A pergola is a permanent wooden structure built in yards and gardens to provide a shady place to sit. The question is: Is the wood of the pergola’s roof considered kosher sekhakh?
Some are permissive based on the rationale that since the pergola is not meant for residence and is not fit for residence, since rain penetrates, its wood is acceptable sekhakh. Nevertheless, it is proper to add a little sekhakh in honor of the festival and so that the pergola is not considered an “old” sukka (as explained above in section 12). If it is more sunny than shady under the pergola, enough sekhakh must be added to change that.
Others are stringent and say that since the pergola is a sturdy, permanent structure, its wooden roof is akin to the wooden roof of a house, which is invalid as sekhakh on the Torah level. The basic principle of sekhakh for a sukka is that it must be impermanent, and a pergola is permanent. In practice, since this uncertainty pertains to Torah law, we must be stringent.
Therefore, if one wants to turn a pergola into an acceptable sukka, this is what he should do: If the majority of the pergola’s roof is made of fixed beams, some should be removed, so that most of the roof is open and there is more sun than shade. Kosher sekhakh can then be placed over the entire surface of the roof, such that even without the beams attached to the pergola, the shade provided by the kosher sekhakh will be greater than the sun it lets through. This makes the pergola into a kosher sukka.
Another way to make a pergola into a kosher sukka whose shade is greater than its sun is to take out the fixed beams and put them back without attaching them or nailing them down. Every re-placed beam is kosher sekhakh (SA 631:9).
As we have seen (section 13), one must make sure to put up the walls before the sekhakh. This is not usually a problem with a pergola, though. As long as “walls” are at least a tefaḥ high and near the sekhakh, they are considered rudimentary walls; if sekhakh is put on them, it is kosher (as explained in note 18). Many pergolas have horizontal beams that support the roofing, and which are more than a tefaḥ high. Thus, it is not necessary to add anything new to the “walls” before putting on the sekhakh.