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 by clicking on the buttons or scrolling down:

  • 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
  • Warranty sign off with our warranty and certificates

Warmshell Internal not only follows the Government's best practice guidance for insulating walls, but it is the only system of its kind with a 3rd party BDA Agrément - so you can rest assured it does what it says.


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

Assess your building for IWI

Successfully 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, click here for a very brief guide to some considerations in England and Wales - 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) wood fibre system independently fire tested in the UK and achieves a classification of Class B, s1, d0.

Design Guide and Principles

ARCHITECTS Specification Clauses





When considering the suitability of which internal wall insulation type to use on a solid masonry wall, you don't just need to take our word for it. Warmshell Internal is independently assessed, verified and audited by KIWA. You can download the BDA Agrément here.

Specifiers can find the system information for Warmshell Internal in NBS source, to make specification a simple process. Follow the NBS specification link below, or find more on our individual product pages.



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 antiseptic 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 performance and the only wood fibre system with a materials warranty!


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

Warmshell Maintenance 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 insulation, 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.

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