Airtightness is the single most under-discussed performance metric in garden-room construction, and the one that most differentiates a well-built room from a poorly-built one. A leaky wall lets warm air escape and cold air enter — no amount of insulation can compensate for uncontrolled air movement.
How airtightness is measured
The standard test is a 'blower door test': a large calibrated fan is fitted to the door, the building is pressurised to 50 Pa (about the equivalent of a 20 mph wind), and the leakage rate is measured. Results are expressed in air changes per hour (ACH). Below 3 ACH is good; below 1.5 ACH is genuinely excellent.
Why stick buildings are inherently airtight
- Factory-bonded panels — the airtight layer is built in during manufacture
- Fewer joints — a insulated shell has roughly 60% fewer joint linear metres than a stud frame
- Spline joints and tapes — where panels meet, industry-grade airtightness tapes are applied
- Sealed penetrations — every service pipe, cable and vent passes through a purpose-made airtight grommet