Why is Airtightness and Moisture Management important?

Research shows that up to half of all heat loss in buildings can be due to unintended air leakage and uncontrolled ventilation. Insulation levels have increased substantially over the last few decades, but heated air is still escaping and can be pinpointed as a majorsource of energy loss.

In signing up to the Kyoto treaty, the UK government has acknowledged the importance of managing CO2 emissions and around 50% of CO2 emissions in the UK are from the built environment. 50% percent of that figure is energy expended in space heating and cooling i.e. Central Heating, Air Conditioning etc. The climate of the UK does not expose us to extremes in temperatures but we are exposed to extremes in wind pressure, especially in coastal areas. While insulation is central to low energy construction, air and windtightness must also be central to an energy efficient design strategy to reduce unnecessary heat loss.

Doesn't Airtightness create a stuffy environment?

As mentioned above, this is a common misunderstanding when thinking of airtight construction. We need ventilation, but unmanaged ventilation wastes vast amounts of energy. The current UK building regulations allow for a hole the size of a 20p in every square metre of the building fabric - this leads to all sorts of problems.

Heat that escapes from buildings carries a significant amount of moisture. This moisture can cause damage to the building fabric as it travells through and may have a severe effect of living conditions and the air quality of the living space. Common problems such as damp, mildew, rot and condensation are caused by the moisture becoming trapped inside the wall. Some of these can lead to structural problems, while others can lead to poor air quality and poor performance of insulation.

So in summary, it is exactly the opposite. If we manage the ventilation of our buildings effectively we can virtually eliminate these problems.

Why build for airtightness?

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 teh 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 maximum protection from structural damage from mousture, mould, rot and damp.

Will installing for airtightness save energy and reduce heating bills?

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 the UK we are not exposed to extremes of temperatures, however our climate is exposed to high wind pressure, particularly in coastal regions.

Insulation tear 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 or 480%!(see diagram on right) This means that the 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.

Measurements were taken at an air temperature difference of +20ºC (69ºF) indoors and -10ºC (14ºF) outdoors, a pressure difference of 20 Pa (equivalent to wind force 2-3) using conventional, fibrous insulating material.

U-value with airtight vapour barrier = 0.30 W/m²

U-value with 1mm gap in vapour barrier = 1.44 W/m²

A gap as small as 1mm in the vapour barrier can reduce the U-value by a factor of 4.8

Measurement carried out by: Institut für Bauphysik, Stuttgart

Is it difficult and costly to install for airtightness?

Achieving and 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.

Short cuts and poor workmanship result in air leakage which if detected at the final "Blower Door" testing stage are difficult to rectify. An 'out of sight out of mind' attitude leads to a leaky building. Forethought and monitoring with intermediate assessments throughout 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 on an average build. The primary cost is related to labour, hence forethought and good design can significantly reduce costs. When put into the context of the energy savings that will be achieved, the costs are negligible...