Air Pressure, Sound Testing and Air Testing Services UK

Head Office: Sayells Farm, 7 Harlington Road, Upper Sundon, Bedfordshire, LU3 3PE
Tel: 07967 233836 or 07775 623464
Offices in London, Luton and Cardiff

Who We Are

Our Services

Why Air Testing

Why Acoustic Testing

Why Thermographic




Air Tightness Testing
Air Pressure Testing Ltd offers a complete range of technical Air Tightness testing, Thermographic surveys and consultancy services to help clients gain compliance to Part L.

If you have any specific requirements that are not detailed, please contact us at we should be able to help whatever your query/question may be if you don’t know the answer we usually do! Note, Air Pressure Testing offers both Air Leakage & Acoustic Testing and would be pleased to offer advice and help on how to comply with both Air Tightness and Acoustic specifications

Design Review
Air Pressure Testing’s design reviews ensure that air tight elements are fit for the intended purpose and will have the necessary life span. Our expertise, skills and experience provide clients with pragmatic design solutions to minimise the risk of the air tightness works failing in the short and long term.

Drawing on our technical knowledge and experience within construction we can identify areas of the building design and specification that pose a risk to the air tightness specification. Aspects to review for air tight elements can include their material specification and physical characteristics, air permeability, detailed design, proposed installation procedures and operational requirements.
Air Pressure Testing’s Design Review is therefore fundamental in eliminating potential problems. Sending us drawing and specification details is a key stage to accruing the long term benefits of achieving the air tightness specification and reducing the risk of a Air Leakage failure.

A Typical Problem
The client required all new Dwellings to be constructed out of Timber frame to improve construction time and ease of buildability issues; however the customer had not taken into account the new Air Leakage regulations and the subsequent greater risk using a Timber Frame construction presented. This wasn’t unique to this large house builder as virtually no one understood (or had heard of) the concept of the term air tightness? The basic problem was first to educate everyone involved about air tightness issues and then implement it across all sites and offices.

Air Pressure Testing was appointed to undertake a complete design review and subsequently helped produce the client's Air Tightness Design Guide to set down the specification required. Then a series of air tightness seminars was undertaken on existing sites/offices. At this pre-contract stage, all parties were at least aware of why and how air tightness targets could be achieved. The client then instigated initial design reviews for all new house designs , prior to a start on-site, to set out the issues for each particular project with Air pressure Testing. Elements of the design and specification were highlighted if there was a risk to the overall air tightness specification being exceeded and solutions put forward. These meetings enabled Project Teams to identify, co-ordinate and manage the installation of the air tightness works on-site. Ultimately, the new dwellings reached their air tightness specification first time.

Air Pressure Testing’s Services Capabilities
In depth knowledge and experience helps Air Pressure Testing solve complex air leakage problems qualifies Air Pressure Testing to specify envelope seals at design stage that will have the necessary design life and be fit for purpose. Various factors have to be taken into account including requirements for thermal insulation, wind loading, adhesion, condensation risk, fixings and so on. The overall plan layout and operational characteristics of the building can also be looked at to ensure that the air tightness requirements are met when the building is open and operational. Drawing on our knowledge at the earliest stage is the most cost effective way to ensure that the project complies with Part L and that the air tightness works last for the design life.

Air Tightness - Site Audits
Building right first time whilst under the experienced eye of Air Pressure Testing Engineers our Clients can avoid the potential high cost of remedial works and even higher costs of delays/LEDS by asking Air Pressure Testing to audit air tightness site works throughout the duration of your project (a good guideline is 3 visits per project) this is undertaken in the presence of a member of the contractor's site team. Air Pressure Testing’s air tightness site audits are carried out by experienced Engineers who have gained a significant amount of experience by carrying out over 1000 projects to date, and also have the experience of general site construction management having been Project/Contract managers in companies such as Amec etc

Our experience of auditing and carrying out air sealing works, on hundreds of different sites, gives the knowledge and experience to ensure your project is built correctly and thereby compiles with Part L first time Audit reports can be prepared, providing a schedule of works, cross referenced with relevant drawing details and photographs, this allows for a quick and easy site reference for all of your site staff and sub-contractors. Site audits carried out at critical points on the build programme can ensure passing air tightness tests first time and that the air tightness specification is fully complied with.

Site Audit Case Study
Air Pressure Testing’s on-site expertise was used to good effect during Mansells Project at Great Ormond St Hospital, on the construction of 4 isolation rooms. The contract specification included an item for the Contractor to achieve an air permeability rate under 1m³/h/m². By carrying out site audits and having a strong proactive approach working alongside the contractor Air pressure Testing enabled the air tightness specification to be met with minimal disruption and costs.

Much of the construction works had already taken place therefore it was too late for Air Pressure Testing to change the specification of the walls from Drylining (met-sec) to a solid masonry wall (a more efficient construction ) unfortunately there was also a small plant room that was also encompassed within the Air Leakage Test. As the plant required full emergency access, a ceiling could not be constructed below the plant, therefore it could not be adequately sealed e.g. where the pipe/duct runs terminated through the walls etc

Using due diligence and sound knowledge of construction detailing Air Pressure Testing visited site to undertake a preliminary Air Leakage test, unfortunately the Isolation rooms building envelope was initially prone to large amounts of Air Leakage, using our small high powered directional smoke machine APT quickly ascertained the pathways of Air Leakage. Details were noted, photographed and recorded and a comprehensive detailed site survey was undertaken with recommendations made for expansive remedial works, this was undertaken in the presence of the client’s Project Manager. Subsequently on the 2nd visit all the isolation rooms passed the Air Leakage Test with a average result of 0.5 m³/h/m² or 5% of the current requirement of part L of the building regulations

Air Leakage Tests - carried out to ATTMA TS1 & CIBSE TM23
Air Pressure Testing has very comprehensive resources for carrying out air tests in the UK, in terms of air testing kit and staff. Air Pressure Testing can supply a range of fans to suit testing from the smallest dwellings up to the largest commercial buildings. These are all operated by Air Pressure Testing’s experienced site teams who have many years experience of air tightness testing and related works. All Air Pressure Testing’s works are carried out to ATTMA and CIBSE standards, which is a minimum requirement for Part L 2006.

Our compact and portable fans are easy to set-up in sets of 1-3 and capable of being used in very restricted areas, this has helped our many clients in areas such as city centers etc. When doubled up these fan sets though portable are still capable of testing buildings up to the largest distribution centers.

All Air Pressure Testing’s air testing rigs come self contained with their door screens, each Air test rig has its own smoke testing equipment, enabling the site team to investigate potential problems there and then. All Air Pressure Testing’s air leakage testers have good experience of air sealing, they are particularly adept at finding where buildings have problems which potentially reduces costs due to not having to pre-book and pay for smoke tests that may not be required.

All Air Pressure Testing’s fan units can both pressurise and depressurise buildings, helping enormously in locating air leakage paths.
Air Pressure Testing’s Thermographic surveys can be undertaken whilst a building is depressurised this helps identify where air tightness needs improving. Air Pressure Testing will forward the survey results in a clear easy to follow format allowing you to undertake what ever remedial action is necessary.

Smoke Tests to highlight Air Leakage
Our powerful yet portable Smoke testing equipment makes up part of Air Pressure Testing’s air test rig; this allows for a rapid visual diagnosis of air tightness problems and possible air leakage paths. The smoke is not harmful but it is a requirement of Air Pressure Testing that you inform the fire brigade prior to any Smoke Test being undertaken.

As part of our standard Test equipment we carry both hand-held and full building smoke generators. The large building smoke generators can be linked together to ensure all parts of large buildings are filled with smoke, which makes for easier diagnostics. When the building is pressurised, smoke is forced out through air leakage paths thereby providing conclusive evidence of areas requiring attention, it is essential that you have a competent person such as your Site/Project manager available to witness the test

Frequently Asked Questions

Air Tightness – A Definition
Air tightness – the resistance of the building envelope to inward or outward air leakage. Excessive air leakage results in increased energy consumption and a drafty cold building. Air leakage is driven by differential pressures, across the building envelope. The mechanisms that create these differences in pressure are the combined effects of – stack (internal warm air rises), external wind (inducing +ve and –ve pressures on the envelope) and mechanical ventilation systems.

The New Building Regulations Part L
Note – Part L1 applies to dwellings, Part L2 to non – domestic buildings. Part L1A and L2A refer to new buildings and L1B and L2B to refurbishments.

The reason the New Building Regulations Part L include for air tightness?
The Government is committed to reduce CO2 emissions from energy consumption by 20% by the year 2010. Many of the buildings constructed today (both dwellings and commercial) consume more energy than necessary. Two major factors in the design and performance of building fabric which affect energy consumption are, air leakage and continuity of insulation. There are also substantial commercial benefits to building owners that will accrue over the life time of the building. Reduced energy costs provide clients with real cash incentives to achieve airtight buildings. Other benefits are gained from increased comfort for building users, office staff and / or customers. Although difficult to total, these are tangible benefits to the client and the welfare of their respective personnel.

When did the latest Part L of the building Regulations come into force?
Air Tightness Testing became a requirement under Part L in April 2002 with a recent update in April 2006. Now, all buildings that pass through the planning and building control processes have to comply with Part L. The Government is looking to tighten up the regulations and further updates are due in 2010. European Legislation has also been enacted, tightening the use of energy in buildings. This was introduced in January 2006 through the European Performance in Buildings Directive.

Rules To Ensure Part L is Met
All parties involved on the project from the client, contractor and consultants to all site staff and operatives and off site suppliers need to understand the concepts of air tightness and how they affect the part of the project they are involved with. It only takes one part of the building to be leaky to ensure a failure to comply, which can lead to costly remedial works and time delays. A real effort needs to be made to educate everyone involved and ensure that a team effort is made.

ALL buildings require designs to incorporate ‘robust details’ to ensure air tightness, continuity of insulation and potential problems with thermal bridging are addressed.

For non domestic buildings, carry out an air leakage pressure test to ATTMA TS1.

For buildings < 500 m² gross floor area, assume an air permeability rate of 15 to calculate the BER or carry out an air tightness test.

Remember that the maximum air permeability rate is 10 m³/h/m² at 50 Pascals. However, the air permeability target may have been set tighter so that the carbon rating is met!!
Changes between Part L 2006 and 2002 for Commercial and Domestic Buildings, New and Existing.
Key Changes for New Commercial Buildings Part L2A

Obtaining compliance is now a five-step procedure.

1. Designers will need to:
• Show a home’s predicted CO2 emission rate will not be greater than the target emission rate.
• Ensure the performance of the building’s fabric, heating, hot water and lighting meets the minimum values set out in the document.
• Introduce passive measures to prevent homes overheating.
• Ensure construction is consistent with the design.
• Provide the occupier with information to order to allow the building to be operated as efficiently as possible.
2. Dwellings now have to be pressure tested
The air permeability of the envelope should be no greater than 10m³/h/m².
3. Dwellings will have to produce 20% less CO2 than they do under the existing regulations.
A carbon comparison must be produced to show how a home’s predicted CO2 emission rate compares to target emission rating based on a national dwelling, compliant with the 2002 regulations. A fuel factor can be applied to the rating if LGP, oil mains electricity or solid fuel is used, making it easier to comply when using these fuels than their carbon content would otherwise allow. So, with careful design, electric heating can still be used in apartment blocks.
4. There are two routes to compliance for apartments.
A penthouse does not have to comply with the carbon emission rate provided the remaining dwellings can compensate, since the compliance for apartment blocks can be demonstrated either as individual SAP calculations for each dwelling or as an area-weighted average for all dwellings in the building.
5. A report should be provided to Building Control
This will identify the features that deliver the CO2 reduction. At completion, additional schedules covering lighting, robust details and non-accredited details are required, together with evidence that air permeability standards have been achieved, systems have been commissioned and operating instructions issued.

How Existing Commercial Buildings Will Be Affected Part L2B
1. More work is subject to the regulations
The rules will apply to: an extension, a change of use or alteration, provision of a controlled fitting or service and a provision of a thermal element.
2. The route to compliance for an extension has not changed
The elemental route to compliance remains for extensions and cases where the use of a building has changed.
3. Individual elements must meet specific standards
Provisions apply to acceptable performance standards for windows, heating and hot water systems, lighting, insulation of pipes, ducts and mechanical cooling systems, commissioning and the provision of information.
4. Entire elements may need to be upgraded
When 25% of a thermal element, such as a roof is upgraded, the entire element should be upgraded to the latest elemental standards if pay back for the work can be achieved within 15 years. If not, it should be upgraded to a standard that does achieve payback within that time.
5. Historic buildings

Energy efficiency measures should be incorporates where they will not prejudice the character of the building.

Key Changes for New Domestic Buildings Part L1A

1. Obtaining compliance is now a five step procedure
• The predicted building CO2 emission rate should be no greater than the target rate.
• The performance of the building fabric, heating and hot water and lighting should comply with the minimum limits in the document
• Passive measures should be included to prevent overheating for areas without cooling.
• The building should be built as designed.
• Provision should be made to enable energy efficient operation.

2. Air Permeability
Tests are required for every building that incorporates a floor area greater than 500m²

3. Overheating
Designers must demonstrate that the combined solar and casual heat gains do not exceed W/m² or that the temperature does not exceed 28C for more than 20 hours a year spaces with no comfort cooling.

4. Fully glazed buildings will comply
A typical mechanically cooled and ventilated building, 40% glazed and built to 2002 standards can comply through a combination of omission of roof lights, improvement in double glazing specification and lighting controls. An equivalent building with 100% glazed facade could comply with a similar improvement strategy, but with an additional improvement in the chillier seasonal efficiency.

5. Calculating energy consumption
Two calculations are required: a preliminary one, as part of the design commission, and a final calculation demonstrating compliance based on ‘as constructed’ information, incorporating any performance changes made during construction.

How Existing Domestic Buildings Will Be Affected Part L1B

1. More work carried out to existing buildings is subject to the regulations
An extension, material change of use, material alteration, the provision or extension of a controlled service or fitting and the renovation of a thermal element are all now subject to the regulations.

2. Consequential improvements
Work to existing heating or cooling systems, windows or walls below the element standards must be upgraded, provided it is technically, functionally and economically feasible.

3. The 10% rule
The requirement for consequential work is limited to 10% of the value of the principle works. The following elements are all subject to the 10% rule: any heating, cooling or air handling system older than 15 years should be replaces by new plant and improved controls; any inefficient lighting system serving more than 100m² should be upgraded; energy metering should be installed; and if the renewable energy contribution is less than 100%, the system upgraded provided payback is less then seven years.

4. Extensions
Elemental standards are given for the building fabric and windows in extensions. There is some flexibility allowed, provided the heat loss for area weighted U-values is no greater than the equivalent compliant extension. Extensions over 100m² and greater than 25% of the floor area of the existing part of the building come under Approved Document L2A

5. Controlled fittings or services
Compliance is largely elemental, with specific minimum standards to be achieved. There are additional requirements governing commissioning, the provision of the sub-meters and log books

Check List to Identify Suitably Qualified Air Testing Companies

1. Check the envelope area calculations refer to the whole building envelope and that this is the envelope that has been actually tested.
Has the envelope area been independently verified - by the architect? Check that the test has been carried out on the same envelope criteria – i.e. no areas have been excluded for the test and included in the calculations.
2. Check the envelope area calculations refer to the whole building envelope and that this is the envelope that has been actually tested.
Has the envelope area been independently verified - by the architect?
3. Check that the test has been carried out on the same envelope criteria – i.e. no areas have been excluded for the test and included in the calculations.
4. The whole building should be tested wherever possible - Not only is the result more accurate but it increases the chance of the test passing and gaining compliance. If areas have been excluded, are the reasons valid?
5. Check that temporary sealing has only been applied to H and V equipment and other permanently open natural ventilations.
6. During the air test, if possible be inside the building and check-
• internal doors are kept open
• no additional temporary seals have been added
• External windows and doors stay closed
• Ambient conditions – wind speed should ideally be a maximum 13 mph
6. The following readings and values should be checked. Any readings outside the parameters detailed below indicate the test has been carried out incorrectly and the test should be carried out again.
• Minimum 6 number readings taken.
• Or 5 x the zero flow pressure difference.
• The minimum pressure differential should be = 10 Pascals and maximum pressure differential = 35 Pascals.
• Correlation coefficient >0.98, any lower than 0.98 indicates the readings are too far spread.
• N has to lie within the range of 0.5 - 1.0 values outside of this range indicate that the test has not been carried out properly.

Check the procedures for the air test if the building is large and multi-cellular or over 5 storeys tall.

Why have major retailers driven air tightness levels down to best practice level in the last 12 years?

Commercial Benefits to the Building Owner and Client.

One reason only – there are substantial commercial benefits to having an airtight building and retailers are accruing those benefits for the life time of the building stock.

A typical example of the real benefits that can be realised was seen on an existing retail store that was sealed in February 1997. The ambient temperature in the store was raised by 5°C, after the store had been air sealed.

Typical air permeability rates of 3 m³/h/m² have been obtained on new retail stores and 5 m³/h/m² on existing stores. These levels of air tightness have been achieved by incremental improvement over a number of years and effort by all parties involved with the projects.
The additional costs to clients on new build retail stores is < 0.5% of the total spend.

The real benefits obtained from achieving a good level of air tightness can be summarised as;
• Lower energy costs for the life time of the building
• Lower initial capital costs due to down sizing of plant and equipment
• Air tightness tests can act as performance tests for fire compartments as well as external envelopes
• The environment within the building becomes less drafty and potentially warmer. Productivity of staff could be raised significantly - a happy worker is a productive worker!
• The risk of interstitial condensation within the building fabric is minimised, if the building fabric is built to an air tightness standard. Degradation should therefore be reduced in the long term.

Different types of buildings require different levels of air tightness. Air conditioned buildings should be tighter than naturally ventilated ones. Archives, cold rooms and museums will all require to be much tighter to ensure the specification levels for the control of humidity, heat loss and the ingress of pollutants are met.

What is the Good Practice Guidelines for Different Building Types?
Good Practice Guidelines for Different Building Types. The following figures are recommended air tightness specifications for various building types as set out in CIBSE TM 23.

Air leakage index Air Permeability m³/h/m² at 50 Pa
Practice Good Best Good Best
Building Type
Office - naturally ventillated 10.0 5.0 7.0 3.5
Offices - balanced mech vent. 5.0 2.5 3.5 2.0
Superstores 5.0 2.0 3.0 1.5
Industrial 15.0 3.5 10.0 2.0
Dwellings 15.0 8.0 10.0 5.0

What is the Theory Of Air Tightness, Air Leakage and Air Sealing Measures?
Theory Of Air Tightness, Air Leakage and Air Sealing Measures

Air tightness / air permeability (air leakage) – defined as the resistance of the building envelope to inward or outward air permeation. Air leakage is driven by pressure differentials between inside and outside a building caused by the wind, stack effect and mechanical ventilation systems. Excessive air leakage leads to increased energy consumption, increased drafts within the building and increased risks of condensation within the building fabric. For the client, air leakage is physically felt with cold drafts caused by the uncontrolled movement of air into or out of a building. Cold drafts usually cause complaints from building users!!

Air barrier or air seal line – the physical components that make up the airtight envelope of the building. The air barrier needs to be continuous around the whole envelope – roof, walls and ground floors, durable and maintainable in the long term. The air seal line should be drawn on construction drawings to communicate the strategy to all relevant parties.

Air tightness test or air leakage pressure test – the building is pressure tested by connecting a fan and measuring the airflow rates required to keep the building at various positive or negative pressures.

Air permeability – expressed as the amount of air leakage in cubic metres, per hour, per square metre of envelope at a nominal pressure differential of 50 Pascals, between inside and outside the building envelope.

Q50 – air flow rate required to pressurise the building envelope to 50 Pascals, measured unit - cubic metres per second.

Information for the Client
Rules to Ensure Part L Is Met Ensure air tightness is thought about at the concept stage of the project and designed in from the start.
Ensure that all materials and components used for air tightness purposes have a similar specification and longevity, as all others used on the project. There is no reason that buildings constructed to an airtight standard should be stuffy for occupiers or be at greater risk from condensation.

The rule is; build tight – ventilate right there a risk from making a building envelope too airtight?

No. Part L is meant to control the amount of uncontrolled air leakage through the building fabric, not the amount of controlled ventilation.
Is the target air permeability rate achievable?

The target air permeability rate of 10 m³/h/m², set down in Part L is achievable when current best practice for buildings is around 2 m³/h/m². However, if no regard is taken to air tightness, it is probable that Part L will not be complied with.

How expensive will it be?
Additional building costs may amount to 0.5%. This ignores cost savings from down sizing heating plant and the life time reduction in energy costs.

When To Get Worried
When a party claims that air leakage problems will be sorted out after the first air leakage test and will be remedied then. Air Pressure Testing’s golden rule is that it costs considerably more to put right second time, rather than doing it right first time. Ensure that maintenance procedures take air tightness into account. Degradation or damage to air tight elements or components needs to be minimised over the long term. We have witnessed how simple it is for an electrician to punch a large hole through a wall, thereby increasing the air permeability figure significantly enough for users of the building to complain about an increase in drafts.

Information for the Architect

Golden Rules To Ensure Part L is Met
Designing airtight buildings is the only means of ensuring long term, low air leakage performance. Build tight – ventilate right. The objective is to minimise uncontrolled air leakage whilst maintaining controlled ventilation. Ensure the air barrier is based on structural elements, wherever possible. Condensation risk will be minimised if the air barrier or seal envelope is correctly positioned, which depends on the make up of the construction element itself. Generally, it should be placed on the warm side of the insulation layer. It is also important for the insulation layer to be continuous and to bear in mind that excessive cold air moving around loose or misplaced insulation can lead to interstitial condensation.

Ensure that the air tightness test is carried out by a member of the British Institute of Non Destructive Testing The DCLG recognises members as being ‘suitably qualified’ and ‘competent’ companies to carry out air tests.

What needs air sealing on site?
Careful consideration is needed on all structural elements. For instance pre-cast concrete floors may look airtight, but consider air leakage along open voids through the slab into cavities in external walls! Also think about non-structural elements such as roof liner sheets or T and G boarding. A 1mm gap along each joint adds up to a considerable area for air to leak through. Please download Air Pressure Testings helpful checklist

Where can I access reference to standard details?
• The Stationery Office – Dwellings BRE Good Building Guides
• Kingspan
• The Stationery Office

When To Get Worried
Any supplier of materials or components who can not state the air leakage rate (permeability) of their product per meter square, as tested to BS / EN standards. Be forewarned, material suppliers who states their components are air tight. NO materials are perfectly airtight, particularly after installation on site!

Using dry lining or vapour barrier as the air barrier is possible with good detailing. However, a high level of site supervision is required to ensure all junctions are air tight and that the lining is not damaged.

Please note: Perforated liner sheets are NOT suitable as an air seal line.
If you have any concerns, request that the material or component under goes an air leakage test.

Information for the Main Contractor

Golden Rules To Ensure Part L Is Met
Ensure that good, sound building practice is delivered so that the building is airtight. If the building is not airtight, the air permeability target of 10 m3/h/m2 will be exceeded. The end user (– client) may also find that ventilation is inadequate and may complain of drafts at times of the year when the building is difficult to heat or cool, an example of this was bought to our attention when a primary school could not achieve their minimum operating temperature due to massive amounts of Air Leakage, this was due to poor design detailing around the eaves, this resulted in the children being sent home every time the temperature dropped below the minimum requirement

State clearly in all pricing enquiries the air tightness specification and ask for details of compliance including specifications, method statements, quality audits, etc, etc. Ensure a person on site is nominated to control and audit all aspects of air tightness works, through out the contract period on site. Do not enclose or cover cavities or gaps before the air tightness works have been quality assured.

How can a large number of suppliers and sub contractors be controlled to ensure air leakage issues are addressed?
Use similar methods to those used at present to control all aspects of contracts specification, method statements, quality management systems, etc. Problems generally occur when responsibilities for each element or package of work are not clearly defined and agreed, prior to site work starting.

If the air leakage test fails, how can air leakage paths be found? A variety of techniques can be used to identify leakage paths – these include;

• Feeling for drafts adjacent to the air barrier, whilst the building is being air leakage pressure tested. It is useful if the air test fan unit can pressurise and de-pressurise buildings so that drafts can be felt for on both the internal and external faces of the air barrier.
• Running localised smoke tests using a hand held directional smoke generator.
• Running a smoke test on the whole building and undertaking a full photographic survey.
• Carrying out a Thermographic survey
• Physically checking over the risk areas looking for holes, gaps, etc

Which building components are particularly prone to air leakage?
Apart from the obvious - unsealed block work, hollow concrete beams or floor planks, joints/junctions in curtain walling and dry lining systems, hollow frames/mullions/transoms, hollow steel sections penetrating the roof or walls, lap joints on roof liner sheets or T & G boarding - to name a few!

What area of leakage holes am I looking for?
Dividing Q50 by 5.5 gives an approximate figure for the total leakage area in metres square. For example; if Q50 = 37 m³/s the total leakage area = 6.7 m². Treat this figure with respect and care as the visual hole seen on the air seal line is not always the actual area that air is ultimately leaking from – the final leakage hole could be a lot smaller.

Envelope Area (m2)
Leakage Rates (m3/hr at 50Pa)

Leakage Rates (m3/hr) by Area (m2)

When To Get Worried
Any sub contract package is proposing to use gaffer tape or plastic sheeting to air seal works. Can we do the air leakage test next Tuesday, if the roof plant comes tomorrow and the fitters come in on Sunday to install it? NO! Plan ahead and ensure the building is ready for the test. Ensure the size – flow rate of the fan is adequate for the job. Ask for calculations to back this up.
Information for Building Services Consultants

Golden Rules To Ensure Part L is Met
Ventilate right – the main contractor should build the envelope tight. This will enable the design, specification and sizing of the heating and ventilation system to be carried out with confidence. Fresh air openings in the envelope constitute massive air leakage paths and will ensure buildings fail the air test. Check the envelope area is correct.

What BS or EN standards are air leakage pressure tests carried out to?

ATTMA TS1 & BS EN 13829:2001(1) Thermal Performance of Buildings: Determination of air permeability of buildings – Fan pressurisation method.

How can air permeability standards be expressed as air changes per hour – each at a test pressure of 50 Pascals?
For a moderately sized single storey building which complies with Part L, Qleakage = <10 m³/h/m², the average ventilation rate will be approximately 0.3 ach. The ventilation rate in ach can be approximately estimated as A/(6*S) ach where A = Area of walls, roof and ground floor and S = area of walls and roof.

What is the heat loss due to air leakage?
Qleakage = rCp * V * n / 3600 W/K where rCp heat capacity of air, V volume of building m³ and n
is the ventilation rate in air changes per hour - ach.

What are typical levels of savings in terms of energy usage?

For an industrial building with a floor area of 5000 m2, currently built without air tightness considerations; air permeability can be > 14 m³/h/m². This equates to a hole in the roof of approximately 5 m²!!

If the air permeability can be reduced to 8 m³/h/m², which comfortably passes Part L, then the energy saving could equal > 60,000 kWh per annum. NOTE. Current best practice for industrial type buildings in regards of air tightness is an air permeability figure of 2 m³/h/m².
How can complicated service penetrations be sealed?

Services can be routed through ducts inside the building envelope. Sealing multiple service penetrations is awkward but similar principles to those used to seal penetrations through fire walls and plant room slabs should be used.

How can the flow rate for the air leakage pressure test be specified in terms of the size of the fan?
ATTMA TS1 states that the fan should be able of achieving > 80% of the required air flow rate at 50 Pascals pressure difference.
Information for Material, Plant & Component Suppliers -

Golden Rules to Ensure Part L is Met
Set our clearly in all documentation the level of air tightness that can be achieved and how it is to be practically achieved on site. Be specific about whose responsibility it is to seal components and also adjacent elements, including works on site. Show these details clearly on all contract and site drawings and ensure that specified materials and components are fit for purpose.

Ensure all site staff and operatives fully understand the concepts of air tightness and the details of how it is to be achieved on site. Ensure training is carried out for all the parties involved, including site operatives.

How can we state air tightness figures for individual components?

Components could be tested in laboratories or tested on site in specially built enclosures as specified in BS EN 12114:2000. The test method allows the air leakage through individual joints to be derived. From this information the building air leakage rate can be estimated by totaling up the leakage rates for all the joints in the building envelope.

What can gaps and joints be sealed with?
As with all gaps and joints, there are many BS EN Standards which specify in detail, how they can be bridged effectively. Materials not to use include materials permeable to air (e.g. mineral fibre) or flimsy sheets, thin gaffer tapes or similar are not suffient materials to seal against Air Leakage. Sealant, expanding foam and tapes can be used, if specified and applied correctly. Ensure that all materials and components are fit for purpose and installed to current standards.

When To Get Worried
If there is no information on air leakage rates for materials or components, there can be no confidence with the final performance on site. Obtain a component air leakage test – contact Air Pressure Testing Ltd for details. Many modern construction systems and designs rely on gaskets or sealants within the joint to seal the system. If these are not installed correctly during installation, the air leakage could be considerable.

A typical example is with block work. Well designed, specified and constructed block work (with full horizontal and perpendicular joints)can achieve a very good standard with air leakage < 2 m3/h/m2. However, without taking due regard can lead some block work walls to have high leakage rates - for a variety of reasons. Sometimes blocks are not specified with an air leakage rate and also the composition and leakage rates of identical blocks, manufactured in different plants, can vary significantly.

On site problems with quality of block work and mortar joints can lead to significant leakage. For example, where block work is concealed above suspended ceilings, vertical mortar joints – perps – may not be filled completely but ‘faced up’, which leak, this is where on site audits are at their most effective as they pick up on problems such as this at the construction phase
Information for Building Control Officers & Approved Inspectors

Golden Rules To Ensure Part L is Met
Ensure that the air tightness test is carried out by a member of BINDT (The British Institute of Non Destructive Testing). The DCLG recognises members as being ‘suitably qualified’ and/or ‘recognised qualifications’ to carry out air tests.

What if and how will a building fail the air tightness Part L?
A building will fail Part L if the air permeability rate is > 10 m³/h/m². More stringent requirements may be in place, depending on the requirements within the building energy calculation to satisfy the carbon emissions target.

If Buildings also fail Thermographic inspections of the visible envelope, it will show that insulation is not reasonably continuous.
How accurate are the tests?

ATTMA TS1 states that fan flow rates should be measured to ± 7%.

The accuracy of the air leakage pressure test itself will be affected by the strength and gustiness of the wind. The wind will impose both positive and negative pressures on the building envelope, which will vary during the test. ATTMA TS1 states that tests should normally only be carried out when wind speeds are below 6 m/s. Occasionally a test may have to be carried out in wind speeds above this. Decisions will be made on a job specific basis. When Wind speed conditions are close to the maximum permitted Air Pressure Testing will use their Wind damping kits to ensure that accurate readings are undertaken at all times

How can fire walls be made airtight?
Use the same principles of design and construction as for other air tightness works but use fire rated materials. Compliance to various sections of Part L1 and L2 can be achieved by a ‘competent person’ reviewing the design and/or site works and deeming them adequate. These Sections include air tightness for buildings and continuity of insulation for all buildings. Air Pressure Testing Ltd can take on this role and issue the necessary declaration to the Building Control Officer.

Air Pressure Testing Ltd Services Ltd has air tightness testing equipment suitable for testing buildings with floor areas from 10 to 40,000 square metres. For the easiness of portability Air Pressure Testing Ltd use their Retrotec 3001 portable high power systems which are 710 mm diameter fans which can be built into sets of up to 3 fans. These are electrically powered, quiet, clean and as the name suggests portable. They can easily test whole buildings or if necessary be erected inside buildings to test plenums, service ducts, fire compartments, upper storey’s, extensions, etc, etc.

To test larger buildings Air Pressure Testing can link up to 6 of their Retrotec 3001 3 fan systems this allows us to undertake tests on buildings upwards of 40,000 Metres, this reduces te need for large trailer fans that can prove to be disruptive to sites with tight access such as city centre’s, when other Air Leakage Testing companies state that they haven’t the equipment to test your building, you know where to come.

Carrying Out Air Tightness Tests & Smoke Tests

Golden Rules To Ensure Part L is Met
Carry out the air tightness test when the building envelope is complete. Temporarily sealing areas of the building is not only difficult and costly to do well, but the risk of failing increases as well. It is far better to delay the test for a week rather than test early, fail, and then have to carry out another test in one weeks time.

Temporarily seal all heating and ventilation equipment and ensure window trickle ventilators are closed. Check all service ducts (including telephone, electric, spare ducts) and water and condensate traps are either sealed or full.
The worst acceptable standard for the leakage rate is < 10 m³/h/m²

Will the building fabric be damaged by pressurising the building to 50 Pascals, during the test?
No. A heavy thunderstorm may impose pressures of 500 Pascals onto the building fabric, so air pressure testing will not cause any structural damage

How long does it take to carry out an air leakage test?
A minimum of 4 hours should be allowed to carry out a test. It will take approximately 1-2 hours to temporarily seal services, however if the client/customer is proactive and the sealing works are undertaken before we visit site the actual test time can be greatly. If the air test runs smoothly, a maximum of 30 minutes is required; but it’s best to allow 1 hour. It takes approximately 1 hour to de-rig all of our air leakage equipment. However, if an air test fails and multiple tests are carried out or the fan is left running to search for drafts and air leakage paths, then the air test can run over the usual 2-3 hrs

Can people carry on working in the in the building when carrying out a test?
Yes, as long as no-one opens a door or access hatch which will obviously compromise buildings air barrier – which basically allows the pressure to drop and the test would need to be run again.

Does the smoke test damage the building?
No. However, the building needs to be empty of all people for Health and Safety reasons due to the poor visibility. It is also essential you inform the Fire Brigade to avoid unnecessary call outs. The smoke is a harmless food grade water based mono-propylene glycol (MPG), but it is a good idea not to expose fresh food or produce to it.

What size fan do we need to carry out the test?

ATTMA TS1 states that the fan must be capable of achieving at least 80% of the required air volume flow rate, at 50 Pascals pressure difference – Q50. Q50 = A * 10 / 3600 m³/s where 10 is the Air Permeability target, A = Area of walls, roof and ground floor
Note. Air Pressure Testings 3001 series fans can deliver from 1 - m³/s to over 70 m³/s so capacity is not a problem.

Thermographic surveys to identify air leakage and/or discontinuous insulation

Air Pressure Testing have many years experience of carrying out Thermographic surveys and can offer clients advice at an early stage as to the most productive method to carry out a Thermographic survey.

Air Pressure Testing Ltd offer wide ranging technical and practical construction experience of building technology, design issues and potential faults in buildings allows us to give a high level of service both in carrying out the survey and interpreting the results.
Building thermography is an effective method of indicating the heat distribution over the surface of a building envelope. This remote-sensing technique can be carried out with minimal disturbance by a single operator and allows qualitative detection of air leakage pathways and insulation discontinuities. The survey will be carried out using an un-cooled thermal imaging camera, which can measure temperatures to 0.1°C and displays the images and reports in full colour. Air Pressure Testing uses a calibrated FLIR camera, which allows full analysis of saved images.

Thermographic Surveys are carried out to BS EN 13187:1999: Thermal performance of buildings - qualitative detection of thermal irregularities in building envelopes - infra-red method and BRE Report 176 - A Practical Guide to Infra-Red Thermography for Building Surveys. Please click here to down load a copy

Our On-site Requirements for Thermographic Surveys
The following outlines the requirements for the above test. Areas of discontinuous insulation will be more readily identified in these conditions:

• The integrity of the building envelope should be complete for the survey
• Drawings (plans and sections) and specification details regarding the areas to be surveyed should be supplied prior to the survey taking place
• Air Pressure Testing have assumed that the survey will be carried out from the outside of the building, usually at night (or on an overcast day in winter) when the weather is dry.
• It is important that the internal temperature of the building is 10°C higher than the external
• If possible, the internal pressure of the building should be raised by 10 Pascals by switching off the extract units

An hand-held infra-red sensitive camera records images of the subject that are compared to conventional pictures of the same areas. "Hot-spots" can then be related to features of the building and an informed view taken of building integrity. Local/component thermography whilst a building is depressurised can identify where air tightness needs improving.

Golden rules to ensure Part L is met
You must ensure there is a minimum temperature differential between inside and outside the building of at least 10°C. This is usually achieved by leaving the heating system turned on inside the building for 12 – 24 hours prior to the survey.

Carry out external Thermographic surveys after dark (or heavy cloud), to ensure problems with sunlight warming up external surfaces can be ignored. Ensure the weather is dry as moist surfaces play havoc with the survey results. Beware items of plant emitting heat inside a building, as they can affect the results.

Why use Thermographic cameras?
A thermal image makes it easy to identify areas of missing, misplaced or discontinuous insulation.
It can also be used to identify air leakage paths if used correctly. Cold air leaking into a building will cause cold patches on the surrounding fabric, which can be identified from thermal images.

Can Thermographic surveys quantify air leakage?

No, but they provide a qualitative appreciation of the thermal properties of a building envelope, quickly over large areas and display the results graphically in colour. Spot temperatures are also measured which can allow for later analysis of the thermal performance of building envelopes, again especially useful in highlighting areas of misplaced or discontinuous insulation, something Air Leakage Testing cannot
How can you interpret the thermal images?

A sound knowledge of construction technology and a sound knowledge of the projects design (U values, emissivity of materials) allied with experience of on site defects is required to identify the true cause of faults identified on site. Particular care needs to be taken with regard to the emissivity and reflectivity of surfaces. Surfaces with low emissivity (e.g. polished steel), appear colder than their surroundings but are sensitive to reflective heat from background sources e.g. equipment, lights, people etc.

When To Get Worried
If the thermal image of the inside face of a building envelope appears to have a low surface temperature compared to their surroundings. Take care to evaluate the results as this could be caused by;

• Missing or damaged insulation or maybe high levels of moisture within the building fabric
• High levels of air leakage cooling the inside face
• Thermal bridging
• Evaporation of moisture from the internal surface
• Cold rooms inside the building cooling the surroundings

Typical Procedures for Carrying Out An Air Test

To ensure the air test is carried out to plan and the risk of failing is minimised, it is necessary for Air Pressure Testing and the client to work together. Once Air Pressure Testing receives an order, a procedure is set into train which ensures that everything swings into action. At least a week prior to the air test, Air Pressure Testing send clients a checklist of procedures which the client needs to confirm that they are ready to test. Please find attached checklist

The e-mail/fax back includes the following points;
1. Air test time and date must be established. Note, the client can change the date of the test up to 72 hours prior to the test without charge. Air Pressure Testing must be informed at least 5 days prior to the air test of any major temporary works, as these may adversely affect the result of the air test.

2. Access to the door where the fan is to be set up, should be flat and accessible.

3. Air Pressure Testing set up the screen for the fan if it is a double door. The client must build a screen if the door to be used is a loading bay door.

4. Air Pressure Testing assume that the building envelope is complete and ready to test. It has been assumed that the works will take 5 hours to complete. 99% of air tests are completed within 5 hours.

5. Air Pressure Testing request that the architect calculates the envelope area figures as it is not always evident from drawings where the envelope of the building lies. The air tightness envelope of the building
follows the insulation in the floor slab, external wall and roof. Plant rooms ventilated to outside
and cold roofs therefore should generally be excluded from the envelope area figures. Note, Air Pressure Testing verify these figures from drawings supplied or on site. The envelope area is required before the test date, in order to give a result on the day.

6. The check list details what temporary sealing needs to be carried out, prior to the test.

7.To summarise temporary sealing is not required on loading bay; external doors/frames/thresholds; windows and cills; lift shaft vents and doors; electrical switch, plant, tank rooms; smoke exhaust fans and vents.

8. Temporary sealing is required on fresh air inlets and exhausts to air handling plant temporarily
sealed. Check that drains, water traps are all filled with water.

9. Attendance from the specialist H & V sub contractors is required to shut off and close down all H and V equipment and any other equipment that form openings or penetrations in the envelope and temporarily seal them. Air Pressure Testing accepts no responsibility for these works, although Air Pressure Testing Ltd check the sealing is adequate. Note service ducts (gas telephone etc) need to be sealed as well.

10. The Client must inform all contractors and personnel that access into and out of the building will be restricted for a period of at least 2 hours and ensure that this is observed. Note, works can still proceed on site as usually access is restricted for periods of 30 minutes at any one time.

11. All internal doors, air sealed plenums / suspended ceilings / raised floor systems are effectively fixed opened to enable unrestricted air flow into all parts of the building envelope.

On the day of the Air Pressure Test, Air Pressure Testing usually turn up early morning and go through site induction procedures.
1. Prior to setting up their own air test rig, Air Pressure Testing walk the site with the clients’ engineer and ensure everything is set up correctly. Once agreed that everything is set up, the air test can proceed. Hopefully, the first test is successful and passes the specification criteria.

2. If the first test fails, Air Pressure Testing again walk the site and identify why it has failed. If this can be put right, remedial works may be applied by the contractor and a second test carried out.

3. Further tests are then carried out and if the test still fails, Air Pressure Testing can look for leakage paths by using portable smoke generators or pencils to identify where air is leaking. Another method usefully employed is to set the air test rig in reverse, thereby de-pressurising the building and feeling for drafts on the inside face of internal walls. Either way, Air Pressure Testing technicians use their experience of air sealing in helping the contractor. It usually becomes obvious whether or not the air test result will be brought under 10m³.h-1.m-² within the day.

4. Prior to leaving site, the air test result is discussed with the clients’ engineer.
Establishing The Size Of Air Test Required For The Size Of Building To Be Tested

This is relatively simple, as the size of the fan determines how much air the fan can blow into the building in per second. The air blown in, equals the air leaking out and linking this to the requirements of Part L2 enables Air pressure Testing to determine what size fan system is required.

Examples of air test rigs for different size buildings.
Building of 1000 m² floor area, assume 2 storeys, 20*25m on plan and average 10 m wall height.
Envelope area = Area of ground floor = 500
+ Area of roof = 500
+ Area of walls = 900
Envelope area = 1,900 m²
Assuming the building is just complying with Part L2 and is leaking at 10 m³.hour-1.m-² at 50 Pascals. The total volume of air leaking out of the building = 1,900 * 10 = 19,000 m³.hour-1
= 5.3 m³.second-1
ATTMA TS1 states that the air testing rig should provide a minimum of 80% of the volume flow rate.
The air test rig must have a volume flow rate up to 80% of 5.3 m³.second-1, 4.24 m³.second-1

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