Airflow resistance

The airtightness of buildings is defined by the air change rate (n50 value). This is composed of the permeability of the material employed (n50 material) and the leakages (n50 unknown leakage). 

n50 = n50 material + n50 unknown leakage < 0.6 ACH
(passive houses <0.6 air change per hour ACH at 50 Pa)

Different OSB brands were investigated for their airtightness in a Belgian study in 2011. The study showed that in most of the OSB brands tested the air leakage already constitutes a significant part of the air permeability permitted by the passive house standard. According to the study, additional measures should be considered when using OSB boards as an airtight layer in passive houses in order to keep the air leakage value of the material (n50 material) as low as possible and thus to ensure appropriate airtightness.

Independent of the Belgian study, ISOCELL carried out investigations had at the same time together with the FIW Munich into the airtightness of the OSB3 boards and improvements in conjunction with cellulose insulation.  The results of the ISOCELL investigations are confirmed by the findings from the Belgian study.

• 160 mm air space without insulation => 0,275 m³/(h.m²) 
• 160 mm glass wool 17 kg/m³ => 0,273 m³/(h.m²) 
• 160 mm ISOCELL cellulose 58 kg/m³ => 0,141 m³/(h.m²)

The ISOCELL cellulose insulation achieved almost a 50% reduction in the measured volumetric flow with the structure tested.
This percentage improvement can be apportioned to the n50 material value. According to the formula specified above, it is easier to achieve the required < 0.6 ACH with a lower n50 material value.