Using wooden planks to block the door.

[BlackDog]

It should be ok as long as the wood is breakable.

One would think this is the logical assumption, and if it is, be prepared to face a swarm of people who do nothing but complain and call an admin about how your prop blocking the moment they see the planks, since they cant take 5 seconds to stop and examine their situation

Also if you had so many it took longer to get though then cracking of a keypad it may cause problems..

Not exactly, 2ish crowbar hits and a plank breaks, not to mention gunfire or a shotgun, a molotov or just breaking specific planks to allow you to squeeze through.

You also have to remember that for each plank a person is useing, their depriving themselves of another prop that could be used for defence or anything else.

So if it is a base your attacking, around 3-5 planks to effecetivly cover a door, if anything its not really logical to use planks to cover a door since you could just use a single prop with a keypad to do the same job. Putting planks over your keypad door though would probably still fall under the double dooring rule.