Solid External Wall Internal Thin Insulation G#11367

By June 4, 2016 Code, Encyclopaedia, Q&A

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Solid External Wall Internal Thin Insulation


  • I noticed that you had latex thermal insulation on display on the table top.
  • What do you think of this product?
  • We have a client who has a very small house in a conservation area with small rooms and I am wondering if this is a “better than nothing” solution for them (they are strongly resisting losing any space whatsoever in the house).
  • Their other option is to do nothing about insulation (which they are favouring!!).
  • I know its not ideal, but as we said yesterday we don’t live in an ideal world.
  • Look forward to hearing your thoughts.


Clarification: Latex

  • Natural Rubber Latex (NRL)
  • Used to make ‘Spitting Image’ Puppets
  • Variants used in ‘Memory foam’
  • Characteristics: Soft, compressible, cellular (still air enables conduction thermal insulating properties)


  • Thin latex foam used as thermal conductivity insulation for internal application on solid masonry external walls
  • Promoted for use with wall paper as an ‘insulating wall paper’ sub-system
  • Availability: ≅ 5 and 10 mm sheets

Internal insulation of solid masonry external walls:

  • Since internal thermal insulation generates many problems that our industry does not seem to understand, I do not recommend it.
    • Normal practice is to batten out the internal surface and insulate with rigid insulating boards not in contact with the wall
    • This can lead to condensation:
      • leading to mould, ill health, asthma, toxic mould, death, unusable building
      • rot, structural failure of embedded timbers, frost damage to outer face of masonry
  • Conventional insulation materials are mostly wrong for this application including: mineral wool and foamed plastics
    • Mineral wools:
      • because they are normally hydrophobic and will hold moisture vapour in the interstices preventing trapped air from doing the job of insulating and reduce the materials performance
    • Foamed plastics:
      • because they will not permit the wall to breath moisture vapour outwards

Latex internal insulation of solid masonry external walls:

  • I will only recommend latex use to the poorest who cannot afford to heat their building fabric, and can only afford to heat the space.
    • Because latex is sold as a thin solution it has a relatively low improvement in stopping heat flow through the wall.
    • Keeping it thin helps to reduce the risk of frost damage to bricks becoming too wet and too cold.
    • However there is an alternative material on the market that can do a similar job.

Alternative materials:

  • An alternative material for very thin insulation for application internally on solid masonry insulation is aerogel
  • These are supplied as a quilt in multiples of 5 mm thickness
  • They are also supplied bonded to lining boards

Further investigation needed:

  • I do not yet understand latex’s moisture permeability or moisture transport characteristics
  • Is it open or closed cell?
  • If latex is vapour open
    • it may allow moisture flow inwards which will allow evaporation inwards when conditions demand and permit.
    • If gypsum or cement plastered walls:
      • remove plaster to permit the wall to breath inwards
      • loss of plaster and gain of insulation will not alter their room size too much.
    • If lime or clay plaster
      • wall will breath without modification
  • If latex is vapour closed
    • then I would be a bit more worried about it.

Soft insulation used with wall paper:

  • A soft material behind wall paper, is how it was promoted to me, is prone to damage
  • Consequences of this approach:
    • Rehanging skirtings, dados, plate shelves, picture rails, selves and wall units is complicated with soft insulation and wall paper.
      • They will need softwood shims the same thickness as the insulation to space off the wall and not compress the insulation
  • Be careful if you choose PVC vinyl wall paper for toughness then you close the wall to moisture permeability in either direction.

If you do not insulate:

  • If you do not insulate then they need to consider green tariff energy supply and/or renewables with pumps, controls, motors, monitors, driven by green tariff electricity.

Heating the spaces:

  • If you were to use radiant heating, it heats the objects in the room, not the air and so warm air is not against cold walls.
  • Floor, ceiling or internal partition mounted radiant or convector heating ‘radiators’
  • Avoid radiators on External wall,
  • Use just below surface hot pipes or electric films.
  • Or hidden pipes in skirting radiators

Other measures:

  • Add reflector panels behind existing and new radiators.
  • Maximise draught stripping to windows and doors
  • You may know this already
  • I hope this is of some help.

© GBE NGS ASWS Brian Murphy aka BrianSpecMan
6th December 2012 – 4th June 2016

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