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Insulation for Internal Solid Walls

High performance PIR insulation boards for internal solid walls suitable for both direct bonding (‘dot and dab’) and mechanical fixing installation.

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Internal insulation is used in traditional, solid walled buildings. Where buildings have no cavities that can be filled with insulation, or where external wall insulation is not possible for practical or aesthetic reasons, insulating internally is the only option to boost thermal efficiency and building performance.

Installing insulation to the internal face of a solid wall must be done sensitively. To avoid upsetting the moisture balance of the building fabric, airtightness and controlled ventilation need to be considered in addition to improving thermal performance.

What Celotex products are suitable for internal insulation?

Celotex GA4000 is a general purpose, high performance, rigid polyisocyanurate (PIR) insulation board with aluminium foil facings both sides. PL4000 is a composite product; featuring the same high performance thermal insulation bonded to a 12.5mm tapered edge plasterboard.

Either can be used as internal insulation for solid masonry wall applications, keeping insulation thickness to a minimum and giving the following benefits:

  • Ideal where no wall cavity exists.
  • Reliable long-term energy savings for buildings.
  • Low emissivity foil facers give improved thermal insulation performance within cavity air spaces (GA4000 only).
  • Provides a vapour control layer (VCL) when board joints are taped.
  • Particularly suited to refurbishment projects.

What do I need to consider when choosing internal insulation?

Whether the existing solid wall is constructed from brick, block, cut stone or random stone influences which internal wall insulation solution is most appropriate. How straight and level the wall is dictates whether rigid PIR insulation can be installed directly against the wall, or whether timber battens are required first.

The moisture content of the masonry, how often the wall is exposed to severe weather, and the condition of the masonry and mortar joints should all be thoroughly checked before starting work.

GA4000 should be fixed to timber battens to give a continuous insulation layer. A separate plasterboard layer is then installed, fixed through the insulation to the timber battens. Door and window reveals can be lined with Celotex TB4000 to help maintain continuity of the building’s thermal envelope.

Celotex PL4000 can be mechanically fixed, or adhered using ‘dot and dab’ plaster, directly to suitable masonry walls. It can also be mechanically fixed to timber battens. With an insulation thickness as low as 15mm, it can also be used to continue the insulated plasterboard finish into door and window reveals.
Both products are capable of providing an air and vapour control layer, subject to appropriate moisture assessment in accordance with BS 5250 (control of condensation in buildings).

(If the solid wall that you’re insulating is under 200mm thick, consider installing insulation using a single timber frame wall lining, helping to avoid condensation. Insulation should not be fitted directly to a wall that is less than 200mm thick.)

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Celotex products to consider

1200 x 2400mm
0.022 W/mK

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1200 x 2400mm
0.022 W/mK

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1200 x 2400mm
0.022 W/mK

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