First thing. An architect is generally not an engineer.
I am not certain of the lifespan of tar. Did you have any sort of written agreement and (or) plans and specifications?
Whenever I installed drain tile around a foundation, we would spead the tar and then ad the train tile. we never messed with the drain sheet or anything like that. But its a lot dryer where I live.
Spring Creek Lawn & Landscape
Veritas and æquitas