NOTES

משנה ה

וחבילי זרדין  - As these are still moist, they are suitable for use as animal feed; when dry they serve as kindling. 

אין מסככין בהן - This פסול is only מדרבנן, as all the materials listed in this mishna would normally be perfectly כשר for use as s'chach.  The problem is that it was common for these materials to be left out to dry for later use as firewood, and if you change your mind after putting them up to dry, it is not תעשה ילא מן העשוי, and so it was banned from being used entirely.  [The concept of תעשה ילא מן העשוי בפסול means that that one must build (תעשה) the succah in a valid way from the start, and it must not be converted from what was previous made improperly (מן העשוי בפסול).  The  פסול in this case is that, even though we hold like like ב"ה in משנה א that a succah need not be built לשם חג, it still must be built  for the purpose of shelter.  Thus, if the bundles were originally installed to dry, they would be פסול מדאורייתא.]

וכלן שהתירן כשרות - This is only if they were originally put in pace on top of the succah for use as s'chach, and not if they were originally put there to dry.  If there were originally put there to dry, besides untying them one would have to also move them up and down for the succah to be תעשה ולא מן העשוי. 

וכלן כשרות לדפנות - This is referring to all of the cases of סכך פסול from the previous משניות, including such items that are מקבל טמאה or מחובר לקרקע.

משנה ו

מסככין בנסרים דברי ר"י - Any unfinished lumber, no matter how wide, is כשר מדאורייתא for use as s'chach, as it is not מקבל טמאה and grew from the ground.  The issue here is another אסור דרבנן what is referred to as גזירת תקרה, or the prohibition on roofs: If a person saw a succah with a large piece of lumber used as s'chach, they might come to believe that they can fulfill the מצוה of succah beneath the roof of their house.  Furthermore, the argument between ר"י and ר"מ is only by a board that is between three and four tefachim in width.  Narrower than that ר"מ would agree a board is not substantial enough to be subject to גזירת תקרה, and is more like the branch of a tree, while ר"י concedes that board wider than 4 tefachim is large enough to be considered a מקום חשוב and thus פסול מדרבנן.  The issue with a board more than three tefachim wide, according to ר"מ, is that since the concept of לבוד would apply to such a width, the use of a board of that size could lead to people thinking that a regular roof is also acceptable.  [The principal of לבוד is that a gap of three tefachim or less is considered to be filled by the surrounding material.]

לע"נ גננדיל בת משה

לע"נ פרץ בן מנחם מאניש