Air Tightness Compliance

Air Leakage is measured in m3 of air, per square-metre of envelope, per hour at 50 Pascals differential pressure (between inside & outside the building).

The ‘envelope’ is the “shell” of the building that contains the “conditioned air”. In most cases this would comprise the ground floor slab, the perimeter walls and the underside of the roof. If the roof-void is naturally ventilated then the top floor ceiling becomes the top part of the envelope

Airtight buildings:

• Waste less energy and cause less CO2
• Reduce energy costs
• Are vital to achieving ‘passive’ builds
• Enable right-sizing of HVAC plant
• Reduce interstitial condensation
• More comfortable for occupants

_{Buildings don’t need to “breathe”, only people do! Therefore… “Build Tight – Ventilate Right”}

The New Part L1A 2010 Air-Tightness Requirements

Part L1A relates to ‘Work in new dwellings’

• Overall 25% reduction in CO2 emissions compared to 2006 version
• SAP2009 is used to calculate the “TER” & “DER”
• Requirement for “TER/DER” to be calculated and submitted at planning stage SAP2009 will provide building control officers with better clarity
• “Limiting air permeability” remains at 10m3/(m2.hr)@50Pa
• Number of tests per dwelling type is 3 or 50% of each dwelling type
• Use of ACDs is no longer a factor in the testing sample size
• If one “fails”, do remedial work on it (and all similar types) then retest it, plus one other
• Recommended that half of tests for each type is conducted among the first 25% that get built
• Separate blocks of flats needs to be treated as separate developments
• Tests to be conducted by a competent person

The New Part L2A 2010

• Instead of SAP2009, SBEM is used to calculated the CO2 emissions rates “TER” & “BER” (target & actual)
• All buildings over 500m2 internal ground floor area (GIFA) must be tested
• Below 500m2, there is the option to use a ‘default result’ of 15
• Lower levels of “Design Air Permeability” may be set as a means to make the SBEM calculation work - If so, the test needs to achieve this set result
• If a building ‘fails’, it must be retested

Stipulations for air-tightness is little changed from 2006 version

• The maximum permitted result is still 10
• However, the need for 25% reduction in overall CO2 emissions will make lower design air permeability inevitable

Air-Tests are relatively cheap… Failing them is not!

Particularly on more complex projects, early input from a reputable air-tightness expert can be crucial Test failures could mean:

• No compliance, no handover
• Possible penalties, liquidated damages and ‘bad-will’
• Remedial works are far more costly at a late stage
• Diminished labour on site
• Carpets down, ceiling grids in, décor finished
• Access restricted

Fundamental Approaches Designing for Air-Tightness

Under Part L, establish what the air-tightness target has to be (10 or less?) within the SAP/SBEM compliance strategy.

• Identify the surfaces within the building that together will form the air-barrier
• Produce marked drawings, showing air barrier line and joint details between air-barrier elements
• Ensure air barrier line is continuous, unbroken and encapsulates the entire conditioned space
• The more convoluted the envelope design, the more leaky it might be!
• Ensure that the ‘air barrier layer’ separates the conditioned space and any naturally ventilated spaces
• Check that the materials and components that are to constitute the air barrier are intrinsically air-tight, as are the joints between them
• Suspended ceiling tiles, fibre-board fire protection, perforated roof liners, mineral wool, course blockwork, etc, are not air-tight.
• Challenge the suppliers of envelope components, such as doors, windows, curtain walling
• Request test data

Choosing the Air-Barrier Layers

Air-tight buildings have an air-tight air-barrier, positioned inside the insulation

• Internal, accessible surfaces are safest bet
• Ideally wet finishes: wet-plaster, screed, paint on fair faced block-work
• Dry-lining, ply, dense boards: OK if sealed at edges.
• Adoption of ‘hidden layers’ is risky. No way to repair when buried in wall/roof construction.

Typical Air-leakage Sites in Dwellings

• Behind ‘dot & dab’ dry-lining
• Interconnecting cavity leakage – stud partitions
• Window gaskets & trickle vents, window cills
• Recessed lighting
• Plug sockets
• Air extract vents/ducts
• Loft hatches
• External door weather seals & thresholds
• Radiator pipe penetrations

Pre-Testing Assistance

• CPD training seminars on Air-Tightness
• Guidance on Building Regulations compliance
• Liaison with Buidling Control Officer (BCO)
• Drawing reviews
• Design workshops
• Site Inspections
• Sample Area Air-Tests
• Mock-up testing