What is air leakage?

Air Leakage can be defined as: The uncontrolled movement of air in to and out of a building which is not for the specific and planned purpose of exhausting stale air or bringing in fresh air.

An airtight building is one which does not lose either cooled or heated air to the outside in an uncontrolled manner.

In practice, no buildings are completely airtight and it would not be desirable (normally) for this to be the case.

Air leakage testing is a method of measuring the extent to which cooled or heated air is lost through leaks in the building.

Air leakage testing can also be referred to as 'Air Permability Testing' and 'Air presure testing'.

Who chooses the units to be tested?

The Building Control Body (BCB) will select the units which are to be tested according to the defined sampling in Part 'L'. On larger developments, units will be chosen from the first completed batch, to ensure that mistakes can be rectified and lessons applied to later batches. It is recommended with each failed unit/model type, that a similar unit/model is subsequently tested to ensure this is not a generic fault.

The problem with air leakage..

Today, many builders are routinely building dwellings that are very airtight, often without realizing it. The common use of building wraps, moisture barriers, high efficiency windows and even simple plywood sheathing all have direct effects on reducing air leakage and infiltration. An airtight dwelling has many fewer openings through which fresh air can enter. Without the addition of mechanical ventilation, a tight dwelling can result in stagnant air, less natural ventilation and dissatisfied property owners. On the other hand, buildings and dwellings with large amounts uncontrolled air leakage are equally troublesome with comfort complaints due to drafts, building failures and high energy bills.

Despite the growing importance of airtightness, few builders, architects or property owners know how tight their buildings are. Until recently, the building industry has tended to rely on subjective estimates of airtightness. Unfortunately, it is impossible to accurately estimate the tightness level of a building by visual inspection alone. And without knowing the airtightness level, it is difficult or impossible to design for effective approaches to ventilation and air quality, or to accurately diagnose performance problems.

What is the Impact of Air Leakage?

ENVIRONMENTAL IMPORTANCE

Buring fossil fuel to generate energy adds to carbon emission levels, which in turn is believed by most scientists to add to the 'Greenhouse Effect'.

Using less energy by being more efficient is the best way of reducing carbon emissions.

The Government is aiming to achieve a 60% reduction in carbon emissions by the year 2050, this is probably impossible without tackling the waste caused by leaky buildings.

It is now widely accepted in the UK that there is little merit in improving the effective U value standards required for envelope assemblies unless the levels of uncontrolled air leakage through such assemblies are significantly reduced. The significant energy penalty which uncontrolled air leakage causes, has been recognised within the amendments to PART 'L' (Conservation of Fuel and Power of the Building Regulations 2006). The amendments introduce maximum envelope Air Leakage Standards for domestic and non-domestic buildings.

As well as the direct energy penalty imposed by air leakage,
other associated problems include:

• Occupier discomfort because of drafts.
• Degradation of the building fabric due to interstitial condensation.
• Poor indoor air quality due to the ingress of fumes, dust, etc.
• Inability to achieve required pressure conditions in controlled
environments.
• Difficulties in balancing air-handling systems.
• Noise transfer through leakage paths.

Why is Building Leakage Important?

The Cost
Energy is wasted by various means usually through a buildings design and construction quality. Lack of attention to air leakage is one of the most costly factors, sometimes causing the fuel bills to double, with rapidly rising energy prices, this is becoming a very important issue. Building tight buildings/dwellings without providing proper ventilation can increase the potential for health and safety problems to occur. Higher moisture levels found in inadequately ventilated houses create an ideal environment for molds, dust mites and other causes of respiratory problems and allergies. Tighter buildings are also more likely to experience problems from backdrafting and spillage of combustion products from naturally drafting furnaces, water heaters and fireplaces. This is because in tight buildings, it is easier for exhaust devices (e.g. dryers, kitchen and bath fans) to create large pressure differences between inside and outside of the building, which can interfere with proper venting of the combustion appliances.

Leaky buildings have their own set of problems ranging from drafts, blistering paint, ice dams and frozen pipes to a house that won't adequately heat or cool. While in the past airsealing efforts concentrated on the easy to find air leaks around windows and door, we now know that the most important leaks in a house are the hard to find leaks in the attic, crawlspace, attached garage and other framing connections. These hidden leaks are responsible for most of the air leakage in typical properties, and are often the cause of performance and durability problems.

And whether a building is tight or loose, nothing will cause it to deteriorate faster than moisture migration and condensation in attics, ceiling and other building cavities. Vapour barriers will stop moisture diffusion, but most moisture problems in buildings are a result of uncontrolled air leakage through the building envelope. And the way most vapour barriers are installed, they do little or nothing to stop uncontrolled air leakage. In many buildings, moisture problems are made worse by the common use of hot tubs, whirlpools and saunas.

 
What Causes Air Leakage?

There are three main driving forces of envelope air leakage:

• WIND. Wind exerts constantly changing positive and negative pressures on the building envelope.

• STACK EFFECT. Rising warm air causes pressure differentials through the building envelope, which are generally positive at high level and negative at low levels.

• MECHANICAL SYSTEMS. Heating and ventilation systems create positive or negative pressures within the building.

Any of these driving forces, or a combination of all three, will lead to a leakage through any cracks or gaps in the building envelope. This leads to cold external air moving into the building, and warm internal air moving out of the building. Whole Building pressurisation tests can establish envelope leakage rates for comparison with client specification or BUILDING REGULATION PART 'L' STANDARDS.

All our tests are in strict accordance with

ATTMA’S TECHNICAL STANDARD 1 (TS1).

Measuring Airtightness..

The easiest way to measure building airtightness is with a diagnostic tool called a Blower Door. The Blower Door consists of a powerful, calibrated fan that is temporarily sealed into a suitable aperture (usually the main door). The fan blows air out of the house to create a slight pressure difference between inside and outside. This pressure difference forces air through all holes and penetrations in the building envelope. Blower Door tests are performed over a range of pressure differences up to at least 50 Pa.

By simultaneously measuring the air flow through the fan and its effect on the air pressure in the building, the Blower Door system measures the airtightness of the entire building envelope. The tighter the building (e.g. fewer holes), the less air you need from the Blower Door fan to create a change in building pressure.

What if a building fails?

In the event of a fail, smoke testing can determine the main areas of leakage. We, at 'AIRTIGHT TESTING', often provide this service on the test day. Smoke generators can be used to pinpoint leakage through the external envelope. They can be used to identify areas of leakage that may need remedial sealing after an unsuccessful test. The benefit of smoke generators is that they can accurately identify those areas that need sealing, allowing carefully targeted rermedial works to be undertaken.

Building Regulations Approved Documents

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