Airtightness Testing for New Buildings

An air tightness test is a whole building test that measures how easy it is for air to leak through a building envelope (walls, floor, and roof). In residential developments, construction air tightness testing is often referred to as blower door tests, this is because the main part of the test equipment is a blower door – basically a large fan. For residential air test, a single blower door is used to pressurise (supply air) into a dwelling. For larger non-dwellings, such as commercial buildings with a floor area of over approx. 500m2 commercial fan testing equipment must be used, this usually comprises of a hard door panel that houses 3 fans.

In all cases, both dwellings and commercial buildings must be fully prepared prior to the air test visit, to offer the best chance of the building passing at the first attempt. The main areas to temporarily seal are AC/HVAC intake and exhaust grills, kitchen, utility and bathroom extract fans, relief dampers, etc.  Here is a more detailed air tightness checklist to help clients prepare for the air test visit.

Why is Air Tightness Testing useful?

The blower door test equipment measures the airflow (how much air is moved into or out of the building) and the corresponding pressure difference acting across the building envelope/enclosure.  There are many reasons the air leakage rate can be useful, such as

• Any air leaking out of the building envelope causes energy to be consumed when replacement air is conditioned, either via cooling or heating. With information from an air leakage test you can estimate how much air will leak in both cold and warm weather, or how much more windy weather will cause a building to leak relative to calm weather.  The resulting energy impact can then be considered and used for equipment sizing calculations and predictions of operating energy consumption.
• You can identify air leakage paths that you didn’t know about.  Via blower door and smoke testing, we can accurately record where your leaks are, sometimes it can be a few large holes, however, more often than not its lots of smaller air leakage paths that account for the main air leakage issues. Our experienced air tightness engineers can quickly identify and record the leakage paths during an airtightness test.
• Draughts, through the building can badly affect the occupiers of the dwellings and commercial buildings such as offices. If cold damp air is blowing into the building it can be uncomfortable in both hot and cold weather. In the past we have undertaken pressurised smoke testing to buildings because the clients’ workers refused to work in the building. When we tested the building, we found it had an air leakage rate of 25m3/hr/m2. Once we had identified the air leakage paths and the clients’ contractors had sealed the areas, the building achieved an air leakage figure below 5m3/hr/m2. The result was further complaints from the occupiers.
• Excess air leakage can lead to condensation issues, as the air can blow through the floors, walls, and ceilings and usually contains water vapour, these uncontrolled air leaks can cause condensation, mould, and rot issues, which can be unhealthy for building occupiers. So, quantifying how much air passes through the building envelope are extremely important to understand. Only with a good air barrier can we know where the air is coming from and have a chance that air quality (and quantity) can be controlled and condensation kept to a minimum.
• Large amount of air leakage can bring polluted outdoor air into a building from, for example, buy main road, fuel garage, bins, restaurants, or external ventilation. Knowing how much air infiltrates through your building enclosure/envelope will help identify how much risk there is of ingress of outdoor pollutants. Any uncontrolled air that enters a building is often loaded with pollutants, especially if you are close to a main road etc. so trying to provide a robust and good air barrier is very important. Only with a good air barrier can we control pollutants within the building enclosure.

Air Tightness Testing for Retrofit Projects

Airtightness targets are useful within the design process for both new buildings as well as retrofit projects. Air tests are the only way you can accurately quantify the building enclosure performance and provide key input into the mechanical designer’s load and energy, as well as helping to lower the air leakage rate of the building via pressurised smoke testing and remedial sealing works. It has been proven that Airtightness tests are one of the most important parts of the construction process, as they provide confirmation that airtightness targets are met and, if timed properly e.g., undertaken before final decorations, give the building contractors an opportunity to address problems via remedial sealing, prior to the final precompletion test and building handover.

What results do you get from an air tightness test?

The results of an airtightness test in basic form are the pressure difference across the building envelope/enclosure, the total airflow, and the airflow direction (pressurise or depressurise).  During the testing 10 airflow measurements are collected using a range of pressure differences and flow directions, the usual pressures are between 25-70Pa in 5Pa increments.  This air test data is plotted to quantify the relationship between the fan airflow and internal and external pressure difference.   Although the test takes into account multiple pressure levels, the result is shown at a single pressure (50Pa) from the curve and reported as such – as shown below.

For dwelling and commercial buildings, the single test pressure used for reporting is almost always 50 Pascals. The airflow is reported in cubic meters per hour per metre square of building envelope (m3/hour/m2).

In most cases, as the size of the building under test increases, the airflow measured will also increase and the types of test equipment will also change from single to multiple blower door units. To allow for easy comparisons between different buildings, two calculation methods are used to calculate the airflow with respect to building size:

• Divide the airflow by the area of the building enclosure being tested (m3/hr/m2)
• Divide the airflow by the volume of the building (ACH@50)

in many cases its more common to use the airflow by the area of the building enclosure being tested or m3/hr/m2. This is mainly due to the differences between surface-to-volume ratios. It is more common, and usually more accurate to provide the leakage rate at a specific pressure (usually 50 Pa) in terms of flow per unit area, in other words as cubic metre per house per square metre of envelope area (m3/hr/m2).

The envelope area means the total six sides of the building, which includes the four walls, floor, and ceiling. It’s worth noting that all (areas) that are exposed to the outdoor air are part of this equation, this can mean awkward ‘one off; envelope protrusions such as large canopy overhangs etc, that are not compartmented from the rest of the building.  This reporting method accounts for the size of the building and therefore allows you to make better comparisons between varying types of buildings.  This envelope area type of testing is increasingly finding favour in the residential community as well that’s why Building Regulations Part L1/L2 stipulates this type of testing.

In some rare cases, clients need the air leakage worked out to account for air changes per hour (ACH). Air changes per hour is simply the volume of air leaked per hour, divided by the volume of the building. The test data is then reported as a number in “ACH@50”.  Air changes per hour is sometimes used to report air leakage for commercial and more unusual buildings and/or enclosures such as laboratories, data centres etc.

Our Air Tightness Testing procedure

Our fan system mounts into a standard size door-sized housing (900mm x 2000mm) and is adjusted to suit the size of the door frame.

We then set up the blower door equipment as follows.

1. Firstly, we find a suitable doorway to temporarily install our blower door fan system (depending on building size).
2. We then undertake the first series of environmental measurements such as internal and external temperatures as well as barometric pressures and internal and external temperatures.
3. We then turn on the fan equipment and take measurements between 25-70Pa in 5Pa increments, recording the pressure differential at each step.
4. Once the pressures have been taken we undertake the second set of environmental measurements.
5. Finally, our technicians will calculate the total air flow required to achieve a pressure differential of 50 Pa, divided by the total building envelope area – this calculation will show leakage rate in m³/h.m² @ 50 Pa.
6. Once the building air leakage rate has been established, we then pressurise the building (blows air into) to around 50 pascals of pressure. This forces air to flow through cracks or air leakage paths throughout the building envelope.
7. We then turn on the smoke machine and walk around the house or commercial building, highlighting, and recording all the air leakage paths through the building envelope.

We usually allow two to three hours to complete each air tightness smoke test; however, we can attend site all day if instructed. If you have the necessary manpower, it allows your operatives to seal all the necessary air leakage paths on the day of the test. If you are planning on undertaking remedial sealing works on the day of the test, your operatives will need to have mastic, expanding foam, draught excluders, plasterboard, grip fill and suitable safe access to undertake the sealing works.

What’s a good level of air tightness for your project?

However you process the data, you still need to ascertain what is a good level of air tightness for your new build or refurbishment project. In many existing Victorian houses or commercial buildings, the air leakage can be as high as 15m3/hr/m2, which when you consider new dwellings are getting between 3-5m3/hr.m2, and commercial buildings below 3m3/hr/m2, it’s a truly terrible result. So, what’s a “good” level of airtightness for your building.  As we previously stated, most new houses that don’t have mechanical ventilation, a good air tightness target would be between 3-4m3/hr/m2. For a dwelling with mechanical ventilation its best if your figure is below 3m3/hr/m2.

With buildings becoming more air-tight, we are seeing the increased impact of known holes, such as air leakage through grills and openings of mechanical systems. In many cases it’s not uncommon to see almost 50% of the buildings total air leakage through the mechanical system.  This means designers and installers have to ensure that backflow dampers are working properly as they should seal tight in the closed state, providing an air-tight barrier. If dampers do not work properly, it will have a negative effect on the overall tightness of the building under test and later in service.

Many modern commercial buildings, constructed since 2006, when the air testing regulations came into force have quite an air-tight envelope, such commercial buildings that has utilised sealed cladding etc. which has elements which are slower to degrade, however, other elements such as external doors and windows, can become air leakage areas due to degraded seals or structurally damaged frames.

Another main area of air leakage can be around the mechanical ventilation system due to poorly maintained or damaged dampers. Even with dampers closed we have seen air leakage double when temporary sealing is removed from the associated internal ventilation louvres. Another common issue is often down to mechanically operated roof lights what don’t shut tightly against the seals and damaged fireproofing that was used as the air tightness barrier in the building eaves and/or to isolate unconditioned areas, such as plant rooms from the main building.

How does airtightness tests fit into the design process? 

With the ever tightening of building emissions, the trend is for greener and more air-tight buildings. The building industry is going to be required to meet more stringent airtightness targets, either because they are added to new building codes, or because owners are looking for better buildings with less energy consumption, more comfort, better indoor air quality, and much cheaper to run. In our experience a robust air-tight building is often a good indictor to client’s that the building contractor has delivered a good, airtight building enclosure.

Airtightness testing can also be used to check the building at various stages. For new construction of commercial buildings, we often undertake an air test approx. one month before handover, just prior to final decorations so any ‘hard to detect’ air leakage paths can be identified, recorded and shown to the site team to undertake remedial sealing works. Thereafter, approximately one week before handover the final precompletion testing can be undertaken to achieve Part L compliance.

On a similarly note, if you are about to do a major refit to improve the building energy efficiency for BREEAM etc, such as adding insulation, replacing windows and doors, replacing electrical rooflights the mechanical ventilation system, it is usually advisable to do a test before you get too far into the design and build process. In many cases it makes good financial sense to undertake an air test as part of the initial assessment of the existing building, to check the amount of air leakage so a more informed decision can be made on remedial basic air sealing works in comparison to more expensive and time-consuming works such as the replacing of new doors and windows within the external envelope.

Thermal imaging and air tightness testing is a powerful combination.

For even better results, we often use thermal imaging surveys at the same time as a blower door test running. The blower door helps exaggerate air leaking through defects in the building shell. Such air leaks appear as black streaks in the infrared camera’s viewfinder depending on the colour palate as well as identifying missing insulation etc.

Combining the best skills in air leakage testing and thermography allows our engineers to gather amazing results, accurately highlighting air leakage points around a building big or small. Thermography uses specially designed infrared video or still cameras to make images (called thermograms) that show surface heat variations. Thermography can also detect damaged or missing insulations in walls, floor, and roofs within building envelopes. Also, as thermal imaging can pick up damp within the building envelope, it can be used to find wet insulation, as its conducts heat faster than dry insulation

Air tightness testing can help mechanical designers

We have found that by using airtightness tests regularly, architects, M&E consultants and building contractors are getting better at designing for strong airtightness performance. Furthermore, once you have established the air leakage target for the building this can then be forwarded to the mechanical systems designer, so heating/cooling systems can be more accurately designed around the buildings air leakage rate.

When mechanical engineers don’t know the air leakage rate of the building they tend to aim on the safe side, which often results in a measure of ‘over design’. Its’ all about having the correct building information at design stage, if you have already ascertained the air tightness target the mechanical engineer will be better informed and will be able to better job of sizing the mechanical systems for heating, cooling, and dehumidification.

Another problem encountered with airtight buildings, is the proposed mechanical systems can over pressurise them, forcing conditioned air out through the building envelope; again, measuring the airtightness of a building allows the mechanical engineer to be better informed when finalising the values to use in system design so over pressurisation is reduced to a minimum.

Reducing air leakage across the building envelope is fundamental to make buildings more comfortable, healthy, durable and to lower energy consumption. In the end, airtightness testing is basically the most important quantitative quality control tool to help lower emissions from new and refurbished buildings, with the added benefit of helping M&E designers to specify the correct mechanical system for the building.

We can help with your Air Tightness Testing

APT Sound Testing we have large amount of experience in understanding the requirements of Approved Document L, along with extensive experience of carrying out thousands of successful air tightness tests on a wide range of developments across London and the UK.

In order to achieve the required air tightness target (which is getting lower all the time) and to avoid the risk of a failed air tightness test, we strongly recommend that early consideration is given to the design of the air leakage line within your project.

By working with our customers throughout their design and construction stages, we can provide advice and guidance on the most feasible ways to avoid air leakage and attain compliance for the air tightness test. Please download our air tightness checklist to help you prepare for your test.