Reciting Kaddish After the Beginning of Pesukei DeZimra

To the honorable Rabbi,

I am a mourner, and in the place where I pray there is often no minyan at the beginning of the prayer service; the minyan gathers only in the middle of Pesukei DeZimra.

It is known that there are poskim who permit a mourner to interrupt in the middle of Pesukei DeZimra in order to recite Kaddish when the minyan gathers.

My question is: Is it preferable, lechatchilah, to wait and not begin Pesukei DeZimra until there is a minyan, even though as a result I will usually need to shorten Pesukei DeZimra in order to manage to pray Shemoneh Esreh with the congregation, or is it preferable to begin Pesukei DeZimra in the proper order and, if necessary, to interrupt for the recitation of Kaddish?

Also, is there a distinction in this regard between Mourner’s Kaddish and Kaddish DeRabbanan, or are they treated the same for this purpose? Thank you very much.

Shalom uverachah 

If a minyan gathered only after they had begun the blessing of “Baruch She’amar,” one should not recite the Kaddish customarily said before “Baruch She’amar” in the middle of Pesukei DeZimra.
An orphan within the eleven months who is in the middle of Pesukei DeZimra may interrupt and recite Kaddish for his father or mother.
However, if possible, they should say it between one chapter and the next, or at least at a point where a subject has concluded. Some have written that if he will find another minyan
at which to say it, he should not say it then.

This is the wording of our teacher Rabbi Amram Fried shlita, in the bulletin Azamrah Lishmecha:
It is written in Responsa Pnei Yehoshua (Orach Chaim siman 5, cited in Be’er Heitev siman 53 se’if katan 3, and in Sha’arei Teshuvah siman 51 se’if katan 2): “A group that did not have a minyan before Baruch She’amar, and they began to recite Pesukei DeZimra, and a minyan arrived, it is forbidden to recite Kaddish during Pesukei DeZimra.” The reason is that since there was no minyan before Hodu, they consequently were not obligated in this Kaddish, and therefore one may not interrupt in the middle of Pesukei DeZimra for it.
This is also what is written in Siddur Beit Oved (laws of Pesukei DeZimra, letter 13), and he explained the reason
that since the Kaddish before Hodu is only a custom, one may not interrupt in the middle of Pesukei DeZimra in order to say it.
However, the Chida (Kesher Godel, siman 7, se’ifim 35–36) wrote that they may recite
Kaddish. The reason may be explained as follows: since according to the Arizal (Pri Etz Chaim, Sha’ar HaKaddishim), part of the order and requirement of the prayer is to recite Kaddish DeRabbanan before
Hodu, it is therefore permitted to interrupt for it even in the middle of Pesukei DeZimra. However, even
according to this, since he has already recited Baruch She’amar, the necessary ascent has already been accomplished
through the Kaddish, and there is no remedy achieved by reciting the Kaddish (see Kaf HaChaim siman 53
se’if katan 13, and Responsa Rav Pe’alim, volume 2, siman 14).

Sources and further discussion:
In Responsa Maharshag (volume 1, siman 48), he wrote simply that it is permitted to interrupt
during Pesukei DeZimra in order to recite Mourner’s Kaddish, and his proof is from the fact that it is permitted
to interrupt during Pesukei DeZimra out of respect [and for this reason it is permitted to inquire
after one’s parents’ welfare during Pesukei DeZimra]; and since the recitation of Mourner’s Kaddish is an honor
to one’s father and mother after their death, he may interrupt in order to say it even in the middle of
Pesukei DeZimra. So too is written in Responsa Rav Pe’alim (volume 2, Orach Chaim siman 14), that if he does not say Kaddish for them, it will appear in the eyes of the congregation as though he is being dismissive and degrading
the honor of his parents. So too, this is cited in Elef HaMagen (on Mateh Ephraim, laws of Mourner’s Kaddish, Sha’ar 4, se’if katan 8) in the name of
the later authorities, that a mourner who is in the middle of Pesukei DeZimra recites Mourner’s Kaddish; and he added that although it is a great leniency to interrupt in the middle of
Pesukei DeZimra, nevertheless, since this is the opinion of the later authorities, this is how one should act. However, he wrote
that it seems to him that if he will later find a minyan in which to recite Kaddish, he should not interrupt in the middle of Pesukei DeZimra (and see Responsa Levushei Mordechai, volume 1, siman 112).
And that which was explained—that it should be recited between the chapters, and at the very least at a place
where the subject has concluded—is from the aforementioned Mateh Ephraim. 

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