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 firstname.lastname@example.org 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
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
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
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
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
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
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
The reason the New Building Regulations Part L include for air
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
• 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
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
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
• Running a smoke test on the whole building and undertaking a full
• Carrying out a Thermographic survey
• Physically checking over the risk areas looking for holes, gaps,
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
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
|Envelope Area (m2)
Leakage Rates (m3/hr at
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
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
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
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
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,
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
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
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
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
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
• Drawings (plans and sections) and specification details regarding
the areas to be surveyed should be supplied prior to the survey taking
• 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
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
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
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
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
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
4. Prior to leaving site, the air test result is discussed with the clients’
Establishing The Size Of Air Test Required For The Size Of Building To
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,
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