated roof comprising a 100mm cavity is installed. A minimum pitch of 3° is required for every flat roof construction to avoid standing water. Pavatex Isolair Multi wood fibre thermal insulation is ideal to use as External Roof Insulation over the rafters. The Isolair Multi boards must be protected with the Pavatex ADB Breather Membrane. The tongue and groove joints mean that there will be no thermal bypass through the junctions as often happens with square-edged insulation. The rafters can then be fully filled with Pavaflex or Pavatextil P flexible insulation to give an excellent U-value while also ensuring that the roof will be vapour-open to eliminate condensation accumulation. It is critical to install an airtightness membrane below the rafters to reduce a large amount of water vapour getting into the roof structure.
The high density of wood fibre insulation means that it adds considerable thermal mass to the roof so regulates the temperature throughout the day – see Summer Heat Protection. This also means that Isolair Multi adds excellent acoustic insulation to the roof area, reducing rain and traffic noise.
U-value examples are shown below.
- Roof Covering (such as green roof or gravel)
- EPDM
- WBP Plywood
- 100mm Battens for ventilation
- PAVATEX ADB / UDB Breather Membrane
- ISOLAIR MULTI 30 / 40 / 52 / 60 / 80 / 100 / 120 / 140 / 160 / 180 / 200mm
- Rafters fully filled with PAVAFLEX or PAVATEXTIL P flexible insulation
- PAVATEX DB 3.5 Airtightness Membrane (taped)
- Optional: 25mm services void
- 12.5mm Plasterboard & skim finish
- 2 coat Baumit render system with mesh
Option 2: New CLT Flat Ventilated Roof (3° Min Pitch)
Pavatex Isolair Multi and Pavatherm wood fibre thermal insulation boards are used as external Roof Insulation over a CLT roof. A minimum pitch of 3° is required for every flat roof construction to avoid standing water. Isolair Multi is water retardant and has tongue and groove junctions, so it is recommended to place a 60mm thick board over the Pavatherm boards for extra protection. The Isolair Multi must also be protected with the Pavatex ADB Breather Membrane due to the risk of rain pooling on flat roofs. Because wood fibre insulation is breathable, water vapour won’t become trapped in the mass timber structure, leading to a dry, healthy and warm building fabric. This greatly reduces the chances of mould, wet rot or dry rot occurring.
U-value examples are shown below.
We can supply all the relevant products below.
- Finish Covering (e.g. green roof or gravel)
- EPDM
- WBP Plywood
- 100mm min Timber Battens for Ventilation. Use HECO TOPIX 6 Structural Fixings (6 - 7/m2, fix through the batten into rafter below - 40mm embedment). The battens must sit on PAVAFIX SN BAND to prevent water ingress.
- ADB / UDB Breather Membrane (UDB is mainly used under and around box gutters - premium product)
- ISOLAIR MULTI wood fibre T&G boards in landscape formation (30 - 200mm). Use STR-H Fixings (1 or 2 per board - 40mm embedment) to initially pin to rafters.
- Rafters fully filled with PAVATEXTIL - P (45, 80, 100, 145mm) or PAVAFLEX (50, 80, 100, 140mm) flexible insulation batts
- DB3.5 Airtightness Membrane (Taped)
- 25mm Services Void
- Plaster Carrying Board (plasterboard, Fermacell board, wood wool etc)
- PAVAFIX SN BAND – Screw & Nail Sealing Band for insertion below battens to prevent water ingress
- PAVACOLL – For sealing membranes onto Wood Fibre boards
- PAVAFIX 60 BLACK TAPE – To seal joints in DB3.5 airtightness membrane
- Roof Covering (such as green roof or metal sheeting) on EPDM
- 25mm WBP plywood deck
- 100x50mm (HxW) Counter-Battens for ventilation on PAVAFIX SN BAND
- PAVATEX ADB Breather Membrane
- 60mm ISOLAIR MULTI
- PAVATHERM 80 / 100 / 120 / 140 / 160 / 180 / 200mm
- PAVATEX DSB2 Airtightness Membrane (if CLT is to be left exposed on the inside)
- Cross Laminated Timber Structure
- 2 coat Baumit render system with mesh
We can supply all the relevant products below.
- DSB 2 Airtightness Membrane taped to structure (if CLT roof is to be left exposed on the inside). If a plasterboard ceiling covering is to be used internally, the DB 3.5 Airtightness Membrane can be used internally instead.
- PAVATHERM wood fibre boards in landscape formation (80 - 200mm). 80-120mm boards are square edged and 140-200mm are ship lapped. Fix with Ejot STR-H Fixings (1 fixing per board to pin in place – 40mm embedment).
- 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 – 40mm embedment). The Isolair Multi boards must be securely covered with the PAVATEX ADB Breather Membrane.
- 100mm min high x 50mm wide Counter-Battens over wood fibre fixed back to CLT structure with Heco Topix-Therm Fixings (6 min. per m2 - 40mm embedment). The battens must sit on PAVAFIX SN BAND to prevent water ingress.
- WBP Plywood
- Finish Covering (e.g. green roof or gravel) on EPDM
- PAVAFIX SN BAND – Screw & Nail Sealing Band for insertion below battens to prevent water ingress
- PAVACOLL – For sealing membranes onto Wood Fibre boards
- PAVAFIX 60 BLACK TAPE – To seal joints in DSB 2 airtightness membrane
Downloads
U-Value Results
Pitched Roofs
New Pitched Roofs - Timber Rafters
- Roof Tiles with 50mm Ventilation Space
- Isolair Multi Wood Fibre over Rafters
- Pavaflex or Pavatextil P between Rafters
- DB 3.5 Airtightness Membrane under Rafters
- 25mm Services Void – uninsulated
- 12.5mm Plasterboard & Skim
| Isolair Multi Thickness (mm) | U-Value for 100mm Rafters filled with Pavaflex (W/m²K) | U-Value for 150mm Rafters filled with Pavaflex (W/m²K) | U-Value for 175mm Rafters filled with Pavaflex (W/m²K) | U-Value for 200mm Rafters filled with Pavaflex (W/m²K) |
|---|---|---|---|---|
| 40mm | 0.27 | 0.21 | 0.19 | 0.17 |
| 60mm | 0.24 | 0.19 | 0.17 | 0.16 |
| 80mm | 0.22 | 0.18 | 0.16 | 0.15 |
| 100mm | 0.19 | 0.16 | 0.15 | 0.14 |
| 120mm | 0.18 | 0.15 | 0.14 | 0.13 |
| 140mm | 0.16 | 0.14 | 0.13 | 0.12 |
CLT Pitched Roofs
New CLT Pitched Roofs – Solid Timber
- Roof Tiles with 50mm Ventilation Space
- 60mm Isolair Multi Wood Fibre over Pavatherm
- Pavatherm Wood Fibre over Membrane / CLT
- DSB2 Airtightness Membrane over CLT
- CLT Structure – left exposed internally
| Pavatherm Thickness (mm) | U-Value for 120mm CLT with 60mm Isolair Multi (W/m²K) | U-Value for 150mm CLT with 60mm Isolair Multi (W/m²K) | U-Value for 200mm CLT with 60mm Isolair Multi (W/m²K) | U-Value for 240mm CLT with 60mm Isolair Multi (W/m²K) |
|---|---|---|---|---|
| 120mm | 0.17 | 0.17 | 0.16 | 0.15 |
| 140mm | 0.16 | 0.15 | 0.14 | 0.14 |
| 160mm | 0.15 | 0.14 | 0.13 | 0.13 |
| 180mm | 0.14 | 0.13 | 0.12 | 0.12 |
| 200mm | 0.13 | 0.12 | 0.12 | 0.11 |
Flat Roofs
New Flat Roofs - Timber Rafters
- Roof Covering on EPDM over Plywood
- 100mm Ventilated Cavity
- ADB / UDB Breather Membrane over Isolair Multi
- Isolair Multi Wood Fibre over Rafters
- Pavaflex or Pavatextil P between Rafters
- DB 3.5 Airtightness Membrane under Rafters
- 25mm Services Void – uninsulated
- 12.5mm Plasterboard & Skim
| Isolair Multi Thickness (mm) | U-Value for 100mm Rafters filled with Pavaflex (W/m²K) | U-Value for 150mm Rafters filled with Pavaflex (W/m²K) | U-Value for 175mm Rafters filled with Pavaflex (W/m²K) | U-Value for 200mm Rafters filled with Pavaflex (W/m²K) |
|---|---|---|---|---|
| 40mm | 0.28 | 0.22 | 0.19 | 0.18 |
| 60mm | 0.25 | 0.20 | 0.18 | 0.16 |
| 80mm | 0.22 | 0.18 | 0.16 | 0.15 |
| 100mm | 0.20 | 0.16 | 0.15 | 0.14 |
| 120mm | 0.18 | 0.15 | 0.14 | 0.13 |
| 140mm | 0.17 | 0.14 | 0.13 | 0.12 |
| 200mm | 0.13 | 0.12 | 0.11 | 0.10 |
CLT Flat Roof
New CLT Flat Roofs - Solid Timber
- Roof Covering on EPDM over Plywood
- 100mm Ventilated Cavity
- ADB Breather Membrane over Isolair Multi
- 60mm Isolair Multi Wood Fibre over Pavatherm
- Pavatherm Wood Fibre over Membrane/CLT
- DSB2 Airtightness Membrane over CLT
- CLT Structure – left exposed internally
| Pavatherm Thickness (mm) | U-Value for 120mm CLT with 60mm Isolair Multi (W/m²K) | U-Value for 150mm CLT with 60mm Isolair Multi (W/m²K) | U-Value for 200mm CLT with 60mm Isolair Multi (W/m²K) | U-Value for 240mm CLT with 60mm Isolair Multi (W/m²K) |
|---|---|---|---|---|
| 100mm | 0.19 | 0.18 | 0.17 | 0.16 |
| 120mm | 0.17 | 0.16 | 0.15 | 0.15 |
| 140mm | 0.15 | 0.15 | 0.14 | 0.14 |
| 160mm | 0.14 | 0.14 | 0.13 | 0.13 |
| 180mm | 0.13 | 0.13 | 0.12 | 0.12 |
| 200mm | 0.12 | 0.12 | 0.12 | 0.11 |
Please contact us if you require other U-values calculated.
The Benefits of External Roof Insulation
Externally insulating a roof with wood fibre sarking boards is very effective because the complete roof structure is covered in insulation, so cold bridges through the rafters are avoided. This type of roof is called a warm roof. This heat retention is very considerable because the rafters typically take up 9 to 15% of the entire roof surface and the heat will escape through these timber elements. Warm roofs are installed when the attic area is being used as living space or where the property has vaulted ceilings. It is more economical to insulate the attic floor if the attic space is not being used.
Because Isolair Multi boards are water-resistant, they can be left exposed on pitched roofs for up to three months so long as any non-T&G junctions, such as at the ridge, valleys or penetrations, are primed and taped. Alternatively, the Isolair Multi boards can be covered with the ADB Breathable Membrane without the need to tape those joints. This means that the internal building structure will remain dry to allow construction work to proceed. The tongue and groove joints on Isolair Multi boards reduce rain and thermal leakage. Wood fibre sarking boards will also keep the roof timbers warm and dry throughout the life of the building, so will reduce any risk of rot or damage.
Pavatex wood fibre insulation boards are a totally natural and renewable product, as well as being vapour-open, hygroscopic and capillary active. This means that condensation and vapour within the property can pass through the wood fibre insulation and evaporate away from the ventilated cavity above the insulation. 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.
Sound insulation through the roof will be greatly enhanced with the addition of dense wood fibre sarking boards so noise from rain, traffic or airplanes should be significantly reduced.
Loft areas of buildings tend to overheat during the summer because there is virtually no thermal mass in a roof covering. With the addition of wood fibre boards, this excess heat from the sun will be stored for between 10 and 12 hours when it will then be released as temperatures drop, whereas other insulation materials can only provide 5 to 8 hours lag time. This keeps buildings a few degrees cooler during the warmer summer months. The reverse happens in winter when the heat from the central heating system will be stored in the wood fibre layer and released at night-time as temperatures drop. This is particularly crucial when the loft space is used as living accommodation.
Quality Assured Products from Pavatex by Soprema
