Insulating Ground Floors with Naturheld Wood Fibre
Suspended Timber Ground Floor Insulation
- Vapour-open, hygroscopic and capillary-active insulation so water vapour can pass through the insulation to keep the structure dry providing there are adequate air vents below the floor joists
- Wood fibre buffers moisture so keeps relative humidity at optimum levels
- Thermal bridging eliminated if a second layer of insulation is laid over the floor joists
- Carbon-negative and natural, sustainable insulation – safe to handle
- Suitable for new build or renovation projects
- Easy to install as a DIY project
Jump to your preferred option by choosing one of the below:
Suspended Timber Floor Insulation
Naturheld Flex flexible insulation batts are ideal to use in suspended timber joist floor structures. There must be 150mm of open ventilation space below the joists and insulation, and the airbricks must not be blocked. The flexible insulation batts will fit snugly in the empty cavity between the floor joists. Naturheld Flex flexible insulation batts are also suitable for insulating between joists in intermediate floors. Naturheld wood fibre insulation is not suitable to use on solid ground floors because there will be no ventilated space below the insulation to allow the water vapour to evaporate away. Instead, we recommend using Glapor Foam Glass Insulation with a Limecrete Screed for a vapour-open construction. See below.
U-value examples are shown below.
- AMPACK AMPATOP PROTECTA PLUS Breather Membrane draped over and between the joists. Alternatively, fix the membrane to underside of joists, if adequate crawl space. This will keep the insulation drier.
- Joists fully filled with NATURHELD FLEX flexible insulation
- Lay OSB sub-deck board over the joists and tape all the joints to provide airtightness.
- Alternatively, lay AMPACK AMPATEX ECO 5 EXTRA Airtightness Membrane over the joists and lay floorboards over this.
- 2 coat Baumit render system with mesh
We can supply all the relevant products below.
- If there is adequate workspace height in the area below the floor joists, fit the Ampack Protecta plus Breather Membrane directly below the joists to prevent excessive moisture from getting into the insulation from the ground. Ensure it is well sealed at the perimeter edges and ensure that the air-bricks are not blocked. If the floor in question is an intermediate timber joist floor, there is no requirement to use a breather membrane.
- If there is no access to the space below the joists, drape Ampack Protecta plus Breather Membrane over, and down along the sides, to the bottom of the joists, making pockets. Staple the membrane to the joists and seal it to the walls with Ampacoll RA Adhesive. There should be no big airgaps between the joists and the membrane.
- Fit 575mm wide NATURHELD FLEX (50, 80, 100, 140mm) flexible insulation batts snugly between joists.
- Optionally, lay Ampack Ampatex Eco 5 Airtightness Membrane over the joists. Tape the joints with Ampacoll INT or Flexx pro Tape. Bond the membrane well to surrounding walls, using Ampacoll RA Adhesive OR lay OSB3 board as the flooring deck. Tape all the OSB3 joints to provide airtightness.
- Fit floorboards as normal over the airtightness membrane.
- OPTIONAL: If more insulation is required, fit NATURHELD 220/180/140 (22-220mm) T&G Wood Fibre Boards over joists (use Rawlplug R-PTX 6 Fixings), omitting the Eco 5 extra Airtightness Membrane over the joists.
- Fit Ampatex Eco 5 extra Airtightness Membrane (joints taped with Ampacoll INT or Flexx pro Tape) over NATURHELD BOARDS and bond well to surrounding walls using Ampacoll RA Adhesive OR lay OSB3 board as the flooring deck. Tape all the OSB3 joints to provide airtightness.
- AMPACOLL RA ADHESIVE – Optionally to bond membranes to all substrates, including masonry, and for bonding membrane ends to each other
- AMPACOLL XT60 TAPE – Optionally to seal joints in Ampatex Eco 5 extra airtightness membrane
- AMPACOLL INT TAPE – Optionally to seal joints in Ampatex Eco 5 extra airtightness membrane
Downloads
U-Value Results
Suspended Timber Floors
Suspended Timber Floors
- Floorboards or OSB3 Boards taped for Airtightness
- Optional: Ampatex Eco 5 Airtightness Membrane
- Optional: Naturheld 140/180/220 over Joists
- Naturheld Flex between Joists
- Ampatop Protecta plus Breather Membrane under Joists
NB: These U-value results are solely indicative, as ground floor U-values are dependent on the area and perimeter of the building, as well as the U-value of the walls etc.
| Naturheld 180/140 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) |
|---|---|---|---|---|
| None | 0.32 | 0.28 | 0.22 | 0.18 |
| 40mm | 0.24 | 0.22 | 0.18 | 0.15 |
| 60mm | 0.21 | 0.20 | 0.16 | 0.14 |
Please contact us if you require other U-values calculated.
The Benefits of Suspended Timber Floor Insulation
Naturheld Flex flexible insulation batts are easily laid between suspended floor joists because they will snugly fit in the available space. If the floor timbers expand or contract, the flexible insulation will adjust accordingly, leaving no gaps at the sides, so thermal leakages are reduced. This is particularly important in old houses where the joists are typically not of uniform thicknesses, so rigid insulation boards would invariably have gaps around them. If floor height allows, a layer of Naturheld 180/140 wood fibre insulation boards can also be fixed perpendicularly over the top of the joists to ensure that there will be no thermal bridging through the joists. The air bricks must not be blocked or moisture will not be able to evaporate away.
It is strongly recommended to use a breather membrane below the insulation to reduce moisture from the cold ground getting into the insulation. An airtightness layer on the warm side of the insulation reduces the possibility of draughts getting through the insulation, in addition to controlling the passage of moisture.
Naturheld Flex is a breathable insulation material that enables the safe passage of water vapour through it, so that it can evaporate away through the airbricks.
Naturheld Flex comes in a 575mm width, so suits joists at 600mm centres. It can be cut, if required, to make fit between narrower spaces.
Naturheld Flex insulation is very safe to handle and won’t irritate the skin like other flexible insulation products. Naturheld Flex is made from waste wood, so is very kind to the environment. Construction products which contain formaldehyde and volatile organic compounds (VOCs) have been shown to emit higher emissions as temperatures rise. As houses are mainly built or renovated to provide a comfortable and healthy living environment, natural building materials should preferably be used in the construction, and Naturheld wood fibre insulation meets this requirement. Thanks to the natural constituents, Naturheld products can be recycled, composted or even incinerated for energy production at the end of their useful life.
Solid Ground Floor Insulation Using Foam Glass and Limecrete
Solid Ground Floor Insulation
- GEOTEXTILE Membrane laid on ground and overlapped 200mm up wall.
- GLAPOR FOAM GLASS AGGREGATE INSULATION (Standard 10/60): 100 – 300mm per layer. Allow 30% compaction.
- GEOTEXTILE Membrane overlapped with the sides pulled in to make an envelope.
- GEOGRID (Optional) Underfloor heating grid with underfloor heating pipes.
- 30/40mm CORK INSULATION around all wall perimeters at 100mm depth.
- Limecrete Screed mix poured at 100mm at a ratio of 1 part NHL5 : 2 parts limecrete aggregate (by volume rather than weight).
We can supply all the relevant products below.
GLAPOR FOAMED GLASS Insulation System
- Lay GEOTEXTILE Membrane on the ground and bring it 200mm min up wall. This is required to wrap around the Foam Glass insulation to keep it all together and to prevent the screed from running down into the insulation.
- Pour GLAPOR FOAM GLASS AGGREGATE over Membrane (Standard 10/60): 100 – 300mm per layer. Required amount is multiplied by 1.3 to allow for compaction e.g. 130mm is required for a 100mm Foam Glass base.
- GEOTEXTILE Membrane lapped over the Foam Glass with the sides pulled in to make an envelope.
LIMECRETE SCREED SYSTEM (Optional underfloor heating system)
- OPTIONAL: Lay GEOGRID Underfloor Heating Grid flat on top of the membrane weighted down to prevent coiling.
- Plumbers to lay underfloor heating pipes, if using
- Fit 30 or 40mm thick CORK INSULATION around all wall perimeters to prevent cold bridging around limecrete – cut boards down to 100mm height to match screed
- Pour 100mm LIMECRETE SCREED MIX at a ratio of 1-part NHL5 to 2-parts limecrete aggregate, by volume (not weight). Concrete gravel mix consisting of fine sand to 20mm max aggregate, sourced from local quarry, is a good option. Mix should be semi-dry to ensure the volume isn't over-increased, this will prevent shrinkage during the curing process.
Downloads
