FAQ: pro clima Airtight Systems

Airtightness is the control of air leakage, i.e., the elimination of unwanted draughts through the external fabric of the building envelope. This may be achieved by the correct and proper installation of a vapour check or vapour barrier. Consequently condensation, mould, rot, damp and structural damage are also eliminated. This ensures a more viable structure, an insulation layer that can perform properly as it is now protected against penetrating moisture reducing the amount of energy-in-use in the building and CO2 emissions. While ventilation is intended, air leakage is not. It is desirable and necessary to have controlled ventilation for healthy comfortable buildings.

A diagram showing a draughty leaky house, the red arrows highlight the potential airleakage pathsand the green arrows show intended ventilation/openings.

A diagram showing a well sealed, well ventilated house.

The key is to build tight and ventilate right.

Sustainable design and construction to achieve low energy, Passivhaus and zero carbon homes are now at the forefront of the building and planning process. Codes and standards are in place which aim to reduce carbon emissions and create homes that are healthier and more sustainable. The only way to achieve Passivhaus, low carbon and zero carbon building is to ensure a high level of airtightness is attained. That means designing and installing a continuous seal around the internal fabric of the external envelope to eliminate unwanted draughts. Once the airtight vapour check is in place and sealed with flexible and durable tapes, seals and glues, it ensures that the insulation functions to its optimum performance, saving energy and drastically reducing carbon emissions for the lifetime of the building. The airtight vapour check also ensures that interstitial condensation risk is minimised, ensuring no structural damage from moisture, mould, rot and damp.

pro clima are innovators and market leaders of an ‘Intelligent’ airtight system. This differs greatly from conventional vapour barriers and vapour checks.

The technology used in pro clima membranes, Intello plus and DB plus ensures membranes may become more vapour ‘diffusion open’ when required. This means that they have the ability to alter their vapour diffusion resistance depending on the average relative humidity surrounding the vapour check.

In winter the membrane remains diffusion tight and will resist the diffusion of vapour from the internal fabric of the building into the insulated layer. However, in summer pro clima’s membranes, Intello Plus and DB Plus, may become more vapour open. This allows any moisture which may be trapped in the insulated fabric of the building to back dry to the inside of the house, something a conventional vapour barrier/check cannot do. This ensures a very high level of safety from structural damage due to moisture accumulation over seasonal periods. An intelligent membrane facilitates significantly more drying compared to a vapour barrier / check.

On the left hand diagram the diffusion current in winter is from the inside to the outside, in these conditions the pro clima Intelligent membrane is diffusion tight, no moisture can penetrate the system. In the Summer the diffusion current is from outside to inside, this is when pro clima Intelligent membranes can become diffusion open.

Unanticipated moisture may be present in buildings; perhaps as a result of extremely adverse conditions during the building stage (e.g. the timber / insulation gets damp) due to flanking, diffusion directly through the membrane or air leakage (e.g., convection). Using an ‘Intelligent’ pro clima vapour check ensures that this moisture can dry as quickly as possible due to its unique diffusion properties. Conventional vapour barriers remain vapour tight under all conditions which may lead to damaging moisture build up. The pro clima system offers superior protection against even extreme unforeseen circumstances.

Research shows that under normal winter conditions around 0.5g of moisture is able to penetrate a gap free vapour check/barrier by diffusion. See Figure 3 with a 1mm tear over a 1 square metre area in the vapour check/barrier as much of 800g of moisture can be transferred into the structure per square metre length by air leakage (convection) – a reduction

It is estimated that we spend up to 90% of our life in buildings. Therefore indoor air quality and anything lending itself to reducing risks associated with mould growth is desirable. Mould, rot and fungus may occur as a result of excessive moisture penetration to the fabric of the building. The pro clima system eliminates any potential for this damage due to its ability to allow drying to occur, resulting in a much higher level of air quality in the house and creating a far healthier home and durable building.

All buildings have to be ventilated for health and comfort and that’s exactly the same for an airtight building. A satisfactory ventilation system has to be planned in the design process for every building. The ventilation system will vary depending upon the levels of airtightness to be achieved and the home owners’ requirements, from passive ventilation to mechanical ventilation systems for zero carbon and Passivhaus design. While ventilation is intended, air leakage is not! The key is to control ventilation and minimise leaks. Of course one can open a window in an airtight house, however, in an airtight house, when the window is closed, no air leakage occurs around the window frame or cill.

Achieving an airtight seal isn’t difficult, but it does need to be designed and planned, and attention to detail given on site - it’s all about thinking two steps ahead in order to ensure overlaps and joints are effectively sealed. Take a look at our installation guide on pages 18-19 of the brochure for more information.

Short cuts and poor workmanship result in air leakage which if detected at the Blower Door testing stage are difficult to rectify. An ‘out of sight, out of mind’ attitude leads to leaky building. Forethought and monitoring with intermediate assessments through the build process by the use of the pro clima Wincon quality control unit to detect air leakage, minimises and mitigates the need for any costly remediation work. We estimate that the material cost of installing the pro clima airtight system is as little as 0.5% of the total build cost on an average build. The primary cost is related to labour, hence forethought and good design can significantly reduce costs. And then think of the energy saved for the life of the building and you also have a healthy building …….

Research shows that we can lose as much as half of all the energy used to heat our buildings through unwanted draughts, inefficient and poor ventilation. We now generally insulate new houses very well but the proportion of energy lost to draughts has increased and in some cases around half of all heat losses are due to air leakage across the building fabric. In Ireland and the UK we are not exposed to extremes in low temperatures, however our climate is exposed to high wind pressure, particularly in coastal regions.

If a vapour check has as little as a 1mm tear within a square metre area, the U value can reduce by a factor of 4.8 (See Figure 4.)! This means that the calculated U value is not achieved if the structure is not airtight and hence you need a lot more energy to heat the house.

Airtightness does not generally increase U values, but ensures the calculated U value is achieved.

The most commonly used unit of measurement for airtightness in Ireland and the UK is referred to as the air permeability of a building or Q50.

To measure air permeability a pressure differential is induced onto a building using a large fan called a Blower Door. An airtightness measurement usually involves a combination of depressurising and pressuring a building to a pressure difference of 50 Pascal’s (50Pa) which is equivalent to a wind speed of about 20 miles per hour on every side of the building envelope at once, by no means an extreme pressure. Once the pressure differential reaches 50 Pa, air leakage may easily be located in the external envelope and an accurate measurement of the air permeability of the external envelope of the building is taken.

The air permeability of a building at a pressure differential of 50Pa is referred to as the Q50 of a building and is measured in m3/hr (of airflow) per m2 (of total external envelope area).

The standard upper limit level of airtightness in buildings in Ireland and the UK at the time of print, is a Q50 of less than 10m3/hr/m2 for all new buildings. Please refer to latest edition of the building regulations for further information. A Q50 of less than 10m3/hr/m2 refers to an air permeability of less than 10m3 of air per hour per m2 of the external envelope of a building when the building is exposed to a pressure differential by depressurisation and/or pressurisation of 50 Pa. This literally means that when we exclude ventilation and design openings, and exert a pressure difference of 50Pa on the external envelope of the building 10m3 of air per hour passes through every square metre of the external envelope. According to the Airtightness Testing and Measurement Association (ATTMA), for airtightness best practice, buildings which are mechanically or naturally ventilated should achieve an air permeability of less than 3m3/hr/m2, this is quite a high level of airtightness. However the highest level of airtightness required in buildings can be as low as less than 0.6m3/hr/m2, which is required in the PassivHaus Standard, which are mechanically ventilated.

As airtightness is a central part to low energy construction, it must be a priority to achieve best practice airtightness when we build, extend or renovate our buildings.

Mould requires Oxygen, a food source and water to grow. By eliminating the build up of moisture and prolonged high humidity within building elements, mould growth can be eliminated. If you take away the moisture you eliminate potential mould growth.