Insulating Attic Floors with Naturheld 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 Naturheld Flex’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
Naturheld FLEX 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 Naturheld FLEX 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.
- AMPACK AMPATEX ECO 5 Airtightness Membrane below the joists, or draped over and down along the joists
- Joists fully filled with NATURHELD FLEX flexible insulation
- Lay another layer of NATURHELD FLEX flexible insulation perpendicularly over all the joists
Airtightness Membrane
If the ceiling below the attic is not being removed in a refurbishment project, then the airtightness membrane can be draped over each joist to make pockets, as per photo. This keeps the insulation drier as it controls the rate at which warm, moist air passes through it into the insulation.
We can supply all the relevant products below.
- If the ceiling below the attic floor is being removed, fit the Ampack Ampatex Eco 5 extra 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 air gaps between the joists and the membrane. Bond the membrane to the structure and perimeter edges.
- Fully fill joists with 575mm wide NATURHELD FLEX (50, 80, 100, 140mm) 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 575mm wide NATURHELD FLEX (50, 80, 100, 140mm) 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.
- AMPACOLL RA – Liquid adhesive for bonding membranes to all substrates, including masonry, and for bonding membrane ends to each other
- AMPACOLL FLEXX PRO TAPE – Optionally for sealing joints in Ampatex Eco 5 extra airtightness membrane
Downloads
U-Value Results
Attic / Loft Floors with Naturheld FLEX Insulation
Attic / Loft Floors
- Naturheld FLEX over Joists
- Naturheld FLEX between Joists
- Ampatex Eco 5 extra Airtightness Membrane under Joists
- 12.5mm Plasterboard & Skim
| Naturheld FLEX Over Joists - Thickness (mm) | U-Value for 80mm Joists Filled with Naturheld FLEX (W/m²K) | U-Value for 100mm Joists Filled with Naturheld FLEX (W/m²K) | U-Value for 150mm Joists Filled with Naturheld FLEX (W/m²K) | U-Value for 200mm Joists Filled with Naturheld FLEX (W/m²K) |
|---|---|---|---|---|
| 100mm | 0.21 | 0.19 | 0.16 | 0.13 |
| 150mm | 0.16 | 0.15 | 0.13 | 0.11 |
| 200mm | 0.13 | 0.12 | 0.11 | 0.10 |
The Benefits of Attic Floor Insulation
If you’re not using your attic as a living space, it’s best to insulate the floor. This saves energy, time and money.
Naturheld FLEX insulation batts are easy to place between the floor joists because they fit snugly. If the wood expands or contracts, the insulation adjusts with it, so no gaps form and heat loss is greatly reduced.
Adding a second layer of Naturheld FLEX insulation across the top of the joists ensures that there will be no thermal bridging through the joists. Just make sure not to block air vents, or moisture will build up in the attic.
You can use loft leg risers to raise floorboards, making the attic floor safe to walk on and useful for storage. An airtight membrane should be installed under the joists if there’s no ceiling cover in place below. If there is a ceiling, the membrane can be draped over, and between the joists instead, with the insulation fitted snugly over it.
The insulation is safe to handle and won’t irritate your skin. It’s made from waste wood, making it environmentally friendly. Naturheld products can be recycled, composted or even incinerated for energy production at the end of their useful life.
Naturheld FLEX comes in a 575mm width, so it suits joists at 600mm centres, but can be easily cut to suit narrower cavities.
It’s a breathable insulation, allowing moisture to pass through and escape via roof vents, which helps prevent damp.
Naturheld FLEX 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.
Overall, it’s a robust, eco-friendly option for insulating attic floors.
