I left you with quite a cliffhanger regarding Dan’s project and the blower door test. I thought I would explain a bit about the Passive House concepts that are affecting the results. Passive House projects are measured in a variety of ways.
For determining the Annual Heat Demand, the Gross Enclosed Volume of the building is used – that is the area enclosed by the extreme outside of the thermal envelope. In this cross-section of one part of Dan’s project the Gross Enclosed Volume is represented by a dashed blue line. The yellow represents the insulation in the walls and under the slab. The red line is the OSB and top of the slab that create the air tight layer.
For Ventilation purposes, the Net enclosed Volume of the building is used. This is where the question of the project passing the blower door test got a little sideways. In America, pressurization tests use different volume measurements normally and a number equivalent to the volume enclosed by the air tight layer (including interior walls and floors) was calculated.
For Passive House purposes a more conservative number is to be used for the Net Enclosed Volume. Basically it is the empty area that is ventilated within the thermal envelope. For this project that is all the blank space within the red air tight layer EXCEPT for the bright green area that makes up the floor and interior walls. The argument can be made that these constructions are not built air tight and will become pressurized and ventilated, but Passive House measurements are conservative and these volumes are not included in the Net Enclosed Volume.
Dan will be crunching the numbers, air sealing some more with the wonderful tape that Siga sent for the project, and trying again to keep under the .6ACH @ 50 pascal requirement that certified Passive House projects must reach. He is very determined to do so. He allowed for this scenario when he planned the blower door test. His air tight layer is still accessible and he does have the opportunity to go back and make changes easily. When planning your Passive House project, make sure you plan ahead so that you too can tighten the air tight layer if necessary without a lot of fuss.
Dan has really done a remarkable job with his project and I for one am learning so much from following it and presenting it to you on this blog. Thanks for following along!
[updated to clarify interior wall and floor volume are not included in the Net Enclosed Volume.]