The Low-Carbon House:
Air tightness in context
Introduction
• Air leakage is a major cause of energy loss, typically around
20% from space heating.
• Air leakage is the uncontrolled movement of air in to and out
of a building which is not for the specific and planned purpose of exhausting
stale air or bringing in fresh air
• Air leakage is measured as the rate of leakage per m2 of external
envelope per hour at an artificial pressure differential through the
envelope of 50 Pa. ie m3/hr/m2@50Pa
• The Energy Saving Trust’s (EST) best practice standard
with balanced mechanical ventilation is 3 m3/hr/m2
• The Building Regulations 2006 standard is 10 m3/hr/m2
• In a recent survey of 100 new houses, none achieved a best practice
standard and around a third failed to achieve the Building Regs standard.
Less than 20% achieved the good practice standard of 7 m3/hr/m2
• Ensuring airtightness is achieved through careful implementation
of strategy throughout the design and construction phases.
• ‘Build tight – ventilate right’
Where it all goes....
| 1 | Around the ends of floor joists or joist hangers |
| 2 | Beneath inner window sills and around window frames |
| 3 | Through windows and/or hollow window frames |
| 4 | Through and around doors – particularly double doors |
| 5 | Beneath doors and doorframes |
| 6 | Along the top and bottom edges of skirting boards |
| 7 | Between and around sections of suspended floors, usually timber floorboards |
| 8 | Around loft hatches |
| 9 | Through the eaves |
| 10 | Around rooflights |
| 11 | Through gaps behind plasterboard on dabs or hollow studwork walls |
| 12 | Cracks or holes through a masonry inner leaf |
| 13 | Around supplies from external meter boxes |
| 14 | Around wall mounted fan or radiant heaters; around and through fused spurs and pull switches |
| 15 | Gaps around boiler flues |
| 16 | Around water and heating pipes that penetrate into hollow floor voids and partition walls |
| 17 | Around waste pipes passing into floor voids or boxed in soil stacks |
| 18 | Around waste pipes passing through walls |
| 19 | Gaps around heating pipes |
| 20 | Around and through recessed spotlights |
| 21 | Around waste pipes, gas and water supplies, cables, which penetrate the lower floor |
| 22 | Around vent pipes passing through to loft void |
| 23 | Through MVHR or warm air heating systems; around terminals |
| 24 | Gaps around pipes to cold water and/or heating header tanks |
| 25 | Around and through wall-mounted extract fans, cooker hood vents, tumble dryer vents |
| Other routes | |
| 26 | Around and through ceiling roses |
| 27 | Through room thermostats and heating controllers |
| 28 | Behind polystyrene coving along wall to roof joints |
| 29 | Through key holes and where locks and bolts prevent effective draughtproofing |
| 30 | Around internal timber joists that penetrate plaster walls |
| 31 | Through subfloor air supplies to solid fuel heaters |
| 32 | Through gaps in the casings of MVHR units |
| 34 | Through airbricks and partially closable hit-and-miss vents |
| 35 | Through window spinner vents |
| 36 | Around and through closed trickle vents |
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