Insulating an Elevator Shaft
I have a project in coastal Delaware, zone 4A. The property is in a flood zone. The house is designed with an elevator attached to the side of the main structure—think of a silo attached to the side of a barn. The elevator shaft cross-section is approximately 6ft x 6ft and the walls are framed with 2×6’s on a short CMU stem wall. The bottom portion of the shaft is framed with pressure treated lumber as it is below the base flood elevation. The elevator shaft interior is within the air and thermal control layers for the overall structure. We need to make some final decisions on how the wall cavities and the roof will be insulated.
Let me also add that my general contractor is good, but the inclusion of a rain screen and some of the air sealing measures I’m having him do are already outside of his standard building practices. I’m looking for something effective and reasonably straightforward for a competent crew.
I had originally thought that the flood prone portion of the shaft would get closed cell spray foam in the wall cavities. However, my GC tells me that when that section of wall does flood I’ll have to remove the insulation in order to insure the walls dry out properly. If that’s the case, I think I’m inclined to use mineral wool in those wall cavities. Above the flood-prone areas, I assume we will use the dense pack blown fiberglass the rest of the structure will get in wall cavities.
A hip roof has been designed for the top of the shaft. My general contractor plans to frame that conventionally. My thought was to ask him to use 2×10 rafters and pad out the bottom of those rafters with some strips of the extra 2-inch foam insulation panels he already has on site. That would give me an 11.5 inch depth to flash and batt with about six inches of closed cell foam and the balance with the mineral wool batts (similar to option 5 in Martin Holladay’s article 5 Catherdral Ceilings That Work).
Does this sound sensible? Would it be easier to use fiberglass batts instead in the roof due to the uneven surface of the cured foam? Do I need to add any strapping to ensure the roof batts stay in place? Better alternatives?
Comments/thoughts welcome. Thanks in advance.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part