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Research: Terraced House Insulation

To help understand the impact of new energy efficiency measures on the thermal performance of older properties, the Society for the Protection of Ancient Buildings (SPAB) has been conducting research into the Government's 'Green Deal'. But it hasn't just focused on castles and stately homes as you might expect, it has been looking at more humble homes too.


The Requirement

So when Lime Green fitted a Warmshell insulation system to a two-bed terraced property in Shropshire, SPAB were interested in monitoring the results.

The Problem

  • Because this property is in a Conservation Area, fitting the Warmshell system to the external face of the property wasn't an option, as this would affect the visual integrity of the terrace in which the property stood. This meant improvements works would have to be carried out internally, where they couldn't be seen.
  • Additionally, it's difficult to assess the thermal efficiency of many older properties with solid brick walls, as the software used for such calculations doesn't recognise this 'non-standard' construction and so won't accurately reflect heat losses.
  • Energy efficiency is also about the behaviour of a building, its structural moisture content, air humidity, temperature and air tightness.

The Solution

To meet conservation requirements, the system was easily fitted to the internal face of the exterior walls. All that was required was for the existing wallpaper to be removed and the system's 40mm thick wood fibre insulation boards to be cut to size and fixed to the brickwork. A single layer of Lime Green's one coat lime plaster, Solo, was then applied to the board.

The Benefits

  • The system was found to offer a great compromise between thermal improvement and minimisation of condensation risk.
  • It was also potentially reversible, so the building could be returned to its previous condition if required - important from a conservation point of view.
  • Though conventional wisdom suggested that the building's external brickwork would become cooler and damper with the system in place, and as wet walls are cold walls, would therefore use extra heat and energy, the reverse happened. The walls in fact became drier and warmer.
  • SPAB's research also revealed that if a 'breathable membrane' had been used on the walls, as is conventional, damp problems might have grown worse.
  • The system worked better than modern synthetic insulation and , while avoiding the issues that can occur with these in terms of breathability.
  • Just 40mm of wood fibre insulation board was enough to give the optimum U value for the walls and maintain heat losses at level that was similar to a modern new-build.

As part of the research sensors and probes were positioned throughout the wall to capture all of the relevant data. A sample of these on-going tests are displayed below. Much of the information gathered from the dozens of traditional buildings examined contradicts current assumtions. Conventional methods of calculating the condensation risks would have the lines below converging, creating condensation and damp within the wall. Using Lime Green's Warmshell insulation system of breathable insulation and lime plasters avoids this.


These findings make interesting reading for anyone who is trying to differentiate between the merits of one insulation system over another, when many claims are made for systems based on synthetic materials.

SPAB's reports into the energy efficiency of buildings are available free and can be downloaded from

For a more technical approach that shows the dynamic data for moisture in the walls, go to


Keywords: Exterior Insulation of A Terraced House, Lime Green, Warmshell Insulation System

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