Frequently Asked Questions - Air Sealing & Fire Stopping

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

Yes. However we would advise against it as particular care must be taken to ensure that there is a robust seal detail at the eaves junction to continue the air seal line from the inner face of the walls across the roof. Particular attention will need to be paid to ensure that any joints and penetrations to the barrier are fully sealed prior to being covered over as they will not be accessible afterwards.

We would advise specifying a rigid insulation board above the liner and using this as the air seal line. Care will need to be taken where the liner over sails external walls etc that air tight profile fillers are installed on the air seal line in the sheet troughs between the board and the liner.

Dry lining – As there may be expansion joints etc behind the lining boards that do not get properly sealed as they are not going to be on display. Additionally if the blockwork used has a high porosity then using the dry lining will reduce the problem caused by air leakage through the blockwork.

Ensure any exposed edges (Including where the lining boards finish below raised access floors and penetrations to the drylining are sealed.

Care will need to be paid to any areas of exposed blockwork above suspended ceilings, below floors and behind demountable panels etc that any joints, junctions and penetrations are sealed with air tight materials  

Yes, if not porous – Rigid and foil faced boards and the pasted batt systems are suitable provided board joints, junctions etc are sealed.

Loose mineral wool is not suitable. Any compressed mineral wool system used say to wall heads should be overcoated with either intumescent or ablative paste for air tightness.