COMPLETE GUIDE: AIRTIGHTNESS OF A BUILDING
To learn everything you need to know about airtightness in new and renovated buildings, check out our comprehensive guide!
COMPLETE GUIDE: EVERYTHING YOU NEED TO KNOW ABOUT BUILDING AIRTIGHTNESS
What is building airtightness?
The airtightness of a building characterizes its sensitivity to unwanted airflow caused by leaks in its envelope. In other words, it is the amount of air that enters or exits in an uncontrolled manner through the envelope. It is quantified by the value of the leakage flow rate through the envelope under a given pressure difference.
When done correctly,airtightnessprevents damage to the building caused by air leaks and and the resulting problems: condensation and mold. It is mandatory and measured in new construction new construction in accordance with RE2020, but is not in renovation only when the owner wants a building whose energy efficiency is recognized by a label.
How is it characterized?
The airtightness of buildings is characterized in thermal regulations by an air permeability coefficient called Q4Pa-surf. This represents the leakage rate per square meter of heat-loss surface area excluding the floor under a pressure drop of 4 Pa, and is expressed in m³/(h.m²).
AIR TIGHTNESS AND RE2020
The 2020 Environmental Regulations (RE2020) require an airtightness test for detached or semi-detached houses and multi-unit residential buildings (collective housing) at the end of construction to verify the project's compliance with Article 19 of thedecree of August 4, 2021. All regulatory measurements must be carried out by an operator authorized by the ministry responsible for construction.
Measuring the airtightness value of the RE2020 building
The measurement of air permeability in buildings, in accordance with the decree of October 26, 2010, or the decree of December 28, 2012, must be carried out in accordance with standard NF EN 13829 "Determination of air permeability in buildings" and its application guide GA P50-784. Both documents are copyrighted and available fromAFNOR.
– for residential buildings, it is obtained by measurement or by adopting an approach to the airtightness quality of the building in accordance with the procedures defined in Annex VII of the Order of August 4, 2021;
– for other types of buildings, the air permeability value of the building may be justified by measurement in accordance with the procedures defined in Annex VII of the Order of August 4, 2021.
In the absence of measurement in accordance with these terms, the value to be used is the default value defined by the calculation method mentioned in Article 8 of the decree of August 4, 2021.
Regulatory threshold for airtightness in RE2020
For detached or semi-detached houses and multi-unit residential buildings, the regulatory thresholds for air permeability of the envelope under 4 Pa, Q4Pa-surf, are:
Permeability test RE2020 | RE2020 regulatory threshold |
Detached or semi-detached houses | ≤ 0.6 m³/(h.m² of heat-loss walls excluding the ground floor) |
Collective housing | ≤ 1 cubic meter per hourper square meter of heat-loss walls excluding the ground floor; |
Please note:
If the airtightness measurement is based on a sampling measurement, the airtightness value entered is multiplied by 1.2. This means that in multi-family dwellings, the threshold value is closer to 0.8 m³/(h.m²) for a sampling measurement. It is also possible to carry out an overall measurement of the building, in which case the measured value will be taken into account without any increase.
In the event that work that could affect the airtightness of the dwellings remains to be carried out after delivery, and in the absence of reservations to prevent any leaks during this work, the airtightness values obtained are increased by 0.3 m³/(h.m²). These two increases are cumulative in this order.
For the tertiary sector, no performance requirements are imposed. A default value is used in the thermal calculation. Another value may also be used in the calculation, in which case justification for the level achieved must be provided at the end of the work.
AIR TIGHTNESS AND RENOVATION
Well-controlled air renewal is essential for protecting the health of the entire family. Good airtightness also helps to limit the risk of condensation in the walls and maintain the performance of thermal insulation throughout the life of the building.
Before starting work, it is advisable to assess the airtightness of the existing building envelope. This assessment can be carried out during the energy audit.
SOME SOLUTIONS FOR BUILDING AIRTIGHTNESS
The vapor barrier
A vapor barrier is a building material that serves two purposes:
• limit water vapor migration to the insulation to reduce the risk of resulting pathologies;
• limit unwanted air infiltration to improve the building's airtightness.
Vapor barrier function:
In winter, the air inside the building becomes humid (due to breathing, household activities, showers, etc.). Excess moisture, present in the air in the form of water vapor, is removed by the ventilation system. The remaining moisture in the air tries to migrate outside through the walls. As it migrates, it passes through areas of the wall that are increasingly colder. The relative humidity level gradually increases and the risk of condensation in the form of liquid water becomes significant. Installing a vapor barrier limits the amount of water vapor that passes through the wall, thereby reducing the exposure of the constituent materials to high humidity levels. High humidity in the wall can affect the performance and durability of materials (framework, certain insulation products, etc.). It can also impact the health of occupants by promoting the growth of fungi and mold.
The resistance to water vapor diffusion of a vapor barrier is expressed by an sd coefficient, measured in meters. Sd refers to the thickness of the air layer equivalent to diffusion.
Some vapor barriers known as moisture-variable membranes may have two different sd values depending on the direction of water vapor flow.
Air impermeability membrane function:
Cold air leaks are a significant source of heat loss. Some of these cold air leaks can be controlled by the ventilation system, which replaces stale air with fresher air from outside, while others are referred to as parasitic leaks, created unintentionally during installation, particularly at joints and penetrations.
A vapor barrier membrane that is correctly installed around the heated space improves the building's airtightness. It limits unwanted air infiltration through the envelope and contributes to energy savings.
When is the installation of an air barrier membrane mandatory?
– NF DTU 31.2 "Construction of houses and buildings with wooden frames";
– NF DTU 31.4 "Wood frame facades";
– NF DTU 25.41 "Plasterboard structures – Cardboard-faced boards";
– NF DTU 20.1 "Small masonry elements – Walls";
– NF DTU 45.10 "Insulation of attics using manufactured mineral wool panels or rolls";
What is the Sd value?
The Sd value indicates water vapor resistance. It is expressed in meters (m) and is determined based on the material's vapor diffusion resistance coefficient μ. It is calculated using the formula Sd (m) = μ x material thickness (m). The reference μ value is that of air, which is equal to 1. The higher the Sd of a vapor barrier, the more impervious it is to water vapor.
The different types of vapor barriers:
There are several types of vapor barriers, among which membranes are the best known and most widely used in construction.
A vapor barrier membrane may be reinforced or unreinforced: if reinforced, it will be particularly resistant to allow the blowing in of loose-fill insulation.
Its Sd value can be fixed or variable: a waterproofing membrane with a variable Sd value is also called a moisture-variable vapor barrier. Moisture-variable membranes have a water vapor permeability that varies according to relative humidity: they are moisture-regulating.
The adhesive
Adhesive is used to ensure a strong bond, effective management of membrane penetrations, and high airtightness. It is an essential accessory for optimal vapor barrier installation. Several adhesives for airtightness are available and meet different needs: indoor and/or outdoor use, resistance to cold, UV rays, and humidity, manual cutting or requiring a tool, etc.
Whether it be at overlap areas and strip ends, window frame edges, areas where technical ducts or structural elements penetrate, adhesives are used to ensure good airtightness in the building.
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