Frequently Asked Questions - Air Tightness Consultancy & Testing

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.

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 Government is committed to reduce CO₂ emissions from energy consumption by 20% by the year 2010. The majority of buildings constructed today 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.

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.

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!!

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 will 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.

 

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.

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.

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.

Click here to see the Part L1A Compliance flow chart for New Dwellings

Click here to see the Part L2A Compliance flow chart for New Commercial Buildings

The Part L regulations implemented in April 2006, state that all air tests must be carried out by 'suitably qualified' companies such as those accredited by ATTMA - Air Tightness Testing Measurement Association. Membership is only gained by those companies who hold UKAS accreditation for carrying out the tests. UKAS accreditation ensures that all equipment is calibrated, staff trained and procedures documented. Using a company such as HRS, who are full members of ATTMA, ensures clients can have confidence that Building Control/Approved Inspectors will accept the air test result. It also means that HRS can negotiate on behalf of their client if dispensation is required on any part of the project.

Click here to download the PDF

Use the check list below to identify whether the test is being carried out correctly.
Calibration of  the air test rig, (not just the fan) has been carried out, within last 12 months, to BS 848
Calibration of all measurement equipment has been carried out, within last 12 months, to UKAS standards.
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 – ie no areas have been excluded for the test and included in the calculations.
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?
Check that temporary sealing has only been applied to H and V equipment and other permanently open natural ventilations.
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
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.

 

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.

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
Offices: Naturally ventillated	10.0	5.0	7.0	3.5
Offices: Balance mechanical 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

Theory Of Air Tightness, Air Leakage and Air Sealing Measures

Terminology

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.

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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

Q) 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.

Q) 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 would take approximately 1-2 hours to temporarily seal services and set up the air tightness test equipment. 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 every thing. 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 on.

Can people be in the building when carrying out a test?

Yes, as long as no-one opens a door or access hatch which forms part of the air barrier – which basically allows the pressure to drop and the test would need to be run again.

Q) Does the smoke test damage the building?

No. However, the building needs to be empty of all people for Health and Safety reasons. It is also a good idea to 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.

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

Q50 * 0.8. 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. HRS SERVICES Portafan system can deliver from 1 - 18 m³/s
Note HRS SERVICES are certified to ISO 9001:2000 and UKAS

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Golden rules to ensure Part L is met

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.

Q) 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.

Q) 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.

Q) How can you interpret the thermal images?

A sound knowledge of construction technology (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 (eg polished steel), appear colder than their surroundings but are sensitive to reflective heat from background sources eg 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

• Note HRS SERVICES have a thermographic camera able to detect temperatures from –10 to 800°C in 0.1 degree intervals. The images can be down loaded and stored and analysed at a later date by the client if required.

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

The FAX back include the following points;

1. 1. Air test time and date. Note, the client can change the date of the test up to 48 hours prior to the test without charge. HRS 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. HRS 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. HRS 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. HRS 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, HRS 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. HRS accepts no responsibility for these works, although HRS 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 20 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 test HRS usually turn up mid morning and go through site induction procedures.

1. Prior to setting up their own air test rig, HRS 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. However …
   
   2. If the first test fails, HRS 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, HRS 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, HRS 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.

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This is relatively simple, as the size of the fan determines how much air the fan can blow into the building in 1 second. The air blown in, equals the air leaking out and linking this to the requirements of Part L2 enables HRS to determine whether a PORTAfan or MIDIfan 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 test 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
HRS PORTAfan air test has been calibrated to BS848 with a volume flow rate between

2.0 – 4.0 m³.second-1