Insulating Attic Floors with Pavatex Wood Fibre
Attic Floor Insulation
- Vapour-open, hygroscopic and capillary-active insulation so water vapour can pass through the insulation to keep condensation at bay
- Wood fibre buffers moisture so keeps relative humidity at optimum levels
- Good acoustic insulation properties due to Pavaflex’s high density and fibrous structure
- Thermal bridging eliminated if a second layer of insulation is laid perpendicularly over the joists with no gaps
- Carbon-negative and natural, sustainable insulation – safe to handle
- Suitable for new build or renovation projects
- Easy to install as a DIY project but air vents must not be covered up
Please see the following for:
New or Existing Attic Floor
Pavatex Pavaflex or Pavatextil P flexible insulation batts are ideal to use as attic floor insulation. They are easily laid between loft floor joists and will snugly fit in the available space. If the attic timbers expand or contract, the flexible insulation will adjust accordingly so there will be no thermal leakages at the sides. Next, lay a second row of flexible insulation perpendicularly over the top of the joists to ensure that there will be no thermal bridging through the structure. If the attic is not to be used as a living space, it is best to insulate the attic floor to save energy, material and labour costs.
U-value examples are shown below.
- PAVATEX DB 3.5 Airtightness Membrane below the joists
- Joists fully filled with PAVAFLEX or PAVATEXTIL P flexible insulation
- Lay another layer of PAVAFLEX or PAVATEXTIL P flexible insulation perpendicularly over all the joists
- 2 coat Baumit render system with mesh
Air Tightness Membrane
If the ceiling below the attic is not being removed, then the airtightness membrane can be draped over each joist to make pockets, as per photo.
We can supply all the relevant products below.
- If the ceiling below the attic floor is being removed, fit the Pavatex DB 3.5 Airtightness Membrane directly below the joists. Ensure that it is well sealed to the perimeter edges.
- If the ceiling below is not being removed, then drape the airtightness membrane over each joist, bring it down along the sides and along the bottom of the joist and then back up the other side. There should be no big airgaps between the joists and the membrane. Bond the membrane to the structure and perimeter edges.
- Fully fill joists with 375 / 575mm wide PAVAFLEX (50, 80, 100, 140mm) or 600mm wide PAVATEXTIL P (45, 80, 100, 145mm) flexible insulation batts. Ensure that the air vents at the eaves are not covered with insulation.
- Fit Loft Leg Risers to the joists wherever floorboards will be required.
- Lay more 375 / 575mm wide PAVAFLEX (50, 80, 100, 140mm) or 600mm wide PAVATEXTIL P (45, 80, 100, 145mm) flexible insulation batts perpendicularly over all the joists so that there are no gaps. However, ensure that the air vents at the eaves are not covered.
- Fit floorboards where required for safe access to the water tank, storage area etc.
- 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 – Optionally to seal joints in DB3.5 airtightness membrane
Downloads
U-Value Results
Attic / Loft Floors with Pavaflex Insulation
Attic / Loft Floors
- Pavaflex over Joists
- Pavaflex between Joists
- DB 3.5 Airtightness Membrane under Joists
- 12.5mm Plasterboard & Skim
| Pavaflex Over Joists - Thickness (mm) | U-Value for 80mm Joists Filled with Pavaflex (W/m²K) | U-Value for 100mm Joists Filled with Pavaflex (W/m²K) | U-Value for 150mm Joists Filled with Pavaflex (W/m²K) | U-Value for 200mm Joists Filled with Pavaflex (W/m²K) |
|---|---|---|---|---|
| 100mm | 0.22 | 0.20 | 0.16 | 0.14 |
| 150mm | 0.17 | 0.16 | 0.13 | 0.12 |
| 200mm | 0.14 | 0.13 | 0.11 | 0.10 |
Attic / Loft Floors with Pavatextil P Insulation
Attic / Loft Floors
- Pavatextil P over Joists
- Pavatextil P between Joists
- DB 3.5 Airtightness Membrane under Joists
- 12.5mm Plasterboard & Skim
| Pavatextil P Over Joists - Thickness (mm) | U-Value for 80mm Joists Filled with Pavatextil P (W/m²K) | U-Value for 100mm Joists Filled with Pavatextil P (W/m²K) | U-Value for 145mm Joists Filled with Pavatextil P (W/m²K) | U-Value for 200mm Joists Filled with Pavatextil P (W/m²K) |
|---|---|---|---|---|
| 100mm | 0.22 | 0.20 | 0.17 | 0.14 |
| 145mm | 0.18 | 0.16 | 0.14 | 0.12 |
| 200mm | 0.14 | 0.13 | 0.12 | 0.10 |
Please contact us if you require other U-values calculated.
The Benefits of Attic Floor Insulation
If the attic is not to be used as a living space, it is best to insulate it at floor level to save energy, labour and material costs. Pavatex Pavaflex or Pavatextil P flexible insulation batts are easily laid between loft floor joists because they will snugly fit in the available space. If the attic timbers expand or contract, the flexible insulation will spring in or out accordingly leaving no gaps at the sides, so thermal leakages are reduced. A second layer of flexible insulation laid perpendicularly over the top of the joists ensures that there will be no thermal bridging through the joists. However, critically the air vents must not be blocked or there will be considerable condensation accumulation within the loft space.
Loft Leg Risers can be used to support floorboards in the loft for safe walking and storage space. It is recommended to seal the Pavatex DB 3.5 Airtightness Membrane directly below the floor joists if the ceiling cover below is not in place. However, if it is in place, the airtightness membrane can be draped between the joists instead. The insulation is then fitted snugly in this space.
Both insulation materials are very safe to handle and won’t irritate the skin. Pavaflex is made from waste wood and Pavatextil P is manufactured from recycled cotton insulation, so they are both very sustainable and ecological materials. Thanks to the natural constituents, Pavatex products can be recycled, composted or even incinerated for energy production at the end of their useful life.
Pavaflex comes in 375mm and 575mm widths so suits joists at 400mm or 600mm centres. Pavatextil P comes in a 600mm width so suits joists at 600mm centres. This is less dense than Pavaflex so squashes a little easier.
Pavaflex and Pavatextil P are breathable insulation materials which enable the safe passage of water vapour through them so that it can evaporate away through the roof air vents.
Pavaflex has a high density of 50kg/m³ so this will add sound insulation to help reduce noise coming through the roof such as rain, traffic or airplane noise. So Pavaflex and Pavatextil P are the ideal solution for excellent attic floor insulation.
Quality Assured Products from Pavatex by Soprema
