Warmshell Internal Wall Insulation

Warmshell Internal Insulation is the complete, comprehensive method for insulating cold masonry walls from the inside. Carefully designed and tested as a system, it uses the remarkable ability of wood fibre and breathable lime plasters to keep your house warm, healthy and dry. Because we use sustainably grown wood, Warmshell is a very low carbon method of retrofit.

But we've also made Warmshell Internal as simple to understand and use as possible; from the Solo Onecoat Lime Plaster to a system materials warranty, we're here to help your project run smoothly. You can see our guidance and certificates below:

  • Assess your building's suitability for Internal Wall Insulation
  • Design and specify how Warmshell will be integrated
  • Install the insulation on to your prepared walls
  • Sign off with our materials warranty and certificates

Warmshell is available thorugh distributors nationally,  or you can see more information about why our Warmshell Woodfibre works better than anything else here.

Assess your building for IWI

Succesfully insulating old walls from the inside requires careful assessment of your building, its location and the technical requirements before you start.

The first step is to have an understanding of how much energy you lose through your walls and how much you can realistically save. Remember a U value is a crude way of measuring heat loss as it ignores thermal bridges like joists which will penetrate through the insulation, so this is just a starting point.

find out how much energy you'll save

Making your walls more energy efficient may require you to comply with building regulations, here is a very brief guide to some considerations in England and Wales, though the regulations are broadly similar in Scotland and Northern Ireland.


Our checklist and guide helps you assess the project you have for the most important pitfalls; it should be used alongside relevant regulations and codes of practise to help you check the building before you start.


Design Warmshell IWI

Once you've assessed the building and the best way to insulate it internally, you can use Warmshell Internal's comprehensive information to design and specify the work in detail. Warmshell is the only Internal Wall Insulation (IWI) woodfibre system indepently fire tested in the UK and the only system with detailed design guidance.

Design Guide and Principles

ARCHITECTS Specification Clauses



Installing IWI

Warmshell Internal is fitted without a cavity or void..

These gaps used in dry lining systems, or dot and dab, are a high-risk method which can cause damp or rot  and allow cold air to circulate, whereas wet plastering with naturally anti-septic lime helps wick moisture away and keeps the wall draft-free.

There are 4 main layers to Warmshell Internal

You can download the guide below showing detailed pictures of the process


Architect: Architecture for London. Photograph: Christian Brailey












Breathe easy...

Once your project is nearly complete, we have the information you need. Warmshell is the only Internal Wall Insulation system with long term monitoring of its real world peformance and the only wood fibre system with a materials warranty!


Our maintanence guide covers the basics you need to know for keeping the system in good condition for the long term.

Warmshell Maintanence Guide

Wood fibre boards lock up  carbon during their manufacture, making them carbon negative. Not only will you reduce the emissions from your house, but Warmshell is much kinder on the environment during manufacture and disposal. 


As part of a wide ranging study on retro-fit inuslation, our plasters and woodfibre were studied in situ for 7 years by SPAB funded by Historic England, showing the wall dried out where plastic insulations did not:


Find out More

To help you on your way, we also offer training, and can put you in touch with a wide network of system-trained installers.

Where to buy

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