R. Wosner on Sechach Letting In Rain (3 Nisan)

שו"ת שבט הלוי ז:ס 3 Nisan 5748 (1988)

How thick can the schach be? What determines the validity of the schach - if rain can get in or if you can't see the stars? What if you can see the stars but rain can't get in?