A Townhouse Case Study: Thermally Upgrading A Traditional Build

Standing proudly at the end of Burrin Street in Carlow town is a building with an incredible history stretching back to at least 1753. This period townhouse originally functioned as the ‘Wheat Sheaf Inn’, serving coach traffic on the busy Dublin to Kilkenny route, and later housed the committee rooms of Daniel O'Connell before and during the elections of the 1840s. The building swapped hands on many occasions in the succeeding years and underwent significant modifications and remedial work. In 2017/2019 the building was fully restored to its original layout by Architect Ken Anderson of Holly Park Studio, with James J. Farrell (Construction) Ltd, Conservation Contractors, as the main contractor.

When the Architect took on the project in 2017 the building was in a poor condition. The walls, constructed of random rubble, with brickwork used in the lining of openings and as relieving arches above original timber lintels, had become unstable and cracks were evident over openings and in the body of the walls. The walls had been rendered in sand and cement in the 1950’s and this render was removed. As part of the works the roof was reconstructed and the top of the walls stabilised using a concrete ring beam. The cold conductive nature of the ring beam presented the danger of a cold thermal bridge along the upper perimeter at the wall/roof junction. At an early stage the possibility of using a thermal plaster, both internally and externally was explored, with a view to maximising overall thermal efficiency and minimising the effect of cold bridging.

Diathonite Evolution, manufactured by Diasen, was chosen as the thermal plaster for this project. This is a cork, lime and clay based insulating plaster perfectly suited for historic or listed buildings such as this. The moisture managing qualities of the plaster allows moisture in various forms to pass through the structure, meaning the walls in older buildings can dry out quicker and there is less chance of moisture related issues. Due to the historical nature of the building Alan Dillon Plastering was contracted to carry out the plastering, rendering and protective finish for the walls. Dillon is a specialist lime plasterer and has been involved in the sensitive restoration of many large-scale period properties using Diasen plasters. Dillon machine applied 25mm of Diathonite Evolution internally and finished this with Argacem HP lime-based surface finish.

A further 35mm of Diathonite Evolution was then applied to the external walls in a similar manner. This too was finished with Argacem HP, drawing on the skill of Dillon to alter the final appearance to suit the client’s taste. Much care and attention was given to maintaining the character of the property by focusing on features such as the neighbouring property, drain positioning and details around the original window sills. As a protective finish, the outer walls were first regulated with a breathable water-based surface primer called Diasen D20 before being sprayed with Diasen Decork. Decork is a cork granule textured paint which is both water repellent and highly breathable. This was sprayed in two coats running in opposite directions and will help prevent moisture from wind-driven rain penetrate the walls.

It is widely agreed that when used appropriately, materials like lime and clay are more compatible with single leaf traditional brick or stone buildings than synthetic insulation, cement or plastics. An important point is made in the recent publication from the Department of Housing, Local Government and Heritage, titled ‘A Living Tradition, a strategy to enhance the understanding, minding and handling of our built vernacular heritage`.

     “It is important that energy retrofitting standards and approaches are suitable for vernacular buildings and do not cause damage, foreseen or unforeseen. It would be ironic if works to improve energy efficiency were to undermine the essential environmental workings of a vernacular building and lead to structural or other failures.”

The use of natural building materials on 58 Burrin Street provided an ideal opportunity to significantly improve the thermal quality of this old structure and extend its lifespan for generations to come. The original U value of the walls varied between 2.1 W/(m²K) and 1.4 W/(m²K) after the cement render and plaster was removed. Depending on the wall thickness and position within the building, the final U value was calculated to be between 0.45 and 0.56 W/(m²K) - a significant improvement. Not only has the thermal efficiency of the walls improved without disruption to important building features, but so too has the ongoing moisture balance. This is critically important for the long-term condition of historic buildings.  

Preserving the vernacular heritage of our buildings takes knowledge and foresight. The impressive transformation of 58 Burrin Street demonstrates that period properties like this can be successfully brought into this century in terms of comfort. There are many similar traditional buildings in existence across Ireland and the UK and the embodied carbon stored in these means they will play a vital role in reaching our climate targets. As a low carbon natural building product, Diathonite Evolution presents a unique opportunity to maintain the low carbon footprint of these buildings, while allowing them to breathe and continue to function as they always have done.

Speak to one of our technical team for advice on how to retrofit a traditional building using natural materials.