Open door zonal pressure test. Should both readings be done at 50 Pa?
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Testing attic with home at 50 Pa and attic reading 40 Pa. Open scuttle hole until attic reads 20 Pa to see what the orginial hole size was. Does the blower door speed saty the same or ramp back up to 50 Pa when scuttle is open?
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If I understand you correctly, you are trying to use the "equivalent hole / pressure doubling" technique first popularized by my friend Jim Fitzgerald, but I think you have it a little confused. You would want to open the hatch large enough to approximately double the pressure between the attic and outside -- meaning that the dP would be about 30 house/attic and 20 attic/exterior with the hatch open (it sounds like you were planning the reverse). Then the size of the hatch opening you created would be about equal to the size of the existing leakage paths between house and attic. And yes -- you do need to bring the blower door back to 50pa to use this rough approach.