Thermal Insulation + Heating System Strategies, Air Tightness Levels + a ‘Fabric First’ Approach: in relation to Traditional Thick Solid Stone Walled Buildings

Some ideas + discussions that recently arose with a Client on a Project:

  • Involving the refurbishment of a traditional Irish Farm House, of existing solid wall construction (typically 600mm thick walls) with a proposed small scale new Front Entrance Lobby Extension.
  • A discussion from the viewpoint of Thermal Insulation, Heating, Air Tightness + Building Fabric in the context of thick Solid Stone Walls in a Traditional Irish Farmhouse (and also applicable to Cottages, Period Houses, Out Buildings, etc.)
  • The Project is at Design Stage (Pre-Tender), where options and decisions on construction systems, build ups and specifications will need to be made, so that a co-ordinated set of technical drawings + documents will be ready for issuing for Tender to Building Contractors for pricing.


  1. INSULATION + HEATING: The optimum and best approach (in a new build house or even in a renovation project) is to focus on a ‘Fabric First’ approach: 
    1. Improve the thermal performance + air tightness of the Building Fabric (walls, roof, floor, etc.) in order to conserve energy and reduce heat loss, ‘V’ spending on a heating system, to generate heat, which will leak out through the Building Fabric / Building Envelope.
    2. An improved Building Fabric (increased u-values, better air tightness, etc.) will save money, reduce energy consumption and reduce carbon emissions in the long run (although it comes with an initial capital cost), ‘V’ the long term spending on ‘heating’ in a poorly insulated or leaky House.
  2. INSULATION: The level of insulation standard required should be reviewed in detail: To assess the u-values required for new floors (to replace existing floors), for treating existing walls, new walls (in the proposed Extension) and the roof constriction.
  • Thermal Insulation Options: 
    • Aim for Building Regulation minimum requirements,
    • Exceed the Building Regulations, OR
    • Aim for Passive House (or near Passive House) insulation standards?
  1. AIR TIGHTNESS + VENTILATION: Equally, the level of Air Tightness needs to be reviewed in detail. However Air tightness levels will be affected by decisions regarding existing open fires and how the House will be ventilated:
    1. Natural Ventilation (open windows, window trickle vents, wall vents), 
    2. Continuous Extract Ventilation
    3. Demand Control Ventilation (DCV), or a 
    4. Mechanical Ventilation System / Mechanical Heat Recovery Ventilation System (MHRV).
  • Ventilation Options:
    • All have different levels of complexity in installation + operation. 
    • And significantly different costs in relation to installation (capital costs).
    • And different performance with regard to achieving the desired ventilation + air tightness level required in the finished House (with the aim of creating a ‘Healthy House’).
  1. HEATING: The Heating System type / design + installation cost (+ running cost) will depend on the decisions made in relation to the above items (the thermal insulation standards, air tightness level + ventilation system selected).
    1. The increased performance of the ‘Building Fabric’; the lower the heating load, the lower energy demand and consequently the reduced need for a complex or high cost (installation cost and / or running cost) heating system.
    2. Options on new heating systems for the Existing House (with an eye on keeping the system simple):
      • Under Floor Heating to the Ground Floor + Radiators / Under Floor Heating on the 1st Floor (where existing floors are being replaced), with an air to water heat pump. Or,
      • Radiators throughout the House, heated from an Oil Boiler Heating System (potentially retaining the existing oil boiler…).
    3. With increased Fabric Performance, towards ‘Passive House’ standards of thermal performance, the requirement for a traditional heating system becomes greatly reduced! 
      • Passive House design standards enable Houses to be heated without the need for a ‘traditional heating system’. The interior space is typically heated through solar gains, the occupants and equipment / fittings in the House and heat loss is greatly reduced due to the thermal performance of the building.
      • However, ‘Hot Water’ will still need to be heated for washing, showers, baths, etc.
    1. Existing ‘solid’ external walls would be understood to be constructed with stone + lime (not cement). Accordingly lime is a breathable material and allows moisture pass in and out of the wall depending on the conditions. Consequently, it is recommended that any thermal insulation dry-lining should be ‘breathable’ as well. 
      • Traditional foil faced rigid board insulation e.g. Phenolic Insulation and other main stream similar foil faced boards, stop moisture and can trap moisture in behind the insulation, which can have a number of negative consequences for the building and for people’s health. (Just to note; Phenolic Insulation boards are great and deliver high performance, in the appropriate construction.)
    2. One recommended breathable insulation system would be Isover Optima Dry Lining System
    3. There are other breathable insulation systems as well, such as iQTherm 
    4. Each system has its advantages and will have different costs.
    5. With the Isover dry-lining system, there is a Habito plaster board, where greater loads or fittings can be fixed to the wall. Habito boards may be required in Kitchen and Utilities for wall-hung cabinetry, etc.

We hope the above gives an overview and insight into the interconnection between the various systems and about what needs to be researched, considered and coordinated when taking on refurbishment and upgrade works of Traditional Solid Walled Buildings.

The above is general advice and is not specific or appropriate to every project. Please seek the advice of a professional consultant or architect when planning to undertake similar works on your own project. The earlier that advice is sought the better, from a cost control and design coordination view point.

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