Insulating Older Buildings

Insulating Older Buildings

Older buildings were typically built using materials to hand, with solid walls of stone or brick bound with a lime mortar. They were often built without a cavity and certainly no insulation.  The lack of insulation and poor thermal properties of the materials used meant they retained very little heat, and even with modern insulated doors and windows older properties are still noticeably colder than more modern buildings.

While insulating the walls of an older building will make it significantly warmer and reduce heating costs, it is important to use the right materials.  Any insulation applied must be breathable or your walls will become saturated.

What do we Manufacture?

We manufacture and supply a number of Insulation products for older buildings but how do you choose the right insulation material for the job you’re undertaking. There are five key types of breathable insulation products available:

  • Natural Hydraulic Lime Insulating Render– Made with NHL2 Natural Hydraulic lime, toughened light weight aggregate and fibres.  Can be applied internally or externally.
  • Wood fibre boards– Made from sustainably sourced softwood bound together by the wood’s own cellulose and lignin.  Can be applied internally or externally.
  • Coarse Stuff with hemp – Uses mature lime putty blended with selected aggregates, for internal application.
  • Sheep wool Insulation (Cosy Wool) - Cosy Wool offers both thermal and acoustic insulation, and provides enhanced performance, breathability, durability and sustainability.  For internal application

Natural Hydraulic Lime Insulating Render
Our Natural Hydraulic Lime Insulating Renders / Plasters are manufactured from top quality NHL2 Natural Hydraulic lime, toughened light weight aggregate and fibres. Both can be applied internally or externally. The two Insulating Renders / Plasters supplied by Womersley’s are:

Designed to improve thermal comfort, reduce heat loss and reduce condensation. They are light weight insulating basecoats for rendering and plastering. The Cornerstone and Ultra renders contain specialist light weight aggregates. Each maintain their structural integrity when applied and will not crush, and provide an excellent insulation layer:

  • Highly breathable
  • Energy Saving – a 50mm application will reduce heat loss by up to 60%
  • Improve Thermal comfort
  • Builds out in thick layers at up to 20mm per pass
  • Natural dehumidifier
  • Suitable for direct application to most surfaces

These insulating renders / plasters are the most popular on the market due to their ease of use. The Cornerstone and Ultra renders can be finished with Lime Green Natural Finish (External), Lime Green Solo (Internal) or Womersley’s Fine Stuff (Internal). If used externally they should be painted with a breathable paint.

A hydraulic lime stipple / slurry coat should be applied first to engineering bricks.

Wood Fibre boards
We have tried different Wood Fibre boards over the years and found that the best product on the market is the Lime Green Warmshell system, for internal or external application. Warmshell is particularly well-suited to older hard to heat homes, irrespective of whether they are brick, masonry or timber frame. 

  • Highly breathable
  • Energy Saving
  • Significantly limit heat loss
  • Tongue and Groove boards
  • Natural and sustainable

Installing Warmshell to your home is surprisingly straightforward. It is well within the reach of a capable DIYer, and should be second nature to most builders.

All you need to do is follow these simple steps:

1. Scour the wall with a coat of Lime Green Duro lime base coat to ensure a level surface

2. Cut the Warmshell boards to size and aim to cover as much of the wall surface as possible

3. Secure the Warmshell boards to the wall surface using suitable fixings and / or Warmshell adhesive

4. Render/Plaster over the Warmshell insulation boards with two-passes of Lime Green Natural Finish (external) with the use of Alkali resistant mesh between coats OR Lime Green Solo Plaster (Internal) with the use of Alkali resistant mesh between coats

Coarse Stuff with Hemp

Uses mature lime putty blended with selected aggregates, for internal application. Like all non-hydraulic lime products, it is extremely flexible and breathable which makes it suitable for use in the restoration of old 'solid wall' construction buildings and is ideal as a 'wattle and daub' replacement in timber-framed buildings.

The addition of hemp fibres not only improves the strength and flexibility of the product, but it also increases the thermal properties of the plaster and so adding some insulation to your wall.  Please be careful as some suppliers advertise this product as Hemp Insulating Plaster which is not quite correct as the insulation values achieved are minimal in comparison to all the other products in this guide.

Hemp Lime Plaster is available in two grades - medium and fine and is manufactured ready to use in bulk bags, and tubs.


Decorating Insulating Lime plaster and renders – It is important that all finishes remain vapour permeable.  If they do not then trapped moisture might eventually build up to affect thermal performance.  A number of decorative finishes are affective at retaining breathability and are all available from Womersley’s Mineral paints, Natural Emulsions and Lime Wash.

Sheeps Wool Insulation

Thermafleece Cosy Wool is the UK’s only British sheep’s insulation. It is very suitable for both traditional buildings and modern construction. Cosy Wool offers thermal and acoustic insulation, and provides breathability, durability and sustainability. Cosy Wool insulation is versatile and insulation rich, the ideal choice if you are looking for all round performance and value for money. Research shows that using 75% wool in combination with recycled fibres outperforms alternative insulation products. This wool rich blend ensures you get the full benefit of sheep’s wool with enhanced performance, durability and sustainability

Cosy Wool insulation can be used in Roofs, Walls and Floors and we supply insulation in a variety of sizes to suit all your performance needs. The Cosy Wool rolls work very effectively in stud wall applications, if you just lay the roll out on the floor for a few minutes, it will fill out and become quite firm, making it ideal for placing between stud battens.

How do these different products compare in relation to Thermal Conductivity which is measured in Watts per metre Kelvin W/(m.K.) the rate at which heat is conducted through each product

Sheep’s wool insulation 0.040

Warmshell Boards 0.044

Cornerstone insulating render 0.123

Ultra insulating plaster 0.18