Air Tightness Compliance

Uncontrolled air leakage from buildings is a significant cause of heat loss and, therefore, energy wastage.  A sound air tightness strategy will control this leakage through informed, efficient design.

For all new-build developments, a robust air-tightness strategy is important, not only to achieve Part L compliance, but also because of the benefits it can deliver to building developers, managers and occupants.

Airtight buildings:

  • Waste less energy and produce less CO2.
  • Reduce energy costs.
  • Are vital to achieving passive builds.
  • Facilitate right sizing of Heating, Ventilation and Air-Conditioning (HVAC) plant.
  • Reduce interstitial condensation – which can stain interior décor; produce mould; and degrade the building fabric, causing structural damage.
  • Are more comfortable for occupants.


What is “Air Tightness”?

Air tightness (also called air leakage or air permeability) is measured in m3 of air, per m2 of envelope, per hour, at 50 Pascals differential pressure between the inside and outside of the building [m3/(].

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, the top floor ceiling becomes the top part of the envelope.


How Stroma can assist: Air Tightness Compliance Consultancy and Pre-Test Services

Stroma Tech can help designers to get the air-tightness strategy right first time, by providing:

  • CPD training seminars on air-tightness.
  • Guidance on Building Regulations compliance – Part L 2013.
  • Liaison with Building Control Officer (BCO).
  • Drawing reviews.
  • Design workshops.
  • Site inspections.
  • Sample area air-tightness testing.
  • Mock-up testing.


Why is ‘right-first-time’ compliance important?

Early input from a reputable air tightness expert can be crucial, particularly on more complex projects. Test failures could mean:

  • No compliance, no handover.
  • Delays to programme and increased costs.
  • The necessity for remedial works at a late stage, often after carpets are down, ceiling grids in, and décor finished.
  • Possible penalties, liquidated damages and ‘bad-will’.

Air tests are relatively cheap… failing them is not!


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 constitute the air barrier are intrinsically air-tight, as are the joints between them.
  • Note that 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, and 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 the safest bet.
  • Ideally wet finishes: wet-plaster, screed, paint on fair faced block-work.
  • Dry-lining, ply, dense boards, which are acceptable if sealed at edges.
  • Adoption of ‘hidden layers’ is risky: they are impossible 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, windowsills.
  • Recessed lighting.
  • Plug sockets.
  • Air extract vents/ducts.
  • Loft hatches.
  • External door weather seals & thresholds.
  • Radiator pipe penetrations.


Here you will find some of our case studies.
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Titanic Belfast, The Signature Building
Phil Carr