How can I add internal insulation using natural/renewable materials?

Click here for more general advice on internal insulation.

Here are a few examples from the displays in CAT's visitor centre:

Internal insulation with cork & wood-fibre batts

Internal insulation for solid brick wall

The Cork acts as a secondary vapour check, inhibiting the passage of water vapour from the room into the wall; it also helps avoid cold spots where battens are fixed against the wall between the insulation batts. The 50x50mm timber battens are fixed to the brickwork through the Cork, holding both in place, using plugs & screws. The wood-fibre batts used here are relatively soft so need timber battens to support them and prevent them being compressed. The battens also support the OSB lining, which is screwed or nailed to the battens & acts as the primary vapour check, inhibiting the passage of water vapour from the room into the wall. It also allows pictures, shelves & cupboards to be fixed anywhere on the walls. Final decorative layer of painted plasterboard.

Typical U-value for the improved wall with the thicknesses of insulation shown: 0.44 W/m2K

  • 9” (225mm) Original brickwork laid to Flemish Bond
  • Original plaster
  • 25mm cork lining against original plaster.
  • 50x50mm vertical softwood battens at 600mm centres plugged & screwed to brickwork
  • OSB (Oriented Strand Board) 9-18mm thickness screwed to battens. Thickness to be determined by loads to be carried. 9mm is adequate for supporting pictures, shelves & light cupboards, 18mm for grabrails & heavy loads.
  • 12mm plasterboard fixed to OSB with drywall screws.
  • Skirting boards
  • Floor


Internal insulation with rigid wood fibre panels

 Internal insulation with wood fibre boardsThe rigid woodfibre panels used here are designed to be fixed directly to the inner face of the wall using special screws supplied by the panel manufacturer. The surface is then finished with a foil-backed plasterboard. This acts as a vapour-check layer to prevent moisture from penetrating the wall & provides a decorative finish for final painting or plastering.

  • Original brickwork laid to stretcher bond
  • 50mm cavity left unfilled to avoid any moisture penetration via the brickwork
  • 100mm lightweight aerated concrete block
  • Original plaster
  • 100mm woodfibre panels screwed or glued against original plaster.
  • 12mm foil-lined ( duplex ) plasterboard lining
  • Skirting boards
  • Floor


Internal insulation using hemp-lime with a lime or earth plaster.

Internal insulation with hemp and limeThis could be particularly good for building with solid slate walls (widely found in Wales) or similar. Natural, breathable insulation layers like hemp-lime and cellulose fibre will prevent moisture getting trapped within the layers and causing damp problems.

Hemp-lime is a mix of the chopped up pith of the stalk of the hemp plant & lime. It can be daubed on to the wall or, as here, lightly tamped into temporary shuttering. The hemp-lime is suitable for dealing with uneven surfaces. The final finish of plaster should provide a surface suitable for decoration. Hemp-lime & earth plasters have very good hygroscopic properties, meaning they can take in & give out moisture. This helps to regulate internal humidity levels.

  • Slate wall (450mm shown, actual wall may be over 600mm thick)
  • Original plaster
  • 100mm hemp-lime lining.
  • 15mm lime or earth plaster
  • Skirting boards
  • Floor


If you want more detailed advice about these techniques, and some hands-on experience, then we run short courses here at CAT on eco-refurbishment and on using hemp & lime techniques.

Please contact us if you need to find suppliers of some of these materials.

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