Insulating Ground Floors with Pavatex 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

Pavatex Pavaflex or Pavatextil P 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. Pavatex Pavaflex or Pavatextil P flexible insulation batts are also suitable for insulating between joists in intermediate floors. Pavatex 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 Geocell Foam Glass Insulation with a Limecrete Screed for a vapour-open construction. See below.

U-value examples are shown below.

  1. PAVATEX ADB Breather Membrane draped over and between the joists. Alternatively lay below the joists if adequate crawl space.
  2. Joists fully filled with PAVAFLEX or PAVATEXTIL P flexible insulation
  3. Lay OSB sub-deck board over the joists and tape all the joints to provide airtightness
  4. Alternatively lay PAVATEX DB 3.5 Airtightness Membrane over the joists and lay floorboards over this
  1. 2 coat Baumit render system with mesh

Breather Membrane

If there is no access to the space below the joists, then the ADB Breather Membrane can be draped over the joists making pockets, as per photo. This will keep the insulation drier.

Installation Method

We can supply all the relevant products below.

  • If there is adequate workspace height in the area below the floor joists, fit the Pavatex ADB Breather Membrane directly below the joists to prevent excessive moisture getting into the insulation from the ground. Ensure that 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 ADB 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 PAVATAPE 12 double sided tape or PAVACOLL 310 ADHESIVE. There should be no big airgaps between the joists and the membrane.
  • Fit 600mm wide PAVATEXTIL P (45, 80, 100, 145mm) or 375 / 575mm wide PAVAFLEX (50, 80, 100, 140mm) flexible insulation batts snugly between joists.
  • Optionally lay Pavatex DB 3.5 Airtightness Membrane (joints taped with PAVAFIX 60 TAPE) over the joists and bond well to surrounding walls using PAVACOLL 310 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 ISOLAIR MULTI (30-200mm) T&G Wood Fibre Boards over joists (use HECO TOPIX 6 Fixings), omitting the DB 3.5 Airtightness Membrane over the joists.
  • Fit DB 3.5 Airtightness Membrane (joints taped with PAVAFIX 60 TAPE) over ISOLAIR MULTI and bond well to surrounding walls using PAVACOLL 310 ADHESIVE OR lay OSB3 board as the flooring deck. Tape all the OSB3 joints to provide airtightness. 
Ancillary Products
  • PAVATAPE 12 – Double-sided tape for bonding membranes to all substrates including masonry and for bonding membrane ends to each other
  • PAVACOLL 310 ADHESIVE – Optionally to bond membranes to all substrates including masonry and for bonding membrane ends to each other
  • PAVAFIX 60 BLACK TAPE – Optionally to seal joints in DB 3.5 airtightness membrane

Downloads

U-Value Results

Suspended Timber Floors

Suspended Timber Floors

  • Floorboards or OSB3 Boards taped for Airtightness
  • Optional: DB 3.5 Airtightness Membrane
  • Optional: Isolair Multi over Joists
  • Pavaflex between Joists
  • ADB 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.

Isolair Multi 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)
None 0.32 0.28 0.22 0.18
40mm 0.25 0.22 0.18 0.15
60mm 0.22 0.20 0.17 0.14

Please contact us if you require other U-values calculated.

The Benefits of Suspended Timber Floor Insulation

Pavatex Pavaflex or Pavatextil P flexible insulation batts are easily laid between 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 boards would have gaps around them. If floor height allows, a layer of Isolair Multi 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.

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 airbricks.

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. These materials can be cut if required, to make fit.

Both insulation materials are very safe to handle and won’t irritate the skin like other flexible insulation products. Pavaflex is made from waste wood, and Pavatextil P is manufactured from recycled cotton insulation, so they are both very kind to the environment. Construction products which contain formaldehyde and volatile organic compounds (VOCs) have been shown to emit higher emissions as temperature rises. 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 Pavatex wood fibre and recycled cotton insulation meets this requirement. Thanks to the natural constituents, Pavatex 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

  1. GEOTEXTILE Membrane laid on ground and overlapped 200mm up wall.
  2. GEOCELL FOAM GLASS AGGREGATE INSULATION (Standard 10/60): 100 – 300mm per layer.
  3. GEOTEXTILE Membrane overlapped with the sides pulled in to make an envelope
  4. GEOGRID (Optional) Underfloor heating grid with underfloor heating pipes
  5. 30/40mm CORK INSULATION around all wall perimeters at 100mm depth 
  6. Limecrete Screed mix poured at 100mm at a ratio of 1 part NHL5 : 2 parts well-graded sharp sand.
  1. 2 coat Baumit render system with mesh
Installation Method

We can supply all the relevant products below.

GEOCELL 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 GEOCELL 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 – cut boards down to 100mm height to match screed
  • Pour 100mm LIMECRETE SCREED MIX at a ratio of 1 part NHL5 to 2 parts well-graded sharp sand. Mix should be semi-dry to ensure the volume isn't over increased, this will prevent shrinkage during the curing process.  

Downloads

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