In a 13r design with residential heads in a heated corridor outside the dwelling units, would I have to calculate 5 heads at a .10 density? Is there anything that allows the use of .05 density?
You may use residential sprinklers in the corridors outside the dwelling unit but the discharge must be the higher of 1)a density of .10 gpm or 2)the discharge required for the listing. Given that corridors are most often are narrow and rectangular this will most often require you to discharge at the listing and not the density.
The density of .05 gpm is only valid inside the dwelling units.
For example Vikings freedom residential pendent sprinkler vk466 (k5.2)
With sprinklers spaced 19' apart in a corridor 6' wide coverage would be 114 sq ft which would require a discharge of 11.4 gpm to obtain a density of .10.
But the listing requires a minimum discharge of 20.0 gpm @ 14.8 psi.
20.0 gpm is higher than 11.4 so you would use the minimum discharge of 20.0 gpm using four sprinklers in accordance with the listing.