This free checklist is crafted to provide you with all the essential information for preparing your project, so you can maximise the benefit of our service.

The airtightness performance of a Passive House is assessed through its air changes per hour at a 50 Pascal pressure difference, known as the n50 value. This value is determined by dividing the volumetric flow of air (v50) required to maintain the pressure difference by the internal air volume (Vn50) of the heated space. The Vn50 volume includes conditioned spaces measured from visible wall, floor, and ceiling finishes, excluding voids between ceilings and floors, internal wall voids, and floor voids. Detailed plans of the final construction are necessary to ensure accurate calculations, as some volumes may not be enclosed during initial tests. External door reveals deeper than 13cm are included, while hidden risers, wall and floor voids, and enclosed air spaces behind partitions are excluded. The accuracy of the Vn50 volume calculation is crucial, as overestimation leads to underestimated airtightness results. Any revisions to the calculated volume must be done early to avoid jeopardising Passivhaus certification. A competent third party should verify the Vn50 calculation, documented within the Passivhaus certification folder. In cases of uncertainty, the lower figure should be used until clarification is provided by the certifying body. Room-by-room calculations are recommended, encompassing all conditioned air spaces within the thermal envelope, while excluding certain enclosed spaces and shallow window and door reveals.

This desk-based service, it’s crucial that a competent person calculates the volume accurately. If you’re seeking Passive House certification, it’s best if the Passive House designer approves our calculations and they align. Any differences should be resolved before the test day.

1. Scaled drawings

Please send us floor plans, sections, and elevations if you haven’t already. This helps us accurately measure the surface area and volume.

2. Third-party volume verification

Details of the Passive House designer, to compare volumetric calculations, as these must align.

3. Window and door reveals

Do your window or door reveals measure 13cm or more in depth? If they do, please provide the depth measurement.