AIRTIGHT SYSTEM

Building an airtight house using a membrane and taping system (red) is imperative to achieving Passive House standard. Where there are any gaps, leaks or draughts in the building envelope, uncontrolled amounts of cold external air will infiltrate the building, resulting in masses of heated internal air haemorrhaging out of the building. This mass loss of heat invariably increases a buildings overall energy demand and significantly heightens heating costs. The airtight system is a critical aspect of the Passive House, as it prevents condensation penetrating the structural timber frame, condensation which can lead to corrosion and decay.

Air tightness is achieved with the careful application of an internal airtight membrane sheeting, which is overlapped at joints and sealed with airtight tape. Where elements puncture through the membrane, such as service pipes, ducting,  joists and electric cabling, or where there is an opening in the building structure, such as an external door or window,  focused attention is given to the application of both membrane and tape to ensure the integrity of the airtight system.

Roof joists coming through airtight membrane and sealed with airtight tape around each individual roof joist

Airtight membrane carefully fitted at window openings and sealed at angles and corners with precision airtight tape application

Blower Door Test

The blower door test uses a pressurised fan machine to measure the air tightness of building. This is achieved by documenting the rate of airflow between building zones and identifying air leakage sites in the building envelope. Air tightness is measured in Air Changes Per Hour (AC/hr) at 50Pa pressure difference between inside and outside. An air permeability result of less than or equal to 0.6 AC/hr is required to satisfy Passive House standards. At MBC we design for and test all our homes for air-tightness using the blower door test.

Blower Door Test Equipment