Yes if you tape the OSB in place correctly.    18mm OSB is generally considered airtight however I reckon 11mm is too if it is a well made board.    Don't bother getting a professional to do a trial. Rather buy something the car fan below. Bigger is better. Then screw and tape it into one of your sheets of OSB. Get some crocodile clips and wire and attach to your car battery.    They develop a howling gale compared to a proper blowerdoor. It makes it easy to find le
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