Publication of the new Technical Guidance Document Parts ‘F’ and ‘L’ in July 2019


It is understandable for our peers to want to reduce energy demands and emissions, because of the increasing global temperatures, rising sea levels and more aggressive weather events. Thus, on the 10th of May 2010, the European Union ‘Performance of Buildings Directive’ was enacted in all member states. This imposed an incremental scale of compliance for new building performance throughout the EU.

The most recent publications of the Irish “Technical Guidance Documents” (for part F and L) reflect another notch on this incremental scale. The target from an EU and energy perspective is to have all member states constructing buildings that have a minimal energy demand. This is referred to as the Nearly Zero Energy Building (NZEB), or near Passive standard of building. The Passive standard is not a national or EU standard, but a voluntary standard which some building owners choose to achieve.

There is a short transitional arrangement for both of these documents. By the 1st of November 2020, all new and substantial renovations will have to comply with the most recent version of the Technical Guidance Documents. Regarding Technical Guidance Document part ‘F’, it will become increasingly unlikely if natural ventilation will provide a comfortable living environment for prospective inhabitants of these future dwellings. Using the natural ventilation method described in the 2019 publication, each habitable room (kitchen, living room, dining room, and bedrooms) will require a clear opening in the wall equivalent to the size of a 5 inch circular duct. This area will have to be increased for any domicile bigger than a 1 bedroom apartment.

Because the regulations now require more air-tight houses with increased insulation thicknesses, the thermal envelope relies on large natural ventilation openings or mechanical systems to ventilate our homes. This will prompt developers and people constructing a new house or adding a large extension to their existing house, to use some form of mechanical ventilation system. Herein lies the problem from an operational and a maintenance perspective. With mechanical systems, more often than not, the home owner does not understand the systems, and how they should interact correctly with other systems, to achieve the correct efficiency that is expected by the Building Energy Rating (BER). The key to these systems is to keep them as simple as possible.

Natural ventilation will seem uncomfortably draughty, particularly where the prevailing wind blows directly into the wall vents. It will feel similar to sitting next to an open window. Alternatively, mechanical and electrical systems require maintenance and will fail prior to the life expectancy of the structure of the house. These systems will need to be replaced with a new unit to maintain air quality within the house for the inhabitants.

As part of the current publication of TGD part ‘L’, the U-Value requirement for each major element of the building, (floors, walls, doors, windows and roof) is required to have increased performance from previous documents. With each notch of this incremental scale, buildings become more complex, in terms of design, details, construction and final certification. In short, new houses will be required to reduce their energy usage and their emissions by 30% to achieve compliance. Going forward, this will mean that houses will need to be more air tight, with the highest leakage level being reduced from 7m³/m²/hour to 5 m³/m²/hour. Thermal bridging at junctions will also feature prominently in future calculations and will have a greater impact on the thickness and quality of the insulation used in the main elements of the building.

The modern house will rely more and more on its electrical supply, which, in the event of a discontinuity of supply, will mean that the mechanical and electrical systems in the house will stop working. Overall, where the house has been thought through and designed correctly, the occupants will have a very comfortable, and economical living space, but will have a greater reliance on the mechanical and electrical systems in the house.

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