Indoor Balcony [i.e. Hallway of upper floor]:[1]

The balcony of an upper floor which oversees the lower floor is Biblically obligated to have a wall or fence or guardrail of ten Tefachim placed around it so no one falls off. It is to be placed with a blessing.

Porch or balcony-Is a porch or balcony obligated to have a fence or guardrail place around it?[2]

Yes, and it is therefore to be placed with a blessing.

A balcony that protrudes from the exterior of the building: Some Poskim[3] rule that a balcony which protrudes from the building and does not have any living quarters under it is not obligated to be fenced unless it is commonly visited by children in which case and even less than 10 Tefach fence suffices. Practically, we do not rule like this opinion, and hence a ten Tefach fence is to be built around even such balconies with a blessing.[4]

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[1] Rav Poalim Y.D. 2:36

Other opinions: The Sifri exempts a balcony or hallway from requiring a fence. The Rambam and Shulchan Aruch omit this opinion, hence negating it [Rav Poalim Y.D. 2:36]

[2] Rav Poalim Y.D. 2:36

Other opinions: The Sifri exempts a balcony or hallway from requiring a fence. The Rambam and Shulchan Aruch omit this opinion, hence negating it [Rav Poalim Y.D. 2:36]

[3] Chazon Ish Likkutim 18:6-7; See Imreiy Yaakov 10 Likutim 6

[4] See Sefer Veasisa Meakeh 21 in a Teshuvah from the Steipler who disputes this notion; Shevet Halevi 7:229-4 argues on the Chazon Ish and says even a blessing is to be said; Imreiy Yaakov 10 Likutim 6