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Calsitherm 250mm x 500mm soffit board
Insulating with Calsitherm soffit boards

Calsitherm Window Soffit Climate Board

250mm x 500mm x 15mm

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  • Product Overview
  • Technical Details
  • Installation guide

Main purpose

Insulation for window and door reveals. Manages moisture, regulates humidity, eliminates mould and minimises heat-loss; especially in older or historic buildings or newer buildings suffering condensation and mould problems.

Use it on

Interior window and door reveals in solid stone or masonry walls, or in confined spaces where thicker boards are impractical.


Calsitherm Window Soffit Climate Board is a smaller and thinner version of Calsitherm’s Calcium Silicate Climate Board. It is conveniently sized for use around windows and doors and is only 15mm thick to provide thermal insulation benefits without affecting the space within the window and door reveal opening too much.

Where to use it 

Calsitherm Window Soffit Climate Board can be installed onto level solid stone or masonry. It is ideally suitable for window and door reveals or any area where the larger standard thickness Climate Board would be unsuitable or difficult to install.  

Space for insulation is often limited around windows and doors because the frames can be easily covered when insulation is applied to the reveals. Thicker insulation in these areas may also affect the window or door’s ability to open and close freely.

What it does

The Soffit Climate Board is part of the Calsitherm solid wall insulation system and is specifically designed for use with Calsitherm Climate Boards. Other than the size and thickness of each board, Window Soffit Climate Boards are identical to Calsitherm Climate Boards with the same capillary active moisture managing insulation properties.

The board is supplied as a 250mm x 500mm board. It is 15mm thick.

Why we love it

The Calsitherm Solid Wall Insulation System provides thermal insulation, moisture control and humidity regulation for a much improved level of comfort and indoor climate for the building’s occupants.

The Window Soffit Climate Board makes the Calsitherm system more versatile in situations where a high level of insulation and moisture control is required but space is limited.

How it works

The Calsitherm solid wall insulation system provides thermal insulation, moisture control and humidity regulation for a much improved level of comfort and indoor climate for the building’s occupants.

While the board is not a solution to rising damp, if there is any issue with residual moisture which may have previously penetrated the wall of an old building, Calsitherm can regulate peaks in unwanted moisture that increase the risk of condensation and subsequent mould growth and allow drying out to occur rapidly. Due to the calcium silicate’s built-in alkalinity, the board is resistant to mould.


  • Prevents mould growth and inhibits condensation
  • Improves thermal comfort
  • Easy installation around windows


  • Prevents condensation and mould at vulnerable window reveals due to the board’s capillarity, breathability and alkalinity.
  • Insulating window reveals significantly increases the surface temperature, helping to eliminate thermal bridges to provide a robust internal wall insulation upgrade. 
  • The board’s weight, size and thickness ensure an easier installation around windows.


Can Climate Board be finished with a gypsum based plaster?

No, we would recommend Calsitherm Finishing Plaster which is part of the Calsitherm Climate Board wall system.  This maintains the breathability and capillarity of the wall and has been developed for its ideal compatibility with Calsitherm Climate Board.

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Technical Details

Key Technical Data

Technical Datasheet

Material Safety Datasheet (MSDS)

Environmental Product Declaration (EPD)

Declaration of Performance (DOP)

Installation Guide

System Brochure

Installation Guide

How to Install

Apply Calsitherm Adhesive Mortar to the window or door reveal with notched trowel >/=10mm. Ensure the gaps between soffit boards and the Calsitherm on the external wall are as small as possible (no more than 2-3mm) and are butted to adjacent Calsitherm boards. 

Apply the board pressing it tightly on to the surface. For optimum performance, the soffit board must be completely bonded to the window or door reveal with no air pockets behind.

Contega Fiden Exo compression tape is then used to seal the joints between the Calsitherm boards and the adjacent building elements such as windows, doors, walls, floors, ceilings or service penetrations. 

Finish by applying a layer of Calsitherm Finishing Plaster (KP Kalkglaette), followed by Reinforcing Mesh to overlap the adjacent wall, then a second coat of Finishing Plaster. 

In order to optimise the performance of the Calsitherm System, the finishing layer should be a breathable paint such as Auro natural paint

Soffit Climate boards fitted to a window reveal bonded with Calsitherm finishing plaster and reinforcing mesh
Soffit Climate boards fitted to a window reveal

Hints & Tips

Calsitherm Window Soffit Climate Boards should be installed on to a level surface where all gypsum plaster has been removed. Any firmly attached cement or lime based plaster may remain in place. All non-breathable paint and wallpaper must be removed prior to application. 

If the wall is uneven, use a lime based plaster or Diathonite (for additional insulation) to level it before installing Calsitherm. Any mould on the stone/brick should be cleaned off before applying the levelling coat.

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