sprinklernotes
Insulation on Combustible Upper Surfaces “We have a horizontal concealed space above the ceiling with a wood upper surface and 2x6 in. wood joists. The joists are filled with noncombustible insulation. It is less than 36 inches between the deck and the ceiling. The materials below the joists are limited or noncombustible. Am I required to use sprinklers listed for a horizontal concealed space?”
We have reviewed the 2016 edition of NFPA 13, Standard for the Installation of Sprinkler Systems, you indicated as the applicable standards. Our informal interpretation is that standard spray sprinklers can be used. Technically, this space is not required to be protected per section 8.15.1.2.17. The insulation is an acceptable covering for the wood material negating it being classified as “exposed” combustible construction. In other words, the insulation is considered the outer boundary of the assembly. I understand that this jurisdiction still requires such spaces to be protected. This leaves the question as to whether sprinklers are listed for horizontal spaces per section 8.15.1.6. This section requires a special listing when three conditions exist. These are: (1) a shallow concealed space less than 36 inches in depth, (2) the space is horizontal (slope not exceeding 2 in 12), and (3) a combustible upper surface. All three conditions have to be present (just like the attic requirements in section 8.6.4.1.4). Although the upper deck is wood construction, it is not the upper surface. That would be the insulation. Although it is a different allowance, section 8.15.1.2.17 explicitly defines insulation as an acceptable covering, removing the wood from the evaluation. Since all three conditions do not exist, the requirement to use sprinklers listed for shallow combustible concealed spaces does not apply. As such, standard spray sprinklers can be used to protect this shallow concealed space. However, while not required, it would be appropriate to use a sprinkler listed for concealed spaces as the sprinkler discharge characteristics are specifically designed to protect narrow spaces. This should be discussed with the local AHJ to determine a proper course of action with which o proceed.
